Anomalies and variants of the endoscopic anatomy for third ventriculostomy

Objective: Endoscopic third ventriculostomy (ETV) is an alternative to shunt placement in occlusive hydrocephalus. The negative impact of anatomic anomalies and variants on ETV have been sporadically reported but not yet investigated systematically. Therefore, the objectives of the present study are 1) to evaluate the frequency of endoscopic anatomic anomalies of the ventricular system, 2) to define their potential to complicate the procedure and to compromise the surgical results, and 3) to investigate the value of preoperative magnetic resonance (MR) imaging for their detection. Method: The video recordings, the operative reports, and the preoperative MR images of 25 hydrocephalic patients who underwent ETV were reviewed. The surgical results were classified into completed and successful, completed, but failed, and unsuccessfully attempted ETV and were correlated with the absence or presence of anatomic variants. Results: In 9 of the 25 patients, 10 anatomic anomalies or variants, respectively, were identified, accounting for an incidence rate of 36%. The single most common anatomic anomaly was a thickened third ventricular floor in 4 patients. Anatomic variants extended the operation time (n = 6), increased the stretching of floor and walls of the third ventricle during perforation (n = 4), were related to minor arteria[ bleeding (n = 3), and obscured the visual control of the basilar artery (n = 2). In 5 of the 9 patients, ETV was completed and successful, but in 2 patients, ETV was finally abandoned, and in an additional 2 patients, ETV was completed, but failed to cure the symptoms of hydrocephalus. In contrast, ETV was completed and successful in all 16 patients with normal anatomy. All anatomic anomalies had been detectable on preoperative MR imaging, with the exception of the thickened floor of the third ventricle. Conclusion: Anatomic anomalies are a frequent finding during ETV. Successful perforation and control of the hydrocephalus correlates with the absence of anatomic anomalies. Most anatomic variants have the potential to increase the operative risk. With the exception of the thickened third ventricular floor, MR imaging allows us to identify all anatomic anomalies preoperatively, and enables the neurosurgeon to weigh the operative risk in a patient with an anatomic anomaly against the chance to perform ETV successfully.