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 nasopharyngeal carcinoma. These characteristics may serve to differentiate radiation-induced changes from intracranial tumor recurrence. MATERIALS AND METHODS. We reviewed the imaging records of 1916 patients with nasopharyngeal carcinoma examined over a 5-year period. Forty-seven patients (2.5%) had temporal lobe changes. Thirty-four patients underwent CT (55 examinations), and 26 patients underwent MR imaging (32 examinations). Thirteen patients underwent CT and MR imaging. These studies were independently analyzed according to imaging technique and were categorized as follows: location of lesions, characteristics of gray or white matter changes, and patterns 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 patterns were noted: ill-defined contrast enhancement in 27 patients (79%); solid enhancement in six patients (18%); and ring enhancement in one patient (3%). On MR imaging, 11 patients (42%) had unilateral lesions, and 15 patients (58%) had bilateral lesions. Simultaneous gray and white matter lesions were noted in 17 patients (65%), and nine patients (35%) had lesions localized to the gray matter. Three patients (6%) had cerebral atrophy, and two patients (4%) had encephalomalacia. CONCLUSION. The temporal lobes show characteristic CT and MR imaging features after radiation injury. Familiarity with these changes may assist in differentiating temporal lobe changes from progressive nasopharyngeal carcinoma.