Age / Sex : 42 / F

Chief complaint: palpable mass

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Two weeks later, you can see the final diagnosis with a brief discussion of this case.

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Courtesy: Hee Jin Park, Kangbuk Samsung hospital

Bizarre parosteal osteochondromatous proliferation (BPOP) or Nora's lesion

Discussion

- Rare, benign lesion that was first described by Nora et al. in 1983 in the hands or feet of young adults.

- Short tubular bone involvement

- Minor trauma is an etiologic factor in the development of BPOP.

- Antecedent trauma is reported in the patient's history from 0% to 50% of cases.

- Myositis ossificans and florid reactive periostitis may progress to BPOP.

- High recurrence rate after surgical resection, up to 55% of cases

- Histologically it is composed of cartilage, bone and spindle cells. The cartilage may form a cap on the surface of the lesion, and undergoes enchondral ossification. As myositis osfficians does, with time it progresses to mature bone

This benign lesion of the bone might be mistaken for malignant processes because of the high frequency of recurrence, the occasional quick growth and atypical histologic appearance.

* Radiographic findings

- Dense, non-homogeneous and often multilobulated mass with a broad base attached to the bone cortex.

- Heavy mineralization with sclerotic appearance.

- Occasionaly, rapid growth and aggressive features on imaging studies.

- No cortical or permeative bone destruction.

- No continuity between mass and medullary cavity of underlying bone.

- Positive scintigraphy with an intense tracer uptake in the lesion.

* MRI features

- Useful in differentiating BPOP from several of its mimickers.

- Low signal on T1WI, high signal on STIR imaging.

- Variable signal on FSE T2 and GRE sequences, probably related to the relative amounts of cartilage present within the lesion.