Incidental tear of the dural sac and cerebrospinal fluid leak is an unfortunate but real complication during lumbar spinal surgery that must be treated by surgeons intraoperatively and postoperatively. Scrupulous attention given to surgical technique will go a long way in preventing many instances of incidental durotomy. However, because of advances in instrumentation, coupled with more aggressive attitudes toward lumbar surgery, dural tears are inevitable and surgeons are likely to encounter increasing numbers of cerebrospinal fluid leaks. Leakage from a dural tear may be visually apparent intraoperatively, but there also are very sensitive tests to detect cerebrospinal fluid in a less impressive exudate. Additionally, cerebrospinal fluid leakage may occur because of a postoperative dural tear. When detected intraoperatively, primary repair is the ideal course of action, but other effective methods of treatment are available should simple suturing not be feasible. Detection of a cerebrospinal fluid leak postoperatively may not be as straightforward, and may require a combination of clinical and radiographic information. Here the standard of treatment is slightly more controversial, and many treatment strategies have been examined. When clinical suspicion exists, detection is prompt, and treatment is adequate, outcomes generally are favorable without long-term sequelae.
Several deleterious consequences of inadequately treated dural leaks have been reported. 3,17,25–28,43 Dural-cutaneous fistulas may form, leading to meningitis, 17 arachnoiditis, or epidural abscess. 43 A subcutaneous fluid collection prevents proper wound healing and may lead to breakdown, infection of the incision, or both. Continuous cerebrospinal fluid leak also predisposes the wound to pseudomeningocele formation, with possible trapping of nerve roots and neurologic symptoms such as sciatica and cranial nerve palsies, particularly of cranial nerve VI, which manifests as strabismus. 3,25,27,28 Finally, a debilitating headache that arises when the patient sits upright and resolves on recumbency may occur. 26 Nevertheless, despite the many possible negative consequences of dural tears, diagnostic and therapeutic modalities exist that can minimize morbidity substantially.
Incidental durotomy is the most frequent complication during spinal surgery. In a series of 641 consecutive patients who underwent lumbar decompression surgery, Wang et al 45 reported 88 dural tears, a rate of 14%. An analysis by Stolke et al 39 of 412 primary and 69 reoperations for herniated disc revealed a dural tear prevalence of 1.8% of microdiscectomies, 5.3% of macrodiscectomies, and 17.4% of reoperations. Other studies have shown prevalence rates of 4%8,15 and 5.3%44 for various lumbar procedures.
In a large study conducted by Deyo et al, 7 18,122 spinal procedures were evaluated for all postoperative complications, including dural tear, and mortality. Morbidity and mortality were lowest for patients undergoing procedures related to herniated discs and for younger patients. This rate increased with age and with procedures for spinal stenosis, degenerative changes, and reoperations; however, even patients 75 years or older had a mortality rate related to the surgery of less than 1%. Although not analyzed specifically for incidental durotomy, this study concluded that complication rates and prolonged hospital stays increased dramatically with age and for procedures other than simple discectomies. 7
Unintended entrance into the dural sac also may occur with instrumentation. Davne and Myers 6 studied 486 patients who underwent 533 variable screw placements during a 5-year period. They reported only occasional dural tears, all of which were repaired primarily, and none of which required reexploration. In another series of 124 patients undergoing posterior spinal fusion with variable screw plate fixation, seven cases of dural tears were reported (5.6 %). 46
Mechanisms of Dural Tear
Dural disruption and subsequent cerebrospinal fluid leak can occur through various mechanisms. Most frequently, during spinal surgery, direct trauma or laceration causes dural tear. Because the environment is controlled and the tear usually is detected intraoperatively, this is the most reported and studied cause of tear. The particular diagnosis also varies, and may include herniated disc, spinal stenosis, spondylolisthesis, and instability from previous spinal surgery. 15 The incidence of dural tear differs depending on the procedure. Dural entry is much more common in revision procedures, usually because of adhesions in the epidural space and dural scarring and fibrosis. Causes of tears during primary procedures include eroded or thin dura, adhesions and fibrosis, or dural redundancy in patients with severe spinal stenosis. 26 Severely herniated discs may render nerve root dissection and dural retraction difficult. A less common cause of an iatrogenic dural tear is failure to recognize spina bifida occulta preoperatively.
Intraoperative mechanisms other than direct laceration of the dura include excessive nerve root traction and implantation of instruments. Excessive and traumatic nerve root traction is rare, and usually can be prevented by meticulous surgical technique. The use of transpedicle screw plates and other cross-links are related to a small but nonnegligible risk of dural tear. 6 In particular, faulty screw placement has been shown to cause a small number of tears. Instrumentation may lead to more dead space, and prevent the paraspinal muscles from effectively tamponading a small dural tear, leading to a greater risk of a clinical cerebrospinal fluid leak. 26
Although less common, other mechanisms may lead to cerebrospinal fluid leak postoperatively. Residual bone spikes may puncture the dural sac postoperatively. The integrity of the dural tissue may break down in the presence of infection, which is particularly relevant in the case of a primarily repaired dural tear. Other factors to consider are any patient actions that act to increase cerebrospinal fluid pressure through a Valsalvalike effect, such as coughing, violent awakening from anesthesia, or postoperative seizures. Increased intraabdominal and intrathoracic pressure, produced through a Valsalva maneuver, has been shown to increase pressure in the epidural space. 40 This effect can be used intraoperatively to distend the dura and visualize cerebrospinal fluid leakage, 36 and any patient action which similarly increases fluid pressure may disrupt a dural repair.
Finally, aside from iatrogenic etiologies of incidental durotomy, many dural tears occur because of trauma. This has been described for many traumatic injuries, including large missile wounds and burst fractures. 5 Cammisa et al 5 evaluated the incidence of dural tears with burst fractures, or axial loading vertebral fractures, and found that a burst fracture with an associated laminar fracture was 100% sensitive and 74% specific for the presence of a dural tear. They theorized that with vertical loading, the pedicles splay laterally, and bone is retropulsed from the vertebral body, impinging on the dural sac. When the load dissipates, the bone retracts and the dura and nerve roots remain trapped in the bony fragments. Improved means of repairing bony injuries of the lumbar spine and increased power of imaging modalities lead to more aggressive repair of spinal injuries, so that posttraumatic dural tear is being encountered more frequently by spine surgeons.
Many opportunities for effective treatment of incidental durotomy exist, but prompt diagnosis and repair is critical. Detection of dural tears involves two different scenarios—intraoperative and postoperative cerebrospinal fluid leak. When durotomy attributable to surgical manipulation does occur, intraoperative identification is ideal. Fortunately, in most cases, fluid extravasation can be visualized directly. Many times, however, a dural tear will not rupture the arachnoid membrane, and cerebrospinal fluid leakage will not occur. Because of the thin, delicate nature of the arachnoid, incidental increases in cerebrospinal pressure almost inevitably will lead to rupture and a fluid leak postoperatively. This must be treated intraoperatively as though a leak does exist. 31 Additionally, continuous cerebrospinal fluid egress will decrease hydrostatic pressure in the thecal sac, leading to decreased tamponade pressure of the local epidural veins. This may lead to rebleeding of sites that had been controlled previously and may be an additional clue of cerebrospinal fluid leakage. 26
Postoperatively, detection of a dural tear may be more difficult. Clinical history, physical examination, imaging studies, and laboratory tests all may be necessary to identify a cerebrospinal fluid leak. A subcutaneous or subfascial fluid collection, or frank wound drainage may be early clinical findings, and a cerebrospinal fluid leak, wound infection, liquefied hematoma, seroma, or abscess all must be considered. Whether instrumentation was used or whether the patient had a revision procedure also must be taken into account. When the diagnosis is in question, immunofixation electrophoresis for β-2-transferrin can be done. Beta-2-transferrin is a protein produced by cerebral neuraminidase and is found only in cerebrospinal fluid and perilymph. 34 The assay requires as little as 1 or 2 drops of the suspected fluid, which may be transported on carriers such as a bed sheet or gauze and decontaminated by the laboratory. 37 The average completion time from receipt of the sample is 3 hours, and most hospital laboratories are equipped for the test. This has been shown to be a very sensitive and specific test for the presence of cerebrospinal fluid. 32,34,37
Severe postural headache is a classic symptom of postoperative cerebrospinal fluid drainage and may be associated with posterior neck pain or stiffness, nausea, vomiting, diplopia, blurred vision, tinnitus, or vertigo. 2 Usually, the headache is retroorbital or frontal, and resolves on recumbency. Decreased cerebrospinal fluid pressure leads to loss of buoyancy and caudal displacement of cranial contents, which stretches the pain-sensitive meninges, and causes a severe headache. 41 Aside from patient discomfort, possible complications of headache caused by cerebrospinal fluid hypotension include subdural hematoma or hygroma and herniation of the cerebellar tonsils. 10 Patients who have pseudomeningocele develop may present with a postural headache after a long asymptomatic period and may have gradually worsening sciatica attributable to nerve root entrapment, often the complaint for which they underwent the initial procedure. Therefore, a postural headache combined with new or worsening sciatica suggests the presence of a pseudomeningocele. 28
Imaging studies are invaluable tools for detection of a cerebrospinal fluid leak postoperatively. Magnetic resonance imaging (MRI) has excellent resolution of soft tissue structures and fluid, and as such is very sensitive for cerebrospinal fluid accumulation and pseudomeningoceles. One study of 24 patients with suspected cerebrospinal fluid fistulas compared the results of MRI with surgical findings and found that MRI was accurate in all 24 patients (100%). 14 In a small series by Vakharia et al, 41 MRI consistently elucidated a focal accumulation of extrathecal clear or blood-stained fluid. High-resolution computed tomography (CT) is most useful in detecting bony defects and may accurately delineate fluid collections adjacent to bony lesions. 12 Although this may be helpful in cerebrospinal fluid rhinorrhea or otorrhea after surgery, most lumbar fistulas will not be amenable to detection by conventional CT scan. 28
In more complex cases, when a cerebrospinal fluid fistula is suspected clinically but not shown by MRI, newer imaging techniques have proved useful. Contrast myelography, with injection of contrast material into the thecal sac, has been used with some success. This technique, often used with CT, may show structural lesions, but several cases have been reported where myelography is unsuccessful in detecting small fistulous tracts. 2,29 Cisternography with CT has become popular recently in localizing cerebrospinal fluid fistulas, but is invasive, time-consuming, and contraindicated in patients with intracranial mass lesions. Moreover, it is insensitive for detecting fistulous tracts that are not actively draining at the time of the study, and it necessitates ionizing radiation. 9,14
Radionuclide cisternography is a technique that involves injection of a radionuclide tracer, as opposed to radiopaque contrast material, into the subarachnoid space, and MR images are obtained. This technique shows cerebrospinal fluid as a high signal without the use of contrast media and can be done relatively quickly without ionizing radiation. Advantages are that it is minimally invasive, is more physiologically sensitive, and usually can detect even the smallest fluid extravasation. 2,9,18,20,29
The most important aspect of treatment of a cerebrospinal fluid leak is prevention. Knowledge that dural tears occur more frequently in patients undergoing multiple spinal surgeries should lead to careful preoperative planning and meticulous, systematic surgical technique during such procedures. It is recommended to begin dissection in areas of unscarred tissue and proceed toward the potentially scarred regions. 26
When dural injury occurs and is detected intraoperatively, primary repair is mandatory. 8,13,16,26,36,45 Adequate exposure and visualization of the involved area is essential. The authors’ choice of repair is a simple running suture with tight apposition of the dural edges creating a watertight seal. This is done in part by using a double passage and one knot above the cephalad end of the tear. An effective repair technique must be easy to master and perform and not be overly time-consuming. One must create a completely watertight seal to avoid reoperation. The technique described below was developed by the senior author (SJB) and has evolved for many years to achieve all of the above.
One first must probe the tear with a Penfield Number 4 dissector, identify the extent of the tear, and expose it completely. This also requires that the laminectomy site be expanded in all directions to give adequate working room. One should gently suction the cerebrospinal fluid from the leak to allow the floating nerve roots to fall anterior and to relax the dural edges. Use of the Trendelenburg position will facilitate this. A very small cottonoid in the defect during the early part of the closure will facilitate a dry field.
The authors prefer to use 5-O Gore-Tex (W. L. Gore & Associates, Flagstaff, AZ) suture on a TT9 needle (W. L. Gore & Associates), but other dural sutures also are available. One may need to bend the curve of the needle a bit more tightly. Benefits of the Gore-Tex® suture material are several, in that it is white, clearly visible, very strong, and flat, creating a very small suture passage hole. The hole does not enlarge during the repair, and leakage through the suture passage hole does not occur. It ties easily with very few knots. The needle is flexible, thin, and malleable.
One should initiate the repair with the first passage a few millimeters proximal to the cephalad edge of the leak and perform a simple running suture to below the distal end of the tear (Fig 1). The first knot should be tied with two throws and the short end should be held with a small hemostat to lift the dura dorsally. During the passage one should maintain light tension on the suture material. When the running suture has passed below the rent, a second row is passed back toward the proximal end where the original knot is located. It then should be tied a second time with three additional throws (Fig 2). This technique, thereby, uses one suture strand doubled up and with one knot proximal to the tear. After closure, a small steroid-soaked Gelfoam is placed anterior to the nerve root extradurally, and may inhibit perineural scar postoperatively. At this point, Trendelenburg position should be reversed to refill the dural sac in the area of the repair. An induced Valsalva maneuver then is done by the anesthesiologist to increase intrathecal pressure. Placement of a small piece of double-layered blood-soaked Surgicel (Ethicon, Inc, Somerville, NJ) over the repair may enhance the dural rent seal.
A tight fascial closure with nonabsorbable suture material is extremely important. Removing the spinous processes and mobilizing the paraspinal muscle on either side can facilitate such closure. In a chronic tear, if the paraspinal muscles will not approximate easily, then lateral relaxing incisions made bilaterally to mobilize the muscle and fascia will allow one to lift and pull the muscle toward the midline over the defect, even in the presence of instrumentation. No wound drains are used, and nonabsorbable fascial sutures are recommended. It is imperative that the closure is watertight and that it withstands the strength of the Valsalva maneuver at the conclusion of the suture repair. Additional sutures may be added if necessary. It is equally as important that the fascial repair be watertight, which can be accomplished consistently with a combination of interrupted sutures followed by a running suture.
A smooth reversal of anesthesia is critical so that coughing and wretching on the endotracheal tube is kept to an absolute minimum. A urinary catheter should be left in place 3 days to facilitate the recommended 3 days of bed rest in the hospital. The catheter may be left in at discharge for 7 additional days at home. If it is removed, the patient is allowed out of the bed during the first 10 postoperative days only for bathroom privileges and meals. Laxatives are indicated and narcotic usage should be minimized to decrease the chance of constipation and urinary retention that requires straining by the patient.
A leak that persists and requires additional surgical repair will be a source of frustration and consternation for the surgeon and the patient. Repeated trips to the operating room for unexpected wound complications such as a persistent dural leak may be a factor in litigation. Careful and meticulous adherence to the principles and techniques described above will minimize these problems. In the senior author’s (SJB) experience, a 10-day course of postoperative bed rest decreases the risk of continued leakage. This period of bed rest and inactivity usually is well tolerated by the patient and is a minor inconvenience in comparison with the need to reoperate on a tear that continues to leak or reopens in the early postoperative period.
If primary suturing is not possible, other options exist for dural closure. Dural lacerations that occur more laterally, are inaccessible, or do not allow approximation of tissues are more challenging. The authors simply will plug the dural rent with a small piece of muscle and use the suture method described above. An easily accessible dorsal lesion that cannot be closed primarily may be amenable to a fascia patch graft. A small piece of autologous fascia from the fascia lata or the paravertebral muscles may be anchored, sutured, and trimmed over the defect, allowing a good watertight seal, but is technically difficult and time consuming. 8 For a lateral inaccessible tear, Mayfield and Kurokawa 22 described the lateral patch technique. A small piece of muscle or fat is tied to a suture and a second midline durotomy is created. The graft then is inserted into the thecal sac and pulled through the lateral defect from the inside out, effectively plugging the tear.
Fibrin glue is a biologic adhesive that has been used to augment dural repairs. Preparation of the glue consists of mixing two solutions: one containing fibrinogen and other clotting factors, and the second containing calcium and thrombin. Mixing the two solutions allows the fibrinogen to be converted to fibrin monomers, which forms a gel-like substance that is pliable and adhesive to tissues. Alternatively, the solutions may be mixed and sprayed on the desired surface. Fibrin glue has several attractive qualities that are necessary in a tissue adhesive: it is readily available, economical, easy to handle, consistently forms a watertight seal, and invokes minimal inflammation while activating the coagulation cascade. 4 Spine surgeons use two critical properties of fibrin glue in dural closure, the adhesive and sealant properties of the fibrin, and the procoagulant effect of the plasma proteins. The risk of communicable disease transmission through pooled plasma products, particularly human immunodeficiency virus and hepatitis, had precluded its use in the United States. The introduction of one donor and even autologous glue has resulted in a greater opportunity for use by surgeons in the United States. 35
Using dura from human cadavers and in vitro rabbit dura, Cain et al 4 found that neither simple interrupted nor running locked sutures adequately maintained a watertight seal at physiologic cerebrospinal fluid pressures. Additionally, when fibrin glue was used to reinforce identical suture methods, the fibrin glue yielded sevenfold greater bursting pressures and no biotoxicity. 4 Shaffrey et al 35 reviewed 134 patients in whom fibrin glue had been used as an adjunct in sealing a dural tear and reported an overall effectiveness of 90%. Patients who had a primary tear repaired intraoperatively were treated successfully by sutures and fibrin glue 93% of the time (111 of 119 patients). Operations for repair of an established cerebrospinal fluid fistula were successful in 67% of patients (10 of 15 patients). Intuitively, augmentation of a local inflammatory reaction should lead to increased fibrosis and scar formation, but researchers using an animal model discovered that because fibrin glue is biologic and completely resorbed, epidural scarring and fibrosis are inhibited. This may be especially useful when spinal reoperation is a consideration. 42 A common feature of fibrin glue that investigators report almost unanimously is that fibrin glue is intended to augment primary dural suturing, and whenever possible, should not replace it. 13,26,35
Newer techniques for reinforcing traditional suture repair of dural leaks, such as laser tissue welding, are being investigated. One study analyzed the leak pressure requirement and the tensile strength of repairs with and without this technique. Primary suturing combined with laser welding produced a higher leak pressure and tensile tissue strength than either technique used alone, and showed no evidence of underlying thermal tissue injury. This may prove to be a valuable method of closure when space constraints are an issue. 11 Cyanoacrylate polymer adhesives once held promise as effective dural sealants, but have fallen out of favor because of reports of toxicity. 47,48
It is important after any intraoperative closure technique to test the strength of the repair. Requesting the anesthesiologist to perform an exaggerated expiration, effecting a Valsalva maneuver, usually identifies any sites of continued cerebrospinal fluid leakage or repair weakness, which should be reinforced. The most important layer of closure is the fascial layer, and a tight fascial seal will provide another essential barrier to cerebrospinal fluid egress and infection. After repair, the patient should be maintained on bed rest, with or without a subfascial drain to prevent hematoma or seroma formation. Eismont et al 8 reported on their experience with five patients, and admonished the use of any drains to avoid the formation of fistulous tracts. However, in a more recent large series, Wang et al 45 evaluated the outcome of 641 consecutive spinal surgeries, in which 88 durotomies were treated. Their treatment scheme consisted of primary suture repair, a subfascial drain, and an average of 3 days of bed rest. Ninety-eight percent of the patients (86 of 88 patients) had a good outcome, and only two patients had a persistent cerebrospinal fluid leak, which was treated successfully by reoperation using the same procedure. No patients had a meningeal infection or a cyst develop, and so this appears to be an effective regimen. Hodges et al 13 retrospectively evaluated another course of therapy in 20 patients, consisting of primary repair using sutures and fibrin glue, without mandatory bed rest. Fifteen patients (75%) were asymptomatic and only one patient required revision surgery.
Regardless of the surgeon’s best efforts, not all dural tears can be recognized and repaired adequately primarily, and the need for postoperative treatment strategies still exists. When a postoperative cerebrospinal fluid leak is diagnosed, the surgeon has several options at his or her disposal. Eismont et al 8 concluded that bed rest alone will not suffice and does not yield predictably positive outcomes. Immediate reoperation and primary repair traditionally has been advocated, particularly to prevent formation of a chronic fistula or pseudomeningocele. 8,26 The power of modern imaging modalities allows excellent preoperative visualization and localization of the fluid collection, and this has become the gold standard to which other treatments have been compared. With recent attempts to minimize invasiveness and to avoid the inherent morbidity associated with surgical procedures, particularly revision procedures, other methods have surfaced and have proven extremely effective.
One nonoperative alternative for treatment of a persistent cerebrospinal fluid leak is the placement of a subarachnoid drain. This technique involves inserting a continuous epidural catheter into the subarachnoid space away from the leak, attaching a blood collection bag, and allowing the cerebrospinal fluid to drain for 4 days. Generally, 200 to 300 mL are collected per 24-hour period, and this can be adjusted by changing the height of the collection bag. McCallum et al 23 found this technique efficacious and safe, but only evaluated four patients. Kitchel et al 16 used subarachnoid drainage in 19 patients and reported similar successful results. These authors describe several theories as to why this technique leads to healing of a cerebrospinal fluid fistula. Decreased fluid pressure through the leak, with preferential egress through the catheter, may lead to healing. Alternatively, drainage may decrease distension of the dural sac, with approximation of the dural edges, facilitating healing. Should this technique fail, surgical treatment still is possible. 16 Stambough et al 38 reported the successful use of subarachnoid drainage for a chronic pseudomeningocele.
Epidural blood patch has gained popularity recently as another nonoperative alternative to treat a cerebrospinal fluid fistula. Twenty milliliters of blood are drawn from the patient’s antecubital vein and injected in the epidural space near the fistulous tract. The injected blood spreads cephalad and caudally in the epidural space and adheres to the defect, forming a gelatinous seal over the dural rent. 33 One study reported an overall success rate of 97.5% in 118 patients, 1 and several other case reports have confirmed its efficacy and safety in patients having spinal surgery. 19,21,24 This may be a valuable tool in small persistent cerebrospinal fluid leaks.
As fibrin glue has begun gaining widespread acceptance as a useful dural sealant during surgery, it also has potential use in postoperative treatment. Patel et al 30 described six consecutive patients with postoperative cerebrospinal fluid leaks who were treated with percutaneous fibrin sealant. Spinal fluid was aspirated under CT guidance, and a cryoprecipitate solution and a calcium chloride and thrombin solution were injected simultaneously; CT imaging confirmed the fibrin adherence. Three patients had immediate resolution of symptoms, two patients required reoperation for persistence of severe symptoms, and one patient did not have adequate fibrin glue coverage of the leak. Although technique refinement and larger studies are required, this may prove to be yet another nonsurgical option for treatment of postoperative cerebrospinal fluid leaks. 30
Choosing which treatment algorithm to implement requires large series of patients in whom objective outcomes are assessed. Outcomes of individual techniques have been mentioned previously. Wang et al 45 concluded from their study of 88 consecutive dural tears that incidental durotomy, when treated appropriately, does not result in a substantial difference in long-term morbidity, nor does it increase the infection or neurologic sequelae. A similar study of 450 patients and 17 dural tears, with an average of 25.1 months followup, concluded that intraoperative dural tear when diagnosed and repaired early does not alter postoperative outcomes. 15
Incidental durotomy during lumbar spinal surgery is not an uncommon complication encountered by spine surgeons. Prevention is the most important aspect of treatment, and preoperative planning and systematic surgical methods can minimize the prevalence. If the leak is observed intraoperatively, it should be repaired with sutures, fibrin glue, fascial grafts, tissue welding, or a combination thereof. When combined with a tight fascial closure, a testing Valsalva maneuver, possibly a subfascial drain or bed rest or both, no increased long-term morbidity should be expected. The surgeon must have a keen suspicion for signs and symptoms of cerebrospinal fluid leak postoperatively, including wound drainage, postural headache, or a subcutaneous or subfascial fluid collection. Immediate reoperation has been the time-honored traditional treatment and is the gold standard. However, to minimize the risks of reoperation, other noninvasive modalities, such as subarachnoid drainage, epidural blood patch, and percutaneous fibrin glue have been devised. Should these methods fail after a reasonable trial period, surgery should be done.
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