MRI features of hemispheric malformations of cortical development (MCD) were correlated with post-hemispherectomy seizure outcome in 13 children treated at The Cleveland Clinic Foundation, OH. At surgery, 11 patients were between 4 months and 2 years of age, and two were aged 8 and 12 years. MRIs were classified in 3 groups: 1) hemimegalencephaly (6 patients); 2) hemispheric MCD with partial cortical sparing (4 patients); 3) hemispheric MCD with atrophy (3 patients). All patients had hemiparesis and developmental delay, and 6 of 7 tested had homonymous hemianopia. Three had epidermal nevus syndrome. Seizures (infantile spasms and focal motor) began in the neonate in 11, and at 6 months and 4 years in the remainder; they recurred daily in the majority. Three had hypsarrhythmia or hemihypsarrhythmia; focal EEG seizures arose from the affected hemisphere in all patients. At functional hemispherectomy (FH), all patients had pathological confirmation of cortical dysplasia. Ventriculoperitoneal shunt for post-surgery obstructive hydrocephalus was required in 3 patients. There was no mortality.
At follow-up (mean 19 months, range 12-48 months), five of 6 patients (83%) in MRI group 1 (with hemimegalencephaly) had persistent although improved seizures after FH, whereas 5 of 6 patients (83%) in MRI groups 2 and 3 (with partial cortical sparing or atrophy) were seizure free. Outcome was not correlated with EEG findings; seizure control was similar among patients with or without bilateral interictal epileptiform discharges, infantile spasms, hypsarrhythmia, or hemihypsarrhythmia. Postoperative video-EEG monitoring in 5 hemimegalencephaly (MRI group 1) patients with persistent seizures showed a seizure focus in the operated hemisphere in 3 and the contralateral hemisphere in 2 patients. 
COMMENT. Patients with hemimegalencephaly and other types of hemispheric malformations of cortical development, as distinguished by MRI, have varying seizure outcomes after surgical functional hemispherectomy. Patients with partial preservation of cortical architecture in one lobe or with atrophy have a better prognosis than those with hemimegalencephaly. Despite the relatively poor seizure outcome in this series, the authors advocate surgery because of an expected improvement in alertness and social interaction and lessened seizure severity. The distinction of various forms of cortical maldevelopment by MRI and molecular genetics before surgery should permit a better prediction of prognosis.