Medical and neuropsychological outcomes following epilepsy surgery

Abstract

The predictors of postoperative seizure freedom are not clearly defined in the literature. The proposed predictive variables, e.g., age at seizure onset, duration of epilepsy and gender, have not been uniformly agreed upon as useful prognostic tools and there is a need for a large-scale study to identify suitable predictors. An understanding of such predictors would be useful in counselling patients in the preoperative work-up, with a view to create an economically efficient healthcare service in which patients have optimal post-operative outcomes. Many scientific papers reduce postoperative outcomes to seizure freedom exclusively, with limited papers evaluating the impact of epilepsy surgery on depression and anxiety, which can also have profound impacts on quality of life. Epilepsy surgery grants researchers an opportunity to assess how brain functions are affected in the absence of particular cerebral structures. Knowledge of how brain function is affected by a lobectomy is important when consenting patients before surgery and informing them of possible post-operative deficits. One brain region in particular, the mesial temporal lobe, is of particular interest given it houses several structures that are alleged to help in memory formation and spatial cognition. However, there is contrasting evidence about the role of the mesial temporal lobe and the extent to which the mesial temporal lobe is involved in representing the environmental layout, the objects within in, as well as binding to the former to the latter (known as feature binding). In particular, it is not clear whether impairments of visual working memory are specifically spatial or rather generalize across visual feature dimensions (e.g., location, colour and shape) following focal temporal lobe lesions. This thesis attempts to address aforementioned gaps in the literature. Firstly, I provide a comprehensive literature review of epilepsy, including the role of epilepsy surgery in its management. Thereafter, I provide a systematic review of the literature exploring postoperative psychiatric and neuropsychological outcomes in patients who undergo epilepsy EPILEPSY SURGERY OUTCOMES 4 surgery in the absence of any pre-operative lesion/s on structural magnetic resonance imaging. Subsequently, I present original data showing the factors that predict post-operative seizure freedom in patients who have undergone resective surgery for epilepsy. The following chapter looks at the predictors of post-operative anxiety and depression in patients who have undergone resective epilepsy surgery. The penultimate chapter explores the factors that predict post-operative changes in working, visual and verbal memory in patients who have undergone resective epilepsy surgery. Finally, in a bench-side study conducted in Saudi Arabia, I studied a cohort of patients who had undergone temporal lobectomies for medically resistant temporal lobe epilepsy to establish whether impairments of visual working memory binding are specifically spatial or generalise across visual feature dimensions following focal mesial temporal lobe lesions. With regards to seizure freedom, I found that pre-operative generalised seizures are less likely to exhibit seizure-freedom than patients without pre-operative generalised seizures. I also found that patients with temporal lobectomies were more likely to exhibit seizure-freedom than patients with extra-temporal. Patients with a unilateral local focus on electroencephalogram and those with a lower frequency of pre-operative seizures were more likely to be seizure free at two years. With regards to anxiety, I showed that postoperative anxiety is improved if patients were female, underwent right-sided cerebral resections or had lateral temporal lobe resections. With regards to depression, patients with pre-operative generaliz