SISCOM localization of a seizure focus within a heterotopia.

A man aged 38 years has a history of refractory epilepsy dating back to age 11 months. His daily seizures are complex partial (see video clip 1 on the Neurology Web site) with nonlocalizing motor components. The events have resulted in numerous bouts of status epilepticus despite having tried seven distinct antiepileptic drugs. An MRI (figure 1A) shows a right parietal area of heterotopic gray matter spanning from the wall of the lateral ventricle to the cortex. The patient underwent video EEG monitoring with subtraction ictal SPECT coregistered on MRI (SISCOM). SISCOM images revealed a discrete focus within the heterotopia (figure 1B). Intracranial EEG monitoring with a subdural grid and an eight-contact strip placed within a prominent anomalous posterior extension of the Sylvian fissure confirmed the SISCOM finding (figure 2). Resection of the epileptogenic tissue (~3 cm) corresponding to the SISCOM finding resulted in complete seizure relief at current postoperative clinic visit (6 months). Gray matter heterotopias often result in focal intractable seizures. Scalp EEGs can be lateralizing but are often nonlocalizing in these conditions. SISCOM may be particularly helpful in these lesions to help guide intracranial EEG coverage. SISCOM detection of a hyperperfusion focus is twice that of conventional SPECT (88% vs 39%).1