Membranous structures affecting the success of endoscopic third ventriculostomy in adult aqueductus sylvii stenosis.

BACKGROUND The purpose of the present study was to observe Liliequist's membrane (LM) and membranous structures located in the prepontine cistern via 3-Tesla magnetic resonance imaging (MRI) with 3D driven equilibrium radio frequency reset pulse (DRIVE) sequence and multiplanar reformat (MPR) images and to evaluate the success of endoscopic third ventriculostomy (ETV) by assessing these membranes in adult aqueduct stenosis. PATIENTS 29 patients (17 female, 12 male) with primary aqueductus sylvii stenosis were included in the study. 19 patients were diagnosed as long-standing overt ventriculomegaly in adults (LOVA) and patients had severe ventriculomegaly, macrocephalus, and aqueduct stenosis on MR imaging. 10 patients were diagnosed as aqueduct stenosis presented with acute onset of hydrocephalus with symptoms of raised ICP. All patients in the study group were analyzed with conventional and cine MRI before and after treatment. We performed 3D DRIVE sequence and MPR at 3-T MR equipment to determine the membranous structures in 3 dimensions. We correlated the success of the procedure considering the preoperative, postoperative MRI and intraoperative images. RESULTS 5 patients (26.3%) with LOVA and 2 patients (20%) with aqueduct stenosis, in total 7 patients (24.1%), did not respond to ETV. Cerebrospinal fluid (CSF) flow was blocked by membranous structures located in the prepontine cistern in 4 of 8 patients. In 2 patients, CSF through the stoma was blocked either by the LM or closed tuber cinerum. In 1 patient insufficient CSF flow was observed through the stoma and the LM accompanying prepontine membranes.Totally closed membranes were observed in the prepontine cistern in 5 patients (17.24%) according to the postoperative MRI. LM was verified in all patients intraoperatively that were also demonstrated in the preoperative MRI. CONCLUSION 3D sequences with MPR may help to observe not only the LM but also other membranes located through the prepontine cistern, which may be the reason of failed ETV.