Different effects of left anterior temporal lobectomy, selective amygdalohippocampectomy, and temporal cortical lesionectomy on verbal learning, memory, and recognition

In the present study, we investigated whether left hemisphere temporolateral resections and left selective amygdalohippocampectomy (SAH), have different effects on verbal learning, memory, and recognition. We evaluated patients who underwent standard two-thirds anterior temporal lobectomy including the hippocampus (TL, n = 22), SAH (n = 21), or temporolateral lesionectomy (TCL, n = 16). Patients with TL and SAH were matched with regard to temporomesial seizure onset and hippocampal pathology. Results were as follows: There were no preoperative group differences on any parameter of verbal learning and memory, but all groups showed impairment as compared with healthy subjects. Postoperatively, both TL and SAH led to a significant deterioration in measures of free recall (after distraction and a delay) and recognition. TL also led to a significant deterioration of immediate recall. No significant change in performance was observed after TCL. Seizure outcome did not account for these results. We conclude that left temporolateral and temporomesial resections have different qualitative rather than different quantitative effects on verbal memory in that they differentially affect short- and long-term aspects of verbal memory. The good neuropsychological outcome of pure lesionectomy (TCL) indicates that the postoperative loss in memory after TL and SAH is largely a function of the resection of still functioning tissue. Consequently, the data favor performance of individually tailored resections restricted to already nonfunctioning or malfunctioning brain tissue. Especially for mesial temporal lobe epilepsy, the surgical consequence would be to restrict the resection to mesiobasal structures.