Increased signal intensity in the normal glenoid labrum in MR imaging: diagnostic pitfalls caused by the magic-angle effect.
OBJECTIVE
To determine the effect of the magic-angle effect on the MR signal in the posterosuperior portion of the glenoid labrum.


METHODS
MR imaging of 15 arthroscopically evaluated shoulders, five with posterosuperior labrum injury and ten intact, was retrospectively reviewed. In the first part of the study, the signal intensity of the posterosuperior labrum on gradient-recalled echo (GRE) T2*-weighted axial images was correlated with the arthroscopy findings. The second part of the study was designed to illustrate the orientation-dependent signal that occurs in the posterosuperior labrum of three asymptomatic volunteers when imaged in the conventional supine position and in a position similar to Trendelenburg's. Another three volunteers were examined with GRE T2*-weighted axial images to assess the echo-time (TE)-dependent signal in the labrum.


RESULTS
The signal increase in the posterosuperior labrum was identified not only in the injured labra but also in nine of 10 intact labra. In the volunteers' studies, the signal in the posterosuperior labrum changed according to the examinees' positions (conventional supine or similar to Trendelenburg's) and according to TE.


CONCLUSIONS
Increased signal intensity due to the magic-angle effect may be misdiagnosed as a labrum injury. Awareness of this pitfall is particularly important in MR imaging of throwing athletes whose posterosuperior labra are frequently injured by posterosuperior glenoid impingement.
Sasaki
Taisuke
T
Department of Radiology, Hirosaki University School of Medicine, 5 Zaifu-cho, Hirosaki, Aomori 036-8562, Japan. sasatai@cc.hirosaki-u.ac.jp
Yodono
Hiraku
H
Prado
Gerson L M
GL
Saito
Yoko
Y
Miura
Hiroyuki
H
Itabashi
Yoko
Y
Ootsuka
Hironori
H
Ishibashi
Yasuyuki
Y
D000293:Adolescent; D000328:Adult; D001265:Athletic Injuries / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011187:Posture / Q000502:physiology; D012189:Retrospective Studies; D012782:Shoulder / Q000033:anatomy & histology*; D000070599:Shoulder Injuries