Bizarre parosteal osteochondromatous proliferation (Nora’s lesion) affecting the distal end of femur: a case report and review of the literature

Abstract

Bizarre parosteal osteochondromatous proliferation (BPOP) or else Nora`s lesion, as it is commonly known, was first described by a pathologist named Nora in 1983. Typically this rare disease is occurred in the small tubular bones of the hands and feet and especially in the proximal and middle phalanges as well as the metacarpal and the metatarsal bones. Here we present a case of a young female with a distal femur lesion originally thought to be an exostosis. A 19-year old, Caucasian female was referred to our outpatient clinic complaining of pain at her right femur. Plain x-rays revealed a 1.25cm, well – delimited, ossified, rounded mass with edema around it. Computed tomography showed a lesion in contact with the femoral metadiaphysis and surrounding by a slight thickening of the cortex. This lesion was more compatible with the presence of an exostosis. Based on the magnetic resonance imaging, the clinical and radiological findings the lesion seemed to represent BPOP. The isotope bone scan showed nothing pathological in other regions of the skeleton. The patient was taken to the operating room for resection of her bone lesion. The diagnosis of BPOP was confirmed by pathologic examination.