Surgical outcome in occipital lobe epilepsy: implications for pathophysiology

Medically refractory occipital lobe epilepsies are increasingly treated with surgery, but outcome and its relationship to etiology, pathological substrate, occipital lobe location, surgical approach, and electroclinical features have not been systematically investigated in a substantial group of patients. Thirty-five patients who underwent surgery for intractable occipital lobe seizures were retrospectively evaluated. Outcome and occipital lobe location were analyzed with respect to surgical procedure, pathology, clinical seizure characteristics, seizure onset and termination locations, and localization of interictal spikes. Most patients had developmental abnormalities (14) or tumors (13, all gliomas). Developmental abnormalities consisted of focal cortical dysplasia (5), heterotopia (2), hamartoma (3), cortical duplication (1), polymicrogyria (1), Sturge-Weber syndrome (1), and tuberous sclerosis (1). There was 1 patient with a vascular abnormality, 1 with chronic inflammatory changes, 4 with gliosis, 1 with cerebral ossification, and 1 with normal pathology. Developmental abnormalities had significantly worse outcome (45% excellent/good) than tumors (85% excellent/good). In the developmental group, low-grade focal cortical dysplasias had better outcome than heterotopia and hamartoma regardless of type of surgical procedure. Pathological groups did not significantly differ with respect to location within the occipital lobe (overall medial [50%] or lateral [38%]); clinical seizure characteristics referable to specific lobe (occipital [14%], temporal [34%], frontal [23%], more than one type [29%]); electroencephalographic localization (to occipital [17%], temporal [27%], or other/multifocal locations [56%]); or intracranial ictal onset or termination location. Electroclinical variables were also unrelated to the occipital lobe location of abnormality. Surgical outcome was not predicted by surgical approach (lesion excision with margins or lobectomy). The main pathological substrates of uncontrolled occipital lobe epilepsy are gliomas and developmental abnormalities. Whereas resection of occipital lobe tumors associated with chronic epilepsy produces nearly uniform seizure control, outcome after resection of occipital lobe developmental abnormalities is less uniform.