title: Magnetic resonance histologic correlation in rotator cuff tendons.
abstract: OBJECTIVE
  To relate histologic changes in rotator cuff tendons to the appearance on T1-weighted as well as fat-suppressed T2-weighted and proton density-weighted magnetic resonance imaging (MRI) sequences.
  
  
  METHODS
  T1-weighted, fat-suppressed T2-weighted and fat-suppressed proton density-weighted sequences of 18 cadaveric shoulders were acquired. The supraspinatus, infraspinatus, and subscapularis tendons were evaluated histologically. Twenty-six abnormalities were found in 23 of 37 tendons. In addition, histologically normal tendon parts (n = 32), including three segments with normal histology but abnormal MR signal, considered to represent magic angle effects, were defined. All regions of interest (ROIs) were evaluated by two musculoskeletal radiologists independently and blinded to histology.
  
  
  RESULTS
  In the 26 areas with anatomically intact tendons but abnormal histological findings mucoid degeneration (n = 13), chondroid metaplasia (n = 11), fatty infiltration (n = 1), and foreign-body granuloma (n = 1) after tendon suture were found. Compared to normal tendon, mucoid degeneration was hyperintense on T2-weighted fat-suppressed (P = 0.007) and on proton density-weighted fat-suppressed images (P = 0.006). Chondroid metaplasia was hyperintense compared to normal tendon in all sequences (P < 0.05). Mucoid degeneration was hypointense compared to chondroid metaplasia on T2-weighted fat-suppressed images (P = 0.038) and hypointense compared to magic angle artifacts on T1-weighted images (P = 0.046).
  
  
  CONCLUSIONS
  Chondroid metaplasia of rotator cuff tendons appears to be more common than expected. Both mucoid degeneration and chondroid metaplasia may explain increased tendon signal on MR images of the rotator cuff.
authors.affiliation: Department of Radiology, Orthopedic University Hospital Balgrist, Zurich, Switzerland. florian.buck@gmail.com
authors.forename: Florian M
authors.initials: FM
authors.lastname: Buck
authors.forename: Holger
authors.initials: H
authors.lastname: Grehn
authors.forename: Monika
authors.initials: M
authors.lastname: Hilbe
authors.forename: Christian W A
authors.initials: CW
authors.lastname: Pfirrmann
authors.forename: Silvana
authors.initials: S
authors.lastname: Manzanell
authors.forename: Juerg
authors.initials: J
authors.lastname: Hodler
mesh_terms: D002102:Cadaver; D015745:Granuloma, Foreign-Body / Q000175:diagnosis; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015588:Observer Variation; D017006:Rotator Cuff / Q000473:pathology*; D000070636:Rotator Cuff Injuries; D013708:Tendon Injuries / Q000175:diagnosis*; D013710:Tendons / Q000473:pathology*