Medically intractable temporal lobe epilepsy in patients with normal MRI: surgical outcome in twenty-one consecutive patients

Abstract

Introduction: Abnormal MRI findings localizing to the mesial temporal lobe predict a favorable outcome in temporal lobe epilepsy surgery. The purpose of this study is to summarize the surgical outcome of patients who underwent a tailored antero-temporal lobectomy (ATL) with normal 1.5 T MRI. Specifically, factors that may be associated with favorable post-surgical seizure outcome are evaluated.

Methods: A retrospective analysis of the Rush University Medical Center surgical epilepsy database between 1992 and 2003 was performed. Patients who underwent an ATL and had a normal MRI study documented with normal volumetric measurements of hippocampal formations and the absence of any other MRI abnormality were selected for this study. Demographic information was collected on all patients. Seizure outcomes were evaluated using Engel's classification. A two-sided Fisher exact test with Bonferroni correction was performed in statistical analyses.

Results: Twenty-one (21) patients met the inclusion criteria of normal 1.5 T MRI and underwent a tailored temporal lobectomy. Mean age at time of surgery was 28 years (SD=8.1, range 11-44) and mean duration of the seizure disorder was 13.4 years (range 2-36). Risk factors for epilepsy included head injury (n=4), encephalitis (n=3), febrile seizures (n=2), and 12 patients had no risk factors. Pathological evaluation of resected tissue revealed no abnormal pathology in 12/21 patients (57%). After a mean 4.8 years follow-up post-surgical period, 15/21 (71%) patients were free of disabling seizures (Engel I outcome). At 8.3 years follow-up, 13/21 (62%) patients had similar results. Absence of prior epilepsy risk factors was the only statistically significant predictor of an Engel class I outcome (p<0.0022).

Conclusion: Patients with medically intractable epilepsy and normal MRI appear to benefit from epilepsy surgery. Absence of prior epilepsy risk factors may be a positive prognostic factor.