Saturday, October 31, 2009

Iliotibial Band Friction Syndrome

Iliotibial band friction syndrome, also known simply as iliotibial band syndrome, is thought to occur through friction between the iliotibial band (ITB) and the lateral femoral condyle during early stages of knee flexion.

The ITB may or may not be thickened in iliotibial band syndrome. Early on in the disease process, there may be fluid signal deep to the iliotibial band that may be difficult or impossible to differentiate from joint fluid that has extended posterolaterally. As the disease progresses, there is fluid surrounding the ITB, making the diagnosis easier.

T2 hyperintensity deep to the ITB is located within a space bounded superiorly by the vastus lateralis muscle, posteriorly by the biceps femoris muscle, laterally by the ITB, distally and medially by the meniscocapsular junction of the lateral meniscus, the lateral collateral ligament, and the lateral femoral epicondyle.

References

Muhle C, Ahn JM, Yeh L, Bergman GA, Boutin RD, Schweitzer M, Jacobson JA, Haghighi P, Trudell DJ, Resnick D. Iliotibial band friction syndrome: MR imaging findings in 16 patients and MR arthrographic study of six cadaveric knees. Radiology. 1999 Jul;212(1):103-10.

Friday, October 30, 2009

Attachments of the Medial and Lateral Collateral Ligaments of the Knee

Medial Collateral Ligament: Originates distal to the adductor tubercle of femur and inserts 5 cm below the joint line medially.

Lateral Collateral Ligament Complex:
  • Biceps femoris: Originates as part of the hamstrings and inserts at the fibular head. Most posterior.
  • Lateral collateral ligament proper (fibulocolateral ligament): Originates along the lateral femoral condyle and inserts at the fibular head.
  • Iliotibial band: Originates at the level of the greater trochanter by the coalescence of the fascial investments of the tensor fasciae latae and the gluteus maximus and medius muscles. On its way down, it attaches to the supracondylar tubercle of the femoral condyle and the intermuscular septum before attaching to the Gerdy tubercle. Most anterior.

References

Muhle C, Ahn JM, Yeh L, Bergman GA, Boutin RD, Schweitzer M, Jacobson JA, Haghighi P, Trudell DJ, Resnick D. Iliotibial band friction syndrome: MR imaging findings in 16 patients and MR arthrographic study of six cadaveric knees. Radiology. 1999 Jul;212(1):103-10.

Thursday, October 29, 2009

Secondary Signs of Anterior Cruciate Ligament Injury

  • Kissing subchondral bone bruises involving one or both posterior tibial plateaus and the corresponding anterior femoral condyle(s) suggests an ACL injury less than 2-months-old.
  • Posterolateral tibial bone bruise by itself has a high predictive value for ACL tear in adults (not so much in pediatric patients due to laxity of the ACL).
  • Posterolateral injuries: lateral collateral ligament, lateral capsule, and popliteus tendon injuries; the Segond fracture (100% associated with ACL tear); and avulsion of fibular head.
  • Avulsion at Gerdy's tubercle (insertion of the iliotibial band).
  • Hemarthrosis: 75% of acute hemarthroses of the knee are due to ACL tears.
  • Hyperangulation of the PCL: A line drawn tangent to the posterior border of the PCL fails to intersect the distal 4-6 cm of the femur.
  • Anterior subluxation of tibia: Lines drawn across posterior margins of lateral tibia and lateral femoral condyle in the region of the mid-lateral tibial compartment are more than 7 mm apart.
  • Posterior subluxation of the posterior horn of the lateral meniscus relative to posterior margin of the lateral tibial condyle.
  • O'Donoghue's unhappy triad: ACL tear, MCL injury, and medial meniscus tear.

Refereces

Musculoskeletal Radiology: The Requisites. Third edition. Chapter 13, pages 234-237.

Wednesday, October 28, 2009

Osteochondritis Dissecans

Osteochondritis dissecans (OCD) is an osteochondral stress injury usually seen in older children and adolescents. It can also be seen in adults, either as a de novo process (less common), or as progression of previously asymptomatic juvenile OCD. Juvenile OCD has a better prognosis and higher response rate to conservative therapy than its adult form.

OCD is characteristically seen at the lateral aspect of the medial femoral condyle. In the knee, OCD can also be seen in the lateral femoral condyle, femoral trochlea, and the patella. OCD can also be seen at the distal capitulum, humeral head, and medial talar dome.

The lesion begins as a sunchondral stress reaction (edema on MRI) with intact overlying cartilage. Enhancement at this stage implies an intact blood supply.

The process may progress, leading to a fracture plane parallel to the cortex, but with a still-intact overlying cartilage.

The fracture plane may completely separate the fracture fragment from the bone and interrupt its blood supply. The fragment may be kept in place, however, by the overlying cartilage, which may still be partially intact.

The next stage is progression to an in situ loose body with complete disruption of the overlying cartilage, and finally progression to an intra-artiular loose body.

Prognosis and MRI

Prognosis has been found to depend on stability of the lesion and MRI can be used to detect unstable lesions. Different MRI criteria have been suggested for adult and juvenile OCD in the knee. The location and size of lesions were not found to be correlated with stability.

Signs of instability in an adult OCD lesion (100% sensitive and 100% specific) are a T2-hyperintense rim or cysts surrounding an OCD lesion.

In juvenile OCD a T2-hyperintense rim was found to be specific for OCD instability only if the rim demonstrated fluid signal intensity, was surrounded by a second outer rim of low T2 signal intensity, or was accompanied by multiple breaks in the subchondral bone plate. In addition, cysts surrounding a juvenile OCD lesion were found to be specific for instability only if they were multiple or larger than 5 mm in size.

References

Tuesday, October 27, 2009

Palmaris Longus Muscle Variants

The palmaris longus muscle is one of the most variable muscles in the human musculoskeletal system. It arises from the flexor tendons at the medial humeral epicondyle and inserts into the palmar aponeurosis in the hand.

The muscle does not affect the function of the wrist and hand, likely because it has lost its purpose as humans began walking upright. Its major use these days is as a donor graft. However, it has been suggested that the palmaris longus tendon does play a role in carpal tunnel syndrome, since it increases intracarpal canal pressure on wrist extension and because there is a lower prevalence of palmaris longus agenesis in patients with carpal tunnel syndrome.

Absent Palmaris Longus Muscle

The most common variation is absence of the muscle. Clinically, there are multiple maneuvers that can be used to detect the presence of the tendon. The Schaeffer test was the first to be introduced: With the wrist flexed, the patient is asked to bring the thumb and small finger together. The palmaris longus tendon should be visible. Mishra's second test (he introduced two tests in his paper) can also be used: The thumb is abducted against resistance with the wrist in slight flexion, which should result in the visualization of the palmaris longus tendon.

In patients with median nerve palsy, who cannot abduct their thumbs, Mishra's first test can be used: There is passive hyperextension of the metacarpophalangeal joints followed by resisted active flexion at the wrist. The palmaris longus tendon should become visible.

Reversed Palmaris Longus Muscle


The normal appearance of the muscle is a short proximal belly and a long tendon. A reversed palmaris longus muscle may have a belly distally or along its mid section.

Accessory Palmaris Longus Muscle

No content yet.

References

  • Keese GR, Wongworawat MD, Frykman G. The clinical significance of the palmaris longus tendon in the pathophysiology of carpal tunnel syndrome. J Hand Surg Br. 2006; 31(6):657-60.
  • Kose O, Adanir O, Cirpar M, Kurklu M, Komurcu M. The prevalence of absence of the palmaris longus: a study in Turkish population. Arch Orthop Trauma Surg. 2009; 129(5):609-11.
  • Sebastin SJ, Lim AY. Clinical assessment of the palmaris longus-too many newer techniques? J Plast Reconstr Aesthet Surg. 2006; 59(7):784-6.

Monday, October 26, 2009

Type II Lunate

The normal (type I) lunate articulates with the radius and ulna proximally, capitate distally, scaphoid laterally, and triquetrum medially.

A type II lunate, on the other hand, has an extra articulation medially with the hamate at its medial or hamate facet. About 50% of lunate bones have a hamate facet.

The hamate and type II lunate rub up against each other during full ulnar deviation of the wrist. This is thought to be the reason that patients with type II lunates have a greater propensity for development of focal chondromalacia and osteoarthritis of the proximal pole of the hamate. About 25% of patients with type II lunates have chondromalacia along the proximal pole of the hamate that is often occult on MRI.

The case shown here shows a type II lunate, no marrow edema in the hamate, and some fluid within the hamatolunate space. Also seen is a multiseptated intraosseous ganglion with associated cortical irregularity in the proximal pole of the lunate at the scapholunate ligament attachment.

References

Sunday, October 25, 2009

The Buford Complex

The Buford complex is a normal anatomic variant of shoulder anatomy seen in up to 2% of the population that is characterized by the absence of the anterior superior labrum and the presence of a cord-like middle glenohumeral ligament.

References

Rudez J, Zanetti M. Normal anatomy, variants and pitfalls on shoulder MRI. Eur J Radiol. 2008 Oct;68(1):25-35.

Saturday, October 24, 2009

Quadrilateral Space

The quadrilateral space is bounded by the teres minor muscle superiorly, teres major muscle inferiorly, the long head of the triceps muscle medially, and by the surgical neck of the humerus laterally. The axillary nerve and the posterior humeral circumfiex artery exit through this space.

This space is important because mass effect on it can lead to compression of the axillary nerve and posterior circumflex humeral artery, resulting in a combination of signs and symptoms referred to as the quadrilateral space syndrome
  • Poorly localized shoulder pain exacerbated by abduction and external rotation.
  • Paresthesia along the lateral shoulder and upper posterior arm (innervated by the axillary nerve)
  • Discrete point tenderness in the lateral aspect of the quadrilateral space
  • Weakness and atrophy of the teres minor and/or deltoid muscles (innervated by the axillary nerve).
The characteristic MRI finding is focal atrophy of or abnormal signal in the teres minor muscle and/or portions of the deltoid muscle. Large paralabral cysts can sometimes be seen in the quadrilateral space and are associated with labral tears. Fibrous bands in the region of the quadrilateral space can also be a cause, but I'm not sure if these can be resolved on MRI.

Differential considerations include:
  • Parsonage-Turner syndrome: Looks for involvement of more than one branch of the brachial plexus.
  • Isolated teres minor tear: Very rare. Look for disruption of the tendon.

References

  • Linker CS, Helms CA, Fritz RC. Quadrilateral space syndrome: findings at MR imaging. Radiology. 1993;188(3):675-6.
  • Cothran RL Jr, Helms C. Quadrilateral space syndrome: incidence of imaging findings in a population referred for MRI of the shoulder. AJR Am J Roentgenol. 2005;184(3):989-92.

Friday, October 23, 2009

Parsonage Turner Syndrome

Parsonage-Turner syndrome (PTS), also known as acute brachial neuritis and neuralgic amyotrophy, is a rare condition that is characterized by acute onset of severe shoulder pain that is soon followed by weakness of at least one shoulder muscle. It is thought to be due to a systemic or localized infectious or immunologic process.

MRI typically demonstrates diffuse T2 hyperintensity involving one or more muscles in the distribution(s) of one or more peripheral nerves originating from the brachial plexus (see below). Atrophy of these muscles, seen on T1-weighted images, may also be present.

The suprascapular nerve (supraspinatus and infraspinatus muscles) is the most commonly affected, followed by the axillary nerve (deltoid and teres minor muscles). The subscapular nerve (subscapularis [upper and lower branches of subscapular nerve] and teres major [lower branches] muscles) is a distant third.

The right side is more commonly involved (~60% vs 30% for the left). Bilateral involvement is seen in about 10% of cases.

PTS is a self-limited condition (although resolution may take several years) that is important to be aware of because it can be clinically confused with more common disorders such as cervical spondylosis, rotator cuff tear, shoulder impingement syndrome, and acute calcific tendonitis, and may even lead to unnecessary surgery.

References

Gaskin CM and Helms CA. Parsonage-Turner Syndrome: MR Imaging Findings and Clinical Information of 27 Patients. Radiology. 2006; 240:501-507.

Thursday, October 22, 2009

Superparamagnetic Iron Oxide

Superparamagnetic iron oxide (SPIO) are liver-specific contrast agents that have an affinity for the reticuloendothelial system (e.g., Kupffer cells of the liver). They result in low signal in hepatic parenchyma on T1- and T2-weighted images. Hepatic metastases do not have Kupffer cells and are generally hyperintense on T2-weighted images, so they are made more conspicuous by SPIO agents.

Some SPIO contrast agents (e.g., Endorem, Feridex) have been associated with side effects like lumbar pain and hypotension. They are infused slowly to avoid these side effects, and scanning is generally started 30 minutes after start of infusion.

A newer SPIO (Resovist, approved in Europe) can be injected as a bolus and scanning can start 10 minutes after start of injection. Resovis can also cause some enhancement of lesions on T1-weighted images, although to a much lesser extent than traditional gadolinium agents, allowing the extraction of additional information using dynamic imaging.

SPIO-enhanced imaging are equal to or more sensitive compared with traditional gadolinium agents. SPIO-enhanced imaging is also significantly more sensitive than PET in the detection of hepatic metastases; however, PET is more specific.

References

Rappeport ED, Loft A. Liver metastases from colorectal cancer: imaging with superparamagnetic iron oxide (SPIO)-enhanced MR imaging, computed tomography and positron emission tomography. Abdom Imaging. 2007;32(5):624-34.

Wednesday, October 21, 2009

Malignant External Otitis

Malignant external otitis, also known as necrotizing external otitis, refers to osteomyelitis of the skull base (characteristically Pseudomonas aeruginosa), usually caused by persistent external otitis in diabetic or immunocompromised patients.

Early in the disease, CT may show thickened mucosa of the floor of the external auditory canal and auricle. As the disease progresses, there is is erosion of bone and maybe even extension into the middle cranial fossa or clivus.

Differential considerations include:
  • Squamous cell carcinoma of the external auditory canal: The two conditions may coexist. Look for history of cutaneous squamous cell carcinoma. But beware that ity may be impossible to differentiate squamous cell carcinoma of the external auditory canal from malignant external otitis radiographically.
  • Cholesteatoma of the external auditory canal: Look for a soft tissue mass with underlying bony destruction and intramural bony flakes.
  • Post-inflammatory medial canal fibrosis: There is fibrous tissue in medial aspect of the external auditory canal without bony erosion. It is usually caused by chronic otitis externa or surgery
  • Keratosis Obturans: Rare condition classically seen in patients with chronic sinusitis and bronchiectasis. There is obstruction of the external auditory canal due to abnormal accumulation of desquamated keratin. Look for homogeneous soft tissue within the external auditory canal, which may be mildly enlarged. No bony erosion is seen.

References

  • Narozny W et al. Infectious skull base osteomyelitis-still a life-threatening disease. Otol Neurotol. 2006;27(7):1047-8.
  • StatDx.

Tuesday, October 20, 2009

Os Trigonum Syndrome

The os trigonum usually joins with the talus by the end of the first year, forming the trigonal process, but It may remain a separate ossicle in up to 15% of patients. Its anterior surface is connected to the lateral talar tubercle by a fibrocartilagenous synchondrosis. Its inferior surface may articulate with the calcaneus.

The os trigonum syndrome, also known as talar compression syndrome, posterior ankle impingement syndrome, and posterior tibial talar impingement syndrome, is a broad term that refers to symptoms produced by pathology of the lateral tubercle of the posterior talar process. Symptoms include chronic pain with stiffness, tenderness, and edema in the posterior ankle, which are exacerbated by activities that result in extreme plantar flexion.

Different processes can lead to os trigonum syndrome:
  • Disruption of the cartilaginous synchondrosis between the os trigonum and the lateral talar tubercle: MRI will show fluid between the os trigonum and the lateral talar process.
  • Trigonal process fracture.
  • Flexor hallucis longus (FHL) tenosynovitis: The tendon for the FHL is located medial to the os trigonum between the medial and lateral tubercles of the talus. Heavy use of the FHL can result in tenosynovitis by rubbing against the os trigonum.
  • Posterior tibiotalar impingement by bone block: A bony protuberance from the calcaneus may articulate with the inferior surface of the os trigonum.
  • Intraarticular loose bodies: Just like other joints, synovial osteochondromatosis can affect the posterior subtalar joint or posterior ankle joint capsule.

References

Karasick D, Schweitzer ME. The os trigonum syndrome: imaging features. AJR Am J Roentgenol. 1996 Jan;166(1):125-9.

Monday, October 19, 2009

Intermetatarsal Bursitis

Intermetatarsal bursitis is a well-known cause of forefoot pain. Intermetatarsal bursae are positioned between the interosseous tendons of the feet dorsal to the deep transverse metatarsal ligament. They are positioned to act as lubricants where tendons move against each other or glide over bone surfaces.

The first intermetatarsal bursa covers the adductor hallucis tendon laterally and is positioned medial to the dorsal interosseous tendon. The second through fourth intermetatarsal bursa are positioned between the dorsal interosseous (medial) and plantar interosseous (lateral) tendons.

In the anteroposterior direction, the bursae in the second and third intermetatarsal spaces extend about 1 cm distal to the deep transverse metatarsal ligament, while those of the first and fourth spaces do not. Inferiorly, the bursae are in close proximity to the neurovascular bundles.

Biomechanically, it is thought that tight and narrow shoes compress the bursae and lead to inflammation, causing pain that may be local or radiate to the toes.

Treatment involves reversing the pressure on the bursae, either through better-fitting (wider) shoes or the use of a rocker bar (to decrease pressure on the metatarsals). Local injection of steroid and/or local anesthesia can also help.

References

Sunday, October 18, 2009

Cumulus Oophorus

The cumulus oophorus ("heap of eggs") is a collection of the cells in a mature follicle that protrude into the cavity of the follicle. It is a sign of imminent ovulation, but its absence has little significance in predicting the maturity of the oocyte.

On ultrasound, the cumulus oophorus appears as a cyst along the wall of the dominant follicle.

Saturday, October 17, 2009

The Whitaker Test

The Whitaker test, also known as the ureteral perfusion challenge, is an invasive provocative maneuver used to differentiate obstructive from non-obstructive uropathy in the presence of a dilated collecting system, for example, in
  • Patients with dilated renal pelves and suspected ureteropelvic obstruction,
  • Patients with dilated ureters and concern for obstruction,
  • Patients following treatment for collecting system obstruction,
  • Renal transplant patients with hydronephrosis, and
  • Patients with urinary obstruction who do not demonstrate dilatation of the collecting system.
Fluid is instilled into the renal pelvis starting at 5 mL/min for up to 5 minutes and the pressure gradient between the kidney and bladder is measured. A normal absolute renal pelvis pressure is less than 25 mm H2O. If the absolute pressure is above 30 mm H2O or an abnormally high resting gradient is detected, we have the diagnosis and no provocative challenge is needed.

If the absolute pressure is normal, the test continues by measuring the pressure gradient between the renal pelvis and urinary bladder during instillation of saline mixed with contrast. Contrast is used in the instillate to visualize the collecting system and possible site of obstruction.

A normal pressure gradient is less than 15 mm H2O at maximal fluid challenge (see below). A pressure gradient above 22 is diagnostic of obstruction. Pressure gradients between 15 and 22 are indeterminate. Higher infusion rates (up to 20 mL/min) can help in these cases. Negative or indeterminate cases can also be repeated with a distended bladder or using different patient positioning.

The renal pelvis pressure is measured while it is being perfused by inserting a second (transducer) needle (two-needle technique) or by inserting the transducer needle after withdrawing the infusion needle (one-needle technique). The bladder pressure is measured via Foley catheter.

Friday, October 16, 2009

Avascular Plane of Brödel

The renal artery divides into anterior and posterior divisions, creating a relatively avascular plane called the avascular plane of Brödel. This plane is the border between the anterior 2/3 and posterior 1/3 of the kideny, approximately 2-3 cm posterior to the lateral border of the kidney. Being relatively avascular, it is the optimal plane for needle insertion.

Update (for Joshua): An image of the kidney with a nice description can be found at RadioGraphics

References

Dyer RB, Regan JD, Kavanagh PV, Khatod EG, Chen MY, Zagoria RJ. Percutaneous nephrostomy with extensions of the technique: step by step. Radiographics. 2002 May-Jun;22(3):503-25.

Thursday, October 15, 2009

Gorham-Stout Syndrome

Gorham-Stout syndrome (also known as vanishing bone disease, phantom bone disease, Gorham disease, and massive osteolysis), is a rare disorder characterized by massive and progressive osteolysis caused by the proliferation of abnormal capillaries of vascular or lymphatic origin. Hemangiomatosis, another common name for the disease, is a misnomer because it implies that the process is neoplastic.

There is progressive osteolysis of one bone or a number of bones in children and young adults; history of minor trauma in approximately 60% of cases; and angiomatosis (capillary, venous, or lymphatic) in the affected bones or in the surrounding soft tissues. The proximal upper extremity, shoulder and pelvic girdle, and mandible are commonly affected.

There can also be altered lymphatic flow, leading to obstruction and edema. Invasion of the thoracic duct or communication of the lymphatic dysplasia with the pleural cavity can lead to chylothorax. Patients with Gorham-Stout syndrome who develop chylothorax need prompt and aggressive surgical intervention, as the condition can be fatal. Mediastinal lymphangioma is a rare association with Gorham-Stout syndrome.

Other associated findings include cystic hygromas in the neck, axilla, chest wall, and mediastinum. Splenic cysts may also be seen.

Early signs of Gorham-Stout syndrome include foci of intramedullary and subcortical lucency that can look like osteoporosis. As the disease progresses, there is tapering the long bones, which can progress to complete resorption. There is typically lack of sclerosis or osteoblastic reaction.

The image shows a case of Gorham-Stout syndrome following a pathologic fracture. The right pelvis is osteopenic and there is compete resorption of the proximal diaphysis. The radiograph was taken at least 10 years after initial diagnosis.

Differential considerations include:
  • Skeletal angioma: You may see osteolysis, but there is a tendency to preserve the cortex. In addition, there is limited growth and soft tissue spread.
  • Angiosarcoma.
  • Essential osteolysis: Multifocal with resorption of the carpal and/or tarsal bones and progressive renal failure.
  • Hereditary osteolysis: Multifocal. Primarily involves of the hands and feet. No vascular proliferation is present.
  • Rheumatoid arthritis.
  • Syphilis.
  • Hyperparathyroidism.
  • Myeloma.
  • Lymphoma.

References

  • Collins J. Case 92: Gorham syndrome. Radiology. 2006;238(3):1066-9.
  • Gorham L and Stout A. Massive osteolysis (acute spontaneous absorption of bone, phantom bone, disappearing bone): its relation to hemangiomatosis, J Bone Joint Surg Am. 1955;37A: 985–1004.

Wednesday, October 14, 2009

Tracheoesophageal Stripe

The tracheoesophageal stripe is the combined thickness of the posterior wall of the trachea and the anterior wall of an air-filled esophagus on the lateral view. It is normally less than 5 mm. Thickening can indicate esophageal carcinoma or nodal disease.

Tuesday, October 13, 2009

Tracheal Dimensions

Transverse diameter in men and women is up to 2.5 cm and 2.1 cm, respectively. The transverse to anteroposterior ratio is 0.6.

Monday, October 12, 2009

Chondrocalcinosis

Chondrocalcinosis, or cartilage calcification, is not always due to calcium pyrophosphate dihydrate crystal deposition (CPPD). The calcium may also be in the form of calcium hydroxyapatite or calcium orthophosphate. Chondrocalcinosis can occur as an isolated finding in an apparently normal joint or coexist with structural changes resembling osteoarthritis. Chondrocalcinosis can be seen with:

Chondrocalcinosis can be seen with:
  • Calcium pyrophosphate dihydrate crystal deposition (CPPD)
  • Degenerative or post-traumatic osteoarthritis
  • Hemochromatosis
  • Hyperparathyroidism, usually secondary (renal osteodystrophy)
  • Idiopathic
  • Ochronotic arthropathy

References

Reeder and Felson's Gamuts in Radiology

Sunday, October 11, 2009

Intersection Syndrome

Intersection syndrome refers to peritendinosis of the second extensor compartment (extensor carpi radialis brevis and longus) tendons due to the crossing tendons of the first extensor compartment (abductor pollicis longus and extensor pollicis brevis) tendons. The intersection occurs 4-8 cm proximal to Lister's tubercle.

MRI shows abnormal signal in the tendons beginning at the location of the intersection.

Saturday, October 10, 2009

Low-Signal-Intensity Renal Cortex

The normal renal cortex is more intense than the medulla on T1-weighted images. Low-signal intensity in the renal cortex on T2-weighted images can be seen with intravascular hemolysis and renal cortical necrosis. Diseases that can give this appearance include:
  • Paroxysmal nocturnal hemoglobinuria:Proteinuria, hematuria, hemosiderinuria.
  • Sickle cell disease: The T2-weighted, fat-saturated image above is from a patient with sickle cell disease (SSD). In SSD, most of the hemolysis is extravascular, which does not lead to low signal intensity in the cortex. Intravascular hemolysis occurs during crises and can be due to multiple transfusions. Other findings in SSD include low signal intensity in the spleen due to extravascular hemolysis and low signal intensity in the liver or pancreas in patients who have received multiple blood transfusions.
  • Mechanical hemolysis (e.g, from heart valves).
  • Renal cortical necrosis: The inner cortex is involved. Can be due to third-trimester obstetric hemorrhage, severe traumatic shock, septic shock, transfusion reaction, severe dehydration, venom toxin, hemolytic uremic syndrome, and renal transplantation.

References

  • Hricak H, Crooks L, Sheldon P, Kaufman L. Nuclear magnetic resonance imaging of the kidney. Radiology 1983; 146:425-432.
  • Jeong JY, Kim SH, Lee HJ, Sim JS. Atypical Low-Signal-Intensity Renal Parenchyma: Causes and Patterns. RadioGraphics 2002; 22:833-846.

Friday, October 9, 2009

Esophageal Intramural Pseudodiverticulosis

Esophageal intramural pseudodiverticulosis refers to the finding of multiple diverticula within the wall of the esophagus. Esophageal intramural pseudodiverticulosis is a rare condition, most commonly associated with strictures.

The cause is not known, but the initiating event is suspected to be chronic inflammation of the submucosal esophageal glands by infectious (e.g., candida, bacteria) or chemical (e.g., gastroesophageal reflux) insult. Obstruction of the ductal orifices due to inflammation and/or fibrosis then leads to dilatation of the ducts.

The diverticula may be distributed in a segmental or diffuse manner. The diffuse form is associated with strictures in the upper or mid esophagus, while the localized form tends to be associated with peptic strictures in the distal esophagus.

On barium swallow, there are multiple flask- or collar button-shaped outpouchings at right angles to the lumen. These outpouchings measure between 1 mm - 4 mm and communicate with the lumen through narrow openings. Intramural tracks can bridge two or more adjoining pseudodiverticula and may mimic a large ulcer when viewed obliquely.

On CT, there is esophageal wall thickening, irregularity of the lumen, and intramural gas.

References

Thursday, October 8, 2009

Spontaneous Osteonecrosis of the Knee

Spontaneous osteonecrosis of the knee (SONK), an old term referring to an insufficiency fracture about the knee, is a cause of (usually) atraumatic acute knee pain in older patients. Women are affected three times more often than men. The most common location is at the medial femoral condyle, followed by the lateral femoral condyle, the medial tibial plateau (uncommon), and the lateral tibial plateau (rare).

The MR images here show a subchondral fracture of the medial femoral condyle with extensive adjacent marrow signal abnormality. The collapsed sclerotic bone is seen as an ovoid hypointense structure. The radiograph, obtained 4 months after the MRI, shows an area of depression and sclerosis along the medial femoral condyle.

Differential considerations include:
  • Osteochondritis dissecans: Younger age group. The abnormality is usually on the non weight-bearing surface of the condyle, closer to the notch.
  • Osteochondral fracture: History of trauma.
  • Neuropathic (Charcot) arthropathy:
  • Articular diseases: Conditions leading to chondral and/or meniscal pathology can have a similar appearance.

References

Houpt JB, Pritzker KPH, Alpert B, Greyson ND, Gross AE. Natural history of spontaneous osteonecrosis of the knee (SONK): a review. Semin Arthritis Rheum 1983; 13:212–227.

Wednesday, October 7, 2009

The Carpal Tunnel View

The carpal tunnel view is obtained by hyperextending the wrist and shooting 20-30 degrees tangent to the long axis of the hand.

References

Meschan, I (1975). An Atlas of Anatomy Basic to Radiology. Philadelphia, PA: W.B. Saunders Company.

Tuesday, October 6, 2009

Plicae Palmatae

The plicae palmatae (Latin for leaf-shaped fold) is a normal cervical structure that is commonly seen on routine MRI of the normal uterus. It is seen in about 50% of women between 20-50, about 25% in women in their 50s.

The median ridge of the plicae palmatae appears on T2-weighted images as a longitudinal ridge of low signal at the midline of the anterior and/or posterior wall that protrudes into the cervical canal. The lateral ridges are typically not seen on MRI, as they branch upward and laterally and upward along the cervical wall.

It can be mistaken for an anomalous uterine septum.

References

Takahata A, Koyama T, Kido A, Kataoka M, Umeoka S, Nishizawa S, Nishimura T, Togashi K. The frequency of the plicae palmatae in the uterine cervix on MR imaging. Abdom Imaging. 2009 Mar-Apr;34(2):277-9.

Monday, October 5, 2009

Bridging Vessel Sign

Bridging vessel sign, also known as the bridging vascular sign, refers to the appearance of multiple vessels between the uterus and a pelvic mass adjacent to the uterus. The sign helps differentiate an exophytic uterine mass (e.g., a subserosal fibroid) from a pelvic mass adjacent to the uterus.

Color or power Doppler ultrasound show the vessels. On MRI, the vessels appear as curvilinear tortuous flow voids.

References

Madan R. The bridging vascular sign. Radiology. 2006 Jan;238(1):371-2.

Sunday, October 4, 2009

Lunula

The lunula (also known as a persisting center of the ulnar styloid and (I think) os ulnostyloideum) is an ossification center within the fibrocartilaginous structure between the triangular fibrocartilage, triquetrum, and the base of the fifth metacarpal. It is found distal to the ulnar styloid between the triangular fibrocartilage and the triquetrum.

It may fuse to ulnar styloid and give it an unusual and long appearance. It may also be difficult to distinguish from an old ulnar styloid avulsion (which may be the case in the image shown).

The lunula is a common finding in non-human primates.

References

Timins ME. Osseous anatomic variants of the wrist: findings on MR imaging. AJR Am J Roentgenol. 1999 Aug;173(2):339-44.

Saturday, October 3, 2009

Bicondylar Intraarticular Humeral Fracture

Bicondylar intraarticular fractures (also known as bicolumn fractures) of the distal humerus make up only 1% of distal humerus.

Distal humeral fractures are classified into three broad categories by the Müller Arbeitsgemeinschaft für Osteosynthesefragen (AO) system. Each category is further divided into 3 subcategories, and each into 3 sub-subcategories, giving a total of 27 types!
  • Type A: Extra-articular - No involvement of displaced fractures extending into the articular surface
  • Type B: Partial intra-articular - Part of the articular component is involved, leaving the other part attached to the metaphysis or diaphysis
  • Type C: Complete intra-articular - Articular surface is involved and the metaphyseal fracture completely separates the articular component from the diaphysis.
    • C1: Articular simple, metaphyseal simple
      • C1.1: Slight displacement
      • C1.2: Marked displacement
      • C1.3: T-shaped epiphyseal
    • C2: Articular simple, metaphyseal multifragmentary
      • C2.1: With an intact wedge
      • C2.2: With a fragmented wedge
      • C2.3: Complex
    • C3: Articular multifragmentary
      • C3.1: Metaphyseal simple
      • C3.2: Metaphyseal wedge
      • C3.3: Metaphyseal complex (current case)
Our case is a type C3.3 fracture. There are two fracture planes through the articular surface (better seen on CT), making this an articular multifragmentary fracture (C3). Multiple metaphyseal fragments are seen, making this a metaphyseal-complex fracture.

The full range of fractures can be found at the OA web site (see below). Another classification scheme, the Jupiter system, is also used.

References

OA Classification

Friday, October 2, 2009

Hemangiopericytoma (Central Nervous System)

Hemangiopericytomas are hyperattenuating extra-axial lesions with dural attachments that may mimic meningiomas. Unlike meningiomas, however, they do not demonstrate calcifications or hyperostosis and often have a heterogeneous enhancement. Meningiomas also demonstrate broad-based dural attachment and are typically round. Hemangiopericytomas, on the other hand, have narrow bases of attachment and are usually lobulated.

Unlike meningiomas, which displace vessels, hemangiopericytomas demonstrate internal flow voids. The angiographic pattern is also different. As opposed to the spoke-wheel pattern of vessels, the vessels in hemangiopericytomas are irregularly arranged.

Differential considerations include:
  • Meningioma
  • Dural metastases
  • Lymphoma
  • Neurosarcoidosis
  • Gliosarcoma
More recently, the concept of hemangiopericytoma as a distinct entity has come into question, with the majority of these tumors now classified as solitary fibrous tumors.

References

  • Gengler C, Guillou L. Solitary fibrous tumour and haemangiopericytoma: evolution of a concept. Histopathology. 2006 Jan;48(1):63-74.
  • Salzman KL. Hemangiopericytoma. StatDx. Updated 2008-06-02.

Thursday, October 1, 2009

Cleidocranial Dysplasia

Cleidocranial dysplasia is a generalized skeletal dysplasia that was originally thought to affect only the skull and clavicles. It is characterized by:
  • Clavicle: Incomplete ossification, ranging from absence to hypoplasia
  • Skull: Wormian bones, enlarged calvaria, frontal bossing, and open fontanelles
  • Chest: Bell-shaped thorax
  • Hand: Brachydactyly with hypoplastic distal phalanges
  • Pelvis: Pelvic hypoplasia, widened pubic symphysis, coxa vara
  • Teeth: Supernumerary teeth and severe dental anomalies

References

Mundlos S. Cleidocranial dysplasia: clinical and molecular genetics. J Med Genet. 1999 Mar;36(3):177-82.