Saturday, December 31, 2011

Kump's Hump

Kump's hump, also known as kump's bump, is named after the radiologist Warren Kump, who described an undulation of the anteromedial aspect of the distal tibial physis.

Kump's hump is the site of first closure of the physis and should not be mistake for a fracture. On MRI, the normal loss of cartilaginous signal intensity of the physis begins at Kump's hump.

Kump's hump can also present a pitfall on MRI. The undulation at this location can simulate physeal closure on T1-weighted images, a phenomenon that is due to partial volume averaging of the physis with the adjacent epiphysis and metaphysis.

References

  • Chung T, Jaramillo D. Normal maturing distal tibia and fibula: changes with age at MR imaging. Radiology. 1995 Jan;194(1):227-32.
  • Keats TE and Anderson MW. Atlas of Normal Roentgen Variants That May Simulate Disease. 8th edition, page 812; Mosby (2004).
  • Kump WL. Vertical fractures of the distal tibial epiphysis. Am J Roentgenol Radium Ther Nucl Med. 1966 Jul;97(3):676-81.

Friday, December 30, 2011

Osteoarthritis and the Metabolic Syndrome

The metabolic syndrome is a complex of disorders that includes abnormalities in triglycerides, high-density lipoprotein, blood glucose, systolic and diastolic blood pressure, and body mass index. Patients with metabolic syndrome have an increased lifetime risk for cardiovascular disease and diabetes.

Osteoarthritis, which is commonly thought of as a degenerative joint disease related to mechanical factors and/or age-related changes in articular cartilage, has recently been shown to be associated with the metabolic syndrome.

For example, patients who develop osteoarthritis at the mean age of the general population have a ~5-fold increased risk of metabolic syndrome even when controlling for obesity. An association has also been found between popliteal artery wall thickness and generalized osteoarthritis, even after controlling for sex, age, and body mass index. In addition, knee osteoarthritis is more common in obese women with metabolic syndrome than in obese women without metabolic syndrome.

Several mechanisms have been put forward for this association: Impaired expression of genes regulating cholesterol metabolism in cartilage, impaired blood flow to bone from endothelial cell damage caused by hypertension, high glucose concentrations leading to reactive oxygen species in chondrocytes, and abnormalities in leptin production by osteoblasts leading to cartilage destruction.

These findings suggest that a common set of factors underlies the development of both osteoarthritis and the metabolic syndrome, and that the development of osteoarthritis isn't simply due to the repetitive microtrauma from obesity. Some have even suggested that the finding of osteoarthritis should prompt a cardiovascular workup.

References

Thursday, December 29, 2011

Denticulate Ligaments

The denticulate ligaments, also known as dentate ligaments, are pia-arachnoid covered thick collagenous bundles that extend from spinal cord to the dura mater. The 20-21 pairs of denticulate ligaments are located between the dorsal and ventral rootlets and divide the spinal canal into posterior and anterior compartments. They are thought to stabilize the cord within the spinal canal and are used by surgeons as landmarks to localize spinal pathways during cordotomy.

The most cephalad denticulate ligaments attach intracranially. They are located just posterior to the vertebral artery and the ventral rootlets of C1 and anterior to the branches of the posterior spinal artery, spinal accessory nerve and, dorsal rootlets of C1.

The dentate ligaments get denser in the lower thoracic spine and tend to attach to the dura mater closer to the exiting nerve roots compared to those of the cervical and upper thoracic spine.

The most caudal of the denticulate ligaments merge with the pia mater surrounding the filum terminale.

References

  • Epstein BS. Cinemyelographic examination of the cervical spinal canal and the craniovertebral junction: the dentate ligaments. Br J Radiol. 1967 Mar;40(471):195-200.
  • Kershner DE, Binhammer RT. Lumbar intrathecal ligaments. Clin Anat. 2002 Mar;15(2):82-7.
  • Sigmund EE, Suero GA, Hu C, McGorty K, Sodickson DK, Wiggins GC, Helpern JA. High-resolution human cervical spinal cord imaging at 7 T. NMR Biomed. 2011 Dec 20. [Epub ahead of print]
  • Tubbs RS, Mortazavi MM, Loukas M, Shoja MM, Cohen-Gadol AA. The intracranial denticulate ligament: anatomical study with neurosurgical significance. J Neurosurg. 2011 Feb;114(2):454-7.
  • Tubbs RS, Salter G, Grabb PA, Oakes WJ. The denticulate ligament: anatomy and functional significance. J Neurosurg. 2001 Apr;94(2 Suppl):271-5.

Wednesday, December 28, 2011

FDG-PET Appearance of Rectus Femoris Origin Injuries

Strain or avulsion injury of the proximal tendon of the rectus femoris muscle can lead to increased FDG activity at the level of the anterior inferior iliac spine and superior acetabular ridge. Recognition of this entity can help avoid confusion for neoplasm on PET and offer a non-neoplastic etiology for pain in this region.

References

Sopov V, Bernstine H, Stern D, Yefremov N, Sosna J, Groshar D. Spectrum of focal benign musculoskeletal 18F-FDG uptake at PET/CT of the shoulder and pelvis. AJR Am J Roentgenol. 2009 Apr;192(4):1029-35.

Tuesday, December 27, 2011

Pinch-off Syndrome

Pinch-off syndrome occurs when a subclavian central venous catheter gets compressed between the clavicle and the first rib. This can result in anything from transient obstruction of the catheter to complete transsection and embolization of the catheter.

The imaging appearance of subclavian central venous catheters can be graded from 0-3 based on the severity of the compression. A normal catheter that runs a smooth curved course in the region of the clavicle and first rib without luminal narrowing is considered grade 0. Grade 1 refers to an abrupt change in course of the catheter without luminal narrowing. This can be seen in up to 1/3 of asymptomatic control patients.

Grade 2 is considered when luminal narrowing is present. This has been referred to as the "pinch-off sign" on chest radiography: indentation of the catheter as it passes deep to the clavicle. This findings represents significant catheter compression and should raise concern for serious catheter complications.

Finally, complete catheter fracture is referred to as grade 3.

The radiograph on the left was obtained 6 months after port placement. The catheter was non-functional. The inset reveals a small indentation (black arrows) as the catheter passes between the clavicle and the first rib, consistent with the pinch-off sign. Contrast injection into the port 5 days later revealed fracture of the catheter at the site of the indentation, with extravasation of contrast at the fracture site (white arrows).

References

Monday, December 26, 2011

Klippel-Trenaunay Syndrome

Klippel-Trenaunay syndrome is a congenital disorder of limb asymmetry associated with vascular abnormalities. It is also known as nevus vasculosus osteohypertrophicus and Parkes Weber syndrome (after Frederick Parkes Weber).

Diagnosis requires 2 or more of the following three classic characteristics:
  • Cutaneous vascular lesions: Port-wine stain (nevus flammeus). These are mostly capillary malformations and usually involve the affected limb. Most common manifestation (seen in 98% of patients). Unlike hemangiomas, the cutaneous vascular lesions don't evolve with time.
  • Abnormal venous and lymphatic structures : Varicosities and venous malformations can be superficial, deep, or perforating.
  • Enlargement of an extremity: Least common of the three abnormalities. Usually unilateral involvement of a lower extremity. Enlargement of the extremity can be caused by circumferential soft-tissue hypertrophy, bone elongation, or both. The bony and soft-tissue enlargement may be due to local hyperemia and venous stasis from the aforementioned venous abnormalities.
The images above are from a patient with left leg hypertrophy, nevi predominantly on the left foot, and varicose veins throughout the left lower extremity.

References

Sunday, December 25, 2011

Dysgerminoma

Dysgerminomas are the ovarian counterpart of testicular seminoma. Dysgerminomas are the second most common ovarian germ cell tumor and the most common malignant germ cell tumor. They are most commonly seen in girls and young women in the 2nd and 3rd decades of life.

The majority of tumors are pure dysgerminomas, which do not secrete any hormones. About 5%, however, contain syncytiotrophoblastic giant cells and produce β−hCG.

Dysgerminomas are multilobulated, usually unilateral, solid masses that can contain speckled calcifications (pink arrow), prominent fibrovascular septa, and central low-attenuation areas representing necrosis and hemorrhage (white arrow).

The differential diagnosis for ovarian neoplasms with calcification was covered earlier.

References

Saturday, December 24, 2011

Flexion-Extension Radiography in Evaluation of Suspected Cervical Spine Trauma

The clinical utility of flexion-extension radiography for diagnosing ligamentous injury in patients with suspected cervical spine trauma is questionable. The rate of technically inadequate studies, low sensitivity, and high false-positive rate make the technique too unreliable. In addition, the risk of inducing spinal cord injury makes flexion and extension radiography contraindicated until other imaging studies have been performed.

Flexion and extension radiography and dynamic fluoroscopy can be useful in assessing the significance of equivocal MR findings such as abnormal ligamentous signal without definite disruption and in patients with a normal MR and continued clinical concern for ligamentous injury.

References

Daffner RH, Hackney DB. ACR Appropriateness Criteria on suspected spine trauma. J Am Coll Radiol. 2007 Nov;4(11):762-75.

Friday, December 23, 2011

Thorotrast Accumulation in the Spleen

Thorotrast (Thorium dioxide) was used as an intravenous contrast agent during World War II. It is taken up by the reticuloendothelial system and is slowly excreted by the kidneys.

Radiographs reveal increased density of a small or normal-sized (depending on how long ago the injection was), granular spleen with a fine mottled appearance. The splenic capsule is not abnormally dense. The liver may also be denser, but this is not as pronounced on radiographs.

On CT scan, the liver and abdominal lymph nodes have slightly higher attenuation, although not to the extent of that of the spleen. The Thorotrast deposits are not seen on conventional MRI or on ultrasound.

The problem with Thorotrast is that it is an alpha-emitter and can cause liver tumors (intrahepatic cholangiocarcinoma and angiosarcoma), decades after injection.

The main differential consideration is gold deposition from prolonged treatment of rheumatoid arthritis, which can look identical across all imaging modalities discussed above. Miliary calcification from miliary tuberculosis or a vascular disorder that results in multiple calcifications can be similar on radiographs, but will have imaging characteristics of calcium on ultrasound and MRI. In addition, on radiography, miliary calcifications are generally coarser in appearance, larger, and fewer in number. Some people mention capsular calcifications and calcifications in splenic cysts in the differential, but these are pretty easy to differentiate from thorotrast spleen.

The image above shows a patient with a history of Thorotrast injection. The chest radiograph shows fine granular densities within the spleen. The CT image with bone windows show the granularity as well. The liver on this non-contrast study has a higher attenuation than normal (70 HU, compared to about 55 HU for normal). The ultrasound shows a small spleen, but is otherwise normal.

Special thanks to Dr. Tommaso Bartalena for adding gold deposition to the differential diagnosis.

References

  • Bartalena T, Rinaldi MF. Hyperdense spleen after prolonged gold therapy. CMAJ. 2010 Dec 14;182(18):E858.
  • Ono N, Hirai K, Ijyuin H, Itano S, Noguchi H, Sakata K, Aoki Y, Aritaka T, Abe H, Tanikawa K. MRI in thorotrastosis. Clin Imaging. 1995 Oct-Dec;19(4):229-33.
  • Samuel E. Thorotrast spleen. Br J Radiol. 1955 Apr;28(328):204-5.
  • Yamamoto Y, Chikawa J, Uegaki Y, Usuda N, Kuwahara Y, Fukumoto M. Histological type of Thorotrast-induced liver tumors associated with the translocation of deposited radionuclides. Cancer Sci. 2010 Feb;101(2):336-40.

Thursday, December 22, 2011

Ossification of the Sacrotuberous Ligaments

Ossification of the sacrotuberous ligaments has a caudocranial direction of growth. On frontal radiographs, pencil-like opacities project over the obturator foramina and extend cephalad and medially towards the sacrum. On cross-sectional imaging, the ossifications have a ventrodorsal flattened appearance and extend cephalad from the ischial tuberosities medially and posteriorly.

It has been suggested that ossification of the sacrotuberous ligaments is a good indicator of diffuse idiopathic skeletal hyperostosis (DISH), although others have contested this association. For what it's worth, our patient, a 50-year-old man, had no manifestations of DISH in the spine. Ossification of the sacrotuberous ligaments has also been associated with pudendal nerve entrapment.

Atherosclerotic calcifications can mimic the appearance of ossified sacrotuberous ligaments, but recognition of the course and tubular nature of these calcifications should be sufficient to avoid confusion.

References

  • Arora J, Mehta V, Suri RK, Rath G. Unilateral partial ossification of sacrotuberous ligament: anatomico-radiological evaluation and clinical implications. Rom J Morphol Embryol. 2009;50(3):505-8.
  • Prescher A, Bohndorf K. Anatomical and radiological observations concerning ossification of the sacrotuberous ligament: is there a relation to spinal diffuse idiopathic skeletal hyperostosis (DISH)? Skeletal Radiol. 1993 Nov;22(8):581-5.
  • Robert R, Prat-Pradal D, Labat JJ, Bensignor M, Raoul S, Rebai R, Leborgne J. Anatomic basis of chronic perineal pain: role of the pudendal nerve. Surg Radiol Anat. 1998;20(2):93-8.

Wednesday, December 21, 2011

Malignant Peripheral Nerve Sheath Tumors

Malignant peripheral nerve sheath tumors make up about 10% of all soft-tissue sarcomas. These are highly highly malignant tumors that tend to recur locally and to metastasize.

Up to half of all cases of malignant peripheral nerve sheath tumors are associated with neurofibromatosis type 1, and deep plexiform neurofibromas have an even higher risk of malignant transformation that superficial or solitary neurofibromas.

It can be difficult to differentiate malignant peripheral nerve sheath tumors from neurofibromas, a task that is even more difficult in patients with neurofibromatosis type 1.

Imaging features can help. A recent study by Wasa et al reviewed 41 cases of malignant peripheral nerve sheath tumor and 20 cases of neurofibroma, about half of whom had neurofibromatosis type 1. They found four statistically significant features that were useful in differentiating malignant peripheral nerve sheath tumors from neurofibromas, and suggest that a tumor with two or more of these features can be considered highly suspicious for malignancy. They also found an additional feature that was useful in patients with neurofibromatosis type 1.

The four (plus 1) features in their study were:
  • Large long-axis dimension: Malignant lesions tend to be larger than about 5 cm in largest dimension.
  • Peripheral enhancement: Focal central enhancement is usually seen in benign neurogenic tumors. Although neurofibromas can also show a peripheral enhancement pattern, this is more commonly seen in malignant peripheral nerve sheath tumors.
  • A perilesional edema-like zone:
  • Intratumoral cystic areas: Can be commonly seen in schwannomas and malignant peripheral nerve sheath tumors, but rarely in neurofibromas. Often is seen in association with peripheral enhancement
  • Heterogeneity on T1-weighted images (in neurofibromatosis type 1): Can be helpful in differentiating malignant peripheral nerve sheath tumors from neurofibromas in patients with neurofibromatosis 1, but doesn't seem helpful in the general population.
The case above doesn't really present a diagnostic dilemma. This is an enhancing soft tissue lesion that is malignant until proven otherwise. I'll try to find a case that better presents the challenge of differentiating a malignant peripheral nerve sheath tumor from a neurofibroma.

References

Wasa J, Nishida Y, Tsukushi S, Shido Y, Sugiura H, Nakashima H, Ishiguro N. MRI features in the differentiation of malignant peripheral nerve sheath tumors and neurofibromas. AJR Am J Roentgenol. 2010 Jun;194(6):1568-74.

Tuesday, December 20, 2011

Retractile and Ascending Testes

A retractile testis is a normally developed testis that can be brought into a stable position at the bottom of the scrotum during physical examination, but can also move into the groin by the cremasteric reflex.

As many as 35% of children's testes are thought to be retractile, with a peak incidence between the ages of 5 and 6 years. A retractile testis can transiently lie between the inguinal canal and scrotum and appear as a lump on physical examination and on imaging. Retractile testes usually descend completely by puberty, and there are no implications for fertility.

An ascending testis, also known as an ascended testis, ascensus testis, secondary cryptorchidism, and acquired cryptorchidism, is one that had previously been in the scrotum, but which can now be classified as undescended. Ascending testes are more frequently seen on the left, and many patients have associated disorders.

The majority of patients with an ascending testis can be shown to have had a history of a retractile testis and about 1/3 of boys with retractile testes go on to have ascending testes. The high position of the testis causes the same damage as seen with congenitally undescended testes and can lead to adverse effects on germ cell development and fertility.

Physical examination criteria have been proposed to differentiate an incompletely descended testis from a retractile testis on a single examination:
  • An incompletely descended testis is smaller than the contralateral testis
  • The incompletely descended testis rapidly retracts out of the scrotum when it is released.
  • Pain is elicited when the incompletely descended testis is manipulated into the scrotum.
Of these, only the first can be applied to imaging, and may be helpful in differentiating an incompletely descended testis from a retractile or ascending testis on a single imaging study. Physical examination is then needed to differentiate a retractile testis from an ascending testis.

The images above are from a 7-year-old boy who in 2010 had descended testes bilaterally. His most recent MRI (in 2011) reveals that the left testis (pink arrow) has moved up into the inguinal canal. Note that the testes are about the same size.

References

  • Guven A, Kogan BA. Undescended testis in older boys: further evidence that ascending testes are common. J Pediatr Surg. 2008 Sep;43(9):1700-4.
  • Kidney DD, Cohen AJ, Seville P. Retractile testis: an incidental CT finding in trauma patients. AJR Am J Roentgenol. 1997 May;168(5):1233-4.
  • Shadbolt CL, Heinze SB, Dietrich RB. Imaging of groin masses: inguinal anatomy and pathologic conditions revisited. Radiographics. 2001 Oct;21 Spec No:S261-71.
  • Shapiro E. The risk of retractile testes becoming ascending testes. Rev Urol. 2006 Fall;8(4):231-2.
  • Yoshida T, Ohno K, Morotomi Y, Nakamura T, Azuma T, Yamada H, Hayashi H, Suehiro S. Clinical and pathological features of ascending testis. Osaka City Med J. 2009 Dec;55(2):81-7.

Monday, December 19, 2011

Rosai-Dorfman Disease

Rosai-Dorfman disease, also known as sinus histiocytosis with massive adenopathy, is a macrophage-related histiocytic disorder of varied biological behavior.

Rosai-Dorfman disease predominantly affects children and adolescents, who most commonly with bilateral painless cervical lymphadenopathy and fever. There is a slight male predominance.

Extranodal involvement, seen in about 40% of cases, can occur with or without lymphadenopathy and can be solitary or multiple. Common extranodal sites include the nasal cavity and paranasal sinuses (shown above), although involvement has also been reported of the soft tissue, central nervous system, orbit, skin, oral cavity, bone, kidneys, upper respiratory tract, gastrointestinal tract, testicles and salivary glands.

The image above is from an atypical presentation in a middle-aged woman who presented with isolated paranasal sinus involvement. Biopsy of the left maxillary sinus lesion revealed the characteristic histopathologic feature of emperipolesis: Histiocytes with intracytoplasmic lymphocytes, plasma cells, erythrocytes, and/or polymorphonuclear leukocytes (from phagocytosis by the histiocytes). Another feature that can be seen is intracytoplasmic eosinophilic globules (Russell bodies) in the phagocytized plasma cells. These features are usually less prominent in extranodal Rosai-Dorfman disease, which was the case in this patient, who required a surgical biopsy for definitive diagnosis.

References

  • La Barge DV 3rd, Salzman KL, Harnsberger HR, Ginsberg LE, Hamilton BE, Wiggins RH 3rd, Hudgins PA. Sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease): imaging manifestations in the head and neck. AJR Am J Roentgenol. 2008 Dec;191(6):W299-306.
  • Gupta P, Babyn P. Sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease): a clinicoradiological profile of three cases including two with skeletal disease. Pediatr Radiol. 2008 Jul;38(7):721-8; quiz 821-2. Epub 2008 Feb 2.

Sunday, December 18, 2011

Response Evaluation Criteria in Solid Tumors (RECIST) 1.1: Imaging Basics

RECIST guidelines exist to standardize objective response to therapy on imaging and clinical examination. We focus here on the basics of imaging criteria. Special cases will be covered in a later post.

Baseline assessment
  • A tumor lesion or soft tissue component of a bony lesion are measurable if they are:
    • ≥ 10 mm on CT (slice thickness ≤ 5 mm).
    • ≥ 20 mm on chest radiography.
    • Lesions with cystic components are considered measurable; however, if non-cystic lesions are present in the same patient, these should be used as target lesions.
  • A lymph node is pathologically enlarged and measurable if it is:
    • ≥ 15 mm in short-axis dimension on CT (slice thickness ≤ 5 mm).
  • Non-measurable lesions include:
    • Small lesions (longest diameter <10 mm, pathological lymph nodes ≥ 10 to < 15 mm in short-axis dimension)
    • Blastic bone lesions
    • Leptomeningeal disease
    • Ascites
    • Pleural or pericardial effusion
    • Inflammatory breast disease
    • Lymphangitic involvement of skin or lung
    • Abdominal masses or organomegaly on physical exam not measurable by reproducible imaging techniques
The lesions should lend themselves to reproducible repeated measurements (i.e., the largest lesion is not necessarily the one that should be selected if it does not lend itself to reproducible measurement).

Measurable disease is defined by the presence of at least one measurable lesion as defined above. A maximum of five total lesions and a maximum of two lesions per organ are identified as target lesions and recorded and measured at baseline.

Overall tumor burden at baseline is then determined as the sum of the longest diameters of non-nodal lesions added to the sum of the short-axis dimension of nodal lesions (if nodal lesions are used as target lesions).

The sum at baseline will be used as a comparator for subsequent measurements. The same target lesions will be recorded and evaluated on subsequent imaging. Based on the behavior of these target lesions, objective tumor response is defined as:
  • Complete Response: Disappearance of all target lesions. Pathological lymph nodes (target or non-target) reduced in short=axis diameter to < 10 mm.
  • Partial Response: At least a 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters.
  • Progressive Disease: At least a 20% increase in the sum of diameters of target lesions AND an absolute increase of at least 5 mm in the sum of diameters of target lesions, taking as reference the smallest sum on prior studies (can include the baseline sum if that is the smallest). The appearance of one or more new lesions is also considered progression.
  • Stable Disease: Neither sufficient shrinkage to qualify for partial response nor sufficient increase to qualify for progressive disease, taking as reference the smallest sum of diameters while on the study.

References

  • Chalian H, Töre HG, Horowitz JM, Salem R, Miller FH, Yaghmai V. Radiologic Assessment of Response to Therapy: Comparison of RECIST Versions 1.1 and 1.0. Radiographics. 2011 Nov;31(7):2093-105.
  • Eisenhauer EA, Therasse P, Bogaerts J, Schwartz LH, Sargent D, Ford R, Dancey J, Arbuck S, Gwyther S, Mooney M, Rubinstein L, Shankar L, Dodd L, Kaplan R, Lacombe D, Verweij J. New response evaluation criteria in solid tumours: revised RECIST guideline (version 1.1). Eur J Cancer. 2009 Jan;45(2):228-47.

Saturday, December 17, 2011

Hydroxyapatite Ocular Implants

Hydroxyapatite ocular implants are porous implants that are derived from sea coral. The porous structure of these implants allows ingrowth of host fibrovascular tissue, which reduces the risk of migration, extrusion, and infection. In addition, the extraocular muscles can be more securely attached to the implants, allowing the implant to move synchronously with the other eye.

An understanding of the sequence of events after enucleation can reduce confusion when evaluating the post-operative eye. In addition, MRI and nuclear medicine may be requested to confirm vascularization of the implant, although this is no longer universally used.

Patient information and surgical demonstration videos for one type of ocular implant provide a good overview of the procedure.

The ocular implant is placed immediately after enucleation and a temporary ocular conformer is placed on top of the implant. This conformer stays in place for about 4 to 8 weeks after surgery, at which point an ocularist fits, shapes, and paints an ocular prosthesis to match the patient's other eye. The prosthesis sits on top of the implant like a large contact lens.

We can sometimes be a bit loose in terminology, but there is a distinction between implant and prosthesis.

Mechanical coupling between the implant and the prosthesis can be improved with a second procedure where a round-headed peg or screw is inserted into the implant (the back of the prosthesis is also modified to accommodate this peg). The hole for the peg is usually not drilled until 6 months after enucleation: Enough time to allow for implant vascularization.

Radiologists used to be called upon to confirm vascularization of the implant by bone scintigraphy or contrast-enhanced MRI prior to drilling the hole for the peg, but this is no longer routinely done. Bone scintigraphy can show increased activity within the implant starting 1 to 6 months after surgery, indicating fibrovascular ingrowth. Contrast-enhanced MRI can also reveal the extent of fibrovascular ingrowth.

The images above are from a patient 4 years post left eye enucleation. CT shows the implant with a high-attenuation prosthesis anterior to it. FDG/PET shows no activity in the implant. The MR images show the attachment of the extra-ocular muscles to the implant. Anterior to the implant is the prosthesis, which is low signal intensity on all pulse sequences. Both CT and MR show linear striations in the implant, which is presumably due to the channels in these implants, although I can't find a reference in this regard. Enhancement along the periphery of the implant indicates fibrovascular ingrowth. No peg was placed in this patient.

References

  • Custer PL, Kennedy RH, Woog JJ, Kaltreider SA, Meyer DR. Orbital implants in enucleation surgery: a report by the American Academy of Ophthalmology. Ophthalmology. 2003 Oct;110(10):2054-61.
  • De Potter P. Advances in imaging in oculoplastics. Curr Opin Ophthalmol. 2001 Oct;12(5):342-6.
  • Domange-Testard A, Papathanassiou D, Menéroux B, Amans J, Liehn JC. SPECT-CT images of an ocular coralline hydroxyapatite implant visible on bone scintigraphy. Clin Nucl Med. 2007 Feb;32(2):132-4.
  • Hamilton HE, Christianson MD, Williams JP, Thomas RA. Evaluation of vascularization of coralline hydroxyapatite ocular implants by magnetic resonance imaging. Clin Imaging. 1992 Oct-Dec;16(4):243-6.
  • Shields CL, Shields JA, De Potter P, Singh AD. Problems with the hydroxyapatite orbital implant: experience with 250 consecutive cases. Br J Ophthalmol. 1994 Sep;78(9):702-6.

Friday, December 16, 2011

Annular Pancreas

Annular pancreas is the second most common congenital pancreatic anomaly (after pancreas divisum), occurring in 1 in 2000 people. Its embryogenesis is unclear, but the end result is pancreatic tissue surrounding the second portion of the duodenum. This may be partial or complete.

Annular pancreas can be extramural or intramural. In the extramural type, the ventral pancreatic duct encircles the duodenum to join the main pancreatic duct. In the intramural type, the pancreatic tissue is intermingled with the duodenal wall muscle and small pancreatic ducts drain directly into the duodenum.

Patients with extramural annular pancreas can present with high gastrointestinal obstruction, sometimes with pancreatitis. Patients with intramural annular pancreas can present with symptoms of duodenal ulceration.

Contrast fluoroscopy can suggest the diagnosis by revealing narrowing at the level of the major papilla. ERCP or MRCP can show the duct of Wirsung encircling the duodenum in the patient with extramural annular pancreas. Cross sectional imaging will show pancreatic tissue around the second portion of the duodenum, as shown above in two patients with annular pancreas.

References

Thursday, December 15, 2011

Benign Notochordal Cell Tumors

Benign notochordal cell tumors are recently discovered intraosseous lesions of notochordal cell origin that are usually asymptomatic or indolent. Synonyms for this tumor include benign chordoma, giant notochordal rest, giant notochordal hamartoma of intraosseous origin, notochordal hamartoma, and ecchordosis physaliphora vertebralis.

These tumors can have histologic findings that overlap with those of chordomas. It has been suggested that benign notochordal cell tumors may be precursors of chordomas, but the evidence for this seems to be lacking at this point.

Like chordomas, benign notochordal cell tumors are most commonly found at the midline in the sacro-coccygeal region and the base of the skull.

On radiography, these are ill-defined and sclerotic lesions, sometimes with the appearance of an ivory vertebra. Radiographs can be normal, however. Regardless of the visibility of these lesions on radiographs, bone expansion should not be seen.

CT can also be normal or reveal sclerosis ranging from mild to severe. Trabecular and cortical destruction should not be seen. The lesions can be central in the vertebral body, extend to the cortex, or occupy the entirety of the vertebral body, resulting in an ivory vertebra.

The lesions are homogeneously hypointense on T1-weighted images, and homogeneously iso- to hyperintense on T2-weighted images. No significant enhancement is typically seen, although the lesion in our case has mild enhancement. Extraosseous extension should not be seen.

Chordomas may resemble benign notochordal cell tumors with cellular atypia on biopsy. Imaging can help in differentiating the two by remembering that in contrast to chordomas, benign notochordal cell tumors are not typically osteolytic and may have sclerosis. In addition, chordomas can have a soft tissue mass, while benign notochordal cell tumors typically do not.

References

Wednesday, December 14, 2011

Autoimmune Pancreatitis

Autoimmune pancreatitis is caused by periductal infiltration with IgG4-positive plasma cells, which leads to periductal and interlobular fibrosis, causing diffuse narrowing of the pancreatic duct and acinar atrophy. Autoimmune pancreatitis may be responsible for up to 10% of cases of chronic pancreatitis. Men are more commonly affected. Patients typically present with fluctuating obstructive jaundice, abdominal pain, weight loss, steatorrhea, and diabetes (~50% of patients).

The Mayo Clinic diagnostic criteria require one or more of the following findings:
  • Histologic findings diagnostic of autoimmune pancreatitis
  • Characteristic CT and pancreatographic findings with elevated serum IgG4 levels
  • Response to steroid therapy
The role of the radiologist is in identifying the characteristic imaging findings and differentiating them from those of acute pancreatitis and pancreatic carcinoma (up to ~10% of pancreatectomy patients for presumed carcinoma actually have autoimmune pancreatitis).

The affected area(s) of the pancreas are typically hypoechoic, hypoattenuating, T1-hypointense, and mildly T2-hyperintense. Decreased enhancement is usually seen during early dynamic imaging, and moderate enhancement is seen in the late phases. A capsule-like rim or halo of low attenuation or intensity is common and is thought to represent fluid, phlegmon, or fibrous tissue. ERCP or MRCP typically reveals a narrow and irregular pancreatic duct in the affected portion(s) of the pancreas.

Three patterns of autoimmune pancreatitis have been recognized
  • Diffuse: Most common type. The pancreas is sausage-like: diffusely enlarged with a sharp margin and loss of the normal lobular contour and pancreatic clefts.

    This form can mimic the appearance of acute pancreatitis. Unlike acute pancreatitis, there is minimal or no peripancreatic stranding and no peripancreatic fat necrosis.
  • Focal: Looks like a relatively well-demarcated focal mass, often involving the pancreatic head.

    This form Can mimic pancreatic carcinoma, but upstream dilatation of the main pancreatic duct is typically milder than in patients with carcinoma (usually smaller than 5 mm). In addition, while the peripancreatic veins may be involved in patients with focal autoimmune pancreatitis and in those with pancreatic cancer, involvement of the peripancreatic arteries is unlikely in the former.

    On ERCP patients with focal autoimmune pancreatitis usually have a stenosed main pancreatic duct longer than 30 mm and an upstream main pancreatic duct that is smaller than 6 mm in diameter.
  • Multifocal: Self explanatory.
The pancreas and pancreatic duct usually return to normal on imaging within 4–6 weeks after initiation of steroid therapy. However, there is atrophy of the affected areas of the pancreas in the burnt-out phase of the disease in about half of patients. Spontaneous regression is can also occur. Diabetes may also resolve following treatment.

Two cases of autoimmune pancreatitis are shown above. The left image has a sausage-like pancreas that is diffusely enlarged with a sharp margin and loss of the normal lobular contour and pancreatic clefts. The pancreas in the right image has a low-attenuation peri-pancreatic halo. Peripancreatic stranding is minimal to absent in both cases.

References

  • Vlachou PA, Khalili K, Jang HJ, Fischer S, Hirschfield GM, Kim TK. IgG4-related sclerosing disease: autoimmune pancreatitis and extrapancreatic manifestations. Radiographics. 2011 Sep-Oct;31(5):1379-402.
  • Yang DH, Kim KW, Kim TK, Park SH, Kim SH, Kim MH, Lee SK, Kim AY, Kim PN, Ha HK, Lee MG. Autoimmune pancreatitis: radiologic findings in 20 patients. Abdom Imaging. 2006 Jan-Feb;31(1):94-102.

Tuesday, December 13, 2011

Aortitis: Differential Diagnosis

Aortitis, the inflammation of the aortic wall, can be due to infectious or noninfectious conditions. Patients present with nonspecific signs, symptoms, and laboratory findings that can include pain, fever, vascular insufficiency, and elevated levels of acute phase reactants.

Differential considerations include:

Noninfectious
  • Large-vessel vasculitides (shown above):
    • Giant cell arteritis: Affects large and medium-sized vessels. Often involves the superficial cranial arteries.
    • Takayasu arteritis: Abdominal aorta most commonly affected. Descending thoracic aorta and aortic arch can also be involved. Look for stenosis or luminal narrowing of aorta and branch vessels. Aneurysmal dilatation less common, but can be seen after destruction of media. Arterial wall calcification (can be seen in chronic cases) is typically linear and spares the ascending aorta.
    • Rheumatoid arthritis: Aortitis is rare. Heart, aortic valve, and great vessels can be affected.
    • Systemic lupus erythematosus: Aortitis uncommon.
    • Ankylosing spondylitis: Aortic root and valve disease seen in 80% of cases. Aortic wall thickening is seen in 60% of affected patients.
    • Reiter syndrome:
  • Medium- and small-vessel vasculitides:
    • Wegener arteritis:
    • Polyarteritis nodosa:
    • Behçet disease: Wall-enhancing saccular pseudoaneurysms can be seen in the aorta and branch vessels in 20% of patients.
    • Relapsing polychondritis: May manifest as aortic root dilatation and aortitis.
    • Cogan syndrome: Ocular, inner ear, and vascular inflammation. Patients are usually white young adults. Aortitis and valvulitis seen in ~10% of patients.
  • Isolated aortitis: Isolated idiopathic (thoracic) aortitis, Chronic periaortitis (Idiopathic retroperitoneal fibrosis, inflammatory abdominal aortic aneurysm, perianeurysmal aortitis, idiopathic isolated abdominal periaortitis).
  • Radiation-induced: Usually years after exposure to high-dose radiation. Can manifest as thrombosis, pseudoaneurysm, rupture, stenosis, and accelerated wall calcification.
Infectious
  • Bacterial: Salmonella, Staphylococcus, Streptococcus pneumoniae
  • Syphilis: The typical calcification of the ascending aorta is uncommon.
  • Mycobacterial: Mycobacterium tuberculosis
  • Viral: HIV.

References

Monday, December 12, 2011

Metformin and 18F-FDG PET

Metformin has been shown to significantly increase 18F-FDG uptake in the colon and, to a lesser extent, the small bowel.

Cells of the intestinal wall are exposed to much higher concentrations of metformin for much longer times compared to other cell types. In addition, animal studies have shown that metformin increases glucose transfer into intestinal mucosal cells and can increase glucose utilization by up to 60%.

This results in intense, diffuse, and continuous uptake along the bowel on 18F-FDG PET imaging. The uptake is seen in both the wall and within the lumen (likely due to excretion of 18F-FDG into the stool).

The pattern is fairly characteristic and confusion with malignant focal bowel uptake is rare. The problem is that this diffuse uptake can mask an existing bowel malignancy and lead to a false-negative result.

References

Gontier E, Fourme E, Wartski M, Blondet C, Bonardel G, Le Stanc E, Mantzarides M, Foehrenbach H, Pecking AP, Alberini JL. High and typical 18F-FDG bowel uptake in patients treated with metformin. Eur J Nucl Med Mol Imaging. 2008 Jan;35(1):95-9.

Sunday, December 11, 2011

Fibrous Hamartoma of Infancy

Fibrous hamartoma of infancy is a rare benign fibrous tumor found in early childhood, more commonly in boys. More than 90% occur during the 1st year of life, and about 25% are congenital. They can be rapidly growing, but are cured by local excision. Recurrence is rare, but also cured by excision.

These are superficial tumors that are usually painless and freely movable, but may also be attached to the underlying fascia. Involvement of the skeletal muscle is rare. They are most commonly located in the axilla, followed by the upper arm and shoulder, thigh and groin, back, and forearm.

Fibrous hamartomas of infancy are poorly circumscribed masses that consist of a mixture of fibrocollagenous tissue, immature -appearing primitive mesenchymal cells, and mature fat.

Ultrasound is usually the first modality used for evaluation of these lesions, but I can't find a reference for the appearance of these lesions on sonography. MR characteristics reflect the different components discussed above: The fibrocollagenous component is low signal intensity on both T1- and T2-weighted images and the mature fat component is hight signal intensity on both T1- and T2-weighted images. Organized trabeculae of fibrous tissue interspersed with fat should suggest the diagnosis.

When fat is identified in these lesions, the differential diagnosis in infants should include lipoma, lipoblastoma, and an involuting hemangioma.

The images above are from a 1-year-old boy with a right forearm mass (pink arrow). The lateral radiograph reveals an ill-defined mass along the volar surface of the proximal forearm. Ultrasound reveals a heterogeneous, predominantly hyperechoic lesion without significant vascularity on Doppler. MRI reveals a lobular, ill-defined mass that is predominantly isointesnse to skeletal muscle on the T1-weighted image and hyperintense on the T2-weighted image, but has internal areas of fat signal. Thin fibrous sepata are seen on the T1-weighted image (black arrow). Mild enhancement is seen.

References

  • Hashimoto H. Fibrous hamartoma of infancy. in Pathology and Genetics of Tumours of Soft Tissue and Bone. Fletcher CDM, Unni KK, Mertens F (eds). IARCPress Lyon, 2002. pp 58-59.
  • Laffan EE, Ngan BY, Navarro OM. Pediatric soft-tissue tumors and pseudotumors: MR imaging features with pathologic correlation: part 2. Tumors of fibroblastic/myofibroblastic, so-called fibrohistiocytic, muscular, lymphomatous, neurogenic, hair matrix, and uncertain origin. Radiographics. 2009 Jul-Aug;29(4):e36.

Saturday, December 10, 2011

Renal Leiomyoma

Renal leiomyomas are benign tumors of the kidneys that most commonly arise from smooth muscle cells of the renal capsule. Other origins include the muscularis of the renal pelvis and cortical vascular smooth muscles. The tumors contain areas of hemorrhage and irregular calcification.

They are relatively uncommon, being found in ~5% of subjects in autopsy series, more commonly in white women.

Most renal leiomyomas are small and asymptomatic, but larger lesions can cause pain or even be palpable.

The imaging appearance of renal leiomyoma is nonspecific. They tend to be well-circumscribed and peripherally located lesions that cause buckling of the renal cortex. Non-contrast CT reveals a high-attenuation mass that can have areas of hemorrhage and cystic degeneration (larger lesions). Calcification is uncommon. Contrast enhanced CT images reveal relatively homogeneous enhancement.

MRI typically reveals a lesion with homogeneously low signal intensity on T1- and T2-weighted images. As on CT, larger lesions can have a complex appearance due to calcifications, hemorrhage, and cystic or myxoid degeneration. The appearance of these large tumors can be identical to that of renal cell carcinoma.

The images above are from a renal tumor protocol CT in a patient with an incidentally detected left renal lesion. The lesion is peripheral, relatively small, and has foci of calcification (uncommon in leiomyomas) as well as an area of low-attenuation/non-entrancement. The lesion is hypervascular. The imaging findings are nonspecific and the lesion should be thought of as renal cell carcinoma until proven otherwsie. Core biopsy prior to radiofrequency ablation revealed a diagnosis of leiomyoma.

References

Prasad SR, Surabhi VR, Menias CO, Raut AA, Chintapalli KN. Benign renal neoplasms in adults: cross-sectional imaging findings. AJR Am J Roentgenol. 2008 Jan;190(1):158-64.

Friday, December 9, 2011

Li-Fraumeni Syndrome

Li-Fraumeni syndrome is an autosomal-dominant familial cancer syndrome that results in an increased lifelong risk of what are considered Li-Fraumeni syndrome spectrum tumors (e.g., soft tissue sarcoma, osteosarcoma, brain tumor, premenopausal breast cancer, adrenocortical carcinoma, leukemia, lung bronchoalveolar cancer), among others. About 3/4 of patients have a mutation in the gene encoding the p53 tumor suppressor protein (TP53). The cancers aren't limited to those listed above, however, and patients can have a wide range of malignancies, including melanoma, germ-cell tumors, gastric carcinoma, Wilms tumor, lymphoma, and lung, laryngeal, prostate, and pancreatic cancers.

The 2009 Chompret (after Agnès Chompret) criteria for germline TP53 mutation screening are as follows:
  • [A Li-Fraumeni syndrome spectrum tumor before age 46 years.] AND [At least one first- or second-degree relative with a Li-Fraumeni syndrome spectrum tumor (except breast cancer if the proband has breast cancer) before the age of 56 years or with multiple tumors.]
    OR
  • [Multiple tumors (except multiple breast tumors), two of which belong to the Li-Fraumeni syndrome tumor spectrum.] AND [The first tumor occurred before the age of 46 years.]
    OR
  • [Adrenocortical carcinoma or choroid plexus tumor (irrespective of family history).]
These criteria result in a mutation detection rate of ~30-35% and sensitivity and specificity of ~80-90% and ~50-60%, respectively.

These screening criteria and the availability of genetic testing raise the question of how best to manage patients, asymptomatic carriers, and relatives of patients with Li-Fraumeni syndrome.

Regarding the patient with Li-Fraumeni syndrome and a known malignancy: Radiation must be carefully applied (if at all), as second malignant tumors frequently arise in the radiotherapy field in these patients.

It has been suggested that women begin breast cancer screening in their mid-20s (the average age of onset is ~30 years in these patients). Beyond that, there are currently no clear clinical surveillance, preventive, or treatment recommendations for patients with Li-Fraumeni syndrome.

The situation seems even less clear when it comes to management of asymptomatic relatives of patients with p53 germline mutations. This is because of the variable expressivity of the mutation, the diverse range of tumors, and, as noted above, absence of clear surveillance, preventative, and treatment recommendations.

PET-CT has been put forward as a surveillance modality for identifying presymptomatic malignancies. In a study of members of Li-Fraumeni syndrome families with germline TP53 mutations, FDG-PET/CT screening resulted in cancer detection in 20% (3 out of 15 subjects).

Prenatal genetic testing can also be offered after careful screening and thorough counseling of parents.

The images above are from a patient with a history of right adrenal cortical carcinoma (note the clips on the right, pink arrow), who developed an anterior mediastinal sarcoma. A p53 mutation was found.

References

Thursday, December 8, 2011

Cystic Retroperitoneal Masses: Differential Diagnosis

  • Epithelial neoplasms: Mucinous cystadenoma or cystadenocarcinoma, serous cystadenocarcinoma, perianal mucinous cystadenocarcinoma (rare, associated with history of anal fistula).
  • Mesothelial neoplasms: Mesothelioma.
  • Germ cell neoplasms: Cystic teratoma.
  • Neuroendocrine neoplasms: Paraganglioma.
  • Neural neoplasm: Schwannoma.
  • Sarcoma: Necrotic areas can appear cystic.
  • Lymphovascular: Lymphangioma, lymphangiomatosis, lymphangioleiomyoma.
  • Developmental: Müllerian cyst, epidermoid cyst, tailgut cyst, bronchogenic cyst (subdiaphragmatic location).
  • Miscellaneous fluid collections: Hematoma, urinoma, abscess, lymphocele (shown above in a patient with testicular cancer, post lymph node dissection), pseudocyst (pancreatic, and nonpancreatic), pseudomyxoma retroperitonei (caused by a ruptured mucocele of the appendix).

References

Rajiah P, Sinha R, Cuevas C, Dubinsky TJ, Bush WH Jr, Kolokythas O. Imaging of uncommon retroperitoneal masses. Radiographics. 2011 Jul-Aug;31(4):949-76.

Wednesday, December 7, 2011

Kikuchi-Fujimoto Disease

Kikuchi-Fujimoto disease, also known as Kikuchi disease and histiocytic necrotizing lymphadenitis lymphadenitis, is a rare, self-limiting condition characterized by characterized by lymphadenopathy, fever, and neutropenia.

Its cause is unknown. Viral etiologies have been proposed, with the usual suspects (EBV, HHV 6 and 8) included in the lineup. An autoimmune mechanism has also been suggested, supported by a strong association with systemic lupus erythematosus and mixed connective tissue disorders.

Patients are typically girls or young women under 30 years of age. The most common presentation is firm, tender, unilateral cervical lymphadenopathy. Patients may also have more generalized adenopathy, low-grade fever, malaise, fatigue, diarrhea, weight loss, nausea, and vomiting. Kikuchi-Fujimoto disease generally has a benign, self-limited course with symptoms lasting between 1–2 months.

Patients can have nonspecific laboratory findings such as neutropenia with atypical lymphocytes, anemia, and elevated rythrocyte sedimentation rate (ESR), lactogen dehydrogenase (LDH), and transaminases. Diagnosis, however, can be made with biopsy revealing effaced nodal architecture with islands of hyperplasia and zonal necrosis. Fine needle aspiration can also be used.

Imaging findings overlap with those of lymphoma, and biopsy cannot be avoided. As noted above, the lymphadenopathy is more commonly found in the neck, where it is more often unilateral. Cervical lymph nodes range in size from 0.5–3.5 cm and the majority of patients show perinodal fatty infiltration and homogeneous nodal contrast enhancement. A minority of cases have lymph nodes with low-attenuation areas, sometimes resulting in ring-shaped lymph nodes mimicking tuberculosis or metastatic lymphadenopathy.

The images above are from a 50-year-old woman with diffuse lymphadenopathy and "mildly positive ANA." Cervical, mediastinal, hilar, and axillary lympahdenopathy was noted, without evidence of retroperitoneal or pelvic lympahdenopathy. Nodal enhancement was homogeneous. Mild perinodal infiltration is well seen in a left level IIA lymph node (red *)

References

Tuesday, December 6, 2011

Subcutaneous Granuloma Annulare

[No Image Available]

Granuloma annulare is an uncommon, benign inflammatory papular eruption. Granuloma annulare is classified as localized, generalized (disseminated), perforating, erythematous, or subcutaneous. The first four types are cutaneous and are diagnosed and managed by dermatologists.

Subcutaneous granuloma annulare, because of its deeper location, can present a diagnostic challenge, leading to multiple referrals and imaging evaluation. Indeed, subcutaneous granuloma annulare is the most frequently biopsied benign soft tissue mass in the lower extremity of children under the age of 5, and is susceptible to inappropriate and sometimes repeated surgical intervention before the correct diagnosis is determined.

Synonyms for subcutaneous granuloma annulare include benign rheumatoid nodule, pseudorheumatoid nodule, deep granuloma annulare, subcutaneous palisading granuloma, palisading granuloma nodosum, and isolated subcutaneous nodule.

Subcutaneous granuloma annulare typically presents as a rapidly growing, firm, painless, subcutaneous mass in children younger than 5 years of age. A pretibial location is typical and lesions along the extensor aspects of forearms and feet, and within the occipital scalp are also common. Atypical presentations with pain and multiple soft lesions have also been reported.

Radiographs reveal a dense subcutaneous mass without calcifications. The lesions are hypoechoic on ultrasound. MRI reveals a subcutaneous lesion with indistinct margins and signal abnormality extending into the adjacent subcutaneous fat. The lesions are iso- or slightly hyperintense to muscle on T1-weighted images and heterogeneously hyperintense on T2-weighted images. Enhancement can be variable.

The imaging findings are nonspecific, but the age and location can suggest the diagnosis. Differential considerations include:
  • Subcutaneous nodules of rheumatoid arthritis: Imaging findings can be identical, and pathological findings can be very similar.
  • Foreign-body reactions:
  • Post-traumatic lesions: Fat necrosis, hematoma,
  • Infectious lesions: Abscess, inflammatory granuloma

References

  • Chung S, Frush DP, Prose NS, Shea CR, Laor T, Bisset GS. Subcutaneous granuloma annulare: MR imaging features in six children and literature review. Radiology. 1999 Mar;210(3):845-9.
  • Jang EJ, Lee JY, Kim MK, Yoon TY. Erythematous granuloma annulare. Ann Dermatol. 2011 Aug;23(3):409-11.
  • Vandevenne JE, Colpaert CG, De Schepper AM. Subcutaneous granuloma annulare: MR imaging and literature review. Eur Radiol. 1998;8(8):1363-5.
  • Wollina U. Granuloma annulare disseminatum responding to fumaric acid esters. Dermatol Online J. 2008 Dec 15;14(12):12.

Monday, December 5, 2011

Alkaptonuria, Ochronosis, and Ochronotic Arthropathy

Alkaptonuria (also known as alcaptonuria) is an autosomal recessive condition caused by homogentisate 1,2-dioxygenase deficiency in the liver. The consequence of this deficiency is homogentisic aciduria (alkaptonuria), which is followed by ochronosis and ochronotic arthropathy.

Ochronosis

Ochronosis is caused by deposition of homogentisic acid as a polymer in collagenous tissues, resulting in a dark blue discoloration of sclera, cornea, cartilage, and heart valves. Ochronosis is seen on physical exam and on biopsy by noting the dark blue discoloration.

Not all cases of ochronosis are genetic. Exogenous ochronosis, which is clinically and histologically similar, is differentiated by its lack of systemic effects. It is most commonly caused by hydroquinone-containing products such as skin lightening creams, which paradoxically cause skin hyperpigmentation in these patients. Exogenous ochronosis can also occur following the use of antimalarial medications and products with resorcinol, phenol, mercury or picric acid.

Ochronotic Arthropathy

Longstanding ochronosis can lead to joint destruction. The mechanism is thought to be a positive feedback loop initiated by pigment deposition, which makes adjacent tissue susceptible to pigmentation and leads to progressive tissue destruction.

Ochronotic arthropathy can be seen on imaging as joint destruction and mineral deposition. Characteristic imaging findings of ochronotic arthropathy include involvement of the thoracic and lumbar spines with relative sparing of the cervical spine. In the thoracolumbar spine, one may see osteopenia, loss of lumbar lordosis, multilevel calcification of the annulus fibrosus, vacuum phenomenon, and progressive narrowing of intervertebral spaces. Patients with longstanding ochronosis can have severe kyphosis, obliteration of the intervertebral spaces, and marginal osteophytes that can look like syndesmophytes.

Findings in the appendicular skeleton are nonspecific and resemble osteoarthritis, except that there is less pronouced ostephyte formation than would be expected for the degree of joint space narrowing. Chondrocalcinosis can be seen. In the knee, which is typically involved, the lateral compartment is more severely affected.

Differential considerations for disk calcifications of ochronotic arthropathy include:
  • Calcium pyrophosphate dihydrate deposition disease
  • Degenerative or post-traumatic osteoarthritis
  • Ankylosing spondylitis
  • Hemochromatosis
  • Hyperparathyroidism
  • Acromegaly
  • Amyloidosis
Differential considerations for chondrocalcinosis include:
  • Calcium pyrophosphate dihydrate crystal deposition disease (CPPD)
  • Degenerative or post-traumatic osteoarthritis
  • Hemochromatosis
  • Hyperparathyroidism
  • Idiopathic

References

  • Aquaron RR. Alkaptonuria in France: past experience and lessons for the future. J Inherit Metab Dis. 2011 Dec;34(6):1115-26.
  • Baeva M, Bueno A, Dhimes P. AIRP best cases in radiologic-pathologic correlation: ochronosis. Radiographics. 2011 Jul-Aug;31(4):1163-7.
  • Bongiorno MR, Aricò M. Exogenous ochronosis and striae atrophicae following the use of bleaching creams. Int J Dermatol. 2005 Feb;44(2):112-5.
  • Taylor AM, Boyde A, Wilson PJ, Jarvis JC, Davidson JS, Hunt JA, Ranganath LR, Gallagher JA. The role of calcified cartilage and subchondral bone in the initiation and progression of ochronotic arthropathy in alkaptonuria. Arthritis Rheum. 2011 Dec;63(12):3887-96.

Sunday, December 4, 2011

Sphenooccipital Synchondrosis

The sphenooccipital synchondrosis is the cartilagenous space between the basal portion of the sphenoid and occipital bones. Radiographs of the open synchondrosis reveal a lucent band 1 to 3 mm in width across the clivus at the level of the petrous apex. It usually closes by the age of 25. Ossification starts above and proceeds down, and is usually evident on radiographs as superior narrowing around the age of 13.

References

Irwin GL. Roentgen determination of the time of closure of the spheno-occipital synchondrosis. Radiology. 1960 Sep;75:450-3.

Saturday, December 3, 2011

Diaphyseal Dysplasias

We'll be dealing with two possibly related disorders: Progressive diaphyseal dysplasia (Camurati-Engelmann disease, Engelmann disease) and hereditary multiple diaphyseal sclerosis (Ribbing disease, shown above). The arguments for and against the relatedness of these disorders are not convincing one way or the other and will not be discussed.

Both are disorders of intramembranous ossification, primarily affecting the diaphysis and sparing the metaphysis and epiphysis, which are formed by endochondral ossification. Both conditions manifest radiographically as periosteal and endosteal hyperostosis of the long bones. Bone scintigraphy can be positive in both. The clinical and imaging presentations diverge after this:
  Camurati-Engelmann Ribbing
Patient age Children Young adults to middle aged
Disease course Progression or regression Slow progression followed by stabilization
Symptoms Waddling gait, bone pain, myopathy, and weakness Bone pain in the affected extremities
Patient appearance Elongated long bones (Marfanoid) Non-Marfanoid
Distribution Bilateral and symmetric Unilateral or asymmetrically and asynchronously bilateral (usually lower extremities)
Skull base involvement Sometimes No


Other conditions can mimic these diaphyseal dysplasias. Medullary osteosclerosis, like Camurati-Engelmann and Ribbing diseases can present radiographically as increased bone formation within the medullary cavity of the long bones of the lower extremities. Like Ribbing disease, the onset is usually in adulthood. Unlike the two diaphyseal dysplasias that are the subject of this post, the sclerosis in medullary osteosclerosis is limited to the medullary space, with minimal or no cortical thickening.

Melorheostosis can also present with both peri- and endosteal hyperostosis, but the endosteal hyperostosis, if present, is usually seen in later stages of the disease and is less advanced than the characteristic periosteal hyperostosis.

Finally, Erdheim-Chester disease may have cortical thickening, narrowing of the medullary cavity, sparing of the epiphyses, and a symmetric lower extremity dominant distribution. In addition to the above, radiographs of patients with Erdheim-Chester disease can show bone infarctions and periostitis.

The images above from a 50-year-old man show asymmetric right lower extremity endosteal and mild periosteal hyperostosis. The skull is normal. The age, skeletal distribution, and skull findings suggest Ribbing disease. Mild periosteal sclerosis is seen, helping differentiate this case from medullary osteosclerosis.

Eponym: The Ribbing in Ribbing disease is not a gerund, but is the last name of the Swedish radiologist (Seved Ribbing) who described the condition in 1949.

References

  • Ihde LL, Forrester DM, Gottsegen CJ, Masih S, Patel DB, Vachon LA, White EA, Matcuk GR Jr. Sclerosing bone dysplasias: review and differentiation from other causes of osteosclerosis. Radiographics. 2011 Nov;31(7):1865-82.
  • Ribbing S. Hereditary, multiple, diaphyseal sclerosis. Acta radiol. 1949 Jun 30;31(5-6):522-36.
  • Seeger LL, Hewel KC, Yao L, Gold RH, Mirra JM, Chandnani VP, Eckardt JJ. Ribbing disease (multiple diaphyseal sclerosis): imaging and differential diagnosis. AJR Am J Roentgenol. 1996 Sep;167(3):689-94.
  • Shier CK, Krasicky GA, Ellis BI, Kottamasu SR. Ribbing's disease: radiographic-scintigraphic correlation and comparative analysis with Engelmann's disease. J Nucl Med. 1987 Feb;28(2):244-8.
  • Ziran N, Hill S, Wright ME, Kovacs J, Robey PG, Wientroub S, Collins MT. Ribbing disease: radiographic and biochemical characterization, lack of response to pamidronate. Skeletal Radiol. 2002 Dec;31(12):714-9.

Friday, December 2, 2011

Birt-Hogg-Dubé Syndrome

Birt-Hogg-Dubé syndrome is a rare autosomal-dominant multiorgan disorder that affects the skin, kidneys, and lungs.

Skin lesions include the characteristic triad of fibrofolliculomas (hamartomas of the hair follicles, 2- to 4-mm, smooth, dome-shaped papules), trichodiscomas (tumors of the hair disk), and acrochordons (skin tags).

Renal involvement includes a predisposition to hybrid chromophobe oncocytomas, chromophobe carcinomas, clear cell carcinomas, oncocytomas, and papillary renal cell carcinomas.

Pulmonary involvement manifests as cystic lung disease and spontaneous pneumothorax. The cysts are variable in shape and size, but are discrete and thin-walled. Larger cysts are usually multiseptated. The cysts tend to be larger and more numerous in the lower lobes, a distribution that can help differentiate Birt-Hogg-Dubé syndrome from other causes of multiple cystic lung lesions such as Langerhans cell histiocytosis and lymphangioleiomyomatosis (see below).

Patients present with the characteristic skin lesions in the 3rd–4th decades of life. Spontaneous pneumothorax occurs in about 1/4 of patients, and renal cancer develops in 15%–30% of patients with skin lesions.

The images above reveal a solid left renal lesion that turned out to be an oncocytoma, as well as cystic lung disease. Note that the typical cysts described are usually larger and more irregular in shape (see the article by Agarwal et al for the full spectrum).

Differential Diagnosis

The main differential consideration in a patient with a solid renal tumor and cystic lung disease is tuberous sclerosis. Sclerotic bone lesions, renal angiomyolipoma, and brain lesions support the latter diagnosis. The pattern and appearance of the cystic lung disease (see below) is also helpful.

The presence of pulmonary cysts without a solid renal tumor widens the differential diagnosis to include other causes of cystic lung disease:
  • Langerhans cell histiocytosis: Upper lung–predominant distribution of irregularly shaped cysts and nodules.
  • Lymphangioleiomyomatosis: Cysts are typically round, more uniform in size, and diffuse in distribution. Cysts are not as large as those in Birt-Hogg-Dubé syndrome.
  • Lymphocytic interstitial pneumonia: Characterized by ground-glass opacities, often in combination with cystic lesions. Typically seen in in patients with Sjögren syndrome, human immunodeficiency virus infection, and variable immunodeficiency syndromes.
  • Pneumocystis jiroveci pneumonia: Typically seen in immunocompromised patients. Look for associated ground-glass opacities.

References

Thursday, December 1, 2011

Melorheostosis

Melorheostosis, a combination of the Greek words melos (limb), rhein (to flow), and ostos (bone), is a rare form of mixed sclerosing dysplasia affecting the skeleton and adjacent soft tissues. In fact, soft-tissue abnormalities such as osseous, chondroid, vascular, and fibrocartilaginous masses can be seen in about 75% of cases

Melorheostosis, also known as candle disease of the bone, Leri disease, and osteosis eburnisans monomelica, has an incidence of fewer than 1 case per one million. It begins in early childhood and is evident by 20 years of age in about half of the cases. It follows a chronic course punctuated with periods of exacerbations and arrest, slowing down as the patient gets older.

The cause is unknown, but various theories have been proposed. The observation that the lesions appear in a monomelic sclerotomal distribution (areas of bone innervated by an individual spinal sensory nerve) has linked melorheostosis to an early somatic mutation, infection, or injury to a segment or segments of the neural crest during embryogenesis. Co-occurrence of melorheostosis, osteopoikilosis, and osteopathia striata (overlap syndrome) has led some to suggest a genetic cause; however, definitive evidence is lacking.

Histologically, melorheostosis is characterized by thickened trabeculae containing irregularly arranged Haversian canals surrounded by cellular fibrous tissue. While a benign condition, skin and soft tissue involvement can cause fibrosis and joint contractures, leading to deformity and limb-length discrepancies. Heterotopic bone formation and soft-tissue calcification can be seen in association with joint ankylosis.

Commonly one or several adjacent bones are affected in a sclerotomal distribution. The long tubular bones of the lower extremity are more frequently affected, with a predilection for the diaphyseal and the epiphyseal regions. However, any bone or any region of bone can be affected, including (rarely), the spine, skull and facial bones.

Para-articular soft-tissue masses seen in melorheostosis are not necessarily contiguous with the bony abnormalities. The masses can be mineralized or non-mineralized and are more commonly found medial to the hip joint and in the popliteal fossa. The case above has an irregular mineralized soft tissue mass lateral to the left greater trochanter.

Characteristic imaging findings include flowing periosteal hyperostosis along the cortex of a long bone that has a linear, segmental distribution. As mentioned above, one or more bones can be involved. Endosteal hyperostosis may be seen in later stages of the disease, obliterating the medullary cavity.

Less characteristic imaging findings include hyperostosis on the outer or inner aspect of the affected bone resembling an osteoma, an osteopathia striata-like pattern with long dense hyperostotic intramedullary striations near the inner cortex (second case, shown below), and nodular soft tissue calcifications that may resemble myositis ossificans.

As seen in the case below, bone scintigraphy can be positive, reflecting the increased bone turnover that is characteristic of melorheostosis. Mineralized soft tissue masses can also have increased uptake, but nonmineralized or minimally mineralized soft tissue masses can be occult on bone scintigraphy.

References

  • Judkiewicz AM, Murphey MD, Resnik CS, Newberg AH, Temple HT, Smith WS. Advanced imaging of melorheostosis with emphasis on MRI. Skeletal Radiol. 2001 Aug;30(8):447-53.
  • Janousek J, Preston DF, Martin NL, Robinson RG. Bone scan in melorheostosis. J Nucl Med. 1976 Dec;17(12):1106-8.
  • Suresh S, Muthukumar T, Saifuddin A. Classical and unusual imaging appearances of melorheostosis. Clin Radiol. 2010 Aug;65(8):593-600.

Wednesday, November 30, 2011

The Yune Soft Tissue Index

The Yune soft tissue index is used to assess the amount of soft tissue at the tips of the distal phalanges. This can help in early detection of acral soft-tissue atrophy (for example, in patients with scleroderma).

You take the amount of soft tissue at the tip of the finger (A) and compare it to the width of the base of the distal phalanx (B). If A is larger than B/4, then the amount of soft tissue is normal. If A is less than B/5, then the amount of soft tissue is abnormal.

The case above in a patient with scleroderma seemed borderline by eye. Let's see if the Yune soft tissue can help.
A = 2.9 mm
B = 13.4 mm

2.9 [?] (13.4/4)
2.9 < 3.35
∴ Not normal

2.9 [?] (13.4/5)
2.9 > 2.68
∴ Not abnormal

∴ Borderline.

References

Freyschmidt J, Brossmann J, Wiens J, Sternberg A. The Hand - Distal Phalanges. In Freyschmidt's Köhler and Zimmer: Borderlands of normal and early pathologic findings in skeletal radiography. Fifth revised edition. Thieme (2003). P 81.

Tuesday, November 29, 2011

Histiocytic Disorders

A new classification scheme for histiocytic disorders has been promulgated by the World Health Organization's Committee on Histiocytic/Reticulum Cell Proliferations and the Reclassification Working Group of the Histiocyte Society.

The new classification scheme is based on the biological behavior of the disease and the lineage of the predominant cell type.

A very cursory review of immunology is helpful before proceeding to the classification. A histiocyte is a cell of the mononuclear phagocyte system (formerly the reticuloendothelial system). The histiocytes we'll be concerned with are monocytes, macrophages, and dendritic cells. Precursor cells in the marrow give rise to circulating monocytes, which differentiate into the tissue-resident phagocytes, macrophages and dendritic cells under the proper cytokine milieu. Langerhans cells are a class of dendritic cells that typically reside in the epidermis.

Under the new classification scheme, histiocytic disorders are classified based on biologic behavior into those with malignant behavior and those with varied biological behavior, and based on predominant cell type into monocyte-, dendritic cell-, or macrophage-related disorders. The term varied biological behavior is meant to convey the spectrum of behavior in this class, which can range in severity from self-limited to lethal.

Langerhans cell histiocytosis, the most well known of the histiocytic disorders by radiologists, is classified as a dendritic cell-related histioctyic disorder of varied biological behavior. Terms such as eosinophilic granuloma, Hand-Schüller-Christian disease, and Letterer-Siwe disease are now (> 10 years) considered obsolete or unnecessary, and should be avoided unless you're trying to be difficult during case conference.

Erdheim-Chester disease, an extremely rare disorder that somehow pops up during radiology residency and on boards, is classified as part of Juvenile xanthogranuloma and related disorders.

The outline below summarizes the current classification scheme:

Disorders of Varied Biological Behavior
  • Dendritic cell-related
    • Langerhans cell histiocytosis
    • Secondary dendritic cell processes
    • Juvenile xanthogranuloma and related disorders
      • Erdheim-Chester disease
      • Solitary histiocytomas with juvenile xanthogranuloma phenotype
    • Solitary histiocytomas of various dendritic cell phenotypes
  • Macrophage-related
    • Hemophagocytic syndromes
    • Primary hemophagocytic lymphohistiocytosis (familial , sporadic)
    • Secondary hemophagocytic syndromes (infection-associated, malignancy-associated, other)
    • Rosai-Dorfman disease (sinus histiocytosis with massive adenopathy)
    • Solitary histiocytoma with macrophage phenotype
Malignant Disorders
  • Monocyte-related
    • Leukemias (Monocytic leukemia M5A and B, acute myelomonocytic leukemia M4, chronic myelomonocytic leukemia)
    • Extramedullary monocytic tumor or sarcoma
  • Dendritic cell-related histiocytic sarcoma (localized or disseminated) based on phenotype
    • Langerhans cells
    • Follicular dendritic cell
    • Interdigitating dendritic cell
    • Others
  • Macrophage-related histiocytic sarcoma (localized or disseminated)

References

  • Chow A, Brown BD, Merad M. Studying the mononuclear phagocyte system in the molecular age. Nat Rev Immunol. 2011 Oct 25;11(11):788-98.
  • Favara BE, Feller AC, Pauli M, Jaffe ES, Weiss LM, Arico M, Bucsky P, Egeler RM, Elinder G, Gadner H, Gresik M, Henter JI, Imashuku S, Janka-Schaub G, Jaffe R, Ladisch S, Nezelof C, Pritchard J. Contemporary classification of histiocytic disorders. The WHO Committee On Histiocytic/Reticulum Cell Proliferations. Reclassification Working Group of the Histiocyte Society. Med Pediatr Oncol. 1997 Sep;29(3):157-66.
  • Lieberman PH, Jones CR, Steinman RM, Erlandson RA, Smith J, Gee T, Huvos A, Garin-Chesa P, Filippa DA, Urmacher C, Gangi MD, Sperber M. Langerhans cell (eosinophilic) granulomatosis. A clinicopathologic study encompassing 50 years. Am J Surg Pathol. 1996 May;20(5):519-52.

Monday, November 28, 2011

Bifid Ribs

A bifid rib, also known as a forked or bifurcated rib, is a relatively common anatomic variant where the sternal end of a rib divides into upper and lower divisions. It is thought that the lower division represents the intended development of the rib, and the upper division represents the anomalous development.

Bifid ribs are more common in males, slightly more common on the right, and occur most frequently in the third and foruth ribs, followed by the fifth, sixth, and second ribs. Both divisions have their own costal cartilage, which may fuse before joining with the sternum.

The space between the upper division and the rib above (white *) is usually narrowed, while the lower intercostal space (red *) is wider than normal.

Familiarity with the underlying muscular, vascular, and neural anatomy may be important for planning surgical and percutaneous procedures.
  • The intercostal muscles traverse the space between the upper and lower divisions.
  • Intercostal nerves run their normal course along the inferior margin of the parent rib and then usually along the inferior margin of the lower division. At least one case of a pair of intercostal nerves traveling along both the upper and lower margins of the parent rib has been reported.
  • I assume that the intercostal arteries take the same course as the nerves, but can't find any supporting evidence.
Bifid ribs are usually isolated, unilateral, and asymptomatic. They may, however, present as a palpable abnormality on physical examination or an asymmetric opacity on chest radiography.

Bifid ribs can also be seen in association with other conditions, most famously with basal cell nevus syndrome, where they may be multiple and bilateral.

References

  • Osawa T, Sasaki T, Matsumoto Y, Tsukamoto A, Onodera M, Nara E, Chen JK, Fujimura A, Nozaka Y. Bifid ribs observed in the third and the fourth ribs. Kaibogaku Zasshi. 1998 Dec;73(6):633-5.
  • Song WC, Kim SH, Park DK, Koh KS. Bifid rib: anatomical considerations in three cases. Yonsei Med J. 2009 Apr 30;50(2):300-3.

Sunday, November 27, 2011

Imaging Features of Fanconi Anemia

Fanconi anemia is a genetically and phenotypically heterogeneous recessive disorder of progressive pancytopenia, various congenital malformations, and predisposition to hematologic and solid malignancies.

Many of the congenital anomalies can be detected on imaging studies. These include:
  • Growth disturbances: Intrauterine growth retardation, short stature, delayed ossification.
  • Central nervous system: Hydrocephalus, single ventricle, absent septum pellucidum/corpus callosum, vascular malformations, moyamoya, Chiari malformations/absent septum pellucidum/corpus callosum.
  • Skull: Microcephaly, craniosynostosis, micrognathia, frontal bossing, small or absent external auditory canal, absent tympanic membrane, microtia, fused ossicles.
  • Spine: Spina bifida, Klippel-Feil anomaly, vertebral body anomalies, sacral agenesis or hypoplasia, kyphosis, scoliosis.
  • Radial ray anomalies: Thenar hypoplasia; dislocation of the radial head; radioulnar synostosis; absence or hypoplasia of the radius, scaphoid, trapezium, and/or thumb; floating thumb; bifid thumb; digitalized thumb; and abnormal thumb placement.
  • Extremities (other): Brachydactyly, arachnodactyly clubfoot, dysplastic or absent ulna, humeral abnormalities, absent clavicles, Sprengel deformity, congenital hip dysplasia/dislocation, Legg-Calve-Perthes disease, leg length discrepancy, soft-tissue syndactylism of the toes, metatarsus varus, medial deviation of the toes, hammer toes.
  • Gastrointestinal: Esophageal atresia, tracheoesophageal fistula, duodenal atresia, duodenal web, malrotation, foregut duplication cyst, anal atresia. Biliary atresia, annular pancreas.
  • Renal anomalies: Renal aplasia, horseshoe kidney, low-lying kidney(s), renal ectopy, hydronephrosis, hydroureter, urethral stenosis, reflux.
  • Genital anomalies: Hypogenitalism, cryptorchidism, hypospadias, bicornate uterus, aplasia or hypoplasia of vagina and uterus, atresia of vagina, hypoplasic uterus, hypoplastic/absent ovary.
  • Cardiopulmonary: Patent ductus arteriosis, ventricular septal defect, pulmonic or aortic stenosis, coarcation of the aorta, double aortic arch, cardiomyopathy, tetralogy of Fallot, pulmonary atresia.
  • Osteoporosis:

References

  • Auerbach AD. Fanconi anemia and its diagnosis. Mutat Res. 2009 Jul 31;668(1-2):4-10.
  • Juhl JH, Wesenberg RL, Gwinn JL. Roentgenographic findings in Fanconi's anemia. Radiology. 1967 Oct;89(4):646-53.
  • De Kerviler E, Guermazi A, Zagdanski AM, Gluckman E, Frija J. The clinical and radiological features of Fanconi's anaemia. Clin Radiol. 2000 May;55(5):340-5.