Anomalies and variants of the endoscopic anatomy for third ventriculostomy

Objective: Endoscopic third ventriculostomy (ETV) is an alternative to shun t placement in occlusive hydrocephalus. The negative impact of anatomic ano malies and variants on ETV have been sporadically reported but not yet inve stigated systematically. Therefore, the objectives of the present study are 1) to evaluate the frequency of endoscopic anatomic anomalies of the ventr icular system, 2) to define their potential to complicate the procedure and to compromise the surgical results, and 3) to investigate the value of pre operative 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 res ults were classified into completed and successful, completed, but failed, and unsuccessfully attempted ETV and were correlated with the absence or pr esence of anatomic variants. Results: In 9 of the 25 patients, 10 anatomic anomalies or variants, respectively, were identified, accounting for an inc idence rate of 36%. The single most common anatomic anomaly was a thickened third ventricular floor in 4 patients. Anatomic variants extended the oper ation time (n = 6), increased the stretching of floor and walls of the thir d ventricle during perforation (n = 4), were related to minor arteria[ blee ding (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 patien ts, ETV was finally abandoned, and in an additional 2 patients, ETV was com pleted, but failed to cure the symptoms of hydrocephalus. In contrast, ETV was completed and successful in all 16 patients with normal anatomy. All an atomic anomalies had been detectable on preoperative MR imaging, with the e xception of the thickened floor of the third ventricle. Conclusion: Anatomi c anomalies are a frequent finding during ETV. Successful perforation and c ontrol of the hydrocephalus correlates with the absence of anatomic anomali es. Most anatomic variants have the potential to increase the operative ris k. With the exception of the thickened third ventricular floor, MR imaging allows us to identify all anatomic anomalies preoperatively, and enables th e neurosurgeon to weigh the operative risk in a patient with an anatomic an omaly against the chance to perform ETV successfully.