Focal hematopoietic hyperplasia of the rib--a form of pseudotumor.

Two patients are presented who had a resection of a solitary expansile rib lesion. The radiologic features were nonspecific and the lesions were thought to represent either fibrous dysplasia, myeloma, or metastatic disease. Histologically, the lesion consisted of focal hyperplasia of the bone marrow involving all hematopoietic elements. The marrow expanded the rib, eroded the cortex, and extended into the adjacent soft tissue. Neither patient had any underlying hematologic abnormality. A search of the English language literature failed to discover a description of a similar lesion. From the clinical course and follow-up information, the process appears to be benign. The authors believe the lesion is a form of pseudotumor, and propose that it be designated as "focal hematopoietic hyperplasia of rib" or "hematopoietic pseudotumor."