MRI evidence of mesial temporal sclerosis in subjects without seizures

The identification of mesial temporal sclerosis (MTS) on magnetic resonance imaging (MRI) is critical in the evaluation for temporal lobectomy. The purpose of this study was to estimate the prevalence of MTS by MRI in the general population. We reviewed the charts of patients undergoing MRI scans over an 18-month period. In order to be included, patients had to have no history of seizures, and the MRIs had to read as 'normal'. Patients were excluded if there was a history of seizures, mental illness, or alcohol abuse, and if they had a family history of seizures. Ages had to be from 5 to 50 years. All patients had MRI scans performed in three planes on 1.5 T systems. MRI diagnosis of MTS was based on standard visual diagnostic criteria analyzing: (1) hippocampal atrophy and (2) increased hippocampal T2 signal. Out of 375 charts reviewed, 204 met the inclusion criteria. Of the 204, 29 (14%) had abnormal and asymmetric mesial temporal structures consistent with a diagnosis of unilateral MTS. Nineteen (9.3%) had hippocampal atrophy only, two (1%) had T2 signal abnormalities, and eight (4%) met both criteria. There are some 'false positives' and MRI evidence for MTS is only meaningful in the proper clinical context.