Nontraumatic skull base defects with spontaneous CSF rhinorrhea and arachnoid herniation: imaging findings and correlation with endoscopic sinus surgery in 27 patients

Abstract

Background and purpose: Defects at the skull base leading to spontaneous CSF rhinorrhea are rare lesions. The purpose of our study was to correlate CT and MR findings regarding the location and content of CSF leaks in 27 patients with endoscopic sinus surgery observations.

Materials and methods: Imaging studies in 27 patients with intermittent CSF rhinorrhea (CT in every patient including 10 examinations with intrathecal contrast, plain CT in 2 patients, and MR in 15 patients) were analyzed and were retrospectively blinded to intraoperative findings.

Results: CT depicted a small endoscopy-confirmed osseous defect in 3 different locations: 1) within the ethmoid in 15 instances (53.6% of defects) most commonly at the level of the anterior ethmoid artery (8/15); 2) adjacent to the inferolateral recess of the sphenoid sinus in 7 patients including one patient with bilateral lesions (8/28 defects, 28.6%); 3) within the midline sphenoid sinus in 5 of 28 instances (17.9%). Lateral sphenoid defects (3.5 +/- 0.80 mm) were larger than those in ethmoid (2.7 +/- 0.77 mm, P < or = 0.029) or midsphenoid location (2.4 +/- 0.65 mm, P < or = 0.026). With endoscopy proven arachnoid herniation in 24 instances as reference, MR was correct in 14 of 15 instances (93.3%), CT cisternography in 5 of 8 instances (62.5%). Plain CT in 1 patient was negative.

Conclusion: In patients with a history of spontaneous CSF rhinorrhea, CT was required to detect osseous defects at specific sites of predilection. MR enabled differentiating the contents of herniated tissue and allowed identification of arachnoid tissue as a previously hardly recognized imaging finding.

Fig 1.

A–C, A 52-year-old man (patient 2) with intermittent CSF rhinorrhea for 2 months. A coronal high-resolution bone window noncontrast CT (A) early in this series reveals a soft tissue lesion within the right olfactory cleft adjacent to an osseous defect at the cribriform plate. After intrathecal administration of contrast material (B), a small loculation of contrast material is visualized (arrow) surrounded by isoattenuation of soft tissue. Endoscopic surgery revealed an arachnoid lined pouch within the olfactory cleft (C).

Fig 2.

A, B, Sagittal high-resolution bone window image depicts a 2-mm defect within the cribriform plate (arrow) in a 30-year-old patient with 4 months of intermittent CSF rhinorrhea (patient 8). The coronal T2-weighted image reveals a normal olfactory cleft. Isointense arachnoid tissue and CSF loculation originate from the junction of the cribriform plate and lamella lateralis and herniate into the frontal recess (long arrow) down to the middle meatus (long arrow). Proximity of the osteodural defect to the entrance point of the ethmoid artery is shown (short arrow).

Fig 3.

A, B, Coronal high-resolution bone window CT image (A) depicts a small erosion of the inferolateral recess (arrow) in a 70-year-old woman (patient 18) with massive intermittent CSF rhinorrhea for 7 months. The coronal T2-weighted MR image (B) shows a fluid level within the left sphenoid sinus, air within ventricles, and an air bubble below the left inferior temporal gyrus. Adjacent subcortical gliotic changes are present. A lesion with soft tissue isointense components and CSF is shown (long arrow), which corresponded to endoscopy, and histologic examination proved the presence of arachnoid tissue.

Fig 4.

A–D, An 18-year-old man with 1 episode of CSF rhinorrhea (patient 22). CT images depict arachnoid pits lateral to sphenoid sinus and osseous erosion lateral to the foramen rotundum (short arrow). The coronal T2-weighted image (C) reveals a CSF-filled pouch extending into the right inferolateral recess with some arachnoid strands (arrow). The endoscopic image (D, view from medial) depicts an arachnoid pouch (arrow) bulging into the sinus lumen.

Fig 5.

A–E, A 38-year-old woman (patient 24) with a history of meningitis 2 months ago. After sudden onset of a headache, the axial CT (A, B) shows a fluid level within the sphenoid sinus and subarachnoid air in the right prepontine and suprasellar cistern. At 14 days later after referral for further evaluation, sagittal CT (C) shows an aerated sinus and a small osseous defect within the posterior wall of the sphenoid sinus (arrow). Sagittal T2 and T1-weighted MR images (D, E) depict a small lesion (arrow) that herniates into the sphenoid sinus. Only in the clinical setting of CSF rhinorrhea the lesion is suspected to correspond to arachnoid herniation.