title: Obturator externus bursa: anatomic origin and MR imaging features of pathologic involvement.
abstract: OBJECTIVE
  To investigate the anatomy of the obturator externus bursa of the hip and describe the magnetic resonance (MR) imaging features of pathologic involvement.
  
  
  METHODS
  The authors dissected eight cadaver hemipelvises to assess for the presence of periarticular bursae of the hip and bursal communication with the fascial plane of the obturator externus muscle. In addition, 10 consecutive patients with obturator externus bursa enlargement were prospectively identified with MR imaging. A bursa was considered present when a fluid collection was seen extending along the obturator externus muscle, continuous with the posterior inferior hip joint. The direction, extent, contour, and thickness of the bursa and hip capsule were recorded. Surgical findings were available for eight of the 10 patients, with histopathologic correlation between the bursal lining and hip capsule.
  
  
  RESULTS
  At cadaveric dissection, one specimen showed a bursa communicating with and extending from the posteroinferior aspect of the hip joint deep to the obturator externus tendon. In all 10 patients, MR images showed a hip joint effusion with a continuous bursa extending medially and displacing the obturator externus inferiorly. At surgery, a bursa was seen displacing the obturator externus muscle inferiorly and originating from the posteroinferior aspect of the hip joint in all eight patients. Results of pathologic analysis confirmed disease identical to the primary hip abnormality in all eight patients.
  
  
  CONCLUSIONS
  The obturator externus bursa is a potential posteroinferior communication of the hip joint capsule, can be a site of disease spread from the hip joint, and can be accurately identified with MR imaging.
authors.affiliation: Department of Medical Imaging, Mount Sinai Hospital and the University Health Network, 600 University Ave, Toronto, Ontario, Canada M5G 1X5.
authors.forename: Philip
authors.initials: P
authors.lastname: Robinson
authors.forename: Lawrence M
authors.initials: LM
authors.lastname: White
authors.forename: Anne
authors.initials: A
authors.lastname: Agur
authors.forename: Jay
authors.initials: J
authors.lastname: Wunder
authors.forename: Robert S
authors.initials: RS
authors.lastname: Bell
mesh_terms: D000328:Adult; D000368:Aged; D002061:Bursa, Synovial / Q000033:anatomy & histology* / Q000473:pathology*; D005260:Female; D006621:Hip Joint; D006801:Humans; D007592:Joint Diseases / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged