Abstract
The surgical management of sphenoid CSF leaks and encephaloceles has evolved significantly over the past century. The major paradigm shifts have included the transition from open to endoscopic approaches and the use of vascularized flap reconstruction techniques. These methods have dramatically improved success rates while reducing morbidity for patients suffering from these disorders.
Keywords
CSF leak, encephalocele, meningoencephalocele, nasoseptal flap, sphenoid
Introduction
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Dandy, in 1926, was the first to report a transcranial technique for the closure of a cerebrospinal fluid (CSF) leak using a fascia lata graft.
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Open approaches were associated with morbidities, including seizures, memory deficits, and intracranial hemorrhage.
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Dohlman pioneered an extracranial technique in 1948 with success rates approaching 80%.
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The first transeptal and fully endonasal approaches were introduced by Hirsch and by Vrabec, respectively.
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The first endoscopic CSF leak repair was reported by Papay et al. in 1989.
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The importance of the lateral extension of the sphenoid sinus with respect to CSF rhinorrhea was recognized as early as 1965 by Morley and Wortzman.
Anatomy
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The majority of the sphenoid bone is formed from the endochondral ossification of five discrete ossification centers beginning in the thirteenth week of development.
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Incomplete fusion of the greater wing can result in persistence of a lateral craniopharyngeal canal, which was first described by Sternberg in 1888 and may be seen in up to 4% of patients.
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A role for the Sternberg canal in the pathogenesis of lateral sphenoid CSF leaks is doubtful.
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The degree of pneumatization may be quite variable and when assessed in the sagittal plane may progress from a relative lack of aeration or “conchal” pattern (5%–10%), through a presellar pattern (25%–30%), and ultimately to a postsellar pattern in which pneumatization extends posteriorly to the level of the clivus (65%).
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When viewed in the coronal plane, lateral pneumatization into the pterygoid plates is evident in 35.3% of subjects and is bilateral in 17.4%.
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Tomazic and Stammberger reported a series of five sphenoid CSF leaks, noting that 100% were associated with a patent canal. Conversely, Bernal-Sprekelsen et al. found that among 25 patients with lateral sphenoid leaks, 24 were lateral to the foramen rotundum, which suggests no association with a Sternberg canal.
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A more accepted etiologic factor in these spontaneous lateral sphenoid lesions is chronic benign intracranial hypertension (BIH).
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Although lateral sphenoid CSF leaks most commonly occur spontaneously, central leaks tend to result from iatrogenic causes, often in the setting of prior transsphenoidal pituitary surgery.
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The vidian canal and its associated neurovascular bundle is a key anatomic landmark in the management of these lesions because it may be used to orient the surgeon in both the approach and the localization of critical intracranial structures adjacent to the defect.
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The vidian nerve can serve as an important landmark in this region because it can reliably be traced to the lateral surface of the anterior genu of the petrous carotid artery.
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In the midline, the sella contains the pituitary gland, which is surrounded by its associated dural reflections, hypophyseal arteries, optic chiasm, and superior and inferior intercavernous sinuses ( Fig. 27.1 ).
Fig. 27.1
Drawing of a coronal cross-section through the sphenoid sinus and associated structures. Note that loss of bone is depicted over the patient’s left cavernous sinus, V2, vidian nerve, and carotid artery as can often present with encephaloceles. a., Artery; n., nerve.
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The cavernous sinus proper lies immediately lateral to the pituitary fossa and transmits multiple cranial nerves as well as the cavernous (or C4) segment of the internal carotid artery.
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With extensive pneumatization, the sphenoid may continue laterally to the foramen rotundum beneath the floor of the middle cranial fossa. Inferiorly, this pneumatization pattern may extend into the pterygoid plates inferolateral to the vidian canal.
Preoperative Considerations
Patient History
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Clinical symptoms may include CSF rhinorrhea (85%), chronic headache (77%), and a history of meningitis (15%). Patients with spontaneous leaks often have increased body mass index with its associated comorbidities, including hypertension, sleep apnea, and BIH.
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Any history of trauma, inflammatory rhinologic disorders, or prior surgeries (particularly transsphenoidal pituitary procedures) should be elicited.
Clinical Diagnosis
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Confirmation of CSF rhinorrhea may be performed by testing the fluid for the presence of β 2 -transferrin. Samples collected by the patient will remain stable for β 2 -transferrin testing for up to 1 week at room temperature.
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Nasal endoscopy may reveal fluid or a meningoencephalocele sac emanating from the sphenoethmoid recess; however, negative examination findings do not preclude the presence of a pathologic process.
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Pneumatic otoscopy should also be performed in these patients to exclude the presence of middle ear fluid, which raises concern for a primary or synchronous temporal bone CSF leak.
Intrathecal Fluorescein Administration
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Intrathecal fluorescein administration is a useful adjunct in the management of these lesions. The most common dose is 0.1 mL of 10% sodium fluorescein mixed with 10 mL of the patient’s own CSF or sterile saline and injected over a 10-minute period.
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Patients must be counseled that this represents an off-label use and that seizures and other neurologic complications have been reported with the use of fluorescein at higher doses.
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Excitation of the fluorescein with blue light leads to emission of green wavelengths and, when used in conjunction with a blue light–blocking filter, helps to maximize visualization of even small volumes of stained CSF.
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Placement of a lumbar drain also provides an opportunity for the measurement of opening pressures, which may help to guide postoperative management.
Radiographic Considerations
Computed Tomography
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Fine-cut, noncontrast, maxillofacial computed tomography (CT) scans should be obtained for any patient with a suspected sphenoid CSF leak or meningoencephalocele.
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The use of image guidance may be quite helpful; if this is planned, the CT images can be ordered using the available institutional image guidance protocol.
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The pneumatization pattern and status of the skull base should be assessed in all three planes. The site of the lesion may be indicated by a focal attenuation of the middle fossa bone or frank dehiscence with soft tissue prolapse.
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The presence of any Onodi cells, laterally based partitions, or dehiscence of the optic nerves or internal carotid arteries should be noted. The location of the vidian canal and foramen rotundum should be identified and the site of abnormalities relative to these structures noted.
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In the setting of BIH, the CT may reveal several additional stigmata, including an empty sella, arachnoid pitting in the middle cranial fossa, and thinning of the tegmen ( Fig. 27.2 ).
Fig. 27.2
Noncontrast coronal computed tomography (CT) images from patients with lateral sphenoid meningoencephaloceles (white arrows). The patient in (A) has a more significantly pneumatized lateral recess than the patient in (B) . Note the significant amount of right middle fossa arachnoid pitting seen in (B) . The relative positions of the optic nerve (O), foramen rotundum (R), and vidian canal (V) are shown.
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The location of the lesion relative to the foramen rotundum should be determined because this will dictate whether a medial, transethmoid, or transpterygoid approach will be required to gain adequate surgical access.
Magnetic Resonance Imaging
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Use of T1- (with and without gadolinium) and T2-weighted magnetic resonance imaging (MRI) allows for soft tissue characterization, which helps to differentiate between a CSF leak, encephalocele, and meningoencephalocele.
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The MRI scan provides additional information on the relationship between the various segments of the internal carotid artery and the site of the defect. Although it is uncommon, the MRI may also provide evidence for any prolapsed intracranial vasculature associated with the defect. If this is a concern, magnetic resonance or interventional angiography should be performed to further characterize these vessels.
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An empty sella resulting from prolapse of the suprasellar arachnoid cistern into the sellar cavity is also easily seen on a sagittal T1-weighted MRI scan and provides confirmatory evidence for the presence of elevated intracranial pressures.
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The MRI may be overlaid with the CT data to provide simultaneous intraoperative information on the local bony and soft tissue anatomy.
Adjunctive Imaging
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The use of angiography, CT/MRI cisternography, and radioactive tracer studies in the workup of these lesions has been previously described. Their use has declined with the increasing popularity of β 2 -transferrin and intrathecal fluorescein confirmatory testing.
Instrumentation
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Adequate exposure of sphenoid CSF leak and meningoencephalocele sites should allow the use of primarily straight instrumentation. The intermittent use of angled endoscopes and instruments with distal angulations may occasionally be required ( Fig. 27.3 ).
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0- and 45-degree endoscopes
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J-curette and ball-tip probe
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15-degree diamond drill
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Straight and curved suction devices
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Upbiting and downbiting 2-mm Kerrison punches
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Straight Blakesley forceps
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Endoscopic clip applier
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Bipolar cautery
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