IntroductionEndoscopic third ventriculostomy (ETV) for obstructive hydrocephalus and endoscopic biopsy (EB) for intra- and paraventricular tumors are recognized as standard therapies because of their minimal invasiveness. Although EB-associated hemorrhagic risk has been well documented, reports on the ETV-associated hemorrhagic risk are only few. Therefore, we conducted this retrospective study to review the incidence of hemorrhage due to EB and/or ETV in a single institution.Material and MethodsWe retrospectively reviewed data, including patient characteristics, procedure, pathological findings, and complications, including hemorrhage, of 100 patients with intra- and paraventricular tumors who underwent EB and/or ETV at our institution from 2000 to 2020.ResultsEB and ETV combined surgery (combined group), EB-alone surgery (EB-alone group), and ETV-alone surgery (ETV-alone group) were performed in 44 (44%), 24 (24%), and 32 (32%) patients, respectively, and all procedures were successful. The rates of definitive and suggestive diagnoses in EB were 76.5% and 23.5%, respectively. Adverse events were observed in six patients. An acute obstruction of the ETV stoma and a transient double vision were observed in the combined group. Two transient aqueductal stenosis/obstructions were recognized in the EB-alone group. Hemorrhage was observed in two patients in the ETV-alone group; these patients developed intratumoral hemorrhage despite ETV-alone surgery. Subsequently, these two patients underwent tumor removal, and the histopathological diagnosis was atypical teratoid/rhabdoid tumor (AT/RT) in both.ConclusionsFor obstructive hydrocephalus with AT/RTs, physicians must be aware of the risk of postoperative intratumoral hemorrhage after performing ETV.Trial registration numberE-2385 (2021/3/11)