Tuesday, January 31, 2012

Heterogeneous Splenic Enhancement in Children

The spleen commonly has heterogeneous enhancement in the first minute after initiation of contrast injection in both adults and children. This heterogeneity is thought to be due to variable rates of flow through the cords of white and red pulp (lymphoid follicles and vascular sinusoids, respectively). Three enhancement patterns have been described. The archiform pattern is the most commonly seen, followed by focally heterogeneous and diffusely heterogeneous.

Different mechanisms affect the heterogeneity in children and adults. Donnelly et al looked at transient splenic heterogeneity and the variables that affect it in children.

They found transient splenic heterogeneity in about 70% of children. This was maximally visualuzed at ~25 seconds and resolved by 70 seconds in the majority (95%) of cases.

They also found that faster rates of contrast injection (≥ 1.0 cc/sec) were more likely to be associated with transient splenic heterogeneity. The time of visualization and time to resolution, however, did not seem to be affected by the rate of injection.

Children older than 1 year were also more likely to have transient splenic heterogeneity, which was thought to be related to the increasing ratio of white pulp (lymphoid follicles) to red pulp (vascular sinusoids) during the first year of life.

The image above is from a 10-year-old boy. The arterial phase reveals the archiform pattern of enhancement, which resolves on the venous phase image.

References

Donnelly LF, Foss JN, Frush DP, Bisset GS 3rd. Heterogeneous splenic enhancement patterns on spiral CT images in children: minimizing misinterpretation. Radiology. 1999 Feb;210(2):493-7.

Monday, January 30, 2012

Trampoline Fracture of the Proximal Tibia

A trampoline fracture refers to a transverse or buckle (torus) fracture of the proximal tibial metaphysis that occurs in young children who jump on a trampoline with a heavier person.

The upward recoil of the trampoline after the heavier person jumps can generate a large force. If the child happens to land on the trampoline during the recoil, the force may be sufficient to cause the typical tibial fracture described.

Special thanks to Dr. Hansel Otero for the case and reference.

References

Boyer RS, Jaffe RB, Nixon GW, Condon VR. Trampoline fracture of the proximal tibia in children. AJR Am J Roentgenol. 1986 Jan;146(1):83-5.

Sunday, January 29, 2012

Pulmonary Alveolar Microlithiasis

Pulmonary alveolar microlithiasis is a rare autosomal recessive disease that is caused by impaired transfer of phosphorus ions from the alveolar space into type II pneumocytes. This leads to the development of microliths composed of calcium and phosphorus (calcospherites) in the alveoli.

Men and women are affected at an equal rate, and patients tend to be younger than 50 years of age at diagnosis. Most patients have at least one sibling with the disease, and there is a high rate of consanguineous marriages in affected families.

Patients typically present with progressive dyspnea, which, after a protracted course, progresses to pulmonary fibrosis, end-stage lung disease, and chronic pulmonary heart disease.

Initial laboratory evaluation usually reveals no underlying disorder calcium metabolism, and pulmonary function testing reveals a restrictive pattern of lung disease and decreased diffusion capacity (transfer factor).

Radiographs reveal fine calcific micronodules in a diffuse (sandstorm) pattern, but with a more dense involvement of the lower zones (thought to be due to the larger surface area and greater thickness of this part of the lungs). There is usually silhouetting of the mediastinal and diaphragmatic borders and a linear lucency between the ribcage and parenchyma (reflecting subpleural cystic changes). Small apical bullae with or without an associated pneumothorax may also be present.

The findings are more subtle in children. Nodular calcific densities are less prominent on children’s chest radiographs and the major finding may be ground-glass opacities.

HRCT reveal widespread involvement of both lungs with microliths, with a predisposition for the posterior segments of the lower lobes, anterior segments of the upper lobes, and the medial aspects of the lungs.

Confluent calcifications may also be seen, and are often found in the upper lobes. There is also micronodulation and thickening of the interlobular septa and bronchovascular and subpleural interstitium.

Multiple small, thin-walled subpleural cysts can also be seen and are responsible for the lucent subpleural line seen on radiographs. Pleural calcifications have also been described.

When extensive, the calcifications can result in interlobular septal thickening. Microliths smaller than 1 mm can produce a ground-glass appearance. Together, these can give an appearance similar to crazy paving.

In children, a ground-glass pattern may predominate, and microliths are seen to a lesser degree.

Differential considerations include:
  • Metastatic calcification: For example, in chronic renal failure and orthotopic liver transplantation.
  • Dystrophic calcification: Caused by granulomatous disorders (silicosis, sarcoidosis), DNA viruses, parasitic infections, and pulmonary amyloidosis.
  • Pulmonary ossification: Multiple causes. Most pimped: chronic chronic mitral stenosis.

References

  • Chan ED, Morales DV, Welsh CH, McDermott MT, Schwarz MI. Calcium deposition with or without bone formation in the lung. Am J Respir Crit Care Med. 2002 Jun 15;165(12):1654-69.
  • Gasparetto EL, Tazoniero P, Escuissato DL, Marchiori E, Frare E Silva RL, Sakamoto D. Pulmonary alveolar microlithiasis presenting with crazy-paving pattern on high resolution CT. Br J Radiol. 2004 Nov;77(923):974-6.
  • Helbich TH, Wojnarovsky C, Wunderbaldinger P, Heinz-Peer G, Eichler I, Herold CJ. Pulmonary alveolar microlithiasis in children: radiographic and high-resolution CT findings. AJR Am J Roentgenol. 1997 Jan;168(1):63-5.
  • Siddiqui NA, Fuhrman CR. Best cases from the AFIP: Pulmonary alveolar microlithiasis. Radiographics. 2011 Mar-Apr;31(2):585-90.

Saturday, January 28, 2012

Tracheal Rupture

Tracheobronchial injury after blunt or penetrating traumatic chest injury is rare, occurring in less than 2% of cases. The majority of intrathoracic tracheobronchial injuries are within 2.5 cm of the carina and most commonly affect the proximal right main stem bronchus.

Tracheal rupture makes up about 1/4 of all tracheobronchial injuries, and is associated with high morbidity and mortality from ventilatory failure, infection (mediastinitis, sepsis), and intermediate- and long-term complications (airway stenosis, recurrent pulmonary infections, bronchiectasis, and permanent pulmonary function impairment).

Clinical and imaging manifestations are subtle and nonspecific, and can result in delayed or missed diagnosis.

Deep cervical emphysema, pneumomediastinum, and paratracheal gas are seen in the vast majority of cases. The tracheal wall injury can sometimes be directly visualized on CT as a tracheal wall defect of discontinuity. Focal tracheal wall deformity or tracheal ring fracture can be more subtle indications of the location of injury.

In the intubated patient, additional signs of tracheal injury include overdistended, extraluminal, or herniated endotracheal tube balloon cuffs.

Pneumothorax and and pneumoretroperitoneum can be secondary findings, and a persistent pneumothorax despite a well-placed thoracostomy tube suggests a diagnosis of tracheobronchial injury.

Special thanks to Dr. Hansel Otero for the case.

References

Friday, January 27, 2012

Iodine-131: Half-Life

In the United States, patients treated with 131I ablation for hyperthyroidism or thyroid carcinoma are sent home with instructions on hygiene and limitations on social interactions. The instructions vary a bit among different centers, but are based on a balance between insurance reimbursement for inpatient isolation, patient comfort, and public safety.

The duration of isolation is usually decided empirically based on the administered dose, ranging from 2-7 days. This is based on the effective half-life of 131I, which is eliminated mainly through urine, but also in stool.

The physical half-life of 131I is fixed by nature at approximately 8 days. The effective half-life, however, depends on a number of patient factors. In healthy subjects, the effective half-life for the clearance of 131I is between 5-7 days. The effective half-life is similar in patients being treated for thyrotoxicosis. In patients with thyroid carcinoma who have been treated with total thyroidectomy, 131I clears faster because of the absence of significant thyroid tissue. The effective half-life in these patients is between 10 hours - 15 hours.

References

  • Greenlee C, Burmeister LA, Butler RS, Edinboro CH, Morrison SM, Milas M; American Thyroid Association Radiation Safety Precautions Survey Task Force. Current safety practices relating to I-131 administration for diseases of the thyroid: a survey of physicians and allied practitioners. Thyroid. 2011 Feb;21(2):151-60.
  • Ravichandran R, Binukumar J, Saadi AA. Estimation of effective half life of clearance of radioactive Iodine (I) in patients treated for hyperthyroidism and carcinoma thyroid. Indian J Nucl Med. 2010 Apr;25(2):49-52.

Thursday, January 26, 2012

Paranasal Sinus Osteomas

Osteomas of the paranasal sinuses are well-defined, slowly growing, non-neoplastic masses that arise from the sinus wall and are covered by the mucoperiosteum of the sinus. Developmental, traumatic, and infective, etiologies have been suggested, but none has been proven.

There is some variability in naming osteomas. Some name them after the sinus invaded by the tumor, while other name then for the sinus of origin.

Osteomas are found in about 3% of the population (more commonly men), and have a peak incidence between the fourth and sixth decades of life. Osteomas can be found sporadically or in association with Gardner syndrome (familial adenomatous polyposis). In the latter case, osteomas tend to be multiple and appear ~15 years before colon polyps. Therefore, gastroenterology referral is suggested when multiple facial or sinonasal osteomas are found.

The majority of patients are asymptomatic, but some can present with sinusitis, headache, and facial pain. Surgery is generally indicated with symptomatic osteomas. The management of asymptomatic osteomas is controversial and variable. Indications for resection of asymptomatic osteomas are not universally accepted and include: Osteomas located near the frontal sinus ostium, frontal osteomas larger than 50% of the volume of the sinus, frontoethmoid osteomas extending beyond the confines of the frontal or ethmoid sinuses, any ethmoid osteoma, and enlarging osteomas.

Recurrence after surgery is rare, even with incomplete resection; however, accelerated growth following incomplete resection has been reported and most will recur if given enough time. Malignant transformation has not been described.

The frontal sinus is most commonly affected, followed by the ethmoid, maxillary, and sphenoid sinuses. In the frontal sinus, there is a predilection to arise at the junction of frontal and anterior ethmoid sinuses. Even a relatively small osteoma in this location can lead to obstruction depending on the drainage pattern of the frontal sinus. The image above shows a relatively large frontal osteoma (pink arrow) leading to obstruction of the drainage pathway of the frontal sinus.

Non-obstructive complications of osteomas are rare, but familiarity with potential problems will help you avoid an incomplete assessment of these often neglected lesions.

Frontal sinus osteomas rarely invade the orbit and cranial fossa. Orbital invasion can cause exophthalmos, proptosis, visual disturbances, or blockage of the nasolacrimal duct. Cranial invasion can lead to pneumocephalus (rarely even tension pneumocephalus), rhinorrhea (from leakage of cerebrospinal fluid), meningitis, and cerebral abscess.

Ethmoid sinus osteomas can extend intracranially through the cribriform plate, laterally into the orbit, or anteriorly to the nasolacrimal duct.

Maxillary sinus osteomas can mimic maxillary antroliths and calcifying odontogenic tumors such as cementomas. An origin from adjacent tooth roots can suggest a calcifying odontogenic tumor such as a cementoma.

Sphenoid sinus osteomas are rare. The major complication of these osteomas is invasion of the sella turcica and associated pituitary issues.

Radiographs are not very sensitive or specific. When seen, osteomas present as well-defined bony lesions within the paranasal sinuses. CT Osteomas can be occult or show increased activity on bone scintigraphy. Lesions with activity have been shown to have potential for growth, while cold lesions tend to remain stable in size.

CT reveals a well-defined mass with attenuation similar to those of normal bone. MRI reveals a mass that is hypointense on all pulse sequences.

References

  • Chen CY, Ying SH, Yao MS, Chiu WT, Chan WP. Sphenoid sinus osteoma at the sella turcica associated with empty sella: CT and MR imaging findings. AJNR Am J Neuroradiol. 2008 Mar;29(3):550-1.
  • Earwaker J. Paranasal sinus osteomas: a review of 46 cases. Skeletal Radiol. 1993 Aug;22(6):417-23.
  • Georgalas C, Goudakos J, Fokkens WJ. Osteoma of the skull base and sinuses. Otolaryngol Clin North Am. 2011 Aug;44(4):875-90, vii.
  • Sadry F, Hessler C, Garcia J. The potential aggressiveness of sinus osteomas. A report of two cases. Skeletal Radiol. 1988;17(6):427-30.

Wednesday, January 25, 2012

Calcium Pyrophosphate Dihydrate Deposition around the Dens

The transverse ligament of the atlas can be involved by calcium pyrophosphate dihydrate (CPPD) deposits in about 6% of the general population and in as many as 2/3 of patients with articular chondrocalcinosis. These deposits can be associated with aging, degenerative disease, or metabolic disorders.

Patients are typically older women, with isolated involvement of the atlanto-axial joints. Crowned dens syndrome refers to acute neck pain due to calcium pyrophosphate dihydrate deposits and calcification surrounding the odontoid process on CT. The neck pain may be accompanied by neck stiffness and fever, and can mimic meningitis. They can be treated with non-steroidal anti-inflammatory medications, and the calcifications usually resorb in about 1-2 weeks.

The deposition can range from linear or stippled calcifications to massive crystal deposition with bone erosion involving the dens. Depending on the extent of CPPD deposition and associated erosions, patients can also be at increased risk for pathologic fracture of the dens.

Radiographs are usually not very sensitive for detection of periodontoid mineralization, and CT is usually needed for characterization. The appearance of the calcifications ranges from curvilinear to stippled, or a mixture of the two. The curvilinear pattern, although less common, is strongly suggestive of calcium pyrophosphate dihydrate deposition. When masslike deposits are present, CT can demonstrate the bony erosions and possible malalignment from associated ligamentous damage and any pathologic fracture of the dens.

MRI, while not as sensitive as CT for the detection of calcification, is better for evaluation of the mass and its effect on the spinal cord, as well as assessment of cartilage, bone, or ligament abnormalities. The retro-odontoid mass is typically hypointense on T2-weighted images and enhances on post-contrast images.

Differential considerations for an extradural mass posterior to the odontoid process include:
  • Pannus: Seen with rheumatoid arthritis, ankylosing spondylitis, and psoriatic arthritis. Does not have calcifications.
  • Os odontoideum:
  • Neoplasm: Epidural metastases, clivus chordoma, foramen magnum meningioma, aneurysmal bone cyst, osteoblastoma. Neoplasms will typically be T2-hyperintense, while the retro-odontoid mass of CPPD will be T2-hypointense.

References

Tuesday, January 24, 2012

Portal Vein Pulsatility

The normal flow in the portal venous system is typically continuously hepatopetal, with minimal if any pulsatility in rhythm with the cardiac cycle. Marked portal venous pulsatility can be classified as continuous pulsatile or reversed pulsatile flow.

The continuous pulsatile pattern is continuously hepatopetal, but with marked pulsatility. This pattern can be seen in patients with congestive heart failure, but can also be seen as a normal finding in thin subjects, where there is an inverse correlation of pulsatility to body mass.

The second pattern, reversed pulsatile flow is characterized by marked pulsatility and reversal of flow direction related to the cardiac cycle. There is a strong correlation of reversed pulsatile flow to high (> 20 mmHg) right atrial pressures in patients with chronic heart failure. However, reversed pulsatile flow can also be seen with tricuspid insufficiency, liver disease (cirrhosis, Budd–Chiari syndrome, hepatic outflow obstruction (constrictive pericarditis, mediastinal hematoma, pericardial mass or effusion), and shunts (portal vein–hepatic vein fistula, portocaval shunt). High abdominal pressures during deep inspiration can also cause transient reversal of flow. This is more commonly seen in patients with severe right heart failure or liver disease, but can also be seen in patients without these conditions.

Therefore, pulsatile portal venous flow by itself should not be construed as a sign of cardiac abnormality, especially if there is no reversal of the portal venous flow. The image above, however, shows a reversed pulsatile flow pattern and is from a patient with congestive heart failure.

Special thanks to Dr. Hansel Otero for the case.

References

Monday, January 23, 2012

Lower Limb Skeletal Traction: Proximal Tibia

Lower limb skeletal traction can be achieved through the proximal tibia, distal tibia, and the calcaneus. Proximal tibial traction is the most frequently used and can be used to reduce and immobilize femoral fractures.

Skeletal traction through the proximal tibia is most commonly achieved under local anesthesia by inserting a pin ~2 cm distal to the tibial tubercle and ~2 cm behind the anterior border of the tibia (measurements are for adults). Ideally, the pin passes through the skin and subcutaneous fat, but will avoid muscle and the common peroneal nerve.

The Steinmann pin (blue bar) is typically used. The pink is usually attached externally to a Böhler-Steinmann stirrup as shown above, which is attached to weights via rope (red arrow) to achieve the desired traction.

The Denham pin can also be used in osteoporotic bone. It is threaded in the middle to engage the cortex and reduce the risk of the pin sliding.

The immediate complication to look for on radiographs is malpositioning of the pin, which can lead to damage to nearby neurovascular bundles. If the traction is maintained for a longer period, radiographs should be inspected for signs of infection. In addition, in cases where the bone is osteoporotic or the applied traction is too heavy, there is a risk of the pin cutting through bone.

References

Cook J, Sankaran B, Wasunna AEO. Chapter 10: Traction. in Surgery at the District Hospital: Obstetrics, Gynaecology, Orthopaedics and Traumatology. WHO(1991).

Sunday, January 22, 2012

Cardiac Tamponade: CT Findings

CT findings of cardiac tamponade can be nonspecific. However, when seen together in the setting of a large pericardial effusion, the following should strongly suggest the diagnosis:
  • Distention of the superior vena cava: ≥ diameter of the adjacent thoracic aorta.
  • Distention of the inferior vena cava: ≥ twice the diameter of the adjacent abdominal aorta. Distension of the hepatic and renal veins can also be seen.
  • Periportal edema: Can also be seen with chronic congestive heart failure, among other conditions.
  • Reflux of contrast into the azygos vein: Can also be seen with massive pulmonary emboli, cor pulmonale, right-sided heart failure, pulmonary arterial hypertension, obstruction of the main pulmonary artery, bilateral pneumothoraces, and positive pressure ventilation.
  • Reflux of contrast into the inferior vena cava: Can also be seen with tricuspid regurgitation, hypovolemic or cardiogenic shock, and pulmonary embolism.
  • Deformity and compression of intrapericardial structures: For example the cardiac chambers (flattened heart sign, shown above), coronary sinus, pulmonary trunk, intrathoracic segment of the inferior vena cava (covered by pericardium anteriorly).
  • Angulation or bowing of the interventricular septum: Correlates with paradoxical motion of the septum. Can also be seen with pressure and/or volume overload of the right ventricle (constrictive pericardial disease, massive pulmonary embolism).
The image above is a CT pulmonary arteriogram from a young patient with a malignant pericardial effusion. We see the flattened heart sign (black arrow). However, the diameters of the superior and inferior venae cavae were normal, no reflux of contrast into the inferior vena cava or the azygos vein was seen, and no periportal edema was present. Echocardiography showed cardiac tamponade.

References

Restrepo CS, Lemos DF, Lemos JA, Velasquez E, Diethelm L, Ovella TA, Martinez S, Carrillo J, Moncada R, Klein JS. Imaging findings in cardiac tamponade with emphasis on CT. Radiographics. 2007 Nov-Dec;27(6):1595-610.

Saturday, January 21, 2012

Transverse Acetabular Fractures

Transverse fractures of the acetabulum involve both the anterior and posterior aspects of the acetabulum, without involvement of the obturator ring or superior extension into the iliac wing. They comprise between 5% and 20% of acetabular fractures.

The fracture plane is not purely transverse in the anatomic sense, but is transverse relative to the acetabulum. The fracture plane courses superiorly and medially in an oblique plane from the acetabulum and separates the innominate bone into an upper iliac fragment and a lower ischiopubic fragment. The ischiopubic fragment can rotate about the pubic symphysis, and the femoral head moves with the iliac fragment medially and superiorly.

Transverse fractures can be classified as transtectal, juxtatectal, and infratectal based on where the fracture plane crosses the articular surface. Transtectal fractures cross the weight-bearing dome of the acetabulum. Juxtatectal fractures cross the articular surface just superior to the cotyloid fossa. Infratectal fractures cross the cotyloid fossa.

The more superior fracture planes are more vertical in orientation and associated with a smaller intact remaining articular surface, which has implications for treatment.

Radiographs reveal disruption of both the iliopectineal (pink arrow) and ilioischial (blue arrow) lines, as well as interrupted anterior and posterior rim lines. Transtectal fractures will also involve the acetabular roof line without disrupting the relationship of the ilioischial line with the teardrop.

When scrolling down (superior to inferior) on axial CT images, the fracture plane moves medially to laterally. Coronal images reveal involvement of both anterior and posterior aspects of the acetabulum. No superior extension to the iliac wing is seen.

Differential considerations include T-shaped and transverse with posterior wall fractures, both of which have transverse components with added features. The T-shaped acetabular fracture is a transverse fracture with inferior extension into the obturator ring, but no superior extension into the iliac wing. The transverse with posterior wall fracture is a transverse fracture with a comminuted (often displaced) posterior wall fracture and an intact obturator ring.

References

Friday, January 20, 2012

Arnold-Hilgartner Staging of Hemophilic Arthropathy

The Arnold-Hilgartner staging system that describes articular changes as the patient progresses through the stages of the disease.
  • Stage I: Soft-tissue swelling from hemarthrosis or bleeding into the periarticular soft tissues. No skeletal abnormality.
  • Stage II: Osteoporosis and overgrowth of the epiphysis without bone cysts or narrowing of the cartilage space.
  • Stage III: Early subchondral bone cysts, squaring of patella, widening of intercondylar notch of distal femur or humerus, preserved cartilage space. This is the final stage at which hemophilic arthropathy is reversible with treatment.
  • Stage IV: Characterized by narrowing of cartilage space. More advanced findings of stage III are also seen.
  • Stage V (shown above): Fibrous joint contracture (as seen in the attempted frontal view), loss of joint cartilage space, marked enlargement of epiphyses, and substantial disorganization of the joint.

References

Thursday, January 19, 2012

Denis Classification of Sacral Fractures

Denis et al classified sacral fractures into three zones. Zone I (extraforaminal) fractures are lateral to the sacral neural foramina. Zone II (transforaminal) fractures extend through the neural foramina, but do not involve the spinal canal. Zone III fractures involve the spinal canal.

They found that zone I fractures were only occasionally associated with partial damage to the L5 nerve root. Zone II fractures were frequently associated with sciatica but rarely with bladder dysfunction. Zone III fractures were frequently associated with saddle anesthesia and loss of sphincter function.

Zone I and II fractures can cause injury to the L5 nerve root in the lumbosacral tunnel (space between the lumbosacral ligament and the S1 sala). Zone II and III fractures can cause injury to the S1 nerve root or pudendal nerve. S1 nerve injury in this setting is usually not isolated and tends to be associated with a lumbosacral plexus injury.

More recent work by Sugimoto et al has found that the incidence of lumbosacral plexus injury was not related to the zone of sacral fracture. Instead they found that risk factors for lumbosacral plexus palsy included longitudinal displacement of the pelvis, transverse sacral fracture, and trauma from a suicidal jump were risk factors.

The image above shows a right zone I sacral fracture (pink arrow). The white arrow indicates the right L5 nerve root/lumbosacral trunk (L4 and L5 nerve roots join up close to this location) is located directly anterior to the fracture.

References

  • Denis F, Davis S, Comfort T. Sacral fractures: an important problem. Retrospective analysis of 236 cases. Clin Orthop Relat Res. 1988 Feb;227:67-81.
  • Sugimoto Y, Ito Y, Tomioka M, Tanaka M, Hasegawa Y, Nakago K, Yagata Y. Risk factors for lumbosacral plexus palsy related to pelvic fracture. Spine (Phila Pa 1976). 2010 Apr 20;35(9):963-6.

Wednesday, January 18, 2012

Flexor Digitorum Accessorius Longus Muscle

The flexor digitorum accessorius longus muscle (white arrows) is an accessory muscle of the medial compartment of the ankle that is seen in less than 10% of the population. It is more commonly seen in males and is frequenly bilateral.

The muscle arises from variety of structures in the posterior compartment of the calf distal to the soleal line. Its tendon passes posterior to the flexor hallucis longus muscle (pink arrows) and the medial malleolus and inserts into the quadratus plantae muscle (blue arrow) or the flexor digitorum longus tendon. The presence of a flexor digitorum accessorius longus muscle has been associated with tenosynovitis of the flexor hallucis longus tendon.

The relationship of the tendon to the neurovascular structures (yellow arrows) of the ankle is also important, as compression of these structures can lead to tarsal tunnel syndrome. The flexor digitorum accessorius longus tendon is located posterior and superficial to the tibial nerve as it courses deep to the flexor retinaculum through the tarsal tunnel.

On axial MR images, the muscle is seen within the tarsal tunnel, typically superficial to the neurovascular bundle. At this point, the appearance may be similar to the peroneocalcaneus internus muscle. The flexor digitorum accessorius longus muscle, however, may contain fleshy fibers in the tarsal tunnel, which may help in differentiating the two. In addition, unlike the flexor digitorum accessorius longus muscle, the peroneocalcaneus internus muscle insert onto the calcaneus.

References

Tuesday, January 17, 2012

Fibrosarcoma of Bone

Fibrosarcomas of bone are typically seen between the third and sixth decades of life, most commonly in the metaphysis or metadiaphysis of the long tubular bones. Fibrosarcomas can be intramedullary (most common) or periosteal (rare, but better prognosis). They can also be categorized as primary or secondary.

Secondary fibrosarcoma of bone can arise from benign bone lesions (Paget disease, bone infarction, fibrous dysplasia, chronic osteomyelitis, giant cell tumor), malignant bone lesions (e.g., chondrosarcoma), or irradiated bone. Fibrosarcomas occurring in the spine or the flat bones are usually secondary lesions.

Radiographs typically reveal a large aggressive lytic lesion with cortical destruction and soft tissue extension. The location is typically metaphyseal and extension into the diaphysis and epiphysis is common.

Differential considerations for high-grade fibrosarcomas include:
  • Multiple myeloma:
  • Metastasis:
  • Lymphoma:
  • Malignant fibrous histiocytoma:
Low-grade fibrosarcomas can have more sclerotic and better-defined borders, and can be similar to:

References

Koplas M and Sundaram M. Fibrogenic and Fibrohistiocytic Tumors. in Imaging of Bone Tumors and Tumor-Like Lesions. Davies AM, Sundaram M, and James SLJ (eds). Springer-Verlag Berlin Heidelberg (2009); pp 310-311.

Monday, January 16, 2012

Isolated Tibial Diaphysis Fractures

An isolated tibial fracture with an intact fibula is the most common tibial fracture pattern seen in children. Displaced fractures can be difficult to reduce because of the splinting effect created by the intact fibula. In addition, the splinting effect of the fibula is though to produce a bending moment that results in varus angulation on healing.

Discussion on whether or not the presence of an intact fibula results in delayed union with non-operative management has been made irrelevant, as the overwhelming majority of surgeons prefer to treat both low-energy and high-energy closed fractures of the tibial diaphysis with intramedullary nailing.

References

  • Bhandari M, Guyatt GH, Swiontkowski MF, Tornetta P 3rd, Hanson B, Weaver B, Sprague S, Schemitsch EH. Surgeons' preferences for the operative treatment of fractures of the tibial shaft. An international survey. J Bone Joint Surg Am. 2001 Nov;83-A(11):1746-52.
  • O'Dwyer KJ, DeVriese L, Feys H, Vercruysse L. Tibial shaft fractures with an intact fibula. Injury. 1993 Oct;24(9):591-4.
  • Sarmiento A, Sharpe FE, Ebramzadeh E, Normand P, Shankwiler J. Factors influencing the outcome of closed tibial fractures treated with functional bracing. Clin Orthop Relat Res. 1995 Jun;(315):8-24.
  • Yang JP, Letts RM. Isolated fractures of the tibia with intact fibula in children: a review of 95 patients. J Pediatr Orthop. 1997 May-Jun;17(3):347-51.

Sunday, January 15, 2012

Central Venous Obstruction in the Chest

Collateral vessels can be recruited to bypass central venous obstruction in the chest via three routes. More central obstructions (superior vena cava) tend to recruit more inferior collaterals, while the more peripheral obstructions (subclavian or brachiocephalic veins) tend to recruit more superior collaterals.

The three routes are:
  • Superior route: Seen with subclavian or brachiocephalic vein obstruction. Blood flows via through the ipsilateral external jugular vein into horizontal veins that communicate across the midline via the transverse arch of the anterior jugular venous system. Once on the contralateral side, blood flows into the external jugular vein into the subclavian vein, and finally into the superior vena cava.
  • Posterior route: Seen in cases of obstruction at the level of the supraazygos superior vena cava. This leaves the azygos vein as a conduit for blood to get into the superior vena cava. Blood from the head and neck flows through paravertebral collaterals into intercostal and paravertebral veins and then the superior intercostal vein, which drains into the azygos vein.
  • Anterolateral: Seen in cases of central superior vena cava obstruction (shown above). Blood flows through anterior intercostal, internal mammary (pink arrow), and long thoracic veins, which, flow to the inferior vena cava (green arrow) via pericardiophrenic (yellow arrow), musculophrenic (blue arrow), lumbar, and hepatic veins. The internal mammary vein can also connect to the left portal vein via the paraumbilical vein and result in increased activity or enhancement in segment IV of liver (white arrow) and is the basis of the focal hepatic hot spot sign on 99mTc sulfur colloid "liver and spleen" scans. IN the image above, we also see aortopulmonary window collaterals (red arrow) that drain into the infraazygos superior vena cava(S), in this patient with combined infraazygos superior vena cava and azygos vein obstruction.

References

  • Dickson AM. The focal hepatic hot spot sign. Radiology. 2005 Nov;237(2):647-8.
  • Gosselin MV, Rubin GD. Altered intravascular contrast material flow dynamics: clues for refining thoracic CT diagnosis. AJR Am J Roentgenol. 1997 Dec;169(6):1597-603.
  • Lee KR, Preston DF, Martin NL, Robinson RG. Angiographic documentation of systemic-portal venous shunting as a cause of a liver scan ""hot spot'' in superior vena caval obstruction. AJR Am J Roentgenol. 1976 Oct;127(4):637-9.
  • Godwin JD, Chen JT. Thoracic venous anatomy. AJR Am J Roentgenol. 1986 Oct;147(4):674-84.

Saturday, January 14, 2012

Button Sequestrum

The button sequestrum is a lucent bony lesion with an internal opacity. It is a nonspecific finding that is an uncommon/rare manifestation of the following conditions:
  • Langerhans cell histiocytosis of bone:
  • Osteomyelitis:
  • Fibrous sarcomas of bone: Includes fibrosarcoma, desmoplastic fibroma and malignant fibrous histiocytoma of bone.
  • Lymphoma:
  • Intraosseous Lipoma: Lucent lipoma with partial calcification.
  • Tuberculous osteitis:
  • Radiation necrosis:
  • Metastatic carcinoma:
  • Fibrous dysplasia:
  • Epidermoid and dermoid cyst:
  • Hemangioma:
  • Meningioma:

References

  • Krasnokutsky MV. The button sequestrum sign. Radiology. 2005 Sep;236(3):1026-7.

Friday, January 13, 2012

Modified Eichenholtz Classification of Neuropathic Joints

Neuropathic (Charcot) arthropathy of the foot and ankle has been divided into three stages by Eichenholtz (1966) and modified by Johnson (1998). The classification is based on the natural history of the disease.
  • Stage I (Dissolution): 2-6 months. Patients present with an acutely inflamed and hyperemic foot that can be mistaken for an infection. Pain is present in most patients, in spite of the underlying sensory neuropathy.

    Radiographs typically reveal periarticular soft-tissue swelling, regional demineralization, periarticular fragmentation, and dislocation. This demineralization is why operative treatment of fractures that occur in this stage have higher rates of failure of fixation, recurrent deformity, and infection.

  • Stage II (Coalescence): Patients present with decreased inflammation and swelling.

    Radiographs reveal absorption of bony debris, organization and early healing of fracture fragments, and periosteal new-bone formation.

  • Stage III (Resolution): The inflammation and swelling are minimal, and there is permanent enlargement of the foot and ankle with fixed deformity.

    Radiographs reveal smoothing of edges of large fragments of bone, sclerosis, and osseous or fibrous ankylosis.

References

Johnson JE. Operative treatment of neuropathic arthropathy of the foot and ankle. J Bone Joint Surg. 1998;80:1700–1709.

Thursday, January 12, 2012

Mirels Classification for Risk of Pathological Fracture

The Mirels system classifies the risk of pathologic fracture based on scoring four variables on a scale of 1-3: location of lesion, radiographic appearance, size, and pain. An overall score is calculated, and a recommendation for or against prophylactic fixation is made.

  1 2 3
Location Upper extremity Lower extremity Intertrochanteric
Radiographic appearance Blastic Mixed Lytic
Sizea < 1/3 1/3 - 2/3 >2/3
Pain Mild Moderate Functionalb
a  Size is determined as a fraction of the cortical thickness.
b  Functional pain is defined as severe pain or pain aggravated by limb function.


Score Fracture Risk Recommendation
≥9 33%-100% Prophylactic fixation is recommended
=8 15% Clinical judgment should be used
≤7 <4% Observation and radiation therapy can be used


As an example, the lytic, intertrochanteric lesion shown above takes up >2/3 of the cortical thickness, getting an overall score of 9 in the absence of any clinical information about the degree of pain.

References

Mirels H. Metastatic disease in long bones. A proposed scoring system for diagnosing impending pathologic fractures. Clin Orthop Relat Res. 1989 Dec;(249):256-64.

Wednesday, January 11, 2012

Cartilage Lesions by Age and Location

Image of the humerus from Human skeleton front en.svg


Once you've made the determination that a long bone lesion is a cartilage tumor, age and location can help narrow your differential diagnosis.

Chondroblastoma and clear-cell chondrosarcoma are epiphyseal lesions that can be indistinguishable. While chondroblastomas tend to affect a younger age group than clear-cell chondrosarcomas, there is some overlap.

Chondromyxoid fibromas are rare metaphyseal lesions that may not have an obvious chondroid matrix on radiography. They most commonly occur in the proximal tibia.

Enchondromas and chondrosarcomas are diaphyseal lesions that have characteristic appearances at their extremes. However, there can be significant overlap, especially between enchondromas and low-grade chondrosarcomas.

Please note that these are rough guidelines: Tumors don't read this blog.

References

  • Greenspan A, Jundt G, Remagen W. Cartilage (Chondrogenic) Lesions. In Differential Diagnosis of Orthopaedic Oncology, 2nd Edition. 2007 Lippincott Williams & Wilkins; pp 162-255.
  • Kindblom LG. Bone Tumors: Epidemiology, Classification, Pathology. in Imaging of Bone Tumors and Tumor-Like Lesions. Davies AM, Sundaram M, and James SLJ (eds). Springer-Verlag Berlin Heidelberg (2009); pp 1-4.

Tuesday, January 10, 2012

Unicameral Bone Cyst of the Long Bones

Unicameral bone cysts (simple bone cystss) are tumor-like lesions of unknown etiology that make up about 3% of all primary bone lesions. They are thought to represent a local reactive or developmental growth disturbance. They are more commonly found in boys in the first 2 decades of life, in the proximal diaphyses of the humerus and femur.

Unicameral bone cysts are well-defined, lucent lesions with sclerotic margins that are located centrally in the metaphysis or diaphysis of long bones. There is frequently cortical thinning and expansion, but the width of the cyst is typically less than that of the nearby physis. Epiphyseal extension is not typical, and periosteal reaction is not seen unless the cyst is complicated by a pathologic fracture.

In about 20% of cases of fractures through unicameral bone cysts, a fallen fragment sign is present, representing a fragment of fractured cortex laying in the dependent portion of the fluid-filled lesion. The forme fruste of the fallen fragment sign is the trap door sign, which represents an infolded fragment of cortex that remains attached to the periosteum.

Radiography is usually diagnostic, and CT can be used in equivocal cases. The cyst fluid has attenuation of 15-20 HU and the radiographic findings noted above can be seen to better advantage. Bone scintigraphy may reveal a nonspecific halo of increased uptake around the photopenic cyst, but can also be normal.

MRI reveals a fluid-filled lesion that is low to intermediate signal on T1-weighted images and homogeneously hyperintense on T2-weighted images.

The main differential consideration in the long bones is an aneurysmal bone cyst. Aneurysmal bone cysts almost invariably have some degree of periosteal reaction (usually solid), are eccentrically located, and can have significant cortical expansion.

The radiograph above is from a 4-year-old boy. There is a central, well-defined lucent lesion in the proximal metadiaphysis of the humerus that results in mild cortical thinning and mild expansion. Pseudoseptations can be seen within the lesion. No periosteal reaction is present.

References

Greenspan A, Jundt G, Remagen W. Miscellaneous Tumors And Tumor-like Lesions. In Differential Diagnosis of Orthopaedic Oncology, 2nd Edition. 2007 Lippincott Williams & Wilkins; pp 400-410.

Monday, January 9, 2012

Compress Compliant Pre-Stress Implant

The Compress Compliant Pre-Stress Implant makes use of stored energy to snap the extramedullary portion of the prosthesis to the native bone. Proximally, an anchor plug is fixed to the native bone via transverse (anti-rotation) pins and connected to an intramedullary traction bar. The bar extends out through the spindle and is loaded with Belleville washers (washer-shaped springs). A nut is tightened at the end of the traction bar to achieve the desired compression of the spindle against the bone.

This compression acts to induce bone hypertrophy, reduce stress shielding seen in stem prostheses, and seal the medullary canal from particulate debris that can cause osteolysis.

The short length of the device allows placement of a prosthesis with as little as 46 mm of bony canal.

References

Bhangu AA, Kramer MJ, Grimer RJ, O'Donnell RJ. Early distal femoral endoprosthetic survival: cemented stems versus the Compress implant. Int Orthop. 2006 Dec;30(6):465-72.

Sunday, January 8, 2012

Signs of Malignancy in Ovarian Teratomas

Malignant transformation is seen in about 1% of ovarian teratomas and can occur in any of the three germ cell layers that make up the teratoma: ectoderm, mesoderm, and endoderm.

The most common type of malignant transformation is squamous cell carcinoma, seen in 80% of reported cases. Increased risk of transformation is seen in patients older than 45 years of age, tumors larger than about 10 cm, and serum squamous carcinoma antigen level greater than 2 ng/mL.

Imaging findings can be nonspecific. Invasion of adjacent structures and lymph node and distant metastases are obviously signs of malignancy. Other findings can suggest malignancy: A complex, predominantly solid tumor, significant areas of necrosis, and poor definition of adjacent soft-tissue planes all suggest malignancy.

The Rokitansky nodule or dermoid plug of ovarian teratomas is a frequent site of malignant transformation and imaging findings suggestive of malignant transformation have been proposed. Transmural growth of the Rokitansky nodule should raise concern for malignant transformation. Softer signs of malignant transformation include contrast enhancement of the Rokitansky nodule and an obtuse angle between the nodule and the inner wall of the cyst.

References

  • Park SB, Kim JK, Kim KR, Cho KS. Imaging findings of complications and unusual manifestations of ovarian teratomas. Radiographics. 2008 Jul-Aug;28(4):969-83.
  • Park SB, Kim JK, Kim KR, Cho KS. Preoperative diagnosis of mature cystic teratoma with malignant transformation: analysis of imaging findings and clinical and laboratory data. Arch Gynecol Obstet. 2007 Jan;275(1):25-31.

Saturday, January 7, 2012

Neurocutaneous Melanosis

Neurocutaneous melanosis is one of the less common phakomatoses. It is a rare, noninherited dysplasia of neuroectodermal cells, which give rise to melanocytes and the basal leptomeninx.

Patients present with large or multiple congenital melanocytic nevi with benign or malignant proliferation of melanocytes in the leptomeninges. The classic appearance is a large melanocytic nevus in a posterior axial location with satellite melanocytic nevi. Leptomeningeal involvement can result in hydrocephalus, spinal cord compression, or other mass effect, usually in the first 2 years of life. Neurological symptoms are usually progressive and rapidly fatal.

MR reveals thickened and enhancing leptomeninges (predominantly over the cerebral convexity and quadrigeminal plate cistern), ventricular dilatation, and inferior vermian hypoplasia. Focal parenchymal melanocytomas can also be seen, sometimes in the absence of leptomeningeal involvement. Leptomeningeal T1-hyperintensity has been reported, but it is not unusual to have amelanotic melanocytoma or amelanotic melanocytosis, so contrast-enhanced images are necessary for full evaluation.

The post-contrast images of the brain and spine above reveal diffuse meningeal enhancement and mild residual dilatation of the ventricles post ventriculoperitoneal shunt (not shown). The enhancement is both leptomeningeal (predominantly on the left) and pachymeningeal. The imaging findings are not pathognomonic. Differential considerations for leptomeningeal enhancement include chronic meningitis (tuberculosis or coccidioidomycosis), and leptomeningeal metastases (e.g., medulloblastoma, ependymoma, high-grade astrocytoma, pineoblastoma and choroid plexus carcinoma).

References

  • Byrd SE, Darling CF, Tomita T, Chou P, de Leon GA, Radkowski MA. MR imaging of symptomatic neurocutaneous melanosis in children. Pediatr Radiol. 1997 Jan;27(1):39-44.
  • Pavlidou E, Hagel C, Papavasilliou A, Giouroukos S, Panteliadis C. Neurocutaneous melanosis: report of three cases and up-to-date review. J Child Neurol. 2008 Dec;23(12):1382-91.

Friday, January 6, 2012

Lymph Node Metastases in Soft Tissue Sarcomas

Lymph node metastases are uncommon in soft tissue sarcomas, occurring in about 5% of cases. The sarcomas that most frequently metastasize to lymph nodes in adults include: Angiosarcoma, rhabdomyosarcoma (embryonal variant), and epithelioid sarcoma (the order varies depending on the study).

Synovial, clear cell, and alveolar soft part sarcomas were previously thought to have high rates of lymph node metastases, but this has not found to be the case in larger case series.

The sarcomas that account for the most lymph node metastases due to their relatively higher prevalence are leiomyosarcoma and pleomorphic undifferentiated sarcoma (formerly malignant fibrous histiocytoma).

Regional lymph node involvement is a poor prognostic factor. In addition, patients with isolated regional lymph node involvement at diagnosis have a poorer outcome than patients who develop isolated regional lymph node involvement later in the course of their disease.

References

Thursday, January 5, 2012

Girdlestone Resection Arthroplasty

The Girdlestone procedure is a resection arthroplasty of the hip that involves removal of portions of the proximal femur. It is named after Gathorne Robert Girdlestone, who popularized the procedure for treatment of late septic arthritis.

Two main types of the procedure have been described: primary and secondary. A primary Girdlestone resection arthroplasty is performed for primary hip disorders (e.g., septic and tuberculous hip and rarely osteoarthritis and rheumatoid arthritis). The secondary or modified Girdlestone resection arthroplasty is used for failed hip replacement or failed construction after hip trauma.

The primary procedure is rarely used in modern practice. The majority of Girdlestone resection arthroplasties performed today are the secondary type and performed in patients who are not healthy enough for further major interventions (e.g., one- or two-stage reimplantations) after failed primary total hip replacement. It is also performed as the first stage of a two-stage revision in selected patients.

References

  • Girdlestone GR. Acute pyogenic arthritis of the hip: an operation giving free access and effective drainage (1943). Clin Orthop Relat Res. 2008 Feb;466(2):258-63.
  • Sharma H, De Leeuw J, Rowley DI. Girdlestone resection arthroplasty following failed surgical procedures. Int Orthop. 2005 Apr;29(2):92-5.

Wednesday, January 4, 2012

Multiple Biliary Hamartomas

Multiple biliary hamartomas of the liver (also known as von Meyenburg complexes) are mulitiple tiny (1 mm - 10 mm), well-circumscribed foci of disorganized bile ductules surrounded by fibrous stroma. It is thought that they are caused by failure of involution of embryonic bile ducts (the same mechanism for polycystic liver disease).

Ultrasound will show multiple irregular hypoechoic lesions are seen throughout the liver. Smaller ductules may cause crowding of the interfaces, leading to hyperechoic lesions.

CT reveals multiple, irregular, low-attenuation lesions throughout the liver. On MRI, the lesions are well-defined, T1-hypointense, and T2-hyperintense (T2 hyperintensity is slightly less than that of water). There are usually mural nodules that are isointense on T1-weighted images and intermediate signal on T2-weighted images and which are between 1-2 mm. These nodules enhance.

Differential considerations include:
  • Metastases: Lesions are usually not as uniform in shape and size as in multiple biliary hamartomas
  • Microabscesses: Usually in immunosuppressed patients
  • Cysts:

References

  • Juchems MS, Jeltsch M, Brambs HJ. Multiple cystic liver lesions on CT: multiple biliary hamartomas. Gut. 2008 Feb;57(2):144, 251.
  • Tohmé-Noun C, Cazals D, Noun R, Menassa L, Valla D, Vilgrain V. Multiple biliary hamartomas: magnetic resonance features with histopathologic correlation. Eur Radiol. 2008 Mar;18(3):493-9.

Tuesday, January 3, 2012

Metallosis

Metallosis is the infiltration of periprosthetic soft tissues and bone by metallic debris. The debris is most commonly from wear of metallic prosthesis (usually of the metal-backed polyethylene patellar prosthesis), but metallic debris can also be generated from hinged prostheses and, as in the case shown above, repetitive contact of fractured prosthesis components.

The particles can lead to metal-induced synovitis, and the release of cytokines by histiocytes stimulated by the metallic debris can lead to significant osteolysis.

Patients often present with pain and a joint effusion, usually 1-2 years after surgery.

Radiographs reveal periprosthetic metallic debris, and sometimes a dense joint effusion is seen. In more than half of patients, a thin opaque line outlines the periprosthetic pseudocapsule: The so-called metal-line sign or bubble sign. (The metal-line sign can also be seen after intraarticular injection of gold salts and dissolution of migrated lead bullets into the joint). Osteolysis may complicate the picture, and a high index of suspicion is appropriate.

References

Heffernan EJ, Alkubaidan FO, Nielsen TO, Munk PL. The imaging appearances of metallosis. Skeletal Radiol. 2008 Jan;37(1):59-62.

Monday, January 2, 2012

Rheumatoid Arthritis and Lymphoma

Patients with longstanding rheumatoid arthritis have been shown to have an increased risk for non-Hodgkin lymphoma in large population-based studies. The mechanism is thought to be related to chronic inflammation and the resultant chronic antigenic stimulation of B-cells by rheumatoid factors, which leads to an increased risk for B-cell transformation. Methotrexate treatment has also been implicated in the development of lymphoma in patients with rheumatoid arthritis, but this has been contested in more recent work.

The Epstein-Barr virus has also been implicated in the past. Recent work, however, suggests that it may only be associated with an increased risk of Hodgkin lymphoma.

The images above are from a patient with longstanding rheumatoid arthritis who developed B-cell lymphoma. The radiograph of the hand reveals severe joint space narrowing and erosions and subluxations that predominantly involve the radiocarpal, intercarpal, and carpometacarpal joints. Axial CT image in mediastinal window reveals an enlarged left internal mammary lymph node (pink arrow). Lung windows reveal multiple pulmonary nodules (blue arrows) in a perilymphatic distribution.

References

Naschitz JE, Rosner I. Musculoskeletal syndromes associated with malignancy (excluding hypertrophic osteoarthropathy). Curr Opin Rheumatol. 2008 Jan;20(1):100-5.

Sunday, January 1, 2012

Differentiation Syndrome

(image by A. Rad)

Acute promyelocytic leukemia is caused by a chromosomal translocation of the promyelocytic leukemia gene to the retinoic acid receptor-alpha gene, which blocks terminal granulocytic differentiation at the promyelocytic stage. Treatment with all-trans retinoic acid (ATRA) relieves this blockage and the promyelocytes go on to differentiate into granulocytes. This treatment results in complete remission in > 90% of patients.

The differentiation syndrome (also know as retinoic acid syndrome and ATRA syndrome) is a cytokine release syndrome that is seen in ~1/4 of patients after induction chemotherapy with ATRA or arsenic trioxide (ATO) for acute promyelocytic leukemia. The symptoms of this potentially fatal syndrome are related to the effects of cytokines released from malignant promyelocytes.

Patients have weight gain, fever, hypoxemia, respiratory distress, hypotension, renal and hepatic dysfunction, serositis (resulting in pleural and pericardial effusions), alevolar infiltrates (hemorrhage and myeloid cells), interstitial infiltrates (edema and myeloid cells), and peripheral edema. The portable chest radiograph above reveals bilateral airspace opacities and bilateral pleural effusions. These findings are nonspecific, but in the patient with acute promyelocytic leukemia on induction therapy with ATRA or ATO, differentiation syndrome should be considered.

Patients are treated with dexamethasone until symptoms resolve. In severe cases (patients with respiratory distress or acute renal failure) ATRA and ATO are stopped until the patient recovers.

References

  • Rego EM, De Santis GC. Differentiation syndrome in promyelocytic leukemia: clinical presentation, pathogenesis and treatment. Mediterr J Hematol Infect Dis. 2011;3(1):e2011048.
  • Luesink M, Jansen JH. Advances in understanding the pulmonary infiltration in acute promyelocytic leukaemia. Br J Haematol. 2010 Nov;151(3):209-20.