MRI Brain Findings in Adults with Lesional Refractory Epilepsy and Correlation to Surgical Outcome

Abstract

Introduction: Refractory epilepsy which is defined as failure of adequate trials of two tolerated, appropriately chosen and used antiepileptic drug schedules (whether as monotherapies or in combination) to achieve sustained seizure freedom is common in patients with structural brain lesions including acquired disorders and genetic abnormalities. High resolution Magnetic Resonance Imaging MRI of the brain has proven its precision as a diagnostic tool for recognition of different structural lesions underlying medically intractable seizures. Objective: To recognize common MRI lesions in a series of adult patients with refractory epilepsy admitted to the epilepsy monitoring unit at Prince Sultan Military Medical City PSMMC for pre surgical evaluation for epilepsy surgery with correlation to surgical outcome and to compare our local data with the international literature. Material and methods: 245 patients (100 Males and 145 Females; 14-53 years) with refractory epilepsy were included in this retrospective analysis. They presented with partial with or without complex partial seizures 112 (46.0%), partial with secondary generalized tonic clonic seizures 76 (31.0%) or generalized seizures in 57 (23.0%) of patients. Clinical diagnosis of epilepsy and seizure classification were based on the revised criteria of the International League Against Epilepsy ILAE. Structural neuroimaging MRI brain, functional neuroimaging which include Interictal Fluorodeoxyglucose Positron Emission Computed Tomography FDG-PET, Ictal Technetium-99m hexamethyl-propylene amine oxime Single Photon Emission Computed Tomography 99 m HMPAO SPECT, Electroencephalography EEG recording, epilepsy history and neurological examination were performed. MRI brain imaging epilepsy protocol used a 1.5 or 3 Tesla MRI scanner. All patients included in this study received appropriate epilepsy surgery and post-operative seizure control was followed in the epilepsy clinic with six-month post-operative inter ictal EEG, follow up MRI brain after epilepsy surgery were performed in all patients and 50 patients had additional video-EEG recording postoperative during the follow up period. Epilepsy surgery seizure control outcome was classified according to Engel Classification system. All patients were followed for at least two years post-operatively to assess seizure control. Pre-operative MRI diagnosis was correlated with the epilepsy surgery seizure control outcome. Results: MRI detected different structural brain abnormalities in 245 (100%) patients, including temporal lobe location in 142 (58%) patients, frontal lobe location in 74 (30%) patients and parieto-occipital lobes location in 29 (12%) patients. On MRI hippocampal sclerosis HS is diagnosed in 86 (35%) patients, cerebral tumors in 74 (30%) patients and among the cerebral tumors MRI suggested the diagnosis of developmental tumors that is; glio-neural tumors in 45 out of 74 (61%) of tumor patients, malformations of cortical development MCD in 42 (17%) patients, vascular malformations in 15 (6%) patients, dual pathologies in 12 (5%) patients and remote gliotic lesions in 16 (7%) patients. The histopathological diagnosis confirmed the MRI brain diagnosis in all included patients. At 2 years of post-operative follow-up 196 (80%) patients were classified as Engel Class I, 37 (15%) patients Engel Class II, 6 (3%) patients Engel Class III and 6 (3%) patients as Class IV seizure freedom. In the class IV group two patients failed epilepsy surgery because they had high grade astrocytoma with postoperative tumor recurrence and four patients failed epilepsy surgery due to incomplete resection of epileptogenic lesions. Patients with MRI diagnosis of HS 82 out of 86 (95%) patients, low grade tumor 59 out of 74 (80%) patients and vascular malformation 12 out of 15 (80%) had best epilepsy surgery outcome. Patients with high grade tumors 2 out 3 (67%) patients and incomplete surgical resection of epileptogenic lesions 4 out of 5 (80%) patients had the worst epilepsy surgery outcome. Conclusion: This study revealed that MRI brain structural lesions were commonly associated with refractory epilepsy. Temporal lobe structural brain lesions were most common lesions in adult epilepsy patients with refractory epilepsy referred for epilepsy surgery. The presence of HS, low grade tumors and vascular malformations correlated with best surgical outcome while high grade tumors and incomplete surgical resection of the lesions correlated with worst surgical outcome. Our results were consistent with the international reported literature.