Abstract
Nora's lesion, also known as bizarre parosteal osteochondromatous proliferation (BPOP), is a very rare benign lesion with few published cases. BPOP is more common in adults during the second to third decades of life, and usually occurs on the hands and feet. Radiologically, it appears as a calcified mass attached to the bone cortex that grows rapidly and that recurs easily following resection. Aggressive features on imaging and confusing histopathological findings usually result in misdiagnosis or mistreatment. Herein, we present a case of a rare bony tumour involving the distal ulna presenting as a painless growing mass. An excisional biopsy with clear margins was performed without disturbing the ulnar nerve and arteries. There was no recurrent mass or calcified lesion 1 year after surgery. Based on its rarity and difficult diagnosis, BPOP should be considered in the differential diagnosis of a painless mass in the distal ulnar region. Careful follow-up after surgery is essential, even without lesion recurrence.