Cerebrospinal fluid (CSF) rhinorrhea is the result of one or more skull base defects permitting direct communication between the CSF-containing subarachnoid space and the paranasal sinuses. The vast majority of cases are thought to occur as the direct result of either accidental or iatrogenic trauma, the latter usually in the setting of rhinologic or neurosurgical procedures. Nontraumatic CSF rhinorrhea accounts for about 4%-5% of cases overall and is attributable to a variety of conditions linked to either intracranial hypertension (eg, obstructive hydrocephalus, intracranial mass) or direct erosion of the skull base (eg, osteomyelitis, sinonasal neoplasm). Most cases of so-called "spontaneous" CSF rhinorrhea are associated with abnormally elevated intracranial pressure (ICP) and occur in obese, middle-aged women.

CSF fistulae provide a route of intracranial access for a variety of microorganisms and are an important risk factor for ascending infection, with complication by bacterial meningitis accounting for the majority of morbidity in patients with active CSF rhinorrhea at an estimated annual risk of approximately 10%. Less frequently, larger skull base defects can lead to meningoencephalocele and/or pneumocephalus and secondary brain compression.