SURGICAL OUTCOME IN OCCIPITAL LOBE EPILEPSY - IMPLICATIONS FOR PATHOPHYSIOLOGY

Medically refractory occipital lobe epilepsies are increasingly treate d with surgery, but outcome and its relationship to etiology, patholog ical substrate, occipital lobe location, surgical approach, and electr oclinical features have not been systematically investigated in a subs tantial 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 su rgical procedure, pathology, clinical seizure characteristics, seizure onset and termination locations, and localization of interictal spike s. Most patients had developmental abnormalities (14) or tumors (13, a ll gliomas). Developmental abnormalities consisted of focal cortical d ysplasia (5), heterotopia (2), hamartoma (3), cortical duplication (1) , polymicrogyria (1), Sturge-Weber syndrome (1), and tuberous sclerosi s (1). There was 1 patient with a vascular abnormality, 1 with chronic inflammatory changes, 4 with gliosis, 1 with cerebral ossification, a nd 1 with normal pathology. Developmental abnormalities had significan tly 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 s urgical procedure. Pathological groups did not significantly differ wi th respect to location within the occipital lobe (overall medial [50%] or lateral [38%]); clinical seizure characteristics referable to spec ific lobe (occipital [14%], temporal [34%], frontal [23%], more than o ne type [29%]); electroencephalographic localization (to occipital [17 %], temporal [27%], or other/multifocal locations [56%]); or intracran ial ictal onset or termination location. Electroclinical variables wer e also unrelated to the occipital lobe location of abnormality. Surgic al outcome was not predicted by surgical approach (lesion excision wit h margins or lobectomy). The main pathological substrates of uncontrol led occipital lobe epilepsy are gliomas and developmental abnormalitie s. Whereas resection of occipital lobe tumors associated with chronic epilepsy produces nearly uniform seizure control, outcome after resect ion of occipital lobe developmental abnormalities is less uniform.