Abstracts

Rationale: Amongst patients who undergo a temporal lobectomy for refractory seizures, those who have a foreign tissue lesion have a higher probability of post-operative seizure freedom than patients with other pathologies. However, there is very little information about post-lobectomy outcome for the specific lesion types within this fairly broad category. We aimed to ascertain whether post-operative seizure recurrence differed according to lesion type. Methods: All patients who underwent anterior temporal lobectomy at Austin Health, Australia, between 1979 and 2006 and who had a temporal lobe foreign tissue lesion were included. Pathology specimens were reviewed by a neuropathologist and divided into five groups: dysembryoplastic neuroepithelial tumour (DNET) (n=17), ganglioglioma (n=16), astrocytoma/oligodendroglioma (n=7), vascular malformations (n=11) and cysts (n=3). Recurrence was defined as a post-operative complex partial seizure ± secondary generalisation, and the time from surgery to first recurrence or last follow-up (if seizure free) was calculated. The rate of recurrence for each lesion type in the foreign tissue lesion group was calculated, and rate ratios were used to compare recurrence rates between groups. Results: Median follow-up was 14.5 yrs (IR 12-18, range 2.4 to 27 years). There were a total of 561 person years in the analysis. Recurrence rate (per 100 person years) was 2.9 for those with DNET, 4.2 for those with ganglioglioma, 5.1 for astrocytoma/oligodendroglioma and 9.7 for vascular malformation. The three patients with cysts remained seizure free (16 to 24 years of follow-up), these were not included in further calculations. As the recurrence rates for vascular malformations were noticeably higher, rate ratios were calculated using this group as the reference group. Compared to the recurrence rate for those with vascular malformations, patients with DNET had 0.30 (95%CI, 0.10-0.93; p=0.036) times the rate of recurrence. Those with ganglioglioma had 0.43 (95%CI, 0.15-1.18; p=0.1) times the rate and patients with astrocytoma/ oligodendroglioma had 0.53 (95%CI, 0.16-1.7; p=0.29) times the rate of recurrence compared to patients with vascular malformations. Compared to these three groups combined, patients with vascular malformations had a rate of recurrence that was 2.5 times (95%CI 1.08-5.9; p=0.03) the rate experienced by the other pathologies. Conclusions: Patients with vascular malformations have a higher rate of seizure recurrence after temporal lobectomy than patients with other lesion pathologies. This may be related to residual hemosiderin after surgery. These findings may assist pre-surgical prognostication.