Bizarre parosteal osteochondromatous proliferation (Nora lesion)

Case contributed by Domenico Nicoletti
Diagnosis certain


Painful swelling on the dorsal aspect of left big toe, gradually increasing in size.

Patient Data

Age: 50 years
Gender: Female

CT shows a small exostotic mass on the dorsal aspect of the proximal phalanx of the 1st toe. The protruding bony mass does not connect with the medullary cavity of the phalanx. No adjacent soft tissue abnormality.

The lesion exhibits low signal intensity on T1 sequences, without involvement of the adjacent bone marrow or soft tissue.

Case Discussion

The patient was operated on, with wide excision of the involved cortex which showed no apparent corticomedullary continuity with the mass. The interphalangeal joint was not found to be involved.

Histological report:

Proliferative and haphazardly arranged spindle cells, chondrocytes, with new and calcified bone, diagnostic of bizarre parosteal osteochondromatous proliferation.

Bizarre parosteal osteochondromatous proliferation (BPOP), also known as Nora lesion, is a rare lesion that occurs in the short bones of the hands and feet and eventually presents as a parosteal mass. It normally arises from the cortical surface and periosteum of these bones. Histologically, these lesions consist of a hypercellular cartilaginous cap covering a bony stalk that is surrounded by ossified areas and spindle cell stroma. The cortical bone and bone marrow compartment are not involved. The etiology of BPOP has yet to be determined.

Radiographer: TSRM Fabio Imola

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