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

Abstract

Background and purpose: The sphenoid sinus is rarely implicated as a site of spontaneous CSF fistula. We undertook this study to evaluate the potential etiopathogenesis of spontaneous CSF fistula involving the sphenoid sinus and to review the imaging findings.

Methods: We retrospectively reviewed the imaging findings of 145 cases of CSF fistula from our departmental archives (August 1995 through August 1998). Fifteen (10%) patients had CSF fistulas involving the sphenoid sinus. Eleven (7%) patients had spontaneous CSF fistulas, whereas in four patients, the CSF fistulas in the sphenoid sinus were related to trauma. Of the 11 patients, 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 included T1-weighted and fast spin-echo T2-weighted 3-mm-thick coronal sequences obtained 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 sections obtained with the patient in the prone position. Similar sections were obtained after injecting nonionic contrast material intrathecally via lumbar 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 determined the presence of pneumatization of lateral recess of the sphenoid sinus, orientation of the lateral wall of the sphenoid sinus, presence of arachnoid pits, presence of brain tissue herniation, and presence of empty sella in each of these patients.

Results: The exact sites of the CSF fistulas were documented for all 11 patients by using plain high-resolution CT, MR cisternography, or CT cisternography. In nine (82%) patients, the sites of the CSF fistulas were at the junction of the anterior portion of the lateral wall of the sphenoid sinus and the floor of the middle cranial fossa. In the remaining two (18%) patients, the sites of the CSF fistulas were along the midportion of the lateral wall 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 wall 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 extensive 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 presence of arachnoid pits, predominantly along the anteromedial aspect of the middle cranial fossa, was shown. In seven (63%) patients, empty sella was shown. For comparison, we reviewed the CT studies of the paranasal sinuses in 100 age-matched control subjects from a normal population. Twenty-three had extensive lateral pneumatization of the sphenoid sinus along with outward concavity of the inferior portion of the lateral wall. None of these 23 patients had arachnoid pits.

Conclusion: The sphenoid sinus, when implicated as a site of spontaneous CSF leak, yields a multitude of imaging findings. These are extensive pneumatization of the lateral recess of the sphenoid sinus, outward concave orientation of the inferior portion of the lateral wall of the sphenoid sinus, arachnoid pits, and empty sella. Considering the normative data, we speculate that this constellation of findings could play a role in the etiopathogenesis of spontaneous sphenoid sinus fistulas. Our findings also show the efficacy of noninvasive imaging techniques, such as plain high-resolution CT and MR cisternography, in the evaluation of sphenoid sinus CSF leak. Our data also suggest that spontaneous sphenoid sinus CSF leak is not an uncommon occurrenc

FIG 1.

Patient 11. A, Coronal high-resolution CT scan, obtained through the sphenoid sinus, shows a defect at the junction of the anterior portion of the lateral wall of the sphenoid sinus on the right side with the floor of the middle cranial fossa (arrow) associated with a meningocele. Note the concave lateral wall on the right side. CSF is seen on both sides of the sphenoid sinuses. B, Coronal T1-weighted (600/15/2) MR image of the brain clearly depicts brain tissue herniating through the bony defects bilaterally (long arrows). The open arrow points to the CSF in the right sphenoid sinus. C, Coronal T2-weighted (4600/90/2) MR image of the brain shows herniation of brain tissue (thick arrow) and CSF (arrowhead) bilaterally. Empty sella is also seen (small arrow).

FIG 2.

Patient 10. A, Coronal high-resolution CT scan, obtained through the sphenoid sinus, shows a defective intersphenoid septum deviated to the left (thick arrow). The long arrow points to the defect in the anterior portion of the lateral wall of the sphenoid sinus on the left side, just inferior to the attachment of the septum. The small arrows depict arachnoid pits. B, Coronal T1-weighted (600/15/2) MR image of the brain shows brain tissue herniating through the defect (curved arrow) in the anterior portion of the lateral wall of the sphenoid sinus on the left side. The straight arrow shows the defective intersphenoid septum. C, CT cisternography scan shows the CSF tracking through the defect in the anterior portion of the lateral wall of the left sphenoid sinus into the right side (small arrows). The defective intersphenoid septum (thick arrow) is seen inserted just superior to this defect.

FIG 3.

Patient 5. Coronal high-resolution CT scan, obtained through the sphenoid sinus, shows the presence of a defect in the lateral wall of the sphenoid sinus on the right side through the region of the foramen rotundum (large arrow). The small arrow points to the normal foramen on the left