Virtual MRI endoscopy: Detection of anomalies of the ventricular anatomy and its possible role as a presurgical planning tool for endoscopic third ventriculostomy

Background. Many anatomical anomalies have the potential to impair the efficacy of endoscopic third ventriculostomy (ETV) and increase the surgical morbidity. By virtual magnetic resonance imaging (MRI) endoscopy, the real endoscopic view into the ventricular system can be simulated. It was the objective of the present study to investigate if this simulation is sensitive enough to detect anatomical anomalies of the ventricular system. Method. In 18 hydrocephalic patients, first neuronavigationally guided ETV, then virtual MRI endoscopy were performed. This study design allowed for selection of a path for virtual MRI endoscopy, which was identical to that used during surgery, making the real and the virtual view on anatomical structures of the ventricular system highly comparable. It was investigated whether the intraoperatively identified anatomical anomalies could likewise be depicted on virtual MR endoscopic images. Findings. Seven anatomical variants (not enlarged interventricular foramen n = 2, atrophic corpus callosum and split fornical bodies n = 1, narrow retroclival space n = I. prominent basilar tip n = 1. opaque and thick/atypically declining third ventricular floor n = 2) were encountered in 5 of the 18 patients during surgery. The five variants of the non-membraneous structures were identified by virtual MRI endoscopy (sensitivity 71%), whereas the anatomical variants of the third ventricular floor were missed. Both the normal as well as the variant third ventricular floor could not be visualised and appeared as a defect. Through this artefact, the anatomy of the major vessels in the interpeduncular cistern could be assessed, Interpretation. The sensitivity of virtual MRI endoscopy for detection of anatomical variants of the ventricular system is low. Its potential usefulness as a presurgical planning tool inspite of this low sensitivity rate is discussed.