Abstracts

RATIONALE:_Mesial temporal sclerosis (MTS) is the most common cause of temporal lobe epilepsy, and identification of MTS on 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. METHODS:_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. MRI had to be performed for vague non-specific symptoms (headaches, dizziness) or screening for metastases or cerebral aneurysms. 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 3 planes on 1.5 T systems. Estimates of hippocampal volume were made exclusively on T2-weighted images unless none were available. In those cases, estimates were made on T1-weighted images post contrast. All images afforded adequate visualization of the mesial temporal lobe structures. MRI diagnosis of MTS was based on standard visual diagnostic criteria analyzing 1) Hippocampal atrophy, 2) Increased hippocampal T2 signal, and 3) Temporal horn enlargement (1, 2). RESULTS:_We reviewed 375 charts, and 204 met the inclusion criteria. Of the 204, 31 (15%) had abnormal and asymmetric mesial temporal structures consistent with a diagnosis of unilateral MTS. Sixteen (7.8%) met at least 2 of the diagnostic criteria, and 5 (2.4%) met all 3 criteria. CONCLUSIONS:_While this was not a normal population, it was an acceptable approximation since the symptoms were clearly irrelevant to MTS, and the patients definitely had no history of seizures. We conclude that there are some false positives and that MRI evidence for MTS is only meaningful in the proper clinical context. REFERENCES 1. Kuzniecky R et al. Predictive value of MRI in temporal lobe epilepsy surgery. Arch Neurol 1993;50:65-69. 2. Jackson GD et al. Hippocampal sclerosis can be reliably detected by magnetic resonance imaging. Neurology 1990;40:1869-75 .