A 54-year-old man had a slowly progressive bilateral brachial plexopat
hy 17 months after surgery and radiation therapy for a stage IV suprag
lottic carcinoma, MR imaging at presentation showed a symmetric patter
n of parascalene and interscalene hyperintense signal on T2-weighted i
mages and after contrast enhancement. Although hyperintense signal has
been more often associated with recurrent tumor than with delayed rad
iation injury or fibrosis, the location and pattern of the signal abno
rmalities suggested a diagnosis of radiation-induced plexopathy. This
diagnosis was confirmed by the relative stability of the neurologic an
d MR findings 30 months after treatment.