Abstracts

Rationale: HME is generally defined as enlargement of at least one lobe of cerebral hemisphere. The pathogenesis is still unknown even though several hypotheses are reported in literature. Clinically, most patients exhibit severe refractory seizures and psychomotor retardation within the first 6 months of life. Early diagnosis and an early surgical treatment are required to prevent the evolution toward catastrophic epilepsy. Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) of brain is the useful functional imaging techniques that study cerebral blood flow (CBF) and glucose metabolism, and an increasingly important tool in the presurgical evaluation of intractable epilepsy. Typically, CBF and glucose metabolism in the epileptogenic zone are decreased during interictus and increased during ictus. In HME, however, comparative study between SPECT and PET is lacking in the literature. Our purpose is to examine clinical efficacy of comparative study between CBF and glucose metabolism in Hemimegalencephaly (HME) for adequate preoperative preparation. Methods: We investigated functional neuroimaging studies in nine cases (three males and six females, between the age of 0.5-20 years) with HME diagnosed by brain MRI. The examination of SPECT was performed using technetium-99m-ethyl cysteinate dimer (ECD) or hexamethylpropyleneamine oxime (HM-PAO) as the radiotracer during the ictal and interictal state. The examination of PET was performed using 18F-fluorodeoxyglucose (FDG) during interictal state. Recent three cases were simultaneously performed monitoring of scalp EEG during SPECT to confirm the ictal and interictal state. Then, we studied the correlation between results of radionuclide scanning and clinical aspects. Results: All seven cases ictal SPECT study performed showed more prominent increase in CBF in the malformed side as compared to those of interictal state. Seven of nine cases showed a same (two cases) or increased (five cases, including three cases with simultaneously EEG recording) CBF in the malformed or epileptogenic zone as compared to the normal contralateral side even during interictal state. These cases seemed to have severe clinical symptoms of refractory seizure and hemispherectomy was performed in six cases. In contrast, all nine cases showed a same (two cases) or decreased (seven cases) glucose metabolism in the malformed side, although two cases showed a localized increase in the uptake of FDG in the malformed cortices probably due to subclinical ictal state. Conclusions: Discrepancy between increased CBF and decreased glucose metabolism in the affected side seems to be characteristic aspect in HME as compared to the other migrating disorders, i.e. focal cortical dysplasia. An increase in CBF in the affected side during interictal state is considered to indicate the severe clinical form, and early surgical treatment is recommended.