27 day old, afebrile boy presented with intermittent seizure, where that CT raised the suspicion of hemimegalencephaly. One day later the MRI confirmed the diagnosis.

About 2 years later the patient underwent left modified functional hemispherectomy.

The patient developed new-onset of seizure five months after surgery, where the MRI showed macroscopically a complete disconnection, however, the diffusion tensor imaging (tractography) showed residual interhemispheric connecting fibers through the anterior corpus callosum and anterior commissure.  

Hemimegalencephaly is a rare malformation characterized by enlargement of one cerebral hemisphere with an increased amount of the gray matter and thickening of the cortical ribbons. This might affect either one lobe or the entire hemisphere. Asymmetric appearance of the cranium may indicate it. The main clinical manifestations include hemiparesis, seizure and developmental retardation.

An afebrile child presenting with seizure should raise suspicions of developmental issues, such as hemimegalencephaly.  We point out the importance of imaging modalities in detecting the operable causes of seizure.

Case contributed by Dr. Christine Saint-Martin, Associate Professor in the Neuroradiology and Pediatric Radiology at McGill University.