Primary obstruction of the fourth ventricle outlets: neuroendoscopic approach and anatomic description

Primary obstruction of the foramina of Magendie and Luschka is an uncommon and still unclear cause of noncommunicating hydrocephalus. The aim of this work is the description, for the first time, of the inner aspect of these velar obstructions of the fourth ventricle outlets and the demonstration of the efficacy of neuroendoscopic treatment.

Of 240 hydrocephalic patients treated in our institution with endoscopic third ventriculostomy, a subgroup of 10 cases with closure of the fourth ventricular outlets without associated Chiari malformation and syringomyelia was selected. In all of these cases, a transaqueductal endoscopic navigation of the fourth ventricle was performed, and the obstructed outlets were inspected. All of the clinical data and, in particular, the videotape records of endoscopic operations, as well as the cine-magnetic resonance imaging scans, were reviewed to evaluate their patency status.

Various degrees of stenosis were found endoscopically: restriction of the Magendie contour with thick and opaque membrane, transparent spider web-like membrane, and dense membrane with fissures acting as valves. Endoscopic third ventriculostomy was effective in almost all patients, although we noticed an unforeseen high incidence of closure of the stoma. The restored normal cerebrospinal fluid flux after ventriculocisternostomy and magendieplasty was demonstrated by comparative study of cerebrospinal fluid flow measurements by cine-magnetic resonance imaging.

This report demonstrates the effectiveness of neuroendoscopic third ventriculostomy as well as magendiestomy in cases of tetraventricular hydrocephalus attributable to primary obstruction of the outlets of the fourth ventricle and, for the first time, presents direct images of various types of outlet obstructive pathology.