Rhombencephalosynapsis as a cause of aqueductal stenosis: an under-recognized association in hydrocephalic children

Background Rhombencephalosynapsis is a rare genetic aberration characterized by variable vermian hypoplasia/aplasia in conjunction with united cerebellar hemispheres. Genetic defects in the isthmic organizer at the mesencephalic–metencephalic junction are presumably responsible for the associated aqueductal stenosis.