Introduction <p>Endoscopic third ventriculostomy (ETV) is an established treatment for obstructive hydrocephalus. Nevertheless, life-threatening late failure may occur. MRI-based assessment of stoma patency, particularly via flow void visualization, is widely used during the follow-up period. However, the clinical and practical significance of an absent flow void in asymptomatic patients remains unclear.</p> Methods <p>An international survey was developed by the International Society of Pediatric Neurosurgery (ISPN) and International Federation of NeuroEndoscopy (IFNE) and distributed to neurosurgeons between May and December 2025. The survey addressed diagnostic interpretation and management of flow void findings following ETV, including scenarios of absent or disappearing flow voids. Responses were descriptive and analyzed accordingly.</p> Results <p>A total of 83 respondents participated. Most (78%) routinely perform postoperative MRI, predominantly using sagittal T2-weighted sequences. Fifty-nine percent considered the presence of a flow void indicative of ETV function. 74.6% regarded absent flow void as the imaging finding most associated with failure. Thirty-six percent interpreted absence of flow void on initial imaging as failure, increasing to 53% when a previously present flow void disappeared. Despite this, the majority favored continued clinical and radiological follow-up rather than intervention for asymptomatic patients. Notably, many respondents reported asymptomatic patients without flow void who later developed clinical failure.</p> Conclusions <p>Management of absent flow void after ETV is heterogeneous. While flow void was perceived as an important marker, its absence alone did not mandate intervention according to most respondents. There is a need for standardized guidelines and further studies to identify reliable predictors of late ETV failure.</p>