Abstracts

RATIONALE: Patients with normal preoperative MRI have been suggested to have a less favorable prognosis for seizure free outcome after epilepsy surgery compared to patients with a focal lesion such as hippocampal sclerosis, low grade tumor, or malformation of cortical development. The results from previous series have been variable.The goal of this study is to determine seizure outcome after epilepsy surgery in pediatric and adult patients with normal preoperative MRI.
METHODS: We retrospectively reviewed patients with normal preoperative MRI who underwent cortical resection for refractory epilepsy at The Cleveland Clinic Foundation between 1994 and 2001. MRIs were assessed as normal by a neuroradiologist prior to surgery, and then reviewed for this study by 2 blinded epileptologists with a blinded neuroradiologist further reviewing any questionable scans. Clinical, laboratory, and outcome data were collected from medical records. The duration of postoperative follow-up was 1 to 5 years (mean 28 months).
RESULTS: The 23 patients were 3 to 46 (mean 20) years of age at the time of surgery. Preoperative seizure frequencies tended to be high: 61% of patients had daily seizures (30% with [gt]5 seizures per day), while remaining patients had weekly seizures. An average of 6 antiepileptic drugs failed before surgery. Resections were frontal (n=19), temporal (n=12), central (n=1), or multilobar (n=1). Histopathologic analysis of resected tissue revealed cortical dysplasia (n=23; 7 [78%] of frontal cases) or nonspecific findings such as mild subpial gliosis (n=13; 9[75%] of temporal cases). Seizure outcome was similar at one year and at latest follow-up. 43% of patients were free of seizures at latest follow-up (n=10), and another 22%(n=5) had [gt]90% improvement with 1 seizure per month to 2 seizures per week. Seizure freedom was achieved for 5 patients (50%) after frontal lobe resections and for 5 patients (42%) after temporal lobe resection. 50% of patients with cortical dysplasia on histopathology were seizure free, compared to 38% of patients with nonspecific histopathology. More localized focal abnormalities on scalp EEG, subdural EEG, PET, and SPECT, did not further improve, in this highly selected patient population, the likelihood of becoming seizure free (41%, 40%, 37%, 50%, respectively)
CONCLUSIONS: All of these patients with normal preoperative MRI were selected for surgery based on strong features from other presurgical tests suggesting a focal epileptogenic zone, in the setting of a high seizure burden and medical intractability. Within this highly selected group, seizure outcome was favorable for the majority of patients, although the percentage of seizure free patients was lower than that typically seen in the setting of some focal MRI lesions such as low-grade tumor or hippocampal sclerosis.