Background: Knowledge of anatomy including variations observed with endoscopy or computerized tomography scan is vital to the performance of safe endoscopic sinus surgery. The lower-than-normal skull base/cribriform plate is an anatomic variation, which if not noted preoperatively, can lead to entrance into the brain causing major injury. Methods: Four case studies of chronic rhinosinusitis are reviewed in which either the whole anterior skull base or the cribriform plate is lower than usual and major complications occurred. Results: All four cases had unilateral or bilateral entrance into the skull base/cribriform plate of the brain in the biopsy specimen, postoperative cerebrospinal fluid leak, and/or brain hemorrhage. One patient died from the injury, three patients had marked neurological sequelae. The low skull base and its meaning for the surgeon is discussed at length. Conclusion: The preoperative anatomy as determined by endoscopy and computerized tomography scanning has to be identified. Variations or abnormalities should be noted and taken into consideration for preoperative and operative planning. Failure to note skull base or cribriform anatomy variations may lead to brain entrance, injury, and death.
