Object: Cortical malformations and inflammatory encephalopathy are among common etiologies for medically refractory epilepsy in children. On rare occasions, lesions can affect an entire cerebral hemisphere while sparing the other; the 2 processes that can manifest in this manner are hemimegalencephaly (HME) and Rasmussen's encephalitis (RE). Although the clinical course and radiological appearance between the 2 disorders are distinct, there is occasional overlapping pathology between RE and cortical migration disorders. One question that arises from these observations is whether RE and HME, diseases with holohemispheric involvement but apparently different etiologies, have any overlapping characteristics.
Methods: The authors performed a retrospective review of all patients with presumed diagnosis of HME or RE who underwent hemispherectomy at University of California, San Francisco, and reviewed their clinical presentation, imaging, and pathology data.
Results: The authors present the clinicopathological features of 14 pediatric patients with unilateral holohemispheric lesions associated with medically refractory epilepsy. Radiological and pathological assessment classified 7 of the patients as having hemimegalencephaly, while the other 7 were diagnosed as having RE. Four of the patients had unusual features suggestive of overlapping developmental and inflammatory (dual) pathology. All patients underwent hemispherectomies. Eight patients (57%) became seizure free (Engel Class I), 5 patients (36%) had rare seizures (Engel Class II), and 1 patient had significant seizure reduction (Engel Class III).
Conclusions: Based on this case series, HME and RE can be distinguished on the basis of their radiological and histological appearance, even though some cases may have overlapping features. Hemispherectomy was effective at eliminating seizures for both HME and RE.
Keywords: EEG = electroencephalography; EPC = epilepsia partialis continua; FCD = focal cortical dysplasia; HME = hemimegalencephaly; RE = Rasmussen's encephalitis; Rasmussen's encephalitis; anatomic hemispherectomy; cortical dysplasia; cortical malformation; epilepsy surgery; functional hemispherectomy; hemimegalencephaly; inflammatory encephalitis; polymicrogyria; seizures.