Optic radiation mapping reduces the risk of visual field deficits in anterior temporal lobe resection

Anterior temporal lobe resection (ATLR) is often complicated by superior quadrant visual field deficits (VFDs) because of damage to the anterior portion of the optic radiation (Meyer's loop). This study reports the evaluation of optic radiation mapping in protecting against VFDs in the ATLR. We retrospectively analyzed 52 patients with medically refractory temporal lobe epilepsy undergoing ATLR between January 2012 and December 2013. The surgical operations in Group I (n=32) were performed with the modified ATLR, and the operations in Group II (n=20) were aided by combining optic radiation mapping by diffusion tensor imaging, microscopic-based neuronavigation and the intraoperative magnetic resonance imaging (iMRI) technique. A t-test was used to compare the size of ATLR, and a chi square test was applied for the postoperative VFD and seizure outcomes. The optic radiation was reconstructed in all patients in Group II. The size of ATLR was 5.11±1.34 cm (3.3-8 cm), and 3.24±0.75 cm (2.2-4.8 cm) in Groups I and II, respectively; the size of ATLR was significantly smaller in Group II (F=9.803; P=0.00). The visual fields assessment by the Humphrey Field Analyser 30-2 test showed 27 patients (84.4%) in Group I suffered VFDs at 3 months post-operation, whereas only eight patients (40.0%) in Group II showed VFDs (Pearson chi square =11.01; P=0.001). The 6-month follow-up survey showed that 90.6% of patients in Group I achieved a good outcome (Engel class I-II), outperforming 85.0% in Group II, however, there was no statistically significant difference (chi square =0.382, P=0.581). This techniques of combining optic radiation mapping, microscopic-based neuronavigation and iMRI aided in precise mapping and hence reduction of the risk of visual field deficits in ATLR. The size of ATLR guided by optic radiation mapping was significantly smaller but the seizure outcome was not significantly affected.