Unilateral hydrocephalus due to idiopathic anomaly of foramen of Monro, treated successfully with endoscopic technique. Report of three cases.

Introduction & Unilateral hydrocephalus of the lateral ventricles may result from a unilateral occlusion of the foramen of Monro (FOM). Causative agents may be either neoplastic (subependymal giant cell astrocytoma, hypothalamic glioma), infl ammatory conditions (bacterial ventriculitis, brain abscess and intraventricular hemorrhage), congenital (choroid plexus cyst, atresia of foramen of Monro, choroid plexus hypertrophy), vascular such as AV malformation of the choroid plexus [4, 16] and basilar artery aneurysm or ectasia [8] , or iatrogenic (unilateral shunt overdrainage) [1] . Of the mentioned pathologies, colloid cyst is the most common [7] . Idiopathic occlusion of the foramen of Monro as an etiology for unilateral hydrocephalus is an extremely rare phenomenon with – to our knowledge – only twenty patients described in the English literature so far [7, 12, 13, 17] . We present three patients with unilateral hydrocephalus due to idiopathic occlusion of the FOM, who underwent endoscopic fenestration of the septum pellucidum to make a communication between two ventricles.