title: Bizarre parosteal osteochondromatous proliferation (Nora's lesion) affecting the distal end of the ulna: a case report.
abstract: BACKGROUND
  Bizarre parosteal osteochondromatous proliferation (BPOP), first described by Nora et al. in 1983 and therefore termed "Nora's lesion", is a rare lesion that occurs in the short bones of the hands and feet and eventually presents as a parosteal mass. Reports of BPOP in the long bones are very rare. A benign disease, BPOP does not become malignant, although a high rate of recurrence following surgical resection is reported. Because of its atypical imaging findings and histopathological appearance, a BPOP might be misdiagnosed as a malignant tumor such as an osteochondroma with malignant transformation, a parosteal osteosarcoma, or a periosteal osteosarcoma.
  
  
  METHODS
  A 58-year-old woman complained of left ulnar wrist pain at the time of her initial presentation. Plain x-rays showed ectopic calcifications in and around the distal radioulnar joint, which supported the diagnosis of subacute arthritis with hydroxyapatite crystal deposition. She was initially given a wrist brace and directed to follow-up, but her persistent pain required the administration of corticosteroid injections into the distal radioulnar joint. Increasing ulnar wrist joint pain and limited forearm pronation and wrist flexion necessitated computed tomography and contrast-enhanced magnetic resonance imaging. BPOP was diagnosed based on the preoperative imaging studies, and a resection of the lesion was performed along with the decortication of the underlying the cortical bone to reduce recurrence rates. The diagnosis of BPOP was confirmed by pathologic examination. Two years after surgery, the patient has no subsequent pain complaints and an improved range of motion.
  
  
  CONCLUSIONS
  BPOP affecting the distal end of the ulna is exceedingly rare. Because BPOP was diagnosed primarily based upon preoperative imaging findings in our patient, decortication of the underlying cortical bone was performed to reduce recurrence rates. Further careful follow-up in these patients is essential, despite the non-recurrence of the lesion.
authors.affiliation: Department of Orthopaedic Surgery, Hokkaido University Graduate School of Medicine, Kita-15 Nishi-7, Kita-ku, Sapporo, 060-8638, Japan.
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Matsui
authors.affiliation: Department of Orthopaedic Surgery, Hokkaido University Graduate School of Medicine, Kita-15 Nishi-7, Kita-ku, Sapporo, 060-8638, Japan.
authors.forename: Tadanao
authors.initials: T
authors.lastname: Funakoshi
authors.affiliation: Department of Orthopaedic Surgery, Hokkaido University Graduate School of Medicine, Kita-15 Nishi-7, Kita-ku, Sapporo, 060-8638, Japan.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Kobayashi
authors.affiliation: Department of Surgical Pathology, Hokkaido University Hospital, Kita-14 Nishi-5, Kita-ku, Sapporo, 060-8648, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Mitsuhashi
authors.affiliation: Faculty of Health Sciences, Hokkaido University, Kita-12 Nishi-5, Kita-ku, Sapporo, 060-0812, Japan.
authors.forename: Tamotsu
authors.initials: T
authors.lastname: Kamishima
authors.affiliation: Department of Orthopaedic Surgery, Hokkaido University Graduate School of Medicine, Kita-15 Nishi-7, Kita-ku, Sapporo, 060-8638, Japan. niwasaki@med.hokudai.ac.jp.
authors.forename: Norimasa
authors.initials: N
authors.lastname: Iwasaki
mesh_terms: D018771:Arthralgia / Q000473:pathology / Q000503:physiopathology; D001696:Biomechanical Phenomena; D001706:Biopsy; D001847:Bone Diseases / Q000473:pathology* / Q000503:physiopathology / Q000601:surgery; D001859:Bone Neoplasms / Q000473:pathology*; D049109:Cell Proliferation; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D015831:Osteochondroma / Q000473:pathology*; D011237:Predictive Value of Tests; D020127:Recovery of Function; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D014457:Ulna / Q000473:pathology* / Q000503:physiopathology / Q000601:surgery; D014955:Wrist Joint / Q000473:pathology / Q000503:physiopathology
keywords: Bizarre parosteal osteochondromatous proliferation; Bone decortication; Distal end of ulna; Nora’s lesion; Preoperative imaging studies