Wednesday, March 31, 2010

The Femoral Head Notch

The femoral head notch is a defect at the vertex of the proximal femoral ossification center in mid-childhood. This may be seen as a normal variant and can be mistaken for early or "abortive" Legg-Perthes disease.

It can be differentiated from Legg-Perthes by noting the absence of associated changes of ischemic necrosis: diminished size and sclerosis of the ossification center, widening of the distance between the medial acetabular wall and the ossification center, and a fracture line.

Defects seen in intermediate stage Legg-Perthes disease may mimic the femoral head notch, but are located lateral to the vertex, not centrally.

Finally, abnormalities in Legg-Perthes disease are characteristically more obvious and better defined on the lateral view, while the femoral head notch is actually less defined on this view.

References

Ozonoff MB, Ziter FM Jr. The femoral head notch. Skeletal Radiol. 1987;16(1):19-22.

Tuesday, March 30, 2010

Bare Areas of the Humerus

The posterolateral surface of the humeral head contains a bare area of bone that is not covered by cartilage. The bare area is located between the articular cartilage of the humeral head and the synovial reflection from the posterior wall of the capsule.

The bare area enlarges with age and degenerative cysts have been described in this region. At least some of these cysts may actually represent pseudocysts, focal dimples of the bone lined with collagen fibroconnective tissue connected with the joint spaces, and not representing degenerative change.

Another bare area may also be seen on the anterior surface of the humeral head superior to the attachment of the subscapularis tendon,

References

  • DePalma, A. F. (1973) Surgery of the Shoulder. 2nd Edition. JB Lippincott, Philadelphia.
  • Jin W, Ryu KN, Park YK, Lee WK, Ko SH, Yang DM. Cystic lesions in the posterosuperior portion of the humeral head on MR arthrography: correlations with gross and histologic findings in cadavers. AJR Am J Roentgenol. 2005 Apr;184(4):1211-5.
  • Snyder, S. J. (2003) Shoulder arthroscopy. 2nd ed. Lippincott Williams and Wilkins, Philadelphia. p 311.

Monday, March 29, 2010

Central vs Marginal Osteophytes

Marginal osteophytes, those found at the margin of the articular cartilage, are almost always present in patients with osteoarthritis and have been shown to be associated with knee pain.

Central osteophytes, those surrounded by articular cartilage on all sides, can also be found in osteoarthritis. Central osteophytes tend to occur adjacent to cartilage defects and are associated with more severe osteoarthritis than marginal osteophytes alone.

MRI is more sensitive than radiographs for detection of central osteophytes, because central osteophytes are obscured by the curved articular surface. When seen on radiographs, central osteophytes can be mistaken for free intra-articular bodies.

On MRI, a rim of fluid-like signal may be seen covering the surface of central osteophytes. This is thought to represent a thin rim of cartilage and is consistent with observations that central osteophytes are usually not visible on inspection of the articular surface at arthroscopy and gross pathology.

References

Sunday, March 28, 2010

Cyamella

The cyamella, also known as the popliteal fabella or the fabella distalis, is an uncommon sesamoid bone of the knee that is typically found in the popliteus tendon, but can also be seen at the myotendinous junction. On radiographs, it is seen as a small, ossified structure in the popliteal groove.

The cyamella is rarely seen, and even more rarely associated with pathology. A case of painful dislocation has been reported.

It is more common in some nonhuman primates, as well as in dogs and kangaroos.

References

  • Le Minor JM. Brief communication: the popliteal sesamoid bone (cyamella) in primates. Am J Phys Anthropol. 1992 Jan;87(1):107-10.
  • Mishra AK, Jurist KA. Symptomatic cyamella. Arthroscopy. 1996 Jun;12(3):327-9.
  • Munk PL, Althathlol A, Rashid F, Malfair D. MR features of a giant cyamella in a patient with osteoarthritis: presentation, diagnosis and discussion. Skeletal Radiol. 2009 Jan;38(1):69, 91-2.

Saturday, March 27, 2010

Medial Meniscal Flounce

A meniscal flounce is considered a normal variant characterized by a wavy or folded appearance of the inner edge of the medial meniscus. It looks like a carpet that has a wrinkled edge.

Because meniscal tears may result in a flouncelike fold, a meniscal flounce should not be called if there is any finding suggestive of a meniscal tear.

References

Friday, March 26, 2010

Red Zone of the Menisci

The vascular portion of the meniscus is called the "red zone," in distinction to the in the avascular portion, or "white zone." Tears in the red zone are far more likely to heal than tears of the white zone; therefore, tears in the red zone may be treated meniscus-preserving techniques, while tears in the white zone are typically treated by means of débridement.

Some have suggested that the more peripheral area of higher signal intensity in the meniscus represents the red zone. Recent work, however, has shown that the entire meniscus, including the vascularized red zone, appears as low signal on MR images. In addition, intravenous contrast does not help differentiate the red zone from the white zone.

The only way to determine if a tear is in the red zone, therefore, is to guess. It has been suggested that the red zone may be considered as the peripheral 10%–15% of the meniscus. The figure shows a tear in the peripheral posterior horn of the medial meniscus, and was assumed to be in the red zone.

References

Hauger O, Frank LR, Boutin RD, Lektrakul N, Chung CB, Haghighi P, Resnick D. Characterization of the "red zone" of knee meniscus: MR imaging and histologic correlation. Radiology. 2000 Oct;217(1):193-200.

Thursday, March 25, 2010

Lipohemarthrosis of the Knee: Some Fine Points

  • The most common types of fracture associated with lipohemarthrosis are tibial plateau and distal femoral fractures.
  • However, the majority (> 60%) of patients with tibial plateau fractures actually do not exhibit lipohemarthnosis.
  • The majority (65%) of intraarticular fractures are not accompanied by fat-fluid levels and demonstrate only hemarthrosis/joint effusion, possibly due to disturbance of the fat-fluid level by movement, insufficient time for a fat-fluid level to form, rupture of the joint capsule, or poor technique (e.g., improper centering)
  • About 10-20 mL of fat and 80-100 mL of blood are thought to be required to form a visible level.
  • Most patients with isolated patellar fractures do not exhibit fat-fluid levels.
  • The presence of a fat-fluid level in the knee joint is almost always due to intraarticular fracture, although proximal fibular fractures may also be associated with fat-fluid levels if there is a communication between the tibiofibular joint and the knee joint.

References

Lee JH, Weissman BN, Nikpoor N, Aliabadi P, Sosman JL. Lipohemarthrosis of the knee: a review of recent experiences. Radiology. 1989 Oct;173(1):189-91.

Wednesday, March 24, 2010

Lipoma Arborescens of the Knee

Lipoma arborescens is a rare intraarticular lesion consisting of lipomatous proliferation of the synovium. It tends to occur in the knee joint, especially within the suprapatelar pouch.

MR findings include a large fatty mass with fronds (hence arborescens: Latin for tree-like) that arises from the synovium with an associated effusion.

References

Feller JF, Rishi M, Hughes EC. Lipoma arborescens of the knee: MR demonstration. AJR Am J Roentgenol. 1994 Jul;163(1):162-4.

Tuesday, March 23, 2010

Hawkins Sign

The Hawkins sign is a subchondral radiolucent band along the dome of the talus. It is a good prognostic sign that is best seen on frontal radiographs of the ankle 6–8 weeks after a vertical fracture of the neck of the talus. The radiolucent band reflects osteoclast activity following disuse or immobilization that results in bone reabsorption and indicates a preserved blood supply. An absent Hawkins sign indicates a high risk of avascular necrosis.

Absence of the Hawkins sign has been shown to be 100% sensitive and 57.7% specific for avascular necrosis in patients with displaced talar fractures.

References

  • Donnelly EF. The Hawkins sign. Radiology. 1999 Jan;210(1):195-6.
  • Tezval M, Dumont C, Stürmer KM. Prognostic reliability of the Hawkins sign in fractures of the talus. J Orthop Trauma. 2007 Sep;21(8):538-43.

Monday, March 22, 2010

Twin Peak Sign

The twin peak (or lambda) sign is a wedge of placental tissue that extends from the placental surface between the layers of the inter-twin membrane and indicates a dichorionic-diamniotic twin gestation. The inter-twin membrane in dichorionic-diamniotic twins is made up of sets of amniotic and chorionic layers from each fetus.

This sign is helpful when there is a single placenta, a dividing membrane and twins of the same gender. The diagnostic dilemma in this case is between a monozygotic gestation (monochorionic-diamniotic) and a dizygotic gestation with fused placentas (dichorionic-diamniotic) whose twins just happen to be the same gender. The twin peak sign will clinch the diagnosis for a dichorionic-diamniotic twin gestation.

References

Trop I. The twin peak sign. Radiology. 2001 Jul;220(1):68-9

Sunday, March 21, 2010

Nutmeg Liver

Nutmeg liver refers to the heterogeneous perfusion of the liver, usually as a result of hepatic venous congestion. Hepatic venous congestion prevents contrast-enhanced blood from diffusing through the liver, resulting in a mottled pattern of enhancement in the arterial and early portal venous phases. There is decreased enhancement of the liver peripherally due to due to decreased portal flow, hepatic congestion, and rarely infarction. The hepatic veins are also not well visualized. Delayed phases reveal a more uniform pattern of enhancement.

Hepatic venous congestion may be caused by hepatic venoocclusive disease, Budd-Chiari syndrome, right heart failure, or constrictive pericarditis. In Budd-Chiari syndrome the caudate lobe enhances normally due to its direct drainage into the inferior vena cava.

References

Reuther WL 3rd, Newman CA, Smith RE, Plavsic BM. Gastrointestinal case of the day. Primary leiomyosarcoma of the IVC with Budd-Chiari syndrome. Radiographics. 1999 Jan-Feb;19(1):248-51.

Saturday, March 20, 2010

Linea Aspera

The linea aspera (rough line) is a bony ridge along the posterior shaft of the middle third of the femur. It provides an attachment site for the thigh adductors and extensors.

Proximally the linea aspera branches laterally to the gluteal ridge. Medially, it divides into the spiral line, which courses towards the lesser trochanter, and the pectineal line, which courses lateral and inferior to the lesser trochanter.

The gluteal ridge is the site of attachment for the gluteus maximus muscle. The spiral line is the site of origin of the vastus medialis muscle, while the pectineal line is the site of attachment of the pectineus muscle.

The linea aspera, when prominent, may appear as a pair of parallel lines on frontal radiographs, and apparent thickening of the posterior cortex of the femur.

References

Pitt MJ. Radiology of the femoral linea aspera-pilaster complex: the track sign. Radiology. 1982 Jan;142(1):66.

Friday, March 19, 2010

Blumensaat Line

The Blumensaat line is a linear shadow on lateral radiographs of the knee that corresponds to the roof of the intercondylar notch. The Blumensaat line forms an angle of between 120 and 153 with the vertical axis of the femur.

The Blumensaat line has been suggested as an indication of the relative position of the patella; however, too much variation is introduced by knee flexion, angle of the Blumensaat line with the femur, vertical length of the patella, and depth of the intercondylar notch for this method to be useful.

References

Seyahi A, Atalar AC, Koyuncu LO, Cinar BM, Demirhan M. Blumensaat line and patellar height. Acta Orthop Traumatol Turc. 2006;40(3):240-7.

Thursday, March 18, 2010

Robson Classification for Renal Cell Carcinoma

Stage Description
I Confined by renal capsule
II Extends through the renal capsule, but confined to the Gerota fascia
IIIA Involves the renal vein or inferior vena cava
IIIB Involves regional lymph nodes (> 1 cm)
IIIC IIIA and IIIB combined
IVA Direct invasion of adjacent organs or structures (excluding ipsilateral adrenal gland)
IVB Distant metastases

References

Sheth S, Scatarige JC, Horton KM, Corl FM, Fishman EK. Current concepts in the diagnosis and management of renal cell carcinoma: role of multidetector ct and three-dimensional CT. Radiographics. 2001 Oct;21 Spec No:S237-54.

Wednesday, March 17, 2010

Radiologic Classification of Renal Injuries

Renal injuries can be classified into four categories:
  • Category I: Renal contusions (intrarenal hematomas), subcapsular hematomas, subsegmental infarctions (wedge-shaped areas of decreased enhancement), minor cortical lacerations with limited perinephric hematoma. Managed conservatively.
  • Category II: Major lacerations extending to the medulla or collecting system. There may or may not be associated urinary extravasation (usually occurs into the lateral perinephric space). Segmental infarctions are also included in this category. Usually treated conservatively but may require surgical exploration depending on the clinical situation.
  • Category III: Multiple renal lacerations ("shattered kidney") and vascular injuries involving the renal pedicle. The presence of active arterial bleeding indicates a category III renal injury. Thrombosis of the main renal artery may also occur, in which case no perinephric hematoma may be seen, although a hematoma may be present around the proximal renal artery. Avulsion of the renal artery may also rarely occur, and manifests on CT as global infarction of the kidney associated with extensive medial perirenal hematoma. Thrombosis or laceration of the renal vein is another complication of renal pedicle injury. Category III injuries generally require surgical exploration, often nephrectomy.
  • Category IV: Ureteropelvic junction injury. Hematuria is absent in one-third of patients. CT will show an intact kidney with good uptake and excretion of contrast, but with excretion of contrast medially. A urine collection may also be seen around the affected kidney (circumferential or circumrenal urinoma), but typically there is no perinephric hematoma. Category IV injuries are further divivded into:
    • Laceration: Incomplete tear. There is contrast in the ureter distal to the ureteropelvic junction.
    • Avulsion: Complete transection. No contrast is seen in the ureter distal to the ureteropelvic junction. Retrograde pyelography should be performed to confirm.

References

Kawashima A, Sandler CM, Corl FM, West OC, Tamm EP, Fishman EK, Goldman SM. Imaging of renal trauma: a comprehensive review. Radiographics. 2001 May-Jun;21(3):557-74.

Tuesday, March 16, 2010

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL): MRI Findings

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a rare, inherited cause of early stroke and dementia.

MRI will show multiple areas of white matter T2-hyperintensity and lacunar infarctions. The highest load of T2-hyperintensity are found in the anterior temporal lobes and in the deep white matter of the frontal and parietal lobes, with relative sparing of the occipital lobes. Anterior temporal pole and external capsule lesions have higher sensitivity and specificity for CADASIL. Digital subtraction angiography is normal in CADASIL.

Differential considerations include:
  • Sporadic subcortical arteriosclerotic encephalopathy: Associated with hypertension. CADASIL has more extensive bilateral involvement of anterior temporal and superior frontal white matter, as well as signal intensity reductions in the dentate nuclei, deep cerebellar white matter, crus cerebri, and thalamus
  • Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes
  • Primary angiitis of the CNS: Unlike CADASIL, digital subtraction angiogram shows lumen irregularities in distal cerebral arteries.
  • Hypercoagulable states

References

Monday, March 15, 2010

ACE Inhibitor-Induced Angioedema

ACE inhibitors rarely (0.2% of patients) cause peripheral angioedema. Visceral angioedema is even less common. For unknown reasons, the vast majority of the cases reported in the literature have been women. Patients may present with an acute abdomen with abdominal pain, vomiting and watery diarrhea. Symptoms are associated with the onset of ACE inhibitor therapy and resolve quickly following discontinuation of the offending medication.

CT findings are nonspecific and consist of circumferential small bowel wall thickening, which may be segmental, as well as mucosal enhancement with prominence of the mesenteric vessels. The low-attenuation submucosa stands out against the enhancement of the thickened mucosa. Ascites is also seen.

Differential considerations of CT findings include:
  • Ischemia
  • Henoch–Schönlein purpura
  • Intramural hemorrhage
  • C1-esterase inhibitor deficiency: May be congenital (hereditary/inherited angioedema) or acquired as part of a paraneoplastic syndrome
  • Contrast reaction

References

  • Fisher AJ, Fleishman MJ, Hancock D. Angioedema of the small bowel: CT appearance. AJR Am J Roentgenol. 2000 Aug;175(2):554.
  • Marmery H, Mirvis SE. Angiotensin-converting enzyme inhibitor-induced visceral angioedema. Clin Radiol. 2006 Nov;61(11):979-82.

Sunday, March 14, 2010

The Gastroduodenal Artery in Celiac Artery Stenosis

The gastroduodenal artery is an important collateral pathway between the celiac axis and the superior mesenteric artery (SMA). Stenosis at the origin of the celiac axis typically results in flow of blood from the SMA to the gastroduodenal artery via the anterior inferior, anterior superior, and posterior inferior pancreaticoduodenal arteries (part of the peripheral pancreatic circulation or pancreaticoduodenal arcade). This increased flow typically results in a dilated gastroduodenal artery.

References

  • Song SY, Chung JW, Kwon JW, Joh JH, Shin SJ, Kim HB, Park JH. Collateral pathways in patients with celiac axis stenosis: angiographic-spiral CT correlation. Radiographics. 2002 Jul-Aug;22(4):881-93.
  • Horton KM, Fishman EK. Multidetector CT angiography in the diagnosis of mesenteric ischemia. Radiol Clin North Am. 2007 Mar;45(2):275-88.

Saturday, March 13, 2010

Seymour Fracture

A Seymour fracture refers to juxtaepiphyseal fractures of the distal phalanx of the finger. These include transverse fractures of the proximal metaphysis of the distal phalanx, as well as Salter 1 and 2 physeal fractures of the distal phalanx.

Clinically, Seymour fractures can mimic a mallet finger (flexion at the distal interphalangeal (DIP) joint and extension at the proximal interphalangeal joint). However, Seymour fractures do not lead to true mallet fingers, because the flexion in a Seymour fracture is at the fracture plane, not at the DIP joint.

The mechanics of the flexor and extensor tendon insertions at the DIP joint help explain the appearance. The terminal extensor tendon inserts on the epiphysis only, while the flexor digitorum profundus tendon inserts at both the epiphysis and metaphysis. Therefore, a fracture of the proximal metaphysis or through the physis will lead to unopposed flexion of the distal fracture fragment.

While traditionally described in children and adolescents, this pattern of fracture can also be seen in adults when the fracture plane is just distal to the insertion of the extensor tendon.

Seymour fractures are often open and associated with tarnsverse lacerations through the nail bed. While Dr. Seymour's initial paper in 1966 reported that Kirschner wire (K-wire) fixation led to unacceptably high rates of complication, recent studies have found that proper debridement and antiobiotic prophylaxis are vital to forestall osteomyelitis with K-wire fixation.

References

  • Al-Qattan MM. Extra-articular transverse fractures of the base of the distal phalanx (Seymour's fracture) in children and adults. J Hand Surg Br. 2001 Jun;26(3):201-6.
  • Ganayem M, Edelson G. Base of distal phalanx fracture in children: a mallet finger mimic. J Pediatr Orthop. 2005 Jul-Aug;25(4):487-9.

Friday, March 12, 2010

Fifth Metacarpal Length

The normal length of the metacarpal of the small finger (5th metacarpal) can be defined as a gap of 2 mm or less between the distal end of the fifth metacarpal bone and a tangential line connecting the distal ends of the third and fourth metacarpal bones.

Short metacarpal of the small finger (brachymetacarpia V) can be seen in children with familial short stature or insulin resistance type A.

References

  • Cervantes CD, Lifshitz F, Levenbrown J. Radiologic anthropometry of the hand in patients with familial short stature. Pediatr Radiol. 1988;18(3):210-4.
  • Patel VK, Davies HA. Insulin resistance Type A and short 5th metacarpals. Diabet Med. 2003 Jun;20(6):500-4.

Thursday, March 11, 2010

False-Negative and False Positive Fat Pad Signs

It is tempting to take the fat pad sign as sine qua non for elbow fractures, but here are some numbers: The negative predictive value for the anterior fat pad sign is close to 90% for radial head and neck fractures and about 80% for other elbow fractures. The anterior fat pad sign is also pretty sensitive (85%) for detecting radial head fractures, but not as sensitive (35%) in detecting other elbow fractures.

A false-negative fat pad sign of the elbow may occur if there is poor positioning of the elbow (true lateral is best), extracapsular abnormality (e.g., massive soft-tissue swelling around the joint), or capsular rupture.

A false-positive fat pad sign of the elbow can be seen with elbow extension. Non-traumatic joint pathologies can also result in a positive fat pad sign, including effusion, purulent exudate, intra-articular bodies, and synovial proliferation.

References

  • Goswami GK. The fat pad sign. Radiology. 2002 Feb;222(2):419-20.
  • Irshad F, Shaw NJ, Gregory RJ. Reliability of fat-pad sign in radial head/neck fractures of the elbow. Injury. 1997 Sep;28(7):433-5.
  • Yu JS. Soft-tissue signs of the upper extremity revisited: radiologic and magnetic resonance imaging correlation. Emergency Radiology (1999) 6: 282-289

Wednesday, March 10, 2010

Yamaguchi Criteria of Adult-Onset Still Disease

Presence of 5 or more criteria, at least 2 of which are major yields a 96% sensitivity and 92% specificity for adult-onset Still disease.

Major Criteria
  • Temperature of >39°C for >1 wk
  • Leukocytosis >10,000/mm3 with >80% PMNs
  • Typical rash
  • Arthralgias >2 wk
Minor Criteria
  • Sore throat
  • Lymph node enlargement
  • Splenomegaly
  • Liver dysfunction (high AST/ALT)
  • Negative ANA, RF

References

Yamaguchi M, Ohta A, Tsunematsu T, Kasukawa R, Mizushima Y, Kashiwagi H, Kashiwazaki S, Tanimoto K, Matsumoto Y, Ota T, et al. Preliminary criteria for classification of adult Still's disease. J Rheumatol. 1992 Mar;19(3):424-30.

Tuesday, March 9, 2010

Lung Segments for V/Q Scans

Got tired of searching for this every time a V/Q scan got ordered. Adapted from http://www.drmaryonline.com/toprad/vq_scan.html
RUL RML RLL LUL LLL
1. Apical 4. Lateral 6. Superior 11. Apico-posterior 15. Superior
2. Posterior 5. Medial 7. Medio-basal 12. Anterior 16. Antero-medial Basal
3. Anterior 8. Postero-basal 13. Superior Lingual 17. Latero-basal
9. Latero-basal 14. Inferior Lingual 18. Postero-basal
    10. Antero-basal    

Monday, March 8, 2010

Mitochondrial Encephalomyopathy with Lactic Acidosis and Stroke-Like Episodes (MELAS)

Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) is a rare disorder of intracellular energy production caused by mutations in mitochondrial DNA. Patients are usually normal at birth and during early infancy, then show delayed growth, episodic vomiting, seizures, and recurrent cerebral injuries resembling strokes that may cause hemiparesis, hemianopsia, hearing loss, or cortical blindness.

CT and MR imaging may show multiple cortical and subcortical infarct-like lesions that cross vascular boundaries, more commonly in the parieto-occipital region and basal ganglia. The lesions have a migrating pattern over time, with appearance, disappearance, and reappearance. Variable degrees of generalized cerebral and cerebellar atrophy may also be seen. Basal ganglia calcifications may also be seen.

CTA and MRA are usually normal, while conventional angiograms in the acute phase may show dilated cortical arteries with prominent capillary blush and no arterial occlusion.

The classic MRS finding is elevated lactate peak in the cerebrospinal fluid and normal brain.

Differential consideration for infarction in a young person:
  • Cardiac embolic disease: Valvular disease, left atrial myxoma.
  • Prothrombic disorder: Sickle cell disease, protein S or C deficiency, factor V-Leiden, lupus anticoagulant, polycythemia, leukemia.
  • Congenital vascular: CADASIL, neurocutaneous syndromes
  • Acquired vascular: Dissection, moya moya.
  • Drugs: Oral contraceptives, stimulants (methamphetamines, cocaine).


Based on the clinical characteristics of MELAS, some have suggested that Friedrich Nietzsche may have suffered from MELAS, and not syphilis as commonly thought.

References

  • Kim IO, Kim JH, Kim WS, Hwang YS, Yeon KM, Han MC. Mitochondrial myopathy-encephalopathy-lactic acidosis-and strokelike episodes (MELAS) syndrome: CT and MR findings in seven children. AJR Am J Roentgenol. 1996 Mar;166(3):641-5.
  • Koszka C. Friedrich Nietzsche (1844-1900): a classical case of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome? J Med Biogr. 2009 Aug;17(3):161-4.
  • Osborn AG. MELAS. StatDx. 2006-09-11.

Sunday, March 7, 2010

Avulsion Fractures of the Tarsal Navicular

Dorsal avulsion fractures of the tarsal navicular (see figure above) are caused by the pull of the talonavicular ligament and joint capsule during acute foot plantar flexion.

Medial avulsion fractures of the tarsal navicular occur at the navicular tuberosity due to pull from the posterior tibialis tendon during eversion injuries.

Medial avulsion fractures may be associated with anterior calcaneal or cuboid fractures or injury to the calcaneocuboid joint. The last is also known as a nutcracker fracture of the cuboid, which occurs when abduction of the forefoot compresses the cuboid between the bases of the fourth and fifth metatarsals distally and the calcaneus proximally.

References

Hunter JC, Sangeorzan BJ. A nutcracker fracture: cuboid fracture with an associated avulsion fracture of the tarsal navicular. AJR Am J Roentgenol. 1996 Apr;166(4):888.

Saturday, March 6, 2010

Displacement vs. Distraction

Distraction refers to separation along the longitudinal axis of a long bone, while displacement is the degree to which the fractured ends are out of alignment with each other.

In the spine, the distraction in flexion-distraction fractures refers to the increase in interspinous distance and possible horizontal fracture lines through the pedicles, transverse processes, and pars interarticularis in association with an anterior wedge compression fracture.

References

Rennie W, Mitchell N. Flexion distraction fractures of the thoracolumbar spine. J Bone Joint Surg Am. 1973 Mar;55(2):386-90.

Friday, March 5, 2010

Groove Pancreatitis

Groove pancreatitis is a form of chronic segmental pancreatitis affecting the pancreaticoduodenal groove. A number of conditions have been associated with groove pancreatitis, including peptic ulcers, gastric resection, true duodenal-wall cysts, and pancreatic heterotopia in the duodenal wall.

Groove pancreatitis has been divided into pure and segmental forms. The pure form affects only the groove, sparing the pancreas, while the segmental form involves the head of the pancreas.

CT may reveal soft-tissue attenuation material between the pancreatic head and the adjacent duodenum with or without small cystic lesions in the thickened duodenal wall (cystic dystrophy of the duodenal wall, see below). MRI may reveal a sheetlike mass corresponding to fibrous scar in the pancreatoduodenal groove that is hypointense relative to the pancreatic parenchyma on T1-weighted images and isointense or slightly hyperintense on T2-weighted images.

Cystic dystrophy of the duodenal wall is most likely related to groove pancreatitis and may be part of the spectrum of paraduodenal pancreatitis, which includes groove pancreatitis, cystic dystrophy of the duodenal wall, and paraduodenal wall cysts. These all occur in and around the minor papilla and have several features in common such as dilated ducts and cysts in the duodenal wall, Brunner gland hyperplasia, and hamartomatous pancreatic tissue in the groove.

References

Thursday, March 4, 2010

Tracheobronchial Papillomatosis

Tracheobronchial papillomatosis is an uncommon (5%–10%) complication of laryngeal papillomas. Extension to the lung can be seen in less than 2% of cases. There is a bimodal age distribution, with most cases presenting early in life with another peak in the fourth decade. Bronchopulmonary manifestations occur about 10 years after the diagnosis of laryngeal papillomas.

Tracheobronchial papillomatosis is thought to result from aerial dissemination of laryngeal disease. Dissemination to the lower airways may result in solid or thin-walled cavitary pulmonary nodules. Endobronchial growth can result in saccular bronchiectasis and mucus plugging.

References

Wednesday, March 3, 2010

Nonobstructive Causes of Hydronephrosis

Nonobstructive causes of hydronephrosis include the following:
  • High renal output
  • Ureterectasis: For example from a prior obstruction that has since resolved
  • Vesicoureteral reflux
  • Congenital megacalycosis and megaureter
  • Papillary necrosis: Obstruction due to sloughed papilla
  • Extrarenal pelvis
  • Prune-belly syndrome
  • Beckwith-Wiedemann syndrome: May be related to reflux

References

Tuesday, March 2, 2010

Urethral Strictures by Site

  • Prostatic:
  • Membranous: Common site for iatrogenic urethral stricture
  • Bulbar: Proximal bulbar is the site of stricture in 70% of patients gonococcal urethritis due to its relatively dependent position.
  • Penile: Proximal penile urethra (at the penoscrotal junction) is a common site for iatrogenic urethral stricture.

References

Zagoria RJ and Tung GA. The lower urinary tract. in Genitourinary Radiology: The Requisites. 1997

Monday, March 1, 2010

Types of Renal Calculi

Calculus Radiopacity on radiographs Comment
Mixed calcium oxalate/phostphate Radiopaque  
Calcium oxalate Radiopaque
  • Often have spiculated or dotted shape (toy jack or mulberry)
  • Easily broken down by extra-corporeal shockwave lithotripsy (EWSL)
  • Causes include inflammatory bowel disease, vitamin C overdose, and renal failure.
  • Increased incidence in patients with short small bowels (e.g., after Roux-en-Y gastric bypass) and a preserved colon.
Calcium phosphate Radiopaque
  • Seen with dehydration, calcium supplements
  • Least responsive to EWSL
Magnesium ammonium phosphate (Struvite) Radiopaque
  • Typically due to infection by urea-splitting bacteria such as Proteus, Klebsiella, and Pseudomonas
  • Despite common infectious cause, large percentage have an underlying metabolic disorder.
  • Can get large and branching
  • May have a laminated appearance due to presence of calcium phosphate
  • EWSL not feasible due to large size
  • Preferred extraction is via percutaneous nephrostomy
Cystine Semi-opaque/faint
  • Homogeneous, low density
  • Least fragile renal cacluli: Smooth stones least responsive to ESWL. Rough stones more responsive.
Uric Acid Lucent
  • Small smooth stones
  • Radiolucent on radiographs but opaque on CT
  • Can also be seen with small-bowel disease or resection
Xanthine Lucent  
Matrix Lucent
  • Caused by inspissation of mucoproteins in patients with a chronic Proteus infection
  • Can have soft tissue attenuation
Indinavir Lucent
  • Caused by inspissation of indinavir
  • May not be visible even on CT

References

  • Bambach CP, Robertson WG, Peacock M, Hill GL. Effect of intestinal surgery on the risk of urinary stone formation. Gut. 1981 Apr;22(4):257-63.
  • Chu G, Rosenfield AT, Anderson K, Scout L, Smith RC. Sensitivity and value of digital CT scout radiography for detecting ureteral stones in patients with ureterolithiasis diagnosed on unenhanced CT. AJR Am J Roentgenol. 1999 Aug;173(2):417-23.
  • Duffey BG, Pedro RN, Makhlouf A, Kriedberg C, Stessman M, Hinck B, Ikramuddin S, Kellogg T, Slusarek B, Monga M. Roux-en-Y gastric bypass is associated with early increased risk factors for development of calcium oxalate nephrolithiasis. J Am Coll Surg. 2008 Jun;206(3):1145-53.
  • Zagoria RJ and Tung GA. The Renal Sinus, Pelvocalyceal System, and Ureter. in Genitourinary Radiology: The Requisites. 1997