Congenital bizarre parosteal osteochondromatous proliferation in unusual location and age: a case report.

Bizarre parosteal osteochondromatous proliferation (BPOP, also known as Nora's lesion) is a rare, benign, locally aggressive condition defined as osteochondromatous exostosis arising from the bony cortex. BPOP presents predominantly in the 2nd and 3rd decades of life, and commonly arises from the periosteum of metacarpals and metatarses, though rare locations have been reported, including the long bones, the maxillae, the bones of calvaria, and the sesamoids. The case of an osteochondromatous lesion in an infant with an intra-abdominal mass arising from the iliac wing, an atypical location of benign solitary lesions, is reported. Benign solitary lesions are exceptional in this age group. The parents of the patient, who was born in term at 3600 grams, discovered a mass in the left groin and observed decreased movement in the lower left extremity. No history of trauma was reported. When the patient was 5 months of age, AP pelvic X-ray, computed tomography, and magnetic resonance imaging revealed a bony mass displacing intra-abdominal organs anteromedially. Biopsy reported an osteocartilaginous lesion with calcified mature cartilaginous fragments surrounded by plasmacytoid, monotone, fibrinoid cells in myxoid background. Differential diagnosis included osteochondroma, osteochondromyxoma, BPOP, fibrocartilaginous mesenchymoma, chondromyxoid fibroma, periosteal chondroma, soft tissue chondroma, myositis ossificans, and juxtacortical chondroma. Biopsy of the resected specimen determined a diagnosis of BPOP. At 6-month postoperative follow-up, neither symptoms nor complaints related to the mass were present.