Septo-optic dysplasia plus. A 6-year-old male with eyelid myoclonus. Coronal T2-weighted MRI scan showing absence of the septum pellucidum and a wide cerebrospinal fluid-filled cleft (arrow) in the right frontal lobe (extending from the polar region to the medium convexity) and the anterior horn of the right lateral ventricle, wrapped in a thickened cortex. The right Sylvian fissure was flat and vertical, with thickened cortical segments, and there was, on the ipsilateral side, polymicrogyria of the insula and frontal operculum (not shown).