Teaching Case

A 47-year-old woman was admitted to the hospital with recurrent meningitis, history of rhinorrhea on exertion. She had prior surgical resection of a right-sided vestibular schwannoma. She underwent a cisternogram a year before with some contrast leak in the mastoid surgical cavity.

A second MRI cisternogram (Figure 1) showed contrast leakage through a surgical defect in the right tegmen tympani into the right middle ear cavity. Gadolinium is seen tracking from the middle ear cavity through the right eustachian tube into the nasopharynx and then in the right nasal cavity confirming CSF leak in the mastoids was the cause for rhinorrhea.

Cisternography is used to evaluate the site and cause of CSF leak by intrathecal injection of contrast in the lumbar spinal canal. With the patient in a prone Trendelenburg position, contrast is directed to flow intracranially to fill the cerebral cisterns and extra-axial CSF spaces. CT and MRI of the head are then performed in a prone position to facilitate the leakage of contrast. Iodinated contrast material and the off-label use of gadolinium have proved to be safe and can accurately demonstrate the site of CSF leak [1, 2, 3].

CSF rhinorrhea occurs due to direct communication between the cranial fossae and the paranasal sinuses, most caused by iatrogenic and traumatic causes. The pathways for CSF rhinorrhea can occur through several routes, including the anterior skull base through the cribriform plate, the lateral attachment of the nasal middle turbinate to the skull base, the fovea ethmoidalis, posterior table of the frontal sinus, the Sella turcica through sphenoid region, the middle ear through eustachian tube and through the temporal bone. Testing for Beta2-transferrin can reliably detect CSF [4], however, imaging studies are still required to localize the site of leak.

Clinical Perspective

The clinical presentation of rhinorrhea in our patient with history of posterior fossa surgery was perplexing. She underwent a cisternogram a year before with possible leak in the mastoid surgical cavity, and the patient had recurrent meningitis. Only the second study clearly showed how CSF leakage from a posterior cranial fossa defect is causing rhinorrhea through indirect pathway.

Imaging Perspective

In cases of suspected CSF leakage with an initially negative MR and CT cisternogram, it is important to check for indirect CSF leakage pathway.

The diagnosis is made in the second MR cisternogram when the contrast was seen leaking through a surgical defect in the right tegmen tympani into the right middle ear cavity through the right eustachian tube into the nasopharynx and then in the right nasal cavity.

Outcome

The indirect CSF rhinorrhea from the middle ear cavity happens when an intact tympanic membrane is present and CSF flows through the path of least resistance, the eustachian tube. If tympanic membrane was not intact, then CSF otorrhea is expected to occur. Finding the cause will guide the management and prevent further complications. The patient underwent surgical reconstruction of skull base defect and no more CSF leakage since then; also by examination, there was no CSF leakage in the ear.

Take Home Message / Teaching Points

Making an early diagnosis by checking for indirect CSF leak will prevent the patients from having rhinorrhea and recurrent meningitis and will facilitate the management.

All patient data have been completely anonymized throughout the entire manuscript and related files.