Bizarre parosteal osteochondromatous proliferation. Difficulty in diagnosis.

Nora's tumor, also known as bizarre paraosteal osteochondromatous proliferation, is an exophytic outgrowth from the cortical surface that consists of a mixture of bone, cartilage, and fibrous tissue. It is a benign lesion with atypical microscopic features and a tendency to recur. Nora reported 35 cases emerging from the bones of the hands and feet. The largest published series is of 65 cases, with 17 lesions involving the long bones. With this exception, most authors report isolated cases. Age range from 8 to 74 years but most patients are between 20 and 35 years of age, and with the lesion affecting males and females in equal proportions. Usually the presenting symptoMs are due to bony mass, with a variable growth rate (months-years), and infrequent pain. In 15-20% of the cases there was trauma in the patient history: nevertheless, Fechner and Mills report no association with trauma. Radiography shows a calcified, rounded mass emerging directly from the surface of the bone. Isotope bone scans show intense tracer uptake in the lesion. With time, the appearance progresses to the more characteristic mature bone architecture.