Frequency, prognosis and surgical treatment of structural abnormalities seen with magnetic resonance imaging in childhood epilepsy

Abstract

The epidemiology of lesions identified by magnetic resonance imaging (MRI), along with the use of pre-surgical evaluations and surgery in childhood-onset epilepsy patients has not previously been described. In a prospectively identified community-based cohort of children enrolled from 1993 to 1997, we examined (i) the frequency of lesions identified by MRI; (ii) clinical factors associated with 'positive' MRI scans; and (iii) the utilization of comprehensive epilepsy evaluations and neurosurgery. Of the original cohort of 613 children, 518 (85%) had usable MRI scans. Eighty-two (16%) had MRI abnormalities potentially relevant to epilepsy ('positive' scans). Idiopathic epilepsy syndromes were identified in 162 (31%) of whom 3% had positive scans. The remainder had non-idiopathic epilepsy syndromes of which 22% had positive MRI findings. Multiple logistic regression analysis identified non-idiopathic epilepsy and abnormal motor-sensory (neurological) examinations as predictors of a positive MRI scan. Of the non-idiopathic patients with normal neurological exams and who were not pharmacoresistant, 10% had positive MRI scans, including four patients with gliomas. Evaluations at comprehensive epilepsy centres occurred in 54 pharmacoresistant cases. To date 5% of the imaged cohort or 8% of non-idiopathic epilepsy patients have undergone surgical procedures (including vagal nerve stimulator implantation) to treat their epilepsy (n = 22) or for tumours (n = 6) without being drug resistant. Applying our findings to the general population of children in the USA, we estimate that there will be 127/1 000 000 new cases per year of pharmacoresistant epilepsy, and 52/1 000 000 childhood-onset epilepsy patients undergoing epilepsy evaluations. In addition, approximately 27/1 000 000 will have an epilepsy-related surgical procedure. These findings support recommendations for the use of MRI in evaluating newly diagnosed paediatric epilepsy patients, especially with non-idiopathic syndromes, and provide estimates on the utilization of comprehensive evaluations and surgery.

Figure 1

(A) Example of a patient with pharmacoresistant epilepsy with EEG suggesting a right temporal focus. MRI shows increased T2 signal in the right hippocampus (arrow). This is the only case so far of a patient with MRI MTS whose seizures are not controlled by drugs and with a concordant EEG. (Table 2; Case #73). (B) Example of another patient with TLE whose seizures are controlled by drugs. Interictal EEG shows greater left than right abnormalities. MRI discloses left HA with some T2 signal changes (arrow; Table 2; Case #69). (C) This patient has electro-clinical findings most consistent with benign rolandic epilepsy including characteristic epileptiform discharges activated during sleep. MRI revealed a cyst in the right mesial temporal lobe (arrow). The MRI finding was considered coincidental in this particular clinical context (Table 2; Case #67). (D) This patient has childhood absence epilepsy, a diagnosis based on the characteristic 3 Hz generalized spike and wave on EEG associated with absence spells induced with hyperventilation. MRI disclosed evidence of an old left intraventricular haemorrhage (arrow) and this patient also has a mild right hemiparesis. The MRI lesion was considered coincidental in the clinical context (Table 2; Case #26).