Friday, December 31, 2010

Pituitary Dwarfism

Patients with pituitary dwarfism can either have isolated growth hormone deficiency or multiple pituitary hormonal deficiencies.

Patients with isolated growth hormone deficiency have a thin or truncated pituitary stalk (the stalk is rarely absent or normal), normal or small anterior pituitary, and an ectopic posterior pituitary.

Patients with multiple pituitary hormonal deficiencies, on the other hand, may have a small or absent pituitary stalk, a small or absent anterior pituitary, and an ectopic or absent posterior pituitary.

To sum up the above: A thin stalk is strongly suggestive of isolated growth hormone deficiency, while an absent stalk is strongly suggestive of multiple pituitary hormonal deficiencies.

A contrast-enhanced MRI is needed to fully define the infundibulum.

The above case is a non-contrast MRI with an absent posterior pituitary bright spot (yellow arrow), an absent or thin stalk (green arrow), and an ectopic bright spot in the region of the median eminence (pink arrow). Without contrast, we can't tell if the stalk is absent or very thin.

An ectopic posterior pituitary lobe can also be seen in cases of pituitary stalk transection and septo-optic dysplasia and as an asymptomatic variant.

References

Thursday, December 30, 2010

Solitary Rib Lesions

  • Healing fracture
  • Fibrous dysplasia
  • Enchondroma
  • Multiple myeloma
  • Metastatic disease
  • Osteomyelitis
  • Osteochondroma
  • Langerhans cell histiocytosis
  • Ewing sarcoma
No pathology for the above case is available; however, it has remained stable for 2 years and is suspected to be fibrous dysplasia.

Wednesday, December 29, 2010

Ligamentum Flavum "Buckling"

From the terminology desk: Thickening of the ligamentum flavum is often attributed to the buckling of a normal ligamentum flavum when the disk at that level narrows. Chokshi et al found that there was correlation between facet joint arthropathy and ligamentum flavum thickening and between facet joint arthropathy and ligamentum flavum enhancement. This new data suggests that the perceived thickening represents actual thickening due to the spread of inflammation from the adjacent facet joints.

References

Chokshi FH, Quencer RM, Smoker WR. The "thickened" ligamentum flavum: is it buckling or enlargement? AJNR Am J Neuroradiol. 2010 Nov;31(10):1813-6.

Tuesday, December 28, 2010

Radiographic Appearance of Glass

The common notion that the opacity of glass on radiographs depends on its lead or heavy metal content is not correct. All glass has some degree of radiopacity on radiographs. Detection can be made easier by projections that free the fragment from overlying structures and expose its greatest diameter. Ultrasound is the imaging modality of choice for superficial foreign objects.

References

Monday, December 27, 2010

Pear-Shaped Urinary Bladder

A pear-shaped urinary bladder on urography, also appreciated as a gourd or inverted tear drop, refers to symmetric bladder compression and elevation and can be seen with the following conditions:
  • Pelvic hematoma: Most common cause.
  • Extraperitoeal urinoma:
  • Pelvic lipomatosis: Also causes increased radiolucency of the pelvis.
  • Inferior vena cava obstruction: Compression is by engorged pelvic collaterals.

Sunday, December 26, 2010

Radiolucent Filling Defects in the Urinary Tract

Differential considerations for radiolucent filling defects in the urinary tract on a contrast study:
  • Radiolucent calculi: For example, uric acid.
  • Neoplasm: Transitional cell carcinoma most common.
  • Blood clot:
  • Infectious debris:
  • Sloughed papilla:
  • Fungal material:

Saturday, December 25, 2010

Incomplete Partition

Congenital malformations of the inner ear can be divided into two types of incomplete partition:

Incomplete partition type I, also known as cystic cochleovestibular malformation, is a condition where the cochlea lacks the entire modiolus and cribriform area, resulting in a cystic appearance. This is accompanied by a large cystic vestibule. On CT, there is an empty, cystic cochlea, a dilated vestibule, and absence of any partition within the cochlea. The vestibular aqueduct is not enlarged.

Incomplete partition type II is the classic Mondini deformity. The cochlea consists of 1.5 turns, in which the middle and apical turns coalesce to form a cystic apex, accompanied by a dilated vestibule and enlarged vestibular aqueduct. CT shows a dilated vestibule, an enlarged vestibular aqueduct, and confluence of middle and apical turns of the cochlea.

References

Sennaroglu L, Saatci I. A new classification for cochleovestibular malformations. Laryngoscope. 2002 Dec;112(12):2230-41.

Friday, December 24, 2010

Large Vestibular Aqueduct Syndrome

Large vestibular aqueduct syndrome (also known as enlarged endolymphatic duct and sac syndrome), is the most frequent cause of bilateral progressive sensorineural hearing loss in children. While the deformity of the endolymphatic duct and sac is congenital, the hearing loss is acquired and thought to be related to minor head trauma (the exact mechanism is unknown).

The vestibular aqueduct is considered enlarged on CT when it measures ≥ 1 mm at its midpoint and ≥ 2 mm at the operculum. T2-weighted images show a high signal intensity enlarged endolymphatic sac.

10%-15% of patients have Pendred syndrome, which is the most common syndromic cause of hearing loss. It is an inherited disorder consisting of a dyshormonogenic goiter (cannot organify iodide efficiently) and sensorineural hearing loss and may be accompanied by vestibular symptoms. Imaging shows a large vestibular aqueduct and inner ear malformations. The perchlorate discharge test is used for diagnosis.

References

Thursday, December 23, 2010

The Swirl Sign and Internal Hernias


Gastric bypass, a one-shot surgical solution for complex, life-long psychosocial issues, has become routine therapy for morbid obesity, with laparoscopic Roux-en-Y being the most commonly performed bariatric procedure in many institutions. Internal hernias, which are more common after laparoscopic gastric bypass than after open gastric bypass, are a dreaded complication. The presentation is often nonspecific, making CT an important part of diagnosis.

A number of CT findings have been associated with internal hernias. The best single predictor of internal hernia is the mesenteric swirl (or whirl) sign: The swirled appearance of vessels and fat at the mesenteric root (see video, which may be blocked by Websense). The problem with the swirl sign is that mesenteric swirling can be seen in healthy persons and post-laparoscopic Roux-en-Y gastric bypass patients without an internal hernia, so the finding must be considered in conjunction with the clinical picture.

The degree of swirl may be used to increase confidence. In one series, all cases of mesenetric swirl of at least 270° were associated with a hernia at surgery. In patients with a mesenteric swirl but no hernia at surgery, the median amount of swirl was less than 90°.

References

  • Iannuccilli JD, Grand D, Murphy BL, Evangelista P, Roye GD, Mayo-Smith W. Sensitivity and specificity of eight CT signs in the preoperative diagnosis of internal mesenteric hernia following Roux-en-Y gastric bypass surgery. Clin Radiol. 2009 Apr;64(4):373-80.
  • Lockhart ME, Tessler FN, Canon CL, Smith JK, Larrison MC, Fineberg NS, Roy BP, Clements RH. Internal hernia after gastric bypass: sensitivity and specificity of seven CT signs with surgical correlation and controls. AJR Am J Roentgenol. 2007 Mar;188(3):745-50.

Wednesday, December 22, 2010

Grynfeltt-Lesshaft Hernia

A Grynfeltt-Lesshaft hernia is a herniation through the superior lumbar (Grynfeltt-Lesshaft) triangle. The superior lumbar triangle is bordered medially by the quadratus lumborum muscle, superiorly by the 12th rib, and laterally by the internal oblique muscle. The floor of the lumbar triangle is the transversalis fascia and the aponeurosis of the transversalis muscle of the abdomen. The roof of the triangle is the external oblique and latissimus dorsi muscles.

References

Orcutt TW. Hernia of the superior lumbar triangle. Ann Surg. 1971 Feb;173(2):294-7.

Tuesday, December 21, 2010

De Quervain Tenosynovitis: Radiographic Findings

De Quervain tenosynovitis is a stenosing tenosynovitis of the first dorsal compartment of the wrist at the radial styloid. While diagnosis is primarily clinical (e.g., the Finkelstein test), MRI can be used for confirmation. Radiographs may be normal or reveal soft tissue swelling along the radial styloid process (seen in above image).

In addition, focal bony radial styloid abnormalities have been found to correlate with the presence of de Quervain tenosynovitis. These include radial styloid periosteal bone formation and cortical erosion without and with sclerosis (image above) distal to the level of the physeal plate remnant.

A normal variant that should not be confused with cortical irregularity of the distal radius is the normal cortical contour bulge or peak at the level of the physeal plate remnant.

References

Chien AJ, Jacobson JA, Martel W, Kabeto MU, Marcantonio DR. Focal radial styloid abnormality as a manifestation of de Quervain tenosynovitis. AJR Am J Roentgenol. 2001 Dec;177(6):1383-6.

Monday, December 20, 2010

Congenital Cochlear Eponyms

  • Mondoni defect: Most common congenital cochlear deformity. Incomplete development of the 2.5 turns of the cochlea, with a relatively well-formed basal turn and ballooning of the middle and apical turns into a cyst. 20% of cases have associated enlarged endolymphatic sacs and vestibular aqueducts.
  • Cock deformity: Also known as Michel dysplasia. Second most common congenital cochlear deformity. Common cavity of the vestibule and cochlea. The modiolus is absent. Semicircular canals may be affected.
  • Michel aplasia: Complete absence of the inner ear structures. Associated with other skull base abnormalities, abnormal course of the facial nerve, jugular vein abnormalities, absent stapes, absent oval window.

References

Neuroradiology: The Requisites (2nd ed). pp 592-594.

Sunday, December 19, 2010

Peliosis Hepatis

Peliosis hepatis is an uncommon vascular disorder of the liver characterized by multiple blood-filled cysts of various sizes. The cysts may be lined by endothelium (phlebectatic variant)or represent hemorrhagic liver cell necrosis (parenchymal variant).

Peliosis hepatis is associated with hormonal stimulation (steroids, oral contraceptives, tamoxifen, estrogens), immunoglobulin therapy, azathioprine, malignancies, hematologic disorders (Hodgkin disease, multiple myeloma), transplantation, and infections (pulmonary tuberculosis, HIV, Bartonella henselae and Rochalimaea henselae).

The lesions appear homogeneously hypoechoic in patients with a fatty livers and hyperechoic in patients with healthy livers. The lesions will appear heterogeneously hypoechoic when hemorrhagic. Doppler can show hypervascularity within and surrounding the lesions.

The lesions are low-attenuation on noncontrast CT, but can be missed when smaller than 1 cm. Lesions may have increased attenuation in cases of hemorrhage or internal calcification. During the arterial phase there is early globular enhancement with small pools of contrast in the center of the lesions (target sign). During the portal venous phase, the lesions may demonstrate a centrifugal (more common) or centripetal (mimicking hemangioma) progression of enhancement. The phlebectatic variant may have late diffuse homogeneous hyperattenuation, but not the parenchymal variant, since the latter is composed of hemorrhagic parenchymal necrosis. Larger cavities that communicate with sinusoids can have the same attenuation as blood vessels.

MRI findings will depend on the stage of the blood within the lesions. The lesions are usually T1-hypointense and usually T2-hyperintense with foci of high signal from hemorrhagic necrosis. Like CT, the enhancement pattern is typically centrifugal. Delayed phase images may show strong enhancement with a branching pattern representing the vascular component of the lesion.

In contrast to the nonspecific appearance seen on ultrasound, CT, and MR, angiographic findings are unique: Multiple pools of contrast on late arterial phase images that persist on parenchymal and early venous phases.

Differential considerations for multiple hemorrhagic hepatic lesions include:
  • Hemorrhagic metastases:
  • Hepatic adenomas: Increased risk with glycogen storage diseases, diabetes mellitus, hemochromatosis, acromegaly, oral contraception and anabolic steroids.
  • Hepatocellular carcinoma:
  • Peliosis hepatis:

References

Saturday, December 18, 2010

Stercoral Colitis

Stercoral colitis is a rare inflammatory colitis caused by increased intraluminal and colonic wall pressure from a fecaloma (large mass of dry, hard stool), which leads to decreased blood supply. If left untreated, it can cause ulceration and perforation. In about 75% of cases, the ulcers are found in the sigmoid colon or rectum, with the most common locations being the anterior rectum just proximal to the peritoneal reflection; the antimesenteric border of the rectosigmoid junction; and the apex of the sigmoid colon.

On CT, in a region of fecal impaction, there is thickening of the colonic wall and stranding of the pericolonic fat. Extraluminal bubbles of gas and an abscess suggest perforation.

References

Heffernan C, Pachter HL, Megibow AJ, Macari M. Stercoral colitis leading to fatal peritonitis: CT findings. AJR Am J Roentgenol. 2005 Apr;184(4):1189-93.

Friday, December 17, 2010

Pyogenic Granuloma and Silver Nitrate

Pyogenic granuloma is a common, benign, vascular lesion of the skin that presents as a rapidly growing papule or polyp that bleeds easily after minor trauma. It is an acquired reactive hyperproliferative vascular response to various injuries (penetrating trauma, infection) and chemical stimuli (hormones, retinoid therapy). The most commonly affected sites are the hands, feet, lips, face, and upper trunk.

On inspection, the typical exophytic pyogenic granuloma pops out of the skin with inward growth of the surrounding rim of epidermis, which can cause a pedunculated appearance of the lesion. You can see this on the lateral oblique view of the thumb (left panel) in the above image.

Many treatment strategies exist, ranging from expectant management to surgical excision. A simple treatment is silver nitrate cauterization, which can be done in the office or the ED. The patient above had silver nitrate cauterization, and the silver nitrate can be seen as small radioopaque fragments near the wound.

The bone destruction seen above (right panel) is osteomyelitis, related to the infectious etiology of the pyogenic granuloma in this patient.

It should go without saying that this is not a radiologic diagnosis.

References

  • Gilmore A, Kelsberg G, Safranek S. Clinical inquiries. What's the best treatment for pyogenic granuloma? J Fam Pract. 2010 Jan;59(1):40-2.
  • Quitkin HM, Rosenwasser MP, Strauch RJ. The efficacy of silver nitrate cauterization for pyogenic granuloma of the hand. J Hand Surg Am. 2003 May;28(3):435-8.
  • Zaballos P, Llambrich A, Cuéllar F, Puig S, Malvehy J. Dermoscopic findings in pyogenic granuloma. Br J Dermatol. 2006 Jun;154(6):1108-11.

Thursday, December 16, 2010

Freiberg Infraction

Freiberg infraction refers to the collapse of subchondral bone with osteonecrosis involving the metatarsal head (usually the second or third). The joint may secondarily be affected by osteoarthritis.

It is felt to be related to acute or repetitive injury or to vascular compromise. High-heeled shoes are thought to be one causative factor and the condition is more common in women.

The image above shows flattening of the second metatarsal head with associated osteoarthritis.

MRI early in the course of the disease will show low T1 and high T2 signal in the metatarsal head. The main differential consideration at this point includes a stress reaction. Later in the course of the disease, there will be flattening of the metatarsal head with low T2 signal corresponding to sclerosis.

References

Ashman CJ, Klecker RJ, Yu JS. Forefoot pain involving the metatarsal region: differential diagnosis with MR imaging. Radiographics. 2001 Nov-Dec;21(6):1425-40.

Wednesday, December 15, 2010

Prestyloid Parapharyngeal Space Masses

The parapharyngeal space is an inverted pyramid extending from the base of the skull to the hyoid bone. It is bordered laterally by the parotid and masticator spaces, medially by the pharyngeal mucosal space, and posteromedially by the retropharyngeal space.

The tensor-vascular-styloid fascia extends through the parapharyngeal space between the tensor veli palatini muscle and the styloid process. It can be used to divide the parapharyngeal space into pre- and post-styloid compartments. The post-styloid compartment contains the carotid sheath and is also known as the carotid space. The pre-styloid compartment is what most people in the field are actually referring to when they talk about the parapharyngeal space.

The post-styloid compartment (also known as the carotid space) contains the internal carotid artery, internal jugular vein, cranial nerves IX-XII, the cervical sympathetic chain, and the glomus bodies. The pre-styloid compartment (also known simply as the parapharyngeal space) contains fat, lymph nodes, minor salivary glands, nerves (branches of V3), arteries (internal maxillary and ascending pharyngeal), and veins (pharyngeal venous plexus).

Most commonly, a mass found in the parapharyngeal space has invaded from adjacent spaces:
  • Salivary gland masses: Pleomorphic adenoma of the parotid gland most common; diving ranula rare.
  • Neurogenic tumors:
  • Glomus tumors: Glomus vagale (post-styloid/carotid space),
  • Pharyngeal carcinoma: Invasion of the parapharyngeal space seen in 65% of cases at time of diagnosis.
  • Tonsillar tumors
  • Synovial sarcoma: Fluid levels, hemorrhage, and calcification.
  • Lymphadenopathy
  • Infection: Tonsillitis, pharyngitis, odontogenic abscess, parotid abscess.
  • Chordoma
  • Meningioma
  • Other: Second branchial cleft cysts (uncommon).
Primary lesions of the prestyloid parapharyngeal space are much less common and can arise from the contents mentioned above:
  • Lymphadenopathy: Most common mass in the prestyloid compartment.
  • Salivary gland tumors: Pleomorphic adenoma and other minor salivary gland tumors (e.g., mucoepidermoid carcinoma, adenoid cystic carcinoma).
  • Neural tumors: Schwannoma.

References

  • Shin JH, Lee HK, Kim SY, Choi CG, Suh DC. Imaging of parapharyngeal space lesions: focus on the prestyloid compartment. AJR Am J Roentgenol. 2001 Dec;177(6):1465-70.
  • Neuroradiology requisites (2nd ed), pp 721-723.

Tuesday, December 14, 2010

Single-Suture Craniosynostoses

Classic appearances associated with premature closure of various sutures:
  • Sagittal suture: Most common form. Scaphocephaly (skaphe=a light boat or skiff) or dolichocephaly (dolicho=long). Long and narrow head.
  • Metopic suture: Trigonocephaly (trigonon=triangle). The head looks triangle-shaped when viewed from above with a ridge along the middle of the forehead. Hypotelorism and parietooccipital bossing.
  • Coronal suture: Unilateral: Harlequin or winking eye, due to ipsilateral frontal bone flattening that leads to elevation of the superior orbital rim and contralateral frontal bossing that leads to depression of the superior orbital rim. Bilateral: Brachycephaly (brachys=short). Decreased anteroposterior dimension and increased bitemporal distance and height.

    The harlequin eye can also be seen with neurofibromatosis (due to dysplasia of the greater wing of the sphenoid) or focal calvarial expansion from an intracranial mass.
  • Lambdoid suture: Very rare. Posterior plagiocephaly (plagio=oblique). Most commonly the appearance represents deformational (positional) plagiocephaly. The ears will be pulled back, in contrast to the much more common positional plagiocephaly, where the ears are pushed forward.

Monday, December 13, 2010

Vascular Loop Syndrome

Vascular loop syndrome refers to the compression of a nerve root by a vascular loop and can most commonly affects the trigeminal and facial nerves.

In the case of the trigeminal nerve, patients may present with trigeminal neuralgia as the result of the contact. High-resolution, heavily T2-weighted images are used to reveal a serpiginous asymmetric vessel in the high cerebellopontine angle along the proximal preganglionic segment of the trigeminal nerve or at its root entry zone.

In the case of the facial nerve (shown above), patients present with involuntary hemifacial spasm. High-resolution, heavily T2-weighted images are used to reveal a serpiginous asymmetric vessel in the mid cerebellopontine angle along the proximal facial nerve or at its root entry zone.

Sunday, December 12, 2010

Masses of the Meckel Cave

Meckel cave tumors are usually asymptomatic and can be followed if characteristically benign findings are seen on MRI or CT. Differential considerations for masses in the Meckel cave include:
  • Trigeminal schwannoma: The case shown above. Relatively rare. Can be seen with neurofibromatosis type 2 or as an isolated entity. Smooth margins, usually low on T1 and high on T2. Avid enhancement with or without cystic components.
  • Epidermoid tumor: Arise from incomplete cleavage of neural ectoderm from cutaneous ectoderm and grow by desquamation of epithelial cells. Lobulated margins, Low on T1 and high on T2, minimal mass effect.
  • Meningioma: Isointense to surrounding normal brain parenchyma on T1- and T2-weighted images. May calcify.
  • Trigeminal lipoma: Rare. Looks like fat. Infiltrates the trigeminal nerve fascicles.
  • Primary lymphoma: Can mimic trigeminal schwannoma. Consider this diagnosis in immunocompromised patients. The presence of an apparent dural tail can suggest lymphoma in the absence of hyperostosis (typically seen with meningiomas).
  • Arachnoid cyst: Fluid signal on all sequences.
  • Chordoma: Arises from adjacent clivus.

References

  • Abdel Aziz KM, van Loveren HR. Primary lymphoma of Meckel's cave mimicking trigeminal schwannoma: case report. Neurosurgery. 1999 Apr;44(4):859-62; discussion 862-3.
  • Beck DW, Menezes AH. Lesions in Meckel's cave: variable presentation and pathology. J Neurosurg. 1987 Nov;67(5):684-9.
  • Yuh WT, Wright DC, Barloon TJ, Schultz DH, Sato Y, Cervantes CA. MR imaging of primary tumors of trigeminal nerve and Meckel's cave. AJR Am J Roentgenol. 1988 Sep;151(3):577-82.

Saturday, December 11, 2010

Eosinophilic Fasciitis

Eosinophilic fasciitis (Shulman disease) is clinically characterized by stiffness, swelling, and pain in the extremities that typically presents suddenly after strenuous activity and responds to steroid therapy. Other causes of eosinophilic fasciitis include exposure to simvastatin, trichloroethylene, and L-tryptophan (contaminated and otherwise).

Patients may have peripheral eosinophilia, hypergammaglobulinemia, elevated sedimentation rate, and sclerodermalike skin findings primarily of the extremities. Involvement of the trunk has also been reported.

MRI in patients with active eosinophilic fasciitis reveals fascial thickening, increased fluid signal within the fascia, and fascial enhancement.

References

Friday, December 10, 2010

Arthritis and Primary Biliary Cirrhosis

Patients with primary biliary cirrhosis may present with an erosive arthropathy distributed in the distal and proximal interphalangeal joints with relative sparing of the metacarpophalangeal joints. These marginal erosions vary from small, punched-out lesions to large defects with sparing of the articular surface. Cartilage loss and joint space narrowing can also be seen.

Chondrocalcinosis, which is seen with liver disorders such as hemochromatosis and Wilson disease can also be seen. Hypertrophic osteoarthropathy is a rare complication.

The picture may be complicated by coexistent rheumatoid arthritis.

References

O'Connell DJ, Marx WJ. Hand changes in primary biliary cirrhosis. Radiology. 1978 Oct;129(1):31-5.

Thursday, December 9, 2010

Carpal Coalitions

Carpal coalition refers to failure of segmentation of the carpal bones. Isolated coalitions tend to occur between two bones in the same carpal row (e.g., luontriquetral and scapholunate), while syndromic coalitions tend to cross carpal rows and involve more than two bones.

Various syndromes and congenital abnormalities have been associated with carpal coalitions.
  • Arthrogryposis: The clinical finding of multiple congenital contractures that affect two or more different areas of the body. Seen as part of more than 300 different disorders. Carpal coalitions more common than tarsal coalitions.
  • Ellis-van Creveld syndrome: Also called chondroectodermal dysplasia. Usually coalition is between the capitate and hamate.
  • Hand-foot-genital syndrome: Limb malformations and urogenital defects. The most common malformation is mild bilateral shortening of the thumbs and great toes, predominantly of the distal phalanges and/or the first metacarpal or metatarsal. Urogenital abnormalities include abnormalities of the ureters and urethra, incomplete Müllerian fusion (females), and hypospadias (males). The most common coalition is between the scaphoid and trapezium.
  • Symphalangism: Partial or total absence of interphalangeal joints sometimes with tarsal and carpal coalition. The most common coalition is between the triquetrum and the hamate.
The case shown here is lunotriquetral coalition, which is the most common of the carpal coalitions and is twice as common in females. Because patients with lunotriquetral coalition tend have widened scapholunate intervals without injury to the scapholunate ligament, this finding should be considered a normal variant in patients with lunotriquetral coalition.

References

  • Bamshad M, Van Heest AE, Pleasure D. Arthrogryposis: a review and update. J Bone Joint Surg Am. 2009 Jul;91 Suppl 4:40-6.
  • Innis JW. Hand-Foot-Genital Syndrome . In: Pagon RA, Bird TC, Dolan CR, Stephens K, editors. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2006.
  • Metz VM, Schimmerl SM, Gilula LA, Viegas SF, Saffar P. Wide scapholunate joint space in lunotriquetral coalition: a normal variant? Radiology. 1993 Aug;188(2):557-9.
  • Poznanski AK, Holt JF. The carpals in congenital malformation syndromes. Am J Roentgenol Radium Ther Nucl Med. 1971 Jul;112(3):443-59.

Wednesday, December 8, 2010

Retroverted or Curled Epiglottis

We came across a curled epiglottis recently as part of a cervical spine evaluation. Keats does not list this as a variant. The otoaryngology literature describes a retroverted epiglottis touching the base of the tongue that can cause symptoms of globus pharyngeus. The symptoms resolved in this case series of 4 patients following laser excision of the retroverted part of their epiglottis. Our patient didn't have any symptoms of globus pharyngeus according to the clinic notes, so the significance of the curled epiglottis in this case is unknown.

References

Agada FO, Coatesworth AP, Grace AR. Retroverted epiglottis presenting as a variant of globus pharyngeus. J Laryngol Otol. 2007 Apr;121(4):390-2.

Tuesday, December 7, 2010

Madelung Deformity

Madelung deformity is a growth disturbance of the distal radius caused by focal dysplasia of the physis that results in triangular deformity and medial and volar tilt of the distal radius. Females are more commonly affected than males.

Radiographs will show increased volar bowing of the distal radius, a widened distal radioulnar joint, increased volar tilt of the distal radial articular surface, and an exaggerated ulnar tilt of the distal radius. The carpal bones wedge into the triangular deformity created by the distal radius. In addition, osteophytes may form along the inferior ulnar border of the radius.

Some measurements can be used for the diagnosis of Madelung deformity. When any one of these thresholds is met, a diagnosis of a Madelung deformity can be made.
  • Ulnar tilt ≥ 33°: On frontal radiographs, the acute angle between the longitudinal axis of the ulna and a line tangential to the proximal surfaces of the scaphoid and lunate is subtracted from 90.
  • Lunate subsidence ≥ 4 mm: On frontal radiographs, the distance between the most proximal point of the lunate and a line perpendicular to the longitudinal axis of the ulna and through its distal articular surface.
  • Lunate fossa angle ≥ 40°: On frontal radiographs, the acute angle between the longitudinal axis of the ulna and a line across the lunate fossa of the radius subtracted from 90.
  • Palmar carpal displacement ≥ 20 mm: Distance between the longitudinal axis of the ulna and the most palmar point on the surface of the lunate or capitate.
The images show a case where a diagnosis of Madelung deformity was suspected, but only the lunate subsidence was positive.

On MRI, in addition to the radiographic findings, there will be a thickened ligament arising from the ulnar aspect of the distal radius to the lunate, the so-called Vickers ligament.

Differential considerations include:
  • Idiopathic Madelung deformity:
  • Turner syndrome:
  • Dyschondrosteosis: Rare form of mesomelic dysplasia. Characterized by short stature and a Madelung deformity.

References

  • Castriota-Scanderbeg A, Dallapiccola B. Chapter 5: Long bones. In Abnormal skeletal phenotypes. Castriota-Scanderbeg A and Dallapiccola B. Springer-Verlag Berlin Heidelberg, 2005. page 313.
  • Dawe C, Wynne-Davies R, Fulford GE. Clinical variation in dyschondrosteosis. A report on 13 individuals in 8 families. J Bone Joint Surg Br. 1982;64(3):377-81.
  • Dubey A, Fajardo M, Green S, Lee SK. Madelung's deformity: a review. J Hand Surg Eur Vol. 2010 Mar;35(3):174-81.
  • Kim HK. Madelung deformity with Vickers ligament. Pediatr Radiol. 2009 Nov;39(11):1251.
  • McCarroll HR Jr, James MA, Newmeyer WL 3rd, Manske PR. Madelung's deformity: diagnostic thresholds of radiographic measurements. J Hand Surg Am. 2010 May;35(5):807-12.

Monday, December 6, 2010

Tarsal Tunnel Syndrome

Tarsal tunnel syndrome refers to pain and paresthesia in the plantar aspect of the foot and toes due to nerve entrapment or compression at the level of the posterior tibial nerve or its branches as they pass through the tarsal tunnel.

The flexor retinaculum forms the roof of the tarsal tunnel. Anteriorly, the flexor retinaculum inserts on the anteromedial surface of the medial malleolus and posteriorly, it inserts into the medial tuberosity of the calcaneus. Inferiorly the flexor retinaculum splits to envelop the abductor hallucis muscle.

The floor of the tarsal tunnel is formed by the medial surface of the talus, the sustentaculum tali, and the medial wall of the calcaneus.

The structures of the tarsal tunnel, from anterior to posterior, include the well-known Tom, Dick, and Harry: the tibialis posterior tendon, the flexor digitorum longus tendon, the posterior tibial neurovascular bundle, and the flexor hallucis longus tendon.

Nerve compression can be intrinsic or extrinsic. Intrinsic causes include accessory muscles, ganglion cysts, neurogenic tumors, varicose veins, lipomas, synovial hypertrophy, and scar tissue. Extrinsic causes include foot deformities, hypertrophic and accessory muscles, os trigonum, and excessive pronation in some sports.

References

Sunday, December 5, 2010

Pulmonary Langerhans Cell Histiocytosis

Pulmonary Langerhans Cell Histiocytosis is a chronic progressive interstitial lung disease strongly associated with cigarette smoking.

The images here show an upper lobe-predominant process characterized by irregular cysts and nodules in a peribronchiolar distribution. Differential considerations include pulmonary Langerhans cell histiocytosis and lymphangioleiomyomatosis. Emphysema, which shouldn't be a consideration once you note that the cysts have perceptible walls, is included in some differentials.

The classic teaching is that cysts associated with pulmonary Langerhans cell histiocytosis are less uniform in appearance than those associated with lymphangioleiomyomatosis and that Langerhans cell histiocytosis is associated with nodules (especially early in the course of the disease), while lymphangioleiomyomatosis is not. However, more recent (2003) work suggests that there is considerable overlap between the appearance of lymphangioleiomyomatosis and Langerhans cell histiocytosis and that CT can't be reliably used to differentiate the two.

References

Saturday, December 4, 2010

Hypoxic-Ischemic Encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is one of the most common causes of severe neurologic deficit in children and occurs in up to about 10/1,000 live births. HIE is thought to occur due to insufficient cerebral blood flow in combination with decreased oxygen content, which leads to loss of normal cerebral autoregulation and diffuse brain injury.

Different patterns of injury have been described in preterm (< 36 weeks) and term (> 36 week) neonates and based on severity. They include:
  • Mild-to-moderate hypotension in preterm infants: The periventricular regions are most affected. MR shows areas of T1 hyperintensity within larger areas of T2 hyperintensity. Periventricular leukomalacia (cavitation and periventricular cyst formation) develops 2 to 6 weeks later. End-stage periventricular leukomalacia refers to progressive necrosis of the periventricular tissue with ex-vacuo enlargement of the ventricles and manifests on cross sectional imaging as ventriculomegaly with irregular margins of the bodies and trigones of the lateral ventricles, loss of periventricular white matter with increased T2 signal, and thinning of the corpus callosum.
  • Severe hypotension in preterm infants: The thalami, brainstem, and cerebellum in are most affected due to their high metabolic activity in the immature brain. Ultrasound shows hyperechogenicity, CT shows hypoattenuation, and DWI shows restricted diffusion in these regions. T2 signal is variable.
  • Mild-to-moderate hypotension in term infants (shown above): The intervascular watershed zones between the anterior and middle cerebral arteries and between the middle and posterior cerebral arteries and the border zone are affected. The parasagittal cortex and subcortical white matter demonstrate restricted diffusion.
  • Severe hypotension in term infants: The lateral thalami, posterior putamina, hippocampi, brainstem, corticospinal tracts, and the sensorimotor cortex are affected. These areas may be hyperechoic on ultrasound and low attenuation on CT. The CT findings may be subtle, with the hypoattenuation of the basal ganglia and thalami manifesting as isoattenuation compared to adjacent white matter. MRI will show abnormal T1 hyperintensity, variable T2 signal, and restricted diffusion in these areas.

References

Chao CP, Zaleski CG, Patton AC. Neonatal hypoxic-ischemic encephalopathy: multimodality imaging findings. Radiographics. 2006 Oct;26 Suppl 1:S159-72.

Friday, December 3, 2010

Endobutton

Endobuttons are used to secure the upper end of a tendon graft, for example in anterior cruciate ligament (top images) or biceps tendon (bottom images) reconstruction. A strip of polyethylene tape (black) is looped around the tendon graft (red) on one end and looped around the center two holes of the Endobutton on the other.

References

Thursday, December 2, 2010

Pilomatricoma

Pilomatricomas (pilomatrixoma, calcifying epithelioma of Malherbe) are benign calcifying tumors that arise from skin appendages and are the most common solid cutaneous tumor in patients under 20 years of age. Imaging is generally not used in the evaluation of pilomatricomas, since they are usually superficial, small, and well-circumscribed.

Pilomatricomas are slow-growing subcutaneous tumors that are usually less than 3 cm in diameter. The majority are found in the head and neck, followed by the upper extremities.

Radiographic features of pilomatricomas include regular contours, sharp demarcation from surrounding fat, and a normal overlying skin. Calcifications, when present, are usually speckled or sand-like, but can be large and dense in some cases.

Different ultrasound features have been described. Classically, these are hypoechoic solid nodules that are either fully or partially calcified. However, Pilomatricomas may also have internal fluid signal and a thick-wall.

MRI reveals a mass that is homogeneously isointense to muscle on T1-weighted images. Pilomatricomas can be hypointense to muscle on T2-weighted images with patchy hyperintense areas and striations that radiate from the center toward a hyperintense peripheral rim. Post-contrast images may reveal patchy or reticular enhancement centrally and peripheral enhancement of a connective tissue capsule. A case pilomatricoma without enhancement has also been reported. Peritumoral edema may be seen in some cases.

The case shown here is from a young woman with a longstanding history of a painless, hard bony mass in the left preauricular region. The images are not very exciting, as they are basically blacked out by the calcium, which goes along with the history of a hard bony mass.

References

  • De Beuckeleer LH, De Schepper AM, Neetens I. Magnetic resonance imaging of pilomatricoma. Eur Radiol. 1996;6(1):72-5.
  • Gustin AF, Lee EY. Pilomatricoma in a pediatric patient. Pediatr Radiol. 2006 Oct;36(10):1113.
  • Haller JO, Kassner G, Ostrowitz A, Kottmeler K, Perfschuk LP. Pilomatrixoma (calcifying epithelioma of Malherbe): radiographic features. Radiology. 1977 Apr;123(1):151-3.
  • Hoffmann V, Roeren T, Möller P, Heuschen G. MR imaging of a pilomatrixoma. Pediatr Radiol. 1998 Apr;28(4):272.
  • Lim HW, Im SA, Lim GY, Park HJ, Lee H, Sung MS, Kang BJ, Kim JY. Pilomatricomas in children: imaging characteristics with pathologic correlation. Pediatr Radiol. 2007 Jun;37(6):549-55.
  • Solivetti FM, Elia F, Drusco A, Panetta C, Amantea A, Di Carlo A. Epithelioma of Malherbe: new ultrasound patterns. J Exp Clin Cancer Res. 2010 May 6;29(1):42.

Wednesday, December 1, 2010

Duodenal Filling Defects

Small
  • Lymphoid hyperplasia: Multiple Little (1 mm - 2 mm) filling defects. May be normal in children. May be associated with giardiasis in adults with hypogammaglobunimeia.
  • Heterotopic gastric mucosa: Multiple mini (few mm) filling defects clustered in a mosaic pattern.
Large
  • Pancreatic rest: Ectopic pancreatic tissue. Smooth (round or lobulated) filling defects 1 cm - 2 cm in diameter. Classical appearance of a central dimple of barium that can be confused with an ulcer. Usually found in the bulb or descending duodenum.
  • Brunner gland hyperplasia: Multiple, Big (up to 1 cm or so), rounded filling defects at the bulb that can extend to the descending duodenum. Often produce a cobble stone appearance.
Miscellaneous/Uncommon
  • Flexural pseudopolyp: Usually in thin patients. Due to sharp angle between the apex of the duodenal bulb and the descending duodenum, which causes mucosa to bunch up at the apex of the bulb.
  • Adenoma: Uncommon. Mucosal polypoid lesions with high potential for malignant degeneration. Usually smaller than 1 cm. Villous adenomas can get larger than 1 cm and are more likely to be found in the periampullary region.
  • Mesenchymal tumors: Leiomyoma or lipoma. Most common benign lesions of duodenum. Smooth, submucosal lesions. Ulceration uncommon.
  • Kaposi: Multiple polypoid and ulcerated lesions.
  • Carcinoid: Typically in the descending duodenum, peripapillary region.
  • Choledochocele: Causes extrinsic compression.
  • Papillitis: Enlarged major papilla due to inflammation, usually recent passage of a calculus.

Tuesday, November 30, 2010

Pseudofracture of the Talus

If lateral views of the ankle are obliqued along the horizontal plane, the talar domes no longer overlap. Similarly, the medial (black arrows) and lateral (pink arrows) inferior margins of the talus can separate and fool you into calling a fracture. The posterior margin (white arrow) can also simulate a cortical defect.

Monday, November 29, 2010

Coned Cecum

A cone-shaped cecum refers to a narrowed and thick-walled cecum. Differential considerations include:
  • Tuberculosis: Terminal ileum can be involved.
  • Crohn disease: Terminal ileum is involved.
  • Amebiasis: Terminal ileum is not involved. Can cause ulcerations with skip lesions.

  • Ulcerative colitis: Dilated terminal ileum (backwash ileitis)
  • Typhlitis
  • Lymphoma
  • Cecal carcinoma
  • Radiation therapy
  • Metastases

References

Sunday, November 28, 2010

Subependymal Giant Cell Astrocytoma

Subependymal giant cell astrocytomas (SEGAs) are the most common cerebral neoplasm in patients with tuberous sclerosis, being found in up to 15% of patients. They are thought to arise from subependymal nodules in the ventricular wall.

Subependymal giant cell astrocytomas are almost always found near the foramen of Monro, are slowly-growing, and are WHO grade I tumors. The majority of cases occur during the first two decades of life.

CT reveals a heterogeneously low to iso attenuation lesion with or without calcifications in the region of the foramen of Monro with avid and heterogeneous enhancement. T1- and T2-weighted images reveal the mass to be hypo- to isointense to gray matter. The mass is heterogeneously hyperintense on FLAIR images. T2* images may show punctate hypointensities corresponding to calcium. Similar to CT, there is avid enhancement.

Differential considerations include:
  • Subependymoma: Most common location is the lower fourth ventricle and the frontal horns of the lateral ventricles. Found in older patients. Typically none to mild enhancement, which is more commonly seen in fourth ventricle subependymomas
  • Central neurocytoma: May also arise near foramen of Monro or septum pellucidum. Found in young adults (SEGAs typically occur during the first two decades). Look for necrosis and cyst formation.
  • Choroid plexus tumors: For example, papillomas or carcinomas. These demonstrate avid enhancement and may have seeding via cerebrospinal fluid. The latter is not seen with subependymal giant cell astrocytoma. In addition, carcinomas may invade the brain parenchyma
  • Astrocytoma: May arise from the fornices of the septum pellucidum or the medial basal ganglia. Enhancement is variable and calcifications are rare.
  • Germinoma: These often arise near the third ventricle, seed via the cerebrospinal fluid.

References

  • Koeller KK, Sandberg GD. Cerebral intraventricular neoplasms: radiologic-pathologic correlation. Radiographics. 2002 Nov-Dec;22(6):1473-505.
  • Hedlund GL. Subependymal Giant Cell Astrocytoma. STATdx. Amirsys, Inc.

Saturday, November 27, 2010

Radiographic Deteremination of Distal Radioulnar Joint Dislocation

Distal radioulnar joint (DRUJ) dislocation can be caused by fractures of the distal radius (most common cause) and distal ulna (e.g., styloid process) and injury to the triangular fibrocartilage complex, dorsal and palmar radioulnar ligaments, interosseous membrane, or joint capsule. Radiography is generally unreliable for diagnosis because of the difficulty in obtaining standard views, but recognition of typical findings and associated injuries is nonetheless important.

Frontal radiographs may reveal an avulsion fracture of the triangular fibrocartilage complex, an ulnar styloid fracture or nonunion, and shortening of the radius. Increased overlap between the radius and ulna indicates volar ulnar dislocation, while increased distance between the sigmoid notch and the distal ulna indicates dorsal ulnar dislocation (more common).

A true lateral radiograph of the wrist with the forearm in neutral rotation (i.e., without supination or pronation) is needed. With true lateral views, the pisoscaphoid distance (between anterior margins of the scaphoid and pisiform) and the radioulnar distance (between the posterior margins of the radius and ulna) can be measured in both wrists. The difference between the two pisoscaphoid distances should be less than 3 mm and the difference between the two radioulnar distances should be less than 5 mm. A radioulnar difference of 6 mm or more is diagnostic of dislocation and a radioulnar difference between 5 mm and 6 mm is considered borderline, requiring additional imaging.

References

  • Tsai PC, Paksima N. The distal radioulnar joint. Bull NYU Hosp Jt Dis. 2009;67(1):90-6.
  • Nakamura R, Horii E, Imaeda T, Tsunoda K, Nakao E.Distal radioulnar joint subluxation and dislocation diagnosed by standard roentgenography. Skeletal Radiol. 1995 Feb;24(2):91-4.

Friday, November 26, 2010

Coracoclavicular Joint

The coracoclavicular joint is a normal variant, where there is a diarthrosis between the conoid tubercle of the clavicle and the superior surface of the horizontal part of the coracoid process of the scapula. The coracoclavicular joint can cause shoulder pain in the setting of arthritis. The images above show radiographs and axial and coronal CTs of a left coracoclavicular joint. The color image is a SPECT/CT fusion of a bone scan obtained for an unrelated condition, showing no evidence of abnormal uptake.

References

Hall FJ. Coracoclavicular Joint. Br Med J. 1950 Apr 1;1(4656):766-768.

Thursday, November 25, 2010

Amputation Stump Neuroma

Amputation stump neuromas are a common cause of stump pain and can be classified as terminal or spindle neuromas. Terminal neuromas are formed as distal axons in a transected nerve grow in an attempt to reunite with non-existent distal axons cells and form a bulbous mass. Spindle neuromas, on the other hand, are not located at the transected nerve, but at a peripheral nerve that has been exposed to microtrauma from stretching or compression by local scar tissue.

Amputation stump neuromas usually present within a year of surgery and can continue to enlarge for 3 years.

MRI is the imaging modality of choice for detection of a neuroma and differentiation of soft tissue stump mass from tumor recurrence. Stump neuromas have low signal intensity on T1-weighted images and intermediate-to-high signal intensity on T2-weighted images. They demonstrate variable contrast enhancement. Ultrasound can also be used for diagnosis of neuromas, which classically appear as oval-shaped, hypoechoic masses that are contiguous with a nerve. The margins of the mass can be well-defined or irregular.

References

Wednesday, November 24, 2010

Pseudodefect of the Capitulum

The capitulum narrows distally, where there is a change in contour at the junction of the capitulum anteriorly with the lateral epicondyle posteriorly. This change in contour at the posterolateral margin can look like an osteochondral defect and is referred to as the "pseudodefect of the capitulum"

Coronal images through the posterior capitulum and sagittal images through the lateral epicondyle can demonstrate this apparent defect.

Real osteochondral defects can be differentiated from this pseudodefect by the presence of flattening and deformity of the anterior surface of the capitulum, which is normally smooth. In addition, acute osteochondral defects are usually accompanied by bone marrow signal abnormalities.

References

Hughes T, Chung CB. Chapter 12. In Chung CB and Steinbach LS. MRI of the Upper Extremity: Shoulder, Elbow, Wrist, and Hand. Lippincott Williams & Wilkins. 2010. pp 462.

Tuesday, November 23, 2010

Proximal Femoral Focal Deficiency

Proximal femoral focal deficiency refers to congenital absence or hypoplasia of the proximal femur. It is characterized by a short femur with proximal deficiency and varus deformity of the femoral neck. The Aitken classification divides proximal femoral focal deficiency into four categories. The Amstutz classification subdivides Aitken class A into Amstutz types 1 and 2. Amstutz types 3, 4, and 5 represent Aitken classes B, C, and D, respectively.
  • Class A: Short femur with coxa vara. Well-formed acetabulum.
    • Amstutz type 1: Cartilaginous femoral neck.
    • Amstutz type 2: Pseudoarthrosis at the femoral neck.
  • Class B: No connection between the femoral head and shaft.
  • Class C: Dysplastic acetabulum. Small or absent femoral head not adjoined to the femoral shaft.
  • Class D: Both the acetabulum and femoral head are absent.
Case courtesy of Dr. Shilpa Pandey.

References

  • Hillmann JS, Mesgarzadeh M, Revesz G, Bonakdarpour A, Clancy M, Betz RR. Proximal femoral focal deficiency: radiologic analysis of 49 cases. Radiology. 1987 Dec;165(3):769-73.
  • Maldjian C, Patel TY, Klein RM, Smith RC. Efficacy of MRI in classifying proximal focal femoral deficiency. Skeletal Radiol. 2007 Mar;36(3):215-20.

Monday, November 22, 2010

Bipartite Sesamoid vs Fractured Sesamoid

Distinguishing a bipartite hallux sesamoid from a fractured hallux sesamoid can be challenging. While the clinician can easily tell by physical examination, the typical history of "rule out pain" that accompanies the majority of radiograph requisitions contains no helpful clues.

Several findings can help differentiate a bipartite hallux sesamoid from a fractured medial hallux sesamoid:
  • Size: A medial sesamoid with a fracture is slightly larger than the lateral sesamoid, whereas a bipartite sesamoid is much larger.
  • Cortication: Fractures have sharp, radiolucent, uncorticated lines, while bipartite sesamoids have two corticated fragments.
  • Fit: The fragments of a fractured sesamoid often fit into each other, while the components of a bipartite sesamoid do not.
The case above shows a much larger bipartite medial hallux sesamoid with well-corticated margins. The two fragments do not fit into each other.

References

Mellado JM, Ramos A, Salvadó E, Camins A, Danús M, Saurí A. Accessory ossicles and sesamoid bones of the ankle and foot: imaging findings, clinical significance and differential diagnosis. Eur Radiol. 2003 Dec;13 Suppl 4:L164-77.

Sunday, November 21, 2010

Ankle Effusions and Trauma

The size of an ankle effusion following trauma can be used to suggest an underlying fracture. The effusion is measured as follows: Imaginary lines (white) are drawn parallel to the tibial shaft and tangential to the effusion margins at level of ankle joint. Another set of lines are drawn parallel to the first at edge of the articular surface of the tibia (dashed line). The distances between these two sets of lines are added. An ankle effusion >e; 13 mm has a positive predictive value of 80% for occult fracture and is suggested as a reasonable threshold to prompt additional imaging.

References

Clark TW, Janzen DL, Ho K, Grunfeld A, Connell DG. Detection of radiographically occult ankle fractures following acute trauma: positive predictive value of an ankle effusion. AJR Am J Roentgenol. 1995 May;164(5):1185-9.

Saturday, November 20, 2010

Os Subtibiale

The os subtibiale is an uncommon accessory ossicle distal and posterior to the medial malleolus that is seen in less than 1% of the population. It is thought to represent an unfused epiphyseal ossification center related to the posterior colliculus of the medial malleolus.

References

  • Coral A. The radiology of skeletal elements in the subtibial region: incidence and significance. Skeletal Radiol. 1987;16(4):298-303.
  • Coral A. Os subtibiale mistaken for a recent fracture. Br Med J (Clin Res Ed). 1986 Jun 14;292(6535):1571-2.
  • Lapidus PW. OS SUBTIBIALE: Inconstant Bone Over the Tip of the Medial Malleolus. J Bone Joint Surg Am. 1933;15:766-771.

Friday, November 19, 2010

Varus instability of the Elbow

Varus instability of the elbow is caused by disruption of the lateral collateral ligament complex, which includes the radial collateral ligament and lateral ulnar collateral ligament.

The lateral collateral ligamentous complex consists of the radial collateral ligament (RCL, blue), lateral ulnar collateral ligament (LUCL, pink), and the annular ligament (AL, yellow).

The radial collateral ligament (RCL, blue) originates on the lateral epicondyle and inserts on the annular ligament. Because of this attachment, injury to the radial collateral ligament may be associated with injury to the annular ligament and vice versa.

The lateral ulnar collateral ligament (LUCL, pink) originates on the lateral epicondyle, passes along the posterolateral margin of the radial head, blends with fibers of the annular ligament, and inserts on the supinator crest of the ulna (SC).

The annular ligament originates from the anterior and posterior margins of the radial notch and surrounds the radial head. It is the primary stabilizer of the proximal radioulnar joint.

The image above shows a tear of the radial collateral ligament (blue arrow) and an intact lateral ulnar collateral ligament (pink arrow). A partial tear of the common extensor tendon is also present (white arrow).

The mechanism of injury in cases of varus instability is force to the medial side of the elbow, causing compression medially and stress applied to the radial collateral ligament. The etiology is usually trauma, but chronic stress, such as from crutches, has also been implicated.

References

Chung CB. Chapter 10. In Chung CB and Steinbach LS. MRI of the Upper Extremity: Shoulder, Elbow, Wrist, and Hand. Lippincott Williams & Wilkins. 2010. pp 426-427.

Thursday, November 18, 2010

Accessory Sacroiliac Joint

10% - 30% of the population has an accessory sacroiliac articulation between the posterior superior iliac spine and the lateral sacral crest at the level of the S2 foramen. These most commonly represent fibrocartilagenous connections that develop in response to weight bearing, but may also be present congenitally and represent true joints.

Here we see bilateral accessory sacroiliac joints (arrows) between the posterior superior iliac spine and the lateral sacral crest at the level of the S2 foramen.

References

Ehara S, el-Khoury GY, Bergman RA. The accessory sacroiliac joint: a common anatomic variant. AJR Am J Roentgenol. 1988 Apr;150(4):857-9.

Wednesday, November 17, 2010

Congenital Dislocation of the Radial Head

Congenital dislocation of the radial head is the most common congenital elbow abnormality and usually occurs in association with other conditions (60% of the time), but can also occur in isolation. The more common associated conditions include lower extremity anomalies, scoliosis, mental retardation, and nail patella and Klippel-Feil syndromes.

The majority of radial head dislocations are posterior (65% of cases), followed by anterior (~15%) and lateral (~15%). Patients are usually asymptomatic in childhood, but may develop pain in adolescence.

The constellation of findings is now believed to be triggered by failure of development of a normal capitulum, which deprives the developing radial head of the contact pressure required for normal development and results in malformation of the radiocapitellar joint. This, in turn, results in altered biomechanics at the proximal radioulnar joint and abnormal development of the ulna.
  • Capitulum: Hypoplastic and flattened
  • Radius: Domed radial head articular surface.
  • Ulna: Severely bowed and relatively short in relation to the radius. Negative ulnar variance at the wrist.
  • Humerus: Mechanical erosion distally at pseudoarticulation with the dislocated radial head.
Early radiographic findings are subtle due to the absence of the capitulum and radial head ossification centers. Before radial head ossification (~ 5 years) a line drawn along the shaft of the radius should normally bisect the capitulum ossification center.

References

Hughes T and Chung CB. Chapter 12. In Chung CB and Steinbach LS. MRI of the Upper Extremity: Shoulder, Elbow, Wrist, and Hand. Lippincott Williams & Wilkins. 2010. pp 487-488.

Tuesday, November 16, 2010

Cubital Tunnel

The cubital tunnel is located posterior to the medial epicondyle and contains the ulnar nerve and posterior recurrent ulnar vessels surrounded by fat.
  • The medial margins of the trochlea and olecranon form its floor, which is lined by the posterior band of the ulnar collateral ligament. A hypoplastic trochlea can predispose patients to ulnar nerve dislocation. The ulnar collateral ligament relaxes and bulges medially during elbow flexion, which results in narrowing of the cubital tunnel.
  • The arcuate ligament forms its roof. This is a fibrous band between the ulnar and humeral heads of the flexor carpi ulnaris muscle and is also known as Osborne's band and the cubital tunnel retinaculum. The arcuate ligament becomes taut with flexion of the elbow. Congenital absence, laxity or a tear of the arcuate ligament can lead to ulnar nerve dislocation.
  • The medial epicondyle makes up its anterior border.
The normal cubital tunnel should contain fat signal surrounding the intermediate-signal–intensity ulnar nerve. Posterior recurrent ulnar vessels can be seen as dot-like, T1-hypointense structures adjacent to the ulnar nerve

The cubital tunnel is the most common site of ulnar nerve compression at the elbow. Cubital tunnel syndrome is due to narrowing of the cubital tunnel or repetitive stress on the ulnar nerve. Elbow flexion in normal subjects results in narrowing of the tunnel by stretching the arcuate ligament; bulging of the medial head of the triceps muscle, which pushes the ulnar nerve anteromedially; and relaxing the ulnar collateral ligament, which bulges medially.

Images through the cubital tunnel during elbow flexion can reveal findings pertinent to cubital tunnel syndrome, including narrowing of the cubital tunnel, attenuation of the perineural fat, bulging of the medial head of the triceps (located more superiorly than the presented slice), and flattening of the ulnar nerve.

Masses in or around the cubital tunnel can cause ulnar nerve compression, including bursae, ganglia, inflammatory synovitis, osteoarthritis, ectopic calcifications, anomalous muscles (e.g., anconeus epitrochlearis) or ligaments (e.g., ligament of Struthers, normally associated with median nerve compression).

Fluid-sensitive sequences often reveal increased signal intensity of the ulnar nerve in the setting of cubital tunnel syndrome.

References

Chapters 2, 10, 11, and 13. In Chung CB and Steinbach LS. MRI of the Upper Extremity: Shoulder, Elbow, Wrist, and Hand. Lippincott Williams & Wilkins. 2010.

Monday, November 15, 2010

Os Acromiale

An os acromiale is an accessory ossification center of the acromion that fails to fuse to the acromion proper by the age of 22 years. The os acromiale may articulate with the acromion by fibrous tissue, cartilage, periosteum, or synovium.

Depending on the location of its articulation with the acromion, an os acromiale may be classified as pre-, meso-, meta-, or basi-acromion (see figure).

An os acromiale can be seen in up to 15% of the population, is bilateral in 60% of cases, and may or may not be symptomatic. Most are meso or meta-acromions.

References

Steinbach LS. Chapter 4. In Chung CB and Steinbach LS. MRI of the Upper Extremity: Shoulder, Elbow, Wrist, and Hand. Lippincott Williams & Wilkins. 2010. p 250.

Sunday, November 14, 2010

Focal Myocardial Thinning

Differential considerations for focal myocardial thinning:
  • Normal Variant: At apex of left ventricle.
  • Old myocardial infarction: Thinning restricted to a coronary artery territory and consistent with ECG findings.
  • Cardiac sarcoidosis: Most commonly in the septum.
  • Muscular left ventricular diverticulum: Tiny crypts in the left ventricular wall that can be seen in normal patients or those with hypertrophic cardiomyopathy.
  • Post myocarditis:
  • Fibro-fatty replacement:
  • Muscular dystrophy: In addition to skeletal muscle involvement, there nearly always is an associated cardiomyopathy in Duchenne or Becker muscular dystrophy.
  • Primary aneurysm:
  • Dilated phase hypertrophic cardiomyopathy:
  • Complete left bundle branch block: Possibly due to redistribution of cardiac mass from chronic asynchronous electric activation.
  • Arrhythmogenic right ventricular dysplasia:

References

  • Prinzen FW, Cheriex EC, Delhaas T, van Oosterhout MF, Arts T, Wellens HJ, Reneman RS. Asymmetric thickness of the left ventricular wall resulting from asynchronous electric activation: a study in dogs with ventricular pacing and in patients with left bundle branch block. Am Heart J. 1995 Nov;130(5):1045-53.
  • Srichai MB, Hecht EM, Kim DC, Jacobs JE. Ventricular diverticula on cardiac CT: more common than previously thought. AJR Am J Roentgenol. 2007 Jul;189(1):204-8.
  • Yoshida N, Funabashi N, Uehara M, Yajima R, Kataoka A, Ueda M, Takaoka H, Komuro I. Differentiation of diagnosis and prognoses of non-coronary arterial primary myocardial diseases with left ventricular focal myocardial thinning evaluated by multislice computed tomography. Int J Cardiol. 2009 Nov 3.

Saturday, November 13, 2010

Curvilinear Subpleural Line

A subpleural line is a thin curvilinear opacity a few millimeters or less in thickness that is usually less than 1 cm from the pleural surface and parallels the pleura.

This is a nonspecific finding that is classically described in patients with asbestos exposure (as in the case of the patient shown above), in whom the lines are thought to represent the proximal extent of a row of subpleural honeycomb cysts, peribronchiolar fibrosis (and resultant collapse of alveoli), or hypoventilation due to pleural thickening. Dependent subpleural lines can also be seen in normal subjects related to atelectasis.

References

Friday, November 12, 2010

Transient Tachypnea of the Newborn

Transient tachypnea of the newborn (TTN), also known as wet lung disease, retained fetal lung liquid, retention of fetal lung fluid, respiratory distress syndrome type II, transient respiratory distress of the newborn, and neonatal retained fluid syndrome, occurs when there is retained fluid in the neonate's lung.

This is a diagnosis of exclusion when no other cause is found for the infant's tachypnea. It is seen in neonates who are sedated or following cesarean section

Radiographs show a normal heart size with findings similar to pulmonary edema: Diffuse, bilateral and usually symmetric increased lung markings. These findings resolve within 1-2 days. Lung volumes may be normal or increased. Pleural effusion and fluid in the fissures may or may not be present.

Differential considerations include:
  • Congenital heart disease: Total anomalous pulmonary venous return (TAPVR), severe aortic obstruction (stenosis, coarctation, interruption), hypoplastic left heart
  • Meconium aspiration syndrome: Hyperinflated lungs with rope-like perihilar markings
  • Neonatal pneumonia:

Thursday, November 11, 2010

Lucent Lesions of the Patella

Differential considerations for lucent lesions of the patella include:
  • Dorsal defect of patella: Normal variant
  • Subchondral cyst: Can be seen with osteoarthritis or pyrophosphate arthropathy.
  • Amyloid deposition: In patients with renal disease.
  • Chondroblastoma: Most common benign neoplasm of the patella. Round or lobulated with a well-defined sclerotic rim.
  • Giant cell tumor: Geographical pattern of bone destruction. Involve more than 3/4 of the patella and lead to cortical thinning and septations. Locally aggressive
  • Pigmented villonodular synovitis:
  • Unicameral bone cyst:
  • Aneurysmal bone cyst:
  • Metastasis:
  • Malignant tumor: Hemangioendothelioma, lymphoma, and osteosarcoma.
  • Gout: Rare. Soft tissue component may be seen on MRI. Has a predilection for the superolateral aspect of the patella.
  • Osteomyelitis: Rare. More common in adolescents (peak vascularity of the patella) or immunocompromised patients. No periosteal reaction (since sesamoids don't have a periosteal layer).

References

Singh J, James SL, Kroon HM, Woertler K, Anderson SE, Jundt G, Davies AM. Tumour and tumour-like lesions of the patella--a multicentre experience. Eur Radiol. 2009 Mar;19(3):701-12.

Wednesday, November 10, 2010

Myxopapillary Ependymoma

Ependymomas are the most common primary spinal cord tumors. They have been classified by the World Health Organization into grades I, II, and III. Grade I tumors include myxopapillary ependymomas and subependymomas. Grade II tumors are just called ependymomas and can be further divided as cellular, papillary, clear cell, or tanycytic. Grade III tumors are called anaplastic ependymomas, tend to occur in the brain, and are rare in the spine.

Myxopapillary ependymomas are thought to arise from ependymal glia of the filum terminale and occur almost exclusively in the conus medullaris and filum terminale. As such, they are intradural and usually extramedullary (in contrast to upper cord lesions that are typically intramedullary). Extradural myxopapillary ependymomas, though rare, can also occur and are thought to arise from extradural remnants of the filum terminale or the coccygeal medullary vestige.

Myxopapillary ependymomas are often encapsulated and may have foci of hemorrhagic or mucinous degeneration. They are usually centered within the filum terminale but can extend into the conus medullaris. Myxopapillary ependymomas usually displace the lumbosacral nerve roots, but may encase them if the tumor gets large enough.

Myxopapillary ependymomas are slow-growing and can get large enough to expand the spinal canal, leading to interpedicular widening on frontal radiographs and widening of the spinal canal and scalloped vertebral bodies on the lateral view. Bone destruction may also be appreciated in advanced cases.

Non-contrast CT images reveal myxopapillary ependymomas to be isoattenuating compared to the spinal cord. The spinal canal may be widened and there may be scalloping of the vertebral bodies with neural foraminal enlargement. Myxopapillary ependymomas typically have intense homogeneous enhancement.

On MRI, myxopapillary ependymomas are typically iso- to hyperintense compared to the spinal cord on T1-weighted images, depending on the amount of proteinaceous mucoid matrix. If present, T1-hyperintensity helps differentiate myxopapillary ependymomas from other ependymoma subtypes, which tend to be hypo- or isointense on T1-weighted images. Myxopapillary ependymomas are T2-hyperintense compared to the spinal cord. As with other ependymomas, myxopapillary ependymomas demonstrate intense enhancement. Heterogeneous enhancement signifies hemorrhage or necrosis.

Most ependymomas of the cauda equina region are slow-growing, and patients present with indolent low back pain. Mass effect from the tumor may cause sciatica or other, less common symptoms, such as sensorimotor disturbance and bowel and bladder dysfunction.

Differential considerations include:
  • Other ependymoma subtypes:
  • Schwannoma: Can have findings almost identical to those of a small myxopapillary ependymoma.
  • Subependymoma: Can have findings almost identical to those of a small myxopapillary ependymoma.
  • Astrocytoma:
  • Hemangioblastoma:
  • Ganglioma:
  • Paraganglioma:
When the mass is large and causes bone destruction, aneurysmal bone cyst, chordoma, plasmacytoma, metastasis, and giant cell tumor may also be considered.

Our patient was a young man who presented with several years of low back and flank pain. A renal tumor protocol CT was performed, which showed a mass in the spinal canal. On MR, the mass is well encapsulated, isointense to the spinal cord on T1-weighted images and heterogeneously hyperintense on T2-weighted images. Post-contrast images reveal intense heterogeneous enhancement. On the axial T2-weighted image, the mass splays the nerve roots of the cauda equina and widens the spinal canal.

Case courtesy of Dr. Sibin Thachet.

References

Tuesday, November 9, 2010

Wall-to-wall Cardiothymic Silhouette in Neonates

  • Ebstein anomaly: Massive right atrial enlargement. Decreased pulmonary blood flow.
  • Pulmonary atresia with intact ventricular septum: Massive right atrial enlargement. Decreased pulmonary blood flow.
  • Large pericardial effusion: Seen in hydrops fetalis, sepsis, cardiac tumors, thyroid dysfunction, and diaphragmatic hernia into the pericardial sac.
  • Atypical large arteriovenous shunts: For example, peripheral arteriovenous malformations or intracardiac arteriovenous malformations (e.g., coronary artery-right heart fistula). Pulmonary vascularity may be normal due to the high pulmonary vascular resistance of newborns.
  • Hypertrophic cardiomyopathy in infants of diabetic mothers:
  • Cardiac or mediastinal mass mimicking massive cardiomegaly: Rhabdomyoma (e.g., in children with tuberous sclerosis), teratomas, and congenital diaphragmatic hernia (before gas enters the bowel).

References

Donnelly LF, Gelfand KJ, Schwartz DC, Strife JL. The wall to wall heart: Massive cardiothymic silhouette in newborns. Applied Radiology. 1997 December; 26(12).

Monday, November 8, 2010

Shunt Vascularity

Shunt vascularity refers to increased number and size of sharply defined pulmonary vessels (in contrast to blurred vessels seen in pulmonary edema) in response to diversion of blood to the lungs. There is no or minimal tapering of these enlarged vessels, especially in the upper lungs (in contrast to the pruning seen in pulmonary hypertension).

The most common causes of shunt vascularity are:
  • Left-to-right: Acyanotic.
    • Atrial septal defect: The left atrium is not enlarged. No significant cardiomegaly unless a complicated atrial septal defect exists.
    • Partial anomalous pulmonary venous return: Some pulmonary veins drain into the right atrium or systemic veins instead of the left atrium. The left atrium is not enlarged, but cardiomegaly may occur if the left-to-right shunt is significant.
    • Ventricular septal defect: Cardiomegaly with an enlarged left atrium and main pulmonary artery.
    • Patent ductus arteriosus: Enlarged left atrium. May see a prominent aortic knob.
    • Endocardial cushion defect: Strong association with Trisomy 21. The heart may be enlarged.

    Simplistic view for boards purposes:
  • Mixed: Cyanotic
    • Total anomalous pulmonary venous return: Normal-sized heart.
    • Complete transposition of the great vessels: Egg-on-a-string. Classically described as thymic atrophy and an enlarged heart with an oval-shape and an upturned apex. The position of the aorta and pulmonary trunk results in a narrow superior mediastinum. Together, the upturned heart and narrow mediastinum result in the egg-on-a-string appearance.
    • Persistent truncus arteriosus: A single-vessel carries outflow from the heart, overrides the ventricular septum, and supplies the systemic, pulmonary, and coronary circulation. The heart is enlarged and there is frequently a right-sided aortic arch.
    • Hypoplastic left heart: Oxygenated blood passes to the right side via an atrial septal defect, and mixed blood travels to the aorta via a patent ductus arteriosus. Typically will see an enlarged heart with a prominent right atrium.
    • Single ventricle: Double outlet right ventricle and double outlet left ventricle are conceptually similar.
  • High-flow state:
    • Arteriovenous malformation: Vein of Galen malformation, for example.
    • Anemia:
    • Thyrotoxicosis:

References

Sunday, November 7, 2010

Rectal Duplication

Rectal duplications are rare anomalies that may be lined with colonic (most common), squamous epithelium, gastric mucosa, and urothelial cells. The vast majority are retrorectal. Rectal duplications may be classified as:
  • Tubular: Associated with urinary or vertebral malformations.
  • Cystic: Associated with anorectal malformations, such as anterior perineal anus and cloacal malformations.
  • Fistulated (internal or external):
  • Diverticular:
  • Exstrophic: May be attached to the rectum or vagina, but does not normally communicate with either.
The image above presents a rectal duplication. Contrast was administered through a mucous fistula, and filled the rectum and then a tubular retrorectal structure. The black dot represents a metallic marker at the site of an anus. The second image shows contrast trickling out around the region of what previously appeared to be an imperforate anus. The MR image shows a cystic structure posterior to the anus.

References

Rajah S, Ramanujam TM, Anas SR, Jayaram G, Baskaran P, Ganesan J, Tin M. Duplication of the rectum: report of four cases and review of the literature. Pediatr Surg Int. 1998 Jul;13(5-6):373-6.

Saturday, November 6, 2010

The Celery Stalk Sign

The celery stalk sign refers to the appearance of hyperintense bands interposed between the fibers of a normally oriented anterior cruciate ligament (ACL). The celery stalk is best appreciated on sagittal, fluid-sensitive sequences. The hyperintense bands correspond to amorphous mucoid matrix collecting between intact, almost parallel anterior cruciate ligament fibers.

The celery stalk appearance corresponds to mucoid degeneration of the anterior cruciate ligament and should not be mistaken for a chronic or acute tear.

The celery stalk sign should not be confused with the celery stalk metaphysis.

References

Papadopoulou P. The celery stalk sign. Radiology. 2007 Dec;245(3):916-7.