MRI in neurofibromatosis 1. The nature and evolution of increased intensity T2 weighted lesions and their relationship to intellectual impairment.

Thirty eight patients with neurofibromatosis 1 (NF1) had neurological examinations, intellectual assessments and MRI scans. Increased intensity lesions on T2 weighted images were found in 13 patients. These abnormalities were more common in patients aged under 18 years. The lesions occurred predominantly in the basal ganglia, brainstem and cerebellum, and were multiple in 11 patients. They did not produce symptoms or neurological deficit in any patient and did not enhance with gadolinium-meglumine-triamine-pentaacetic acid contrast medium (Gd-DTPA). In 2 patients, however, the abnormalities exerted mass effect distorting the brain and in 3 patients they occurred in conjunction with known gliomas. The lesions remained unchanged over a three year follow up period. The nature of the lesions is uncertain but the fact that they may produce mass effect and occur in association with gliomas suggests that they have malignant potential. There was no correlation between the presence of these abnormalities and intellectual impairment.