The sinuses are separated from the brain by a layer of bone and the tissue layer that protected the brain, called the dura. Between the dura and the brain is a space filled with fluid known as cerebrospinal fluid (CSF). When there is a communication between this space and the sinuses, patients may notice clear drainage from the nose and a salty or metallic taste. CSF leaks can occur from trauma, surgery, tumors, or underlying brain disorders. If there is herniation of brain tissue into the sinus, this is referred to as a meningoencephalocele. The origin and size of the defect may determine the appropriate treatment. It is believed that continued CSF leak or untreated meningoencephaloceles place the patient at some risk of bacterial spread into the brain from the nasal cavity, known as meningitis. The vast majority of CSF leaks, meningoencephaloceles, and skull base defects of the sinuses can be surgically closed in minimally-invasive endoscopic procedures.