Seizures in patients with supratentorial oligodendroglial tumours. Clinicopathological features and management considerations.

In this study of 34 consecutive histologically confirmed oligodendroglial brain tumours (15 oligoastrocytoma, 12 oligodendroglioma, 7 anaplastic oligodendroglioma) twenty five patients (75%) presented with symptoms related to seizures. Although the seizure incidence was lowest in anaplastic oligodendroglioma (57%) it was not statistically different from either pure (75%) or mixed (80%) oligodendroglial tumours. Patients with seizures had a significantly lower age (p < 0.001) at diagnosis (median 36 years) than those without seizures (57 years). The types of seizure disorder, that were present for a median of 15 months prior to surgery, were variable with 32% having generalised, 36% partial and 32% mixed patterns. There were no significant differences between either the type or incidence of seizures and the particular cerebral location of the oligodendroglial tumour. Twenty four of the patients presenting with seizures underwent surgery (5 stereotactic biopsy, 5 stereotactic guided resection and 14 conventional craniotomy and resection) without intraoperative electrocorticography (ECoG). Eighteen (75%) of these patients also had postoperative radiotherapy (40 to 54 Gy in 30 fractions. Following these treatments the percentage of patients fit free at 6, 12, and 24 months were 67%, 56%, and 53%, respectively. Median time to first post operative seizure was 32 weeks (range 5 weeks to 5.3 years). After a median follow up time of 30 months 20 of the 25 patients who presented with seizures were still alive. Eight (40%) were seizure free and three other patients (15%) had experienced less than three postoperative seizures in follow-up periods ranging from 42 to 62 months. Although the numbers of patients on preoperative (87%) and postoperative (83%) anticonvulsant medications were similar, some had their medications either withdrawn (17%) or reduced (4%) whilst others had it introduced (12%) after interventional management. Only five (20%) patients who presented with seizures, compared to 6 (67%) who had not presented with seizures had died during median follow-up of 28 months. Three of nine patients (33%), who were initially seizure free, developed seizures between 25 and 36 months after initial surgery and radiotherapy. This study (i) confirms the high incidence of epilepsy in supratentorial oligodendroglial tumours; (ii) has shown that seizures associated with these tumours are significantly more common in younger patients; (iii) suggests that younger age, but not the presence of seizures, is a significant independent prognostic variable; (iv) that seizure control following a second operation is generally disappointing and (v) suggests that tumour resection and radiotherapy often facilitate control of the seizures by anticonvulsants. Because of the multiple clinicopathological and management variables involved a prospective study would be required to assess the optimal management of patients with seizure disorders associated with oligodendroglial brain tumours.