A retrospective analysis of spontaneous sphenoid sinus fistula: MR and CT findings

BACKGROUND AND PURPOSE: The sphenoid sinus is rarely implicated as a site o f spontaneous CSF fistula. We undertook this study to evaluate the potentia l etiopathogenesis of spontaneous CSF fistula involving the sphenoid sinus acid to review the imaging findings. METHODS: We retrospectively reviewed the imaging findings of 145 cases of C SF fistula from our departmental archives (August 1995 through August 1998) . Fifteen (10%) patients had CSF fistulas involving the sphenoid sinus. Ele ven (7%) patients had spontaneous CSF fistulas, whereas in four patients, t he CSF fistulas in the sphenoid sinus were related to trauma. Of the 11 pat ients, nine underwent only plain high-resolution CT and MR cisternography. One patient additionally underwent contrast-enhanced CT cisternography, and one other patient underwent MR cisternography only. For each patient, the CSF fistula site was surgically confirmed. The MR imaging technique include d T1-weighted and fast spin-echo T2-weighted 3-mm-thick coronal sequences o btained with the patient in the supine position. The plain high-resolution CT study included 3-mm-thick, and sometimes 1- to 1.5-mm-thick, coronal sec tions obtained with the patient in the prone position. Similar sections wer e obtained after injecting nonionic contrast material intrathecally via lum bar puncture for the CT cisternographic study. We evaluated each of the 11 patients for the exact site of CSF leak in the sphenoid sinus. We also dete rmined the presence of pneumatization of lateral recess of the sphenoid sin us, orientation of the lateral wall of the sphenoid sinus, presence of arac hnoid pits, presence of brain tissue herniation, and presence of empty sell a in each of these patients. RESULTS: The exact sites of the CSF fistulas were documented for all 11 pat ients by using plain high-resolution CT, MR cisternography, or CT cisternog raphy. In nine (82%) patients, the sites of the CSF fistulas were at the ju nction of the anterior portion of the lateral wall of the sphenoid sinus an d the floor of the middle cranial fossa. In the remaining two (18%) patient s, the sites of the CSF fistulas were along the midportion of the lateral w all of the sphenoid sinus. Of these 11 patients, one had bilateral sites of the CSF fistula at the junction of the anterior portion of the lateral wal l of the sphenoid sinus with the floor of the middle cranial fossa. In nine (82%) patients, the presence of brain tissue herniation was revealed, and this finding was best shown by MR cisternography. Ten (91%) patients had ex tensive pneumatization of the lateral recess of the sphenoid sinus, with an equal number having outward concave orientation of the inferior portion of the lateral wall of the sphenoid sinus. In seven (63%) patients, the prese nce of arachnoid pits, predominantly along the anteromedial aspect of the m iddle cranial fossa, was shown. In seven (63%) patients, empty sella was sh own. For comparison, we reviewed the CT studies of the paranasal sinuses in 100 age-matched control subjects from a normal population. Twenty-three ha d extensive lateral pneumatization of the sphenoid sinus along with outward concavity of the inferior portion of the lateral wall. None of these 23 pa tients had arachnoid pits. CONCLUSION: The sphenoid sinus, when implicated as a site of spontaneous CS F leak, yields a multitude of imaging findings. These are extensive pneumat ization of the lateral recess of the sphenoid sinus, outward concave orient ation of the inferior portion of the lateral wall of the sphenoid sinus, ar achnoid pits, and empty sella. Considering the normative data, we speculate that this constellation of findings could play a role in the etiopathogene sis of spontaneous sphenoid sinus fistulas. Our findings also show the effi cacy of noninvasive imaging techniques, such as plain high-resolution CT an d MR cisternography, in the evaluation of sphenoid sinus CSF leak. Our data also suggest that spontaneous sphenoid sinus CSF leak is not an uncommon o ccurrence.