Endoscopic Management of Cerebrospinal Fluid Leaks

The diagnosis and management of a CSF leak involves three critical steps:

• Distinguishing a CSF leak from other sources of rhinorrhea

• Locating the fistula

• Ruling out high intracranial pressure secondary to altered CSF dynamics

  • Demographic information can help to guide the workup; spontaneous CSF leaks are most commonly seen in young or middle-aged obese females.

  • Hydrocephalus can be the result of posttraumatic, postsurgical, and postinfectious scenarios due to obstruction of the arachnoid villi.

A clinical diagnosis of a CSF leak is based on a history of rhinorrhea:

• Clear, watery nasal drainage

• Usually the rhinorrhea is unilateral.

• Commonly associated with headache

• Increased rhinorrhea when the patient leans over, tilts the head forward, or performs a Valsalva maneuver

History of tumor, trauma, or previous surgery involving the paranasal sinuses or cranial base heightens the level of suspicion.

Occasionally, a life-threatening complication arising from the CSF leak, such as pneumocephalus, or ascending bacterial meningitis may be the initial presentation.

Conditions such as vasomotor rhinitis and sympathetic denervation can cause profuse rhinorrhea that may be confused with a CSF leak.

Nasal irrigations during ESS (or used as part of the postoperative care) may accumulate in the paranasal sinuses and later present as postoperative rhinorrhea.

A full examination of the head and neck, including endoscopic examination of the nasal cavity, should be completed to attempt to identify the source of CSF rhinorrhea.

Having the patient “provoke” the leak, by bending over in a “head down” position, can sometimes help to identify the site of an active leak.

When CSF rhinorrhea develops after sinus surgery, the endoscopic surgeon typically has an impression as to the possible site of injury to the cranial base.

• A thorough endoscopic office examination of the nasal cavity may corroborate the site of the leakage.

• Fistulas with low-pressure leaks are difficult to identify, especially in the presence of postoperative tissue edema and blood clots.

Biochemical testing is indicated to confirm the true nature of the nasal drainage and should be done prior to ordering expensive imaging tests.

• CSF will typically be high in glucose and low in protein.

• Normal nasal discharge has been shown to be falsely positive for glucose in 45% to 75% of cases.

• β ₂ -Transferrin is a protein found in CSF, aqueous humor, and perilymph but not in blood or nasal secretions; therefore β ₂ -transferrin is a reliable chemical marker of CSF leakage.

• A second protein, β-trace protein, is also available but not as widely used as β ₂ -transferrin.

Multiple imaging modalities have been advocated for the diagnosis of CSF leak, each with their own advantages and disadvantages.

• Scintigraphy with indium (In-111) is one test that has been advocated for the identification of a CSF leak.

• Radiotracing is a very sensitive test; however, it is associated with a high false-positive rate and has poor resolution that precludes establishing the specific point of leakage; at our institution, scintigraphy is rarely performed.

In our practice, the presence of the CSF leak is typically confirmed with β ₂ -transferrin electrophoresis, and its site of origin is identified by computed tomography (CT), magnetic resonance (MR) or CT cisternography ( Fig. 116.1 ), and/or endoscopy.

An important consideration in a patient presenting with spontaneous rhinorrhea or rhinorrhea after skull base trauma is to distinguish whether the CSF rhinorrhea arises from the sinonasal tract or from other sites, such as the middle ear or mastoid ( Fig. 116.2 ).

A CSF fistula in the temporal bone may drain into the nose through the eustachian tube.

Radiographically, a high-resolution computed tomography (HRCT) can be used to identify a cranial base defect.

• HRCT is our preferred initial imaging study to aid in the identification of the site of injury and its extent (see Fig. 116.1 ).

• HRCT with contrast also provides information about the possibility of intracranial complications, such as hematoma or brain contusion, that occur in the setting of acute trauma (iatrogenic or accidental).

• HRCT with cuts taken in the coronal and sagittal planes is essential to evaluate the integrity of the bony wall in question.

• Coronal CT views are best to evaluate defects of the cribriform plate, fovea ethmoidalis, or planum sphenoidale, whereas axial views are superior to evaluate the posterior wall of the frontal or sphenoid sinuses.

• Indirect signs of a CSF leak include collection of fluid in a sinus and pneumocephalus.

We use magnetic resonance imaging (MRI) to differentiate meningocele and meningoencephalocele ( Fig. 116.3 ), as well as to better delineate the vascular anatomy, which is important when considering a surgical repair.

HRCT, although an excellent first imaging choice, may not identify small areas of surgical trauma or linear nondisplaced fractures.

• HRCT can be used in conjunction with intrathecal contrast to identify the fistula, a so-called CT cisternogram; this test has been documented to be both sensitive and reliable.

• However, identification of the fistula using contrast studies requires the presence of an active leak, which is not always the case clinically.

• Intermittent leaks that are temporarily sealed by edema, inflammation, or brain herniation may yield a false-negative result.

• Intrathecal injection of saline solution to increase the CSF pressure, a “saline challenge,” enhances the sensitivity of the test.

MR cisternography has been suggested to complement the information offered by an HRCT; however, in our experience this technique has yielded inconsistent results.

CSF leak with biochemical confirmation

Failure to confirm the presence of a CSF fistula on biochemical testing

Patient medically unfit for general anesthetic

Active infection of the sinonasal tract

Intrathecal fluorescein may be used to aid in the diagnosis and localization of the CSF leak.

During this test, 0.15 mL of fluorescein, of a concentration no greater than 5%, is diluted with 10 mL of CSF, obtained through a lumbar puncture, and is then injected slowly intrathecally over 3 to 5 minutes.

Fluorescein is neurotoxic and a low concentration–low volume injection is mandatory to avoid the neurologic complications associated with higher concentrations.

After intrathecal injection of the fluorescein solution, the CSF leak may be visualized using the nasal endoscope.

• Under a Wood lamp (i.e., black light), fluorescein will appear as bright yellow-green; nonetheless, the yellowish color of fluorescein may be identified without the need for special lighting.

Some clinicians have been discouraged from using fluorescein because of:

• The logistics of performing a lumbar puncture in an outpatient setting

• Medicolegal considerations (the fluorescein drug package insert includes an advisory warning against intrathecal use)

Intrathecal injections, in any case, are rarely critical to the identification of the CSF fistula.

Exceptional patients are those with multiple fistulas, such as those who suffered skull base fractures, and the rare patient who presents with repeated episodes of meningitis in the absence of an apparent cranial base defect or other predisposing factors, such as rhinosinusitis or otitis media.

Others have advocated the intrathecal injection of air, which can “bubble” out at the fistula site, thus aiding in its identification.

• Of note, air is an irritant to the brain and may induce seizures.

• Alternatively, normal saline solution may also be injected into the intrathecal space to increase the pressure within the subarachnoid space and increase flow at the site of the leak.

As with all ESSs, controlled hypotension is beneficial in improving visualization.

An oral Ring, Adair, Elwyn (RAE) tube may be beneficial to ensure the anesthesia circuit does not interfere with the surgery.

The use of topical vasoconstrictors is essential to improve visualization, and communication with anesthesia is important because of their vasoactive properties.

It is important to communicate with the anesthetist and anesthesia team that theoretically there is a risk of pneumocephalus with an open skull base defect and positive pressure mask ventilation should be avoided; a nasal airway can be considered.