There is a reportedly higher risk of CSF leak and CSF fistula with ventral cervical surgery than with dorsal cervical surgery. The overall prevalence of CSF leaks after any type of primary ventral cervical spinal surgery is difficult to estimate but is probably slightly greater than 1%. In a large clinical series, Tew and Mayfield noted the occurrence of dural tears but did not report an exact incidence. Similarly, in a 5-year analysis of a survey of the membership of the Cervical Spine Research Society, Graham (2) reported that CSF leaks secondary to accidental dural injury had been observed, without reporting the precise rate of occurrence. Fielding (3) also mentioned the potential for dural tears, particularly during the opening of the overlying posterior longitudinal ligament (PLL). In their large series (450 patients) of anterior cervical discectomy, Bertalanffy and Eggert (4) encountered a dural tear in eight cases (1.8%), leading to a CSF fistula and consequent meningitis in single case (0.2%).

The reported incidence of dural tears and CSF fistulas after anterior cervical corpectomy for cervical spine stenosis resulting from various pathologic entities ranges from 0% to 8.3% (5). Hannallah et al. reviewed 1,994 patients undergoing elective cervical spine surgery over an 11-year period. The prevalence of CSF leaks was higher in patients with revision ventral procedures (1.92%), men (1.56%), and patients undergoing anterior cervical corpectomy and arthrodesis (1.77%) (6). MacDonald et al. reported an 8.3% incidence of CSF fistulas following multilevel anterior cervical corpectomies with fusion in a series of 36 patients who underwent two- to four-level cervical corpectomies for a variety of pathologies including spondylosis, ossification of the posterior longitudinal ligament (OPLL), and mixed pathologies. Three of these patients developed postoperative CSF fistulas.

The prevalence of CSF leaks is higher in patients with OPLL. In studies reporting exclusively on patients with OPLL, the rate can exceed 32% (Smith et al. (7)). Epstein and Hollingsworth (8) reported a 6% incidence of ventral CSF fistulas following circumferential cervical fusion in patients undergoing either corpectomies or multilevel cervical discectomies for OPPL. In her series of 82 patients with an average of 2.8 levels fused ventrally and 7 levels fused dorsally, there were 5 ventral cervical CSF fistulas (6% incidence) (8).

The risk for an incidental durotomy following cervical laminectomy ranges from 0.3% to 13%. The risk increases to up to 18% with revision procedures. Deen et al. reported a 1% incidence of dorsal CSF fistula following dorsal cervical fusion with lateral mass screws. Postoperative leakage may also occur along the dural suture line after intradural procedures or as a consequence of inadvertent durotomy during discectomy or laminectomy.

Though CSF leaks and fistulas can occur with any type of cervical spine surgery, recognition of the common clinical scenarios where the potential for these complications to arise is greater is the first step in avoiding this hazard. Meticulous preoperative planning specifically tailored to the underlying pathology will likewise help avoid creating a dural laceration. For example, patients with OPLL are at higher risk for dural violation and resultant CSF leak during ventral decompressive procedures. Preoperative recognition of dural involvement by the OPLL can be made on a computed tomography (CT) (C sign) and can lead to anticipation of problems and therefore more controlled management of an intraoperative CSF leak should it prove ultimately unavoidable (10).

The signs of dural ossification can be divided into two types based on the shape in relation to OPLL. Hida et al. (11) originally defined two CT findings that were indicative of dural ossification in cervical OPLL. The first, the single-layer sign, was defined by a large focal mass of uniformly hyperdense OPLL. This definition has been modified to include a hyperdense mass with a downward and/or upward tail along the dura mater on sagittal reformation of the CT scan and/or a single homogeneous mass on axial CT scan (10,12). The second sign, the double-layer sign, is characterized by ventral and dorsal rims of hyperdense ossification separated by a central hypodense mass, the hypertrophied, unossified PLL. Dural defects were identified intraoperatively in 10 of the 12 patients with double-layer OPLL compared with only one of the nine patients with single-layer OPLL (11). More severe stenosis of the spinal canal due to the OPLL was also associated with dural defect.

Min et al. retrospectively reviewed their outcomes in 197 patients with cervical OPLL who underwent anterior decompression and fusion. Signs of dural penetration were found in 30.5% of patients. The type of OPLL, singleand double-layer signs of dural penetration, and the diameter of the central hypodense mass of the double-layer sign were correlated with the actual incidence of dural penetration. Again, dural defects were more prevalent among patients with double-layer signs than those with single-layer signs (12). These results argue for obtaining a CT scan prior to ventral surgery if OPLL is suspected. Surgeons should be aware of the increased possibility of a dural defect in patients with a double-layer sign or a thick central hypodense mass in nonsegmental OPLL (11,12).

Even small dural tears can behave as one-way valves, with CSF egressing during maneuvers such as coughing, straining, and Valsalva maneuvers, then failing to reenter the subarachnoid space through the dural defect. Therefore, it is generally better to treat all dural defects, small or large, aggressively and effectively once they are recognized.

The conventional technique for repairing dural breaches involves direct suture primary closure, especially in dorsal defects or following intradural surgery. However, primary suture closure is not always feasible, and it does not always result in watertight closure, especially with lateral or ventral defects. Proponents of watertight dural repair often also augment the repair with fibrin glue. The potential for persistent CSF leaks has led to novel synthetic materials to assist in repairing dural defects (13). Adjunctive methods include the use of dural patches; fibrin glue products; autografts such as fat, pericranium, and fascial grafts; and a variety of synthetic and protein-based compounds including microfibrillar collagen. Other fundamental principles in treating intraoperative CSF leaks during cervical surgery include avoidance of Gelfoam and consideration of some method for CSF diversion.

Abe et al. successfully used gelatin sponge alone to repair a dural tear in three patients. The largest dural defect they encountered measured 350 mm² (14). Harsh et al. (15) covered the dural defect with gelatin sponge or a patch graft in the three patients who developed intraoperative CSF leak. However, it is worth noting that the use of gelatin sponges has occasionally been associated with significant mass effect complications in cervical spinal surgery. Given more recently available dural patch options, use of Gelfoam is probably best avoided (16,17).

Tew and Mayfield (18) reported covering the dural opening by a fascial graft with success. Gokaslan and Cooper (19) advocated coverage of the dural opening with a fascial graft for treating patients with dural tears along with insertion of a lumbar drain.

Smith et al. did not use immediate placement of lumbar drain (except in a single patient with a 300-mm² dural defect) routinely in patients with intraoperative dural tear. However, following their experience with 22 OPLL patients (7 of whom had intraoperative dural tears), they recommended patching of dural defects with a graft of muscle and fascia using an onlay technique, and insertion of a lumbar drain under the same anesthesia to be kept in place for at least 4 days (7).

Epstein and Hollingsworth (8) describe a technique of suturing or using microdural staples to anchor a pericardial graft in place for dural defects encountered following ventral surgery for OPLL. If the dural edge cannot be everted for the staples to catch, a simple onlay graft is placed, in all cases followed by application of fibrin sealant and dural graft matrix and a wound-peritoneal or a lumboperitoneal shunt (8). It is worth noting that in Epstein’s series of 65 patients, 1 of 3 patients who developed postoperative CSF fistula had dural absence from C2 to C7. These elaborate techniques are probably necessary for such large dural tears or for persistent or recurrent dural fistulas.

Additional recommendations to prevent formation of a CSF fistula in patients with dural absence due to OPLL include modifications of the usual postoperative regimen, such as limitation of mechanical pulmonary ventilation to the shortest time that is safely possible and use of antiemetic and antitussive medications to protect the remaining coverings of the spinal cord.

Finally, for a ventral dural tear during more limited decompressive procedures such as discectomy, a small
amount of fat can be gently packed into the dorsal portion of the disk space to seal off the ventral dural leak, being careful not to allow displacement into the spinal canal or compression of the spinal cord during graft or cage placement.

Midline dorsal dural lacerations are generally readily repairable primarily and can be treated effectively with a watertight dural closure and fibrin glue. Patients can be permitted to ambulate immediately after surgery and should generally not be kept at bed rest more than 24 hours (1).

Fat is an effective sealant because it is impermeable to water (20). A thin sheet of autologous subcutaneous fat that covers the dural repair as well as all exposed dura can be gently tucked into the edges of the laminectomy defect. Fibrin glue can be spread over the surface of the fat graft to augment the repair. Mayfield (21) demonstrated that an autologous fat transplant serves as an excellent water sealant, prevents scar formation, and does not adhere to the neural elements and that the fat survives for a long time and becomes revascularized.

A far-lateral tear can pose a technically more difficult problem for placement of sutures because these sites are inaccessible. In addition, a repair of a tear that is close to a nerve root is potentially dangerous because the suture may impale neural fascicles or cause traction or scarring of the nerve root. Given this use of a patch such as autologous fat transplant can be considered as a rapid, effective means for repair of a dural tear or defect that is inaccessible or unsuitable for standard suture technique.

Defects repaired with suture alone may leak at physiologic pressurization levels, while those supplemented with tissue adhesives may remain patent at higher pressures. Histologic sections obtained from dura treated with fibrin adhesive sealant demonstrates minimal inflammatory response, although sections obtained at the site of dural repair augmented with cyanoacrylate polymer feature significant inflammatory responses, including dural thinning, gliosis, and cortical necrosis (22).

Fibrin glue, a biologic adhesive, is made with highly concentrated human fibrinogen and clotting factors. It is used frequently in spine and neurosurgical procedures, in particular in the closure of the dura to prevent CSF leakage (23). It should be remembered that fibrin glue is best suited for dural closure augmentation and is not a substitute for surgical techniques; that is, it should be added to other modalities. The optimal method for using fibrin glue on the surface of the dura is as a spray. Fibrin plate/clot made by the spray method seals the dura so well that it can sustain a water pressure of over 80 cm H₂O, which is far greater than normal physiologic pressure of CSF (24). The identification of the definite site of CSF leakage is also of great importance and substantially improves the success rate. Muscle graft in combination with fibrin glue (presumably owing to its adhesive sealing properties) is superior to either muscle packing alone or fibrin glue in isolation.

Shaffrey et al. have reported a 93% effectiveness rate in cases with no preoperative CSF leakage (prophylactic use) and 67% in preestablished CSF fistula (therapeutic use). These investigators treated 15 patients with CSF leakage with fibrin glue and were successful in 10 cases (25). Milde (26) has reported an anaphylactic reaction to fibrin glue.