Reoperation after selective amygdalohippocampectomy: an MRI analysis of the extent of temporomesial resection in ten cases.

Background: Selective amygdalohippocampectomy (SAHE) yields 60-80% of patients with medically refractory mesial temporal lobe epilepsy seizure-free and seems to be equally effective compared to the more extended temporal lobe resections. The resection of the entire entorhinal cortex (EC) is of crucial importance to warrant complete seizure control for those patients. Thus, evidence of residual EC could be a predictor of a potentially successful reoperation in patients with recurrent seizures after SAHE. We performed an analysis of preoperative and postoperative magnetic resonance imaging (MRI) in patients who underwent a reoperation after an unsuccessful transsylvian SAHE to assess the presence of residual EC before reoperation and to determine whether certain anatomical variants may dispose patients to incomplete resection of EC.
Materials and Methods: Ten patients who underwent reoperation after SAHE for the recurrence of medically refractory seizures were studied. MRI after SAHE was assessed for the presence of residual EC using T2-weighted and inversion recovery sequences perpendicularly to the main axis of the hippocampus. The results were compared with a control group of ten patients who became seizure-free after SAHE. In the nine patients of the study group, the sulcal anatomy of the basal temporal lobe was graphically outlined and analysed on MRI scans performed before SAHE to characterise the sulcal boundaries of the EC.
Findings: Residual EC was found in nine of ten patients and was absent in the control group. After reoperation (median follow-up of 36.5 months), eight out of ten patients were completely seizure-free. In seven out of nine patients, a discontinuous course of the lateral sulcal boundaries of the EC was determined.
Conclusions: Careful analysis of MRI verified residual mesiotemporal structures in the majority of patients who became seizure-free after reoperation. Certain temporobasal sulcal patterns might dispose for a higher risk of incomplete resection of the EC. The study confirms that reoperation is an effective treatment modality for patients with recurrent seizures after transsylvian SAHE.