Objective: To explore several characteristics of patients with pharmacoresistant epilepsy without distinct lesions on magnetic resonance images (MRI(-)), who account for a relevant proportion of presurgical patient cohorts.
Design: Retrospective case series.
Setting: University epilepsy center.
Patients: A cohort of 1200 patients who had comprehensive presurgical assessment from January 1, 2000, through December 31, 2006.
Main outcome measures: Frequency of MRI(-) patients in the total presurgical cohort, seizure-free outcome rates in patients who had surgery and those who did not, outcome predictors, and spatial properties of epileptogenic areas in MRI(-) patients with epilepsy. All MRI(-) patients were retrospectively analyzed. Presurgical MRIs were reevaluated for subtle cortical dysplasias by postprocessing and visual reassessment.
Results: One-hundred ninety MRI(-) patients were identified (16% of all presurgical candidates); 29 (15%) had surgery. Eleven (38%) became seizure free (including those with auras only; 45%). Surgical therapy was more frequently offered to MRI(+) patients (76%; P < .001), and their outcome was also superior (66% seizure-free; P = .001). The seizure-free rate of 16% in MRI(-) patients who did not have surgery was, however, inferior to that of the MRI(-) patients who did (P = .008). Nine MRI(-) patients who had surgery had distinct histopathological lesions, 8 of which turned out to be retrospectively detectable on presurgical MRI. Seven of the MRI(-) but histopathologically lesional patients became seizure free compared with only 4 of 20 patients without histopathological lesions (P = .003). Three-fifths of the histopathologically nonlesional patients had multifocal or extensive epileptogenic areas.
Conclusions: Patients with epilepsy who are MRI(-) can be successfully treated with surgery. Improved sensitivity of MRI will improve the outcomes of presurgically studied patients. Surgical failures in patients without histopathological lesions mostly result from extensive epileptogenic areas.