 Sinus surgery is a common procedure in rhinology for the treatment of chronic inflammation, tumors and other pathologies. These procedures are performed in the immediate vicinity of the skull base. The risk of injuring the membranes covering the brain in a way that requires further treatment is less than 1 1. Such Injuries to the skull base could lead to the loss of cerebrospinal fluid CSF. The destruction of the natural barrier raises the potential risk of ascending infections of the membranes and the brain itself from the nose. Leakage of cerebrospinal fluid in the usually bloody surgical field of view is not always distinguishable and is sometimes only noticed postoperatively. The spontaneous closure of a leaky membrane of the brain without further surgical treatment is known. This is why small traumata in the skull base often remain undetected. 