Hamartomas in the setting of chronic epilepsy: a clinicopathologic study of 13 cases

Hamartomas are a poorly defined group of lesions and a rare cause of chronic epilepsy. We studied 13 patients, nine males and four females, whose cause of seizures was attributed to a hamartoma. The patients ranged in age from 6 to 33 years (mean, 21 years). Seizure duration before surgery ranged from 1.5 to 22 years (mean, 10 years). Seven hamartomas were located on the right side and six on the left. Six were located in the frontal lobe, five in the temporal lobe, and two in the occipital lobe. Twelve patients underwent gross total resection of the lesion and one a partial resection. All consisted of a circumscribed, disorganized collection of glial cells, primarily astrocytes. Rarely a neuronal component was admixed. One lesion contained an increased number of small blood vessels. Eight (62%) hamartomas contained eosinophilic granular bodies, and focal microcalcification was observed in three lesions (23%). Adjacent cortical architectural abnormalities (cortical dysplasia) were identified in eight (62%) resection specimens. Necrosis, mitoses, and prominent cytological atypia were absent in all lesions. Differential diagnostic considerations include low grade astrocytoma, ganglioglioma, dysembryoplastic neuroepithelial tumor, and cortical dysplasia. Postoperatively, 10 patients (77%) had complete resolution or greater than 90% reduction of seizure frequency. Two patients (16%) developed recurrent seizures 8 and 13 months postoperatively. One patient who underwent a partial resection showed no decrease in seizure frequency. No lesion recurrence on imaging studies has been observed in the 12 patients who underwent gross total resection of their hamartoma during 1 to 51 months (mean, 14 months) follow-up. We conclude that hamartomas seen in the setting of chronic epilepsy are generally low-grade lesions that respond well to gross total resection. Circumscription and lack of significant cytological atypia help distinguish these lesions from other neoplastic causes of epilepsy. Hamartomas that arise in the setting of chronic epilepsy appear to be associated with increased incidence of cortical architectural abnormalities (cortical dysplasia) and represent maldevelopmental lesions.