gms | German Medical Science

Objectives/Interrogation: We report on a serie of cases of Bizarre Parosteal Osteochondromatous Proliferation (BPOP).

Case 1 A 63-year-old woman presented with right thumb pain since November 2017. Radiographs and an ultrasound demonstrated findings suggestive of osteomyelitis. MRI Findings remained suggestive for terminal tuft right thumb osteomyelitis and small palmar phlegmon/collection. Surgical excision was performed and no evidence of necrotic, inflammatory or infective tissue was found. BPOP was reported by the pathology department.

Case 2: A 76-year-old, right-handed man presented with a growing solid lump over the last 8 months on his right ring finger. MRI scan reported an osteochondroma with features suspicious for sarcomatous degeneration to chondrosarcoma. CT guided biopsy followed by surgical excision were consistent with BPOP.

Case 3: 55 year-old, female, presented with a reasonably painful lump in her right wrist with constant growth in the last 2 years and ulnar nerve symptoms. CT scan reported bony exostosis from the volar and radial aspect of the distal ulna (20 x 16 x 15mm). Surgical excision was performed with ulnar nerve release and the specimen reported as BPOP.

Results and Conclusions: Bizarre parosteal osteochondromatous proliferation was first described by Nora et al. in 1983. It is an extremely rare lesion (less than 200 cases reported in the literature), with reported age onset as being anywhere between 5 months to 74 years old, absolutely benign and without sex predilection.

Clinically, presents as a slowly growing hard protuberance, painless in most cases, unless due to mass effect.

The classical radiographic pattern consisted of a pedunculated or broad-based osseous protuberance along the cortical surface of the bone, mostly seen in tubular small bones metaphysis.

Typical MRI features of BPOP are low signal intensity on T1-weighted sequences, high signal intensity on fast spinecho T2-weighted and short inversion time inversion recovery sequences with a normal cortex, medullary cavity, and adjacent soft tissues.

Histologically, BPOP presents as a cartilage-capped exostosis. The cap is cellular with focal atypia. The subchondral area is composed of fibrovascular tissue. The presence of calcified cartilage that stains blue on hematoxylin and eosin (H & E) stain is characteristic.

Generally, BPOP does not induce metastatic lesions and the most effective and safe treatment is radical excision surgery, including the fibrous pseudo-capsule and part of the compromised cortical bone.