Radiation-induced temporal lobe changes: CT and MR imaging characteristics

OBJECTIVE. This article documents the CT and MR imaging characteristics of patients with temporal lobe changes after radiation therapy for nasopharyng eal carcinoma. These characteristics may serve to differentiate radiation-i nduced changes from intracranial tumor recurrence. MATERIALS AND METHODS. We reviewed the imaging records of 1916 patients wit h nasopharyngeal carcinoma examined over a 5-year period. Forty-seven patie nts (2.5%) had temporal lobe changes. Thirty-four patients underwent CT (55 examinations), and 26 patients underwent MR imaging (32 examinations). Thi rteen patients underwent CT and MR imaging. These studies were independentl y analyzed according to imaging technique and were categorized as follows: location of lesions, characteristics of gray or white matter changes, and p atterns of late changes. RESULTS. On CT, 12 patients (35%) had unilateral temporal lobe changes, and 22 patients (65%) had bilateral temporal lobe changes. The following patte rns were noted: ill-defined contrast enhancement in 27 patients (79%); soli d enhancement in six patients (18%); and ring enhancement in one patient (3 %). On MR imaging, 11 patients (42%) had unilateral lesions, and 15 patient s (58%) had bilateral lesions. Simultaneous gray and white matter lesions w ere noted in 17 patients (65%), and nine patients (35%) had lesions localiz ed to the gray matter. Three patients (6%) had cerebral atrophy, and two pa tients (4%) had encephalomalacia. CONCLUSION. The temporal lobes show characteristic CT and MR imaging featur es after radiation injury. Familiarity with these changes may assist in dif ferentiating temporal lobe changes from progressive nasopharyngeal carcinom a.