Objective and HypothesisPosttraumatic clear rhinorrhea should result in immediate concern for a suspected cerebrospinal fluid (CSF) fistula in patients with skull base injuries, including surgical trauma. However, in addition to CSF rhinorrhea, the differential diagnosis may also include postinjury autonomic dysfunction. Pseudo–cerebrospinal fluid rhinorrhea (PCSFR) is a term used to describe rhinorrhea resulting from injury to preganglionic parasympathetic fibers supplying the sphenopalatine ganglion. This ganglion plays a critical role in this pathway secondary to its anatomic course and physiologic function. Differentiating between PCSFR and true CSF rhinorrhea can be a diagnostic challenge and may result in unnecessary and costly invasive testing and treatment.Case StudyThe authors present an illustrative case of noniatrogenic posttraumatic PCSFR in a previously healthy patient who experienced a head injury in a horseback riding accident.DiscussionFeatures of PCSFR include a history of skull base surgery or trauma with involvement of autonomic structures in this region, rhinorrhea within months or years after injury, decreased lacrimation on the involved side, absence of clinical signs of meningitis, and a negative &bgr;2-transferrin test result. Management of PCSFR is aimed at restoring the normal autonomic homeostasis in the nasal cavity. Treatment options include topical medicines such as anticholinergics and the various surgical procedures aimed at disruption of parasympathetic preganglionic fibers proximal to or at the sphenopalatine ganglion.ConclusionThis case and its diagnosis and management provide an additional mechanism of PCSFR, a clinical entity that must be considered in the evaluation of all patients with previous skull base trauma.