Bizarre Parosteal Osteochondromatous Proliferation: Report of a Case with Hallmark Characteristics

Bizarre parosteal osteochondromatous proliferation (BPOP), also known as the Nora’s lesion, is a part of the spectrumof reactive lesions with a difficult diagnosis. To date, only limitednumberof Nora’s lesions have been reported in the literature. Here, we report a case of Nora’s lesion and discuss the differential diagnosis of the case. Case Presentation: A34-year-old male that was referred to thehandclinic of our center with a painfullumpat the dorsoulnar aspect of the first metacarpal bone of his left hand. The diagnosis of BPOP was suspected using its clinical and radiographic characteristics. Subsequently, excisional biopsy was performed and the extracted lesion was sent to the pathology for definitive diagnosis. The histopathologic evaluation confirmed the diagnosis of BPOP. One year follow-up of the patient showed no radiographic or clinical sign of recurrence. Conclusions: BPOP can be confused with malignant lesions such as parosteal osteosarcoma and chondrosarcoma. Thus care should be taken to combine the radiographic and pathologic information in the correct diagnosis of this lesion, especially when the BPOP presents with atypical features.