CASE 152
BY: Dr. Nizar Al-Nakshabandi MD, FRCPC
HISTORY: 29-year-old complaining of shoulder pain.
What are your findings?
What is the differential diagnosis?
What are the causes?
FINDINGS:
Plain radiograph of left shoulder (A) demonstrate periarticular osteopenia. In addition, a subchondral lucency is seen in the humeral head (crescent sign of AVN).
Coronal T1 (B) weighted image shows diffuse low signal changes involving the whole left shoulder consistent with edema.
Coronal T2 (C) weighted image shows a mixture of low and high signal changes in the humeral head representing the double line sign which is the serpiginous outer dark signal and inner bright signal (granulation tissue). In addition, the crescent sign that was seen on the plain radiograph becomes the rim sign on T2WI which is the result of osteochondral fragmentation.
DIFFERENTIAL DIAGNOSIS:
· Avascular necrosis.
· Infection (osteomyelitis with or without septic arthritis).
· Neoplasm -less likely.
DIAGNOSIS:
Stage III b Avascular necrosis of the left shoulder.
CAUSES OF AVN:
There are many mnemonics. I discourage you to use them unless you are stuck. The reason is that you may mention the least cause first in your region such as Caisson disease (Diver’s disease) in a desert country which will make you look strange in front of the examiner. The way I remember it is by imaging a blood vessel, so in the vessel is RBC, if defected then—Sickle cell disease, Medications—Exogenous steroids, endogenous steroids (Cushing’s disease), and finally in the blood alcohol can run. Vessel wall—Vasculitis. Outside vessel—Trauma, Radiotherapy.
There are other causes such as pregnancy related AVN, Pancreatitis, Gout, and Gaucher’s disease, but if you mention them before mentioning Sickle cell disease, examiner will not be pleased.
PEARLS AND DISCUSSION:
Remember that examiners like testing a common disease in an uncommon location. Hence, be aware the AVN usually affecting the hips can also involve the shoulders.
In cases of non-traumatic AVN, bilateral involvement is common.
Always screen the other side on MRI.
Many staging systems used, the most comprehensive is the ARCO staging system is used to grade AVN.
Stage 0
Patient is asymptomatic.
Radiography findings are normal.
Histology findings demonstrate osteonecrosis.
Stage I
Patient may or may not be symptomatic.
Radiography and CT scan findings are unremarkable.
AVN is considered likely based on MRI and bone scan results.
Stage II
Patient is symptomatic.
Plain radiography findings are abnormal and include osteopenia, osteosclerosis, or cysts.
Subchondral radiolucency is absent. MRI findings are diagnostic.
Stage III
Patient is symptomatic.
Radiographic findings include subchondral lucency (crescent sign) and subchondral collapse.
Shape of the femoral head is generally preserved on radiographs and CT scans.
Subclassification depends on the extent of crescent, as follows:
Stage IIIa: Crescent is less than 15% of the articular surface.
Stage IIIb: Crescent is 15-30% of the articular surface.
Stage IIIc: Crescent is more than 30% of the articular surface.
Stage IV
Flattening or collapse of femoral head is present.
Joint space may be irregular.
CT scanning is more sensitive than radiography.
Subclassification depends on the extent of collapsed surface, as follows:
Stage IVa: Less than 15% of surface is collapsed.
Stage IVb: Approximately 15-30% of surface is collapsed.
Stage IVc: More than 30% of surface is collapsed.
Stage V
Radiography findings include narrowing of the joint space, osteoarthritis with sclerosis of acetabulum, and marginal osteophytes.
Stage VI
Findings include extensive destruction of the femoral head and joint
FURTHER READING:
1. Bonakdarpour A, Reinus WR. Diagnostic Imaging of Musculoskeletal Diseases: A Systematic Approach. Springer (2010).
2. Resnick D, Kransdorf MJ. Bone and joint imaging. W B Saunders Co. (2005).
3. Kaplan P. Musculoskeletal MRI. W B Saunders Co. (2001).
