Spontaneous CSF rhinorrhea arising from the middle cranial fossa: CT demonstration.

When patients present with spontaneous cerebrospinal fluid (CSF) rhinorrhea the primary diagnostic goal is localizing the site of leakage so that an appropriate approach for surgical repair can be selected. Metrizamide computed tomography (CT) has become the preferred method for investigating CSF rhinorrhea for several reasons [1-4]. CT provides superb bone detail so that fractures or areas of bony discontinuity can be identified. If the patient is actively leaking at the time of the examination, opacified CSF can often be visualized directly as it passes through the fistula, providing the sine qua non for localization. CT also allows examination of the paranasal sinuses for evidence of air-fluid levels and abnormalities that may be associated with CSF rhinorrhea, such as hydrocephalus or empty sella. The most common sites of spontaneous CSF leak occur in the anterior fossa , sella, and parasellar regions, allowing communication with the paranasal sinuses or nasal fossa. The petro us bone is also a potential source of rhinorrhea via CSF carried by way of the eustachian tube [5] . We report a case of CSF rhinorrhea arising from a relatively uncommon site, the middle cranial fossa, accurately demonstrated by metrizamide CT and confirmed surgically. Bone/dura/arachnoid defects at the floor of the middle fossa formed a fistula between the subarachnoid space and the pterygoid recess of the sphenoid sinus. Although such fistulae have been described [6-9] , they have not been demonstrated by metrizamide CT. Our case emphasizes the importance of examining the full lateral extent of the sphenoid sinus and appreciating the morphology of the middle cranial fossa floor when studying patients with CSF rhinorrhea. The CT findings also lend credence to the hypothesis that middle fossa fistulae can be formed by spontaneous rupture of congenital "pits" at the skull base rather than as the result of previous trauma [8, 9].