Sternberg's canal – A rare cause of spontaneous cerebrospinal fluid rhinorrhea

N Jayaprakash, R Raja Kumar, B Devanand, Vinu AS Vaishnavi 
 Department of Radiology, PSG Institute of Medical Sciences and Research, Peelamedu, Coimbatore, Tamil Nadu, India

Correspondence Address:
Dr. N Jayaprakash
Department of Radiology, PSG Institute of Medical Sciences and Research, Peelamedu, Coimbatore - 641 004, Tamil Nadu
India

Full Text

Sir,

We present the case of a 37-year old female patient with complaint of acute-onset profuse watery discharge, neither foul-smelling or blood-stained, from the right nostril, which increased on bending forward. The patient had no history of trauma or symptoms of raised intracranial pressure. Local examination showed deviation of the nasal septum towards the left.

High-resolution computed tomography (CT) cisternogram was performed by instilling 8–10 ml of an iodinated nonionic low-osmolar contrast agent into the thecal sac following a lumbar puncture. The reviewed plain images showed an osseous defect of size 3.5 mm in the inferolateral wall of the right sphenoid sinus [Figure 1]. On post-intrathecal contrast images, an active leak of iodinated contrast and its pooling was noted in the right sphenoid sinus, which was draining through the right nostril [Figure 2]a, [Figure 2]b, [Figure 2]c.{Figure 1}{Figure 2}

On, endoscopic transpterygoid approach, the dehiscent area with the visible dura in the right sphenoid sinus was identified and was cauterized [Figure 3]a and [Figure 3]b. The sinus was cleared of all its mucosal lining and obliterated with fat and gelfoam.{Figure 3}

The presence of cerebrospinal fluid (CSF) rhinorrhea indicates the existence of an abnormal communication between the intracranial CSF spaces and the nasal cavity. Posttraumatic CSF rhinorrhea as a complication of a base of skull fracture is the most common cause. The incidence of non-traumatic causes of CSF rhinorrhea is approximately 3–4%. The causes of nontraumatic CSF rhinorrhoea are skull base tumors, destructive granulomatous processes such as Wegener's granulomatosis, and complicated sinonasal infections.[1],[2],[3]

Spontaneous CSF fistula is a separate entity with no underlying cause accounting for the CSF leak. Spontaneous leaks are more common in middle-aged women, and commonly a co-existing encephalocele is seen.[2] The pathogenesis of this condition is thought to be a combination of embryological and acquired factors. The medial aspect of the temporal bone may fail to develop, resulting in a persistent lateral craniopharyngeal canal (also known as the Sternberg canal) between the middle cranial fossa and the pneumatized inferolateral recess of the sphenoid sinus.[3] A patent Sternberg's canal has been reported in up to 4% of adults.[3],[4] Spontaneous CSF fistulae are most common in the anterior cranial fossa at the ethmoid roof and cribriform plate. Less common sites include the sphenoid sinus, around the sella, or at the inferolateral or pterygoid recesses.

The goals of imaging in CSF fistulae are to confirm the diagnosis, evaluate for any underlying cause, localize the defect site, and exclude an associated meningoencephalocoele responsible for the CSF leak through the defect.[4],[5] Successful treatment depends on the accurate preoperative localization of the site of the fistula, especially in the present era when a vast majority of CSF leaks are now repaired by endoscopic surgery.

A high-resolution computed tomographic (CT) scan without intrathecal contrast administration has a low sensitivity for the detection of the osseous-dural defect. Accuracy is significantly increased by introducing a low-osmolar contrast material into the subarachnoid space (CT cisternography), which improves the sensitivity for detection of active leaks to 80–85%.[6],[7] Inactive or intermittent fistulae may not be demonstrated; however, a high-resolution CT scan is best for detecting the bony anatomical details and is useful in the preoperative planning of these patients.

Imaging helps in deciding whether transcranial or transnasal endoscopic surgical management would be useful. The reported success rates approach 90% in transnasal endoscopic management, which is superior to the technique of open repair.[4] Some cases, however, are not amenable to endoscopic techniques; these include patients with high-pressure leaks, multiple defects, large defects, or those with a very well-pneumatized sphenoid sinus with lateral recesses.[4] All these conditions may be very well identified using CT cisternography.

To conclude, spontaneous or primary CSF fistula is a rare cause of CSF rhinorrhea. Various imaging modalities including a CT scan with bone windows, CT cisternography, and radioisotope scanning may be used for its preoperative evaluation. CT cisternography is most valuable in the preoperative localization and characterization of the defect, especially if a transnasal endoscopic approach is planned.

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Nil.

Conflicts of interest

There are no conflicts of interest.

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