Endoscopic septostomy for insufficient function of foramen Monroi became not only a significant treatment method, but also a safety precaution after reconstruction of interventricularcommunication. During surgery in the third ventricle, when the endoscope limits the flow through foramen Monroi, septostomy additionally moderates in a preventive way pressure fluctuations related to irrigation of the operative field. Connecting both ventricles increases the surface area on which the pressure of the fluid acts, consequently, the specific pressure per unit area, also called tension in hydrology, decreases in proportion. In an ensemble of almost 200 endoscopic surgeries inside but also outside the ventricular system of the brain, septostomy was used in 14% and only on one occasion after concurrent reconstruction of foramen Monroi the patient was transiently mildly confused for a short time. Septum pellucidum – because of its embryonic evolution – can be considered a functionless structure of the brain. Spontaneous septal defects will have no clinical manifestations. It is recommended, though, to navigate the endoscopic trajectory for septostomy in a reliable way using a stereotactic technique and program.

        Key words: endoscopic septostomy, interventricular communication, noncommunicating hydrocephalus