MRI assessment of the anatomy of optic radiations after temporal lobe epilepsy surgery

Abstract

Objective: The aim of this study was to determine the course of the temporal optic radiations.

Material and methods: Eighteen patients were included in this prospective study. All of them underwent a temporal lobectomy for epilepsy, including the mesial temporal structures and a variable extent of lateral neocortex (from 2 to 7 cm behind the temporal tip). An MRI was performed 2 months postoperatively, allowing assessment of the extent of lateral resection. Postoperative visual fields were determined by automatic static perimetry (ASP).

Results: (1) No patient complained of a disabling visual field deficit. (2) ASP, a highly sensitive technique, however, detected postoperative visual field deficits in 83% of patients, confined to the superior homonymous field contralateral to the resection. (3) A strong correlation was found between the presence of a visual field deficit and the extent of laterotemporal resection. (4) The smallest anteroposterior resection resulting in a field defect was limited to 20 mm from the temporal tip.

Conclusion: (1) This study confirms a strong correlation between postoperative visual field deficits and the extent of lateral neocortical temporal resection. (2) The anterior limit of Meyer's loop is likely to be located more rostrally than previously believed. (3) Despite this, lateral resection remains useful in some cases for seizure control.