Abstracts

Rationale: Visual Field deficits following temporal lobe surgery have been reported in the literature. Hitherto there has been no mention of a left / right hemispheric asymmetry of the geniculocalcarine tracts in the temporal lobes. In this prospective study, we present our experience of visual field assessment in 105 cases undergoing temporal lobe surgery focussing on the laterality of the deficit. Methods: 105 cases undergoing temporal lobe surgery for epilepsy, between March 1998 and June 2004 were selected. 53 had a left-sided resection and 52 a right-sided resection. 91 patients had mesial temporal sclerosis, 3 gangliogliomas, 2 DNETs, 2 Neurocytomas, 2 cavernomas and 5 had other lesions. Pre and post-operative visual field tests were obtained using the Humphrey Esterman binocular functional test for all cases. The test was set to stimulus white III, with a single intensity of 10 DB on the background of 31.5 ASB for all patients. The mean age of patients was 35 years (range, 19-60 years). A minimum follow up period of 12 months post surgery was employed. Post-operative MRI scans were obtained on all patients and the extent of temporal lobe resection calculated manually for each. Results: Of the 105 cases, 16 patients had a visual field deficit post operatively, which was not present pre operatively; 12 following a left temporal lobectomy and 4 following a right-sided resection. In 4 patients the deficit was severe enough to preclude them from driving in the UK (3 left and 1 right sided resection). The Odds Ratio was calculated as 4.43 with a p value of 0.01356 employing Fisher exact test (CI=1.15-20.63). These results were correlated with the extent of tissue resection and this data will be presented.Conclusions: This study suggests, a hitherto unmentioned, left / right hemispheric asymmetry in the Geniculocalcarine tracts with field deficits being 4 times more likely following left sided temporal lobe resections compared with right sided resections. This has significant implications on counselling patients for these procedures. Tractography is likely to shed further light on this hypothesis.