Bizarre parosteal osteochondromatous proliferation (Nora's lesion) in the hand

The purpose of this study was to review our experience with a benign surface bone lesion referred to as bizarre parosteal osteochondromatous proliferation (BPOP) or Nora's lesion, named for the pathologist who described it in 1983. The lesion may be confused with a variety of tumors, particularly solitary osteochondromas, which are rare.

The files in the Department of Pathology at the Hospital for Joint Diseases were reviewed over a 21-year period for all surface bone lesions involving the tubular bones in the hand. There were a total of 10 cases of BPOP compared with only a single case of an osteochondroma.

Radiographs generally showed a well-marginated uniformly dense mass arising from the surface of the affected bone without any disruption in its bony architecture. Surgical excision is the definitive treatment and included the fibrous pseudocapsule over the lesion, any periosteal tissue beneath the lesion, and any area of the cortex of the host bone that appeared abnormal. Although in the medical literature the recurrence rate for BPOP is high, we had only one recurrence in our series.

BPOP is a benign surface bone lesion that may be confused with benign and malignant tumors. Although there is a cleavage plane between the lesion and host bone, we recommend excising the pseudocapsule over the lesion, any periosteal tissue beneath the lesion, and decorticating any abnormal-appearing areas in the underlying host bone. This may explain the low recurrence rate in our series.