Abstracts

Rationale: Hemimegalencephaly (HME) is a rare, sporadic developmental malformation of the brain characterized by congenital hypertrophy of one cerebral hemisphere. Severe developmental delay and intractable epilepsy are usually unavoidable in HME. Hemispherectomy (HST) is the most effective treatment for controlling seizures, and it is expected to yield a good developmental outcome when performed early. Near-infrared spectroscopy (NIRS) is a noninvasive technique for measuring cerebral blood volume dynamics closely correlated with the neural activity of the brain. This study aimed to evaluate the clinical efficacy of NIRS to predict seizure outcome by determining pre- and postsurgical changes in cerebral blood flow (CBF) and cerebral blood oxygenation in patients with HME. Methods: Subjects included 5 patients with HME who were admitted between January 2008 and June 2011. Hemodynamic patterns of oxy- and deoxyhemoglobin (Hb) following photic stimulation during sleep were evaluated before and after HST using ETG-4000 (Hitachi Medical Corp). Informed consent was obtained from the patients parents, and the project was approved by the Ethics Committees of National Center of Neurology and Psychiatry. The probes were placed on the bilateral occipital region, with the center of the bottom edge at the inion. We measured time courses of oxy-Hb and deoxy-Hb levels at 24 channels. Seizure outcome was investigated from medical records. The cross correlation (r) between changes in oxy-Hb patterns and the referential increasing pattern was employed. A threshold of r = 0.65 was empirically chosen to select the channel as the normal activated channel. Sequentially, we estimated the number of activated channels of the affected and unaffected hemisphere after surgery.Results: Before surgery, NIRS showed increased CBF in the affected hemisphere and decreased CBF in the unaffected hemisphere in all patients. Compared with their CBF in the operated and unaffected hemispheres before HST, four seizure-free patients showed decreased CBF in the operated hemisphere and increased CBF in the unaffected hemisphere after HST. However, 1 patient with relapsing seizures showed no significant increase in CBF in the unaffected hemisphere. In addition, NIRS revealed interesting hemodynamic patterns, such as arrhythmic or asynchronous changes in oxy- and deoxy-Hb, in the unaffected hemisphere before HST. Number of normal activated channels increased in four of five patients after HST, who achieved good seizure outcome and psychomotor development, and one patient with decreased number of them had relapsing seizures and poor development. Conclusions: NIRS is a useful, noninvasive tool for confirming hemodynamic patterns in patients with HME. We believe that estimation of the sequential increase of number of normal activated channels might be useful for NIRS measurement in infants as a predictive indicator for postsurgical seizure and developmental prognosis.