Supplementary sensorimotor area epilepsy. Seizure localization, cortical propagation and subcortical activation pathways using ictal SPECT

We studied clinical signs, EEGs and ictal cerebral blood flow by single-photon emission computed tomography (SPECT) in eight patients with intractable supplementary sensorimotor area (SSMA) seizures. SPECT scans were performed after injection of the regional cerebral blood flow tracer 99mTcHMPAO (hexametylpropylene amine oxime) early in the ictal phase (2-5 s after seizure onset). Ictal SPECT demonstrated unilateral predominance of hyper-perfusion of the SSMA in all patients, concordant with either lateralizing clinical signs, lateralization of ictal scalp EEG or with the site of ictal onset of seizures, obtained from intracranial electrodes. Two distinctive cortical blood-flow propagation patterns were identified in SSMA seizures. The type I pattern consisted of primary involvement of the ipsilateral SSMA and dorsal premotor and motor cortex. The type II pattern consisted of bilateral but asymmetric mesial frontal propagation. Ictal contraversive head and eye movements were associated with a type I propagation pattern (P < 0.03). Activation of subcortical structures led to variable hyper-perfusion of the basal ganglia and thalamus. Contralateral cerebellar hyperperfusion was observed in all cases. We conclude that ictal SPECT is a useful method for seizure localization in patients with SSMA epilepsy. The observed heterogeneity of clinical features in SSMA epilepsy correlates with propagation to, and activation of, specific cortical structures, and is consistent with known anatomical interconnections between the SSMA, ipsilateral cortical and transcallosal cortical structures.