Unique discrepancy between cerebral blood flow and glucose metabolism in hemimegalencephaly

Hemimegalencephaly (HME) presents as severe refractory seizures and requires early surgical treatment to prevent progression to catastrophic epilepsy. Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) are useful imaging techniques for the presurgical evaluation of patients with intractable epilepsy. However, the results in HME are variable and no study has compared SPECT and PET performed at around the same time. We performed SPECT and PET for nine patients with HME, which was defined as a whole or part of affected hemisphere enlargement (three males, six females; age range 0.5-20 years). The ictal and interictal states were determined based on the presence or absence of clinical seizures during all PET examinations and majority of SPECT examinations. The perfusion pattern in the malformed hemisphere was increased or equal, despite the reduced glucose metabolism in six out of nine patients. Five of the six patients who underwent early surgical treatment showed this kind of perfusion/metabolism discrepancy. Importantly, even the non-affected hemisphere in early infantile cases already lacked the normal hypoperfusion and hypometabolism patterns of immature frontal lobes, which was most prominent in case with poor surgical prognosis. In all six surgical patients, epileptic seizures appeared before 4 months of age. By contrast, none of the non-surgical patients had seizures before 4 months of age. In conclusion, although the number of patients examined is small and the result is still preliminary, the perfusion/metabolism discrepancy found in this study may show potential characteristic aspect of HME and further study with simultaneous EEG recording will make clear if this finding can be useful indicator for early surgical treatment in HME.