title: Ectopic insertion of the pectoralis minor tendon: inter-reader agreement and findings in the rotator interval on MRI.
abstract: OBJECTIVE
  To evaluate magnetic resonance imaging (MRI) observer variability to detect ectopic insertion of the pectoralis minor tendon (EIPMT) and to investigate changes in the rotator interval in patients with EIPMT using MRI.
  
  
  METHODS
  A total of 507 shoulder MRIs (male:female = 259:248; mean age, 55.4 years) were classified into 1) normal type insertion of the pectoralis minor tendon, 2) complete type EIPMT, and 3) partial type EIPMT independently by two radiologists. Inter-observer agreement was calculated using the kappa coefficient. Thickness of the fibrotic scar tissue in the subcoracoid triangle and humeral side axillary recess was measured. MRIs were reviewed by consensus with regard to the grade of fibrotic scar tissue proliferation in the rotator interval. Comparisons were made between normal and EIPMT and between partial and complete type EIPMT.
  
  
  RESULTS
  The incidence of EIPMT was 13.4% (complete type, 7.7%; partial type, 5.7%). Inter-observer agreement was substantial (κ = 0.775). Fibrotic scar tissue in the subcoracoid triangle was thicker, and the grade of fibrotic scar tissue proliferation in the rotator interval was higher in the EIPMT group than those in the control group. No significant difference was observed in the thickness of humeral side axillary recess. The thicknesses of fibrotic scar tissue in the subcoracoid triangle and humeral side axillary recess as well as the grade of fibrotic scar tissue in the rotator interval were not significantly different between complete and partial type EIPMT.
  
  
  CONCLUSIONS
  MRI enabled detection of EIPMT with substantial observer agreement. Patients with EIPMT show a high tendency for fibrotic scar tissue proliferation in the rotator interval.
authors.affiliation: Department of Radiology, Asan Foundation, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung 210-711, Korea.
authors.forename: Cheong-Bok
authors.initials: CB
authors.lastname: Lee
authors.affiliation: Department of Radiology, Asan Foundation, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung 210-711, Korea.
authors.forename: Soo-Jung
authors.initials: SJ
authors.lastname: Choi
authors.affiliation: Department of Radiology, Asan Foundation, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung 210-711, Korea.
authors.forename: Jae-Hong
authors.initials: JH
authors.lastname: Ahn
authors.affiliation: Department of Radiology, Asan Foundation, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung 210-711, Korea.
authors.forename: Dae-Sick
authors.initials: DS
authors.lastname: Ryu
authors.affiliation: Department of Radiology, Asan Foundation, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung 210-711, Korea.
authors.forename: Man-Soo
authors.initials: MS
authors.lastname: Park
authors.affiliation: Department of Radiology, Asan Foundation, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung 210-711, Korea.
authors.forename: Seung-Mun
authors.initials: SM
authors.lastname: Jung
authors.affiliation: Department of Radiology, Asan Foundation, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung 210-711, Korea.
authors.forename: Dong-Rock
authors.initials: DR
authors.lastname: Shin
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011859:Radiography; D017006:Rotator Cuff / Q000000981:diagnostic imaging* / Q000473:pathology; D012782:Shoulder / Q000000981:diagnostic imaging / Q000473:pathology; D013710:Tendons / Q000000981:diagnostic imaging* / Q000473:pathology; D055815:Young Adult
keywords: Ectopic insertion of the pectoralis minor tendon; MR; Rotator interval