Cystic degeneration of medullary bone infarction evaluated with magnetic resonance imaging correlated with pathologic examination.

Objective: To evaluate the imaging pattern of cystic degeneration of medullary infarcts of the long bones. Medullary infarction of the long bones is a well-recognized entity. Cystic degeneration, however, is extremely rare and may frequently cause difficulty in the differential diagnosis.

Methods: We reviewed 15 cases of cystic degeneration of infarction of the long bones in 13 women and 2 men whose mean age was 41 (range 21-82) years. Conventional radiographs were obtained in every case. Eleven of the 15 cases were evaluated by magnetic resonance imaging (MRI).

Results: Six of the lesions occurred in the humerus, 5 in the femur, 2 in the tibia and 2 in the iliac bone. Fourteen patients presented with dull pain over the area; 1 patient was asymptomatic. The size of the lesions ranged between 1.5 cm and 12 cm in their greatest diameter. All of the 15 lesions proved to be benign on pathologic examination. On plain radiographs, about half of the lesions showed an expansile pattern and contained faint-to-dense calcifications. Using MRI, the lesions showed decreased signal intensity on T,-weighted imaging and appeared heterogeneously bright on T2-weighted imaging. After contrast injection, a well-defined unenhanced lesion was consistent with fluid collection.

Conclusion: MRI is a valuable tool in diagnosing cystic degeneration of medullary infarction. Findings such as unenhanced lesions with well-defined margins are suggestive of fluid collection. The presence of dystrophic calcification and the thinned, but intact, cortex may suggest a benign underlying process such as medullary infarct.