title: Bizarre parosteal osteochondromatous proliferation: a locally aggressive benign tumor.
abstract: BACKGROUND
  Bizarre parosteal osteochondromatous proliferation (BPOP) is a benign lesion of bone, and numerous questions remain unresolved regarding its etiology, diagnosis, and treatment.
  
  
  OBJECTIVE
  We present the Scottish Bone Tumour Registry experience of this rare lesion.
  
  
  METHODS
  We performed a retrospective analysis of the Scottish Bone Tumour Registry records. Histologic specimens were reexamined by a musculoskeletal pathologist. Radiographs were reevaluated by a musculoskeletal radiologist.
  
  
  RESULTS
  From 1983 to 2009, 13 cases (13 patients; six male, seven female) were identified. Their ages ranged from 13 to 65 years. All patients presented with localized swelling. Pain was present in five. Antecedent trauma was present in two. Nine lesions affected the hand, three the foot, and one the tibial tuberosity. Twelve lesions were excised and one was curetted. There were seven recurrences of which six were excised. One lesion recurred a second time and was excised. There were no metastases. Radiographs showed densely mineralized lesions contiguous with an uninvolved cortex. Cortical breakthrough was present in one case and scalloping in another. Histologic analysis characteristically showed hypercellular cartilage with pleomorphism and calcification/ossification without atypia, bone undergoing maturation, and a spindle cell stroma.
  
  
  CONCLUSIONS
  BPOP is a rare benign lesion that probably is neoplastic, with no gender predilection, and affecting patients over a wide age range. Previously trauma was considered an etiologic factor, but this no longer seems to be the case. The rate of recurrence was 50%, which may indicate a more extensive resection is required for this locally aggressive lesion. No metastases were reported. BPOP should not be mistaken for, or treated as, a malignant tumor.
  
  
  METHODS
  Level IV, retrospective case series. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Trauma and Orthopaedics, Glasgow Western Infirmary, Glasgow, UK. jibujohnjoseph@hotmail.com
authors.forename: Jibu
authors.initials: J
authors.lastname: Joseph
authors.forename: David
authors.initials: D
authors.lastname: Ritchie
authors.forename: Elaine
authors.initials: E
authors.lastname: MacDuff
authors.forename: Ashish
authors.initials: A
authors.lastname: Mahendra
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001859:Bone Neoplasms / Q000209:etiology / Q000473:pathology* / Q000601:surgery; D049109:Cell Proliferation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local; D015831:Osteochondroma / Q000209:etiology / Q000473:pathology* / Q000601:surgery; D010146:Pain; D012042:Registries; D012189:Retrospective Studies; D014947:Wounds and Injuries / Q000150:complications; D055815:Young Adult