Management of Intraoperative Cerebrospinal Fluid Leaks
BACKGROUND
Management of intraoperative durotomies and the postoperative management of cerebrospinal fluid (CSF) leaks can pose serious problems in spinal surgery.
This chapter discusses risk factors that can predispose patients to the occurrence of an intraoperative durotomy.
We review the surgical instruments, biologic agents, and drainage catheters that are of assistance with repair of durotomies.
A discussion then occurs with respect to the particular challenges at varying locations within the spinal axis when it is approached either anteriorly or posteriorly.
AVOIDANCE OF DUROTOMY
Careful study of preoperative imaging studies may yield valuable information with respect to potential pitfalls during exposure of the spine.
Look out for postoperative changes from previous laminectomies or laminotomies.
Spina bifida occulta is reported in up to 10% to 15% of normal healthy adults and is a potential site for durotomy during exposure.
Incomplete ossification of the C1 laminar arch should be kept in mind during any posterior approach to the high cervical spine or craniocervical junction.
The L5-S1 interspace is a widened interspace and is a frequent area for incidental durotomy during exposure of the lumbar spine.
Ossification of the posterior longitudinal ligament, especially in the cervical and thoracic spine can often be recognized on preoperative imaging studies and carries a high risk of intraoperative CSF leak.
PRINCIPLES OF REPAIR
Often, these durotomies occur in the midline and can be repaired primarily with simple interrupted or running sutures. A 4-0 or 5-0 monofilament suture such as Prolene (Ethicon, Somerville, NJ) or nylon are appropriate.
We prefer a repair with a small tapered needle such as an RB-1 in a simple running fashion. A good needle driver such as Castro-Viejo can be helpful to repair a tear in the lateral recess.
GENERAL PRINCIPLES AND PATIENT SAFETY
When an intraoperative durotomy has occurred, care should be taken to avoid any injury to the underlying neural elements.
Surgical cautery (Bovie) use should be limited when in proximity to neural elements.
Minimize the use of high-speed cutting drill bits near the spinal canal. A diamond drill bit is a much safer
instrument especially in less experienced hands.
The use of appropriate-sized suction tips is recommended once a durotomy has occurred. The smallest suction tip that can be used to keep the surgical field clear should be employed.
Suction tips that allow for regulation of the strength of the suction at the handpiece are extremely useful.
Suction tips that have their apertures on the side and not on the tip (Grossman suction tips) are also very useful in these situations.
Suction lines that are soft and flexible allow for rapid “clamping off” when a durotomy has occurred. This can prevent a suction tip from inadvertently sucking up nerve roots.
Make sure that you have a capable and experienced assistant. Sometimes, what you really need is an extra pair of experienced hands to maximize your exposure so that you can work on primary repair of the dural defect.
Once a durotomy has taken place, protect the neural elements with a soft Cottonoid (Codman, Warsaw, IN).
Focus is then directed toward minimizing and further extension of the durotomy and attaining sufficient bone exposure to allow for primary dural repair when possible.
Whenever possible, achieve a watertight primary dural repair and reinforce with dural sealant when indicated.
Decompression of the lumbar cistern through the release of spinal fluid can also alleviate the extramural forces on the epidural venous plexus. This can result in large amounts of bleeding, which can normally be controlled with bipolar cautery or thrombin-soaked Gelfoam (Baxter Healthcare Corp., Hayward, CA).
PRODUCTS
Dural Substitutes
There are a number of commercially available dural substitute materials, most of which are derivatives of bovine collagen.
They are available as suturable or onlay dural grafts.
Bovine pericardium is also commercially available as a suturable dural graft. There are case reports of aseptic or chemical meningitis associated with bovine pericardial grafts.
Autologous grafting materials include pericranium, fascia lata, and autologous muscle grafts that can be used as a plug to prevent a leak.
Dural Sealants
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There are a number of commercially available dural sealants, most of which are derivatives of fibrin glue. Thin layers of these sealants can be applied with aerosolizers to reinforce a dural repair.
Some of these products have been reported to swell postoperatively. For this reason, a minimum of product
should be used to reinforce the repair and avoid postoperative compression of the neural elements.
TECHNIQUES
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Durotomies during Posterior Lumbar Surgery
Lumbar dural tears may occur during exposure of the lumbar spine, during the course of decompression of the neural elements, or during the placement of spinal hardware.
If possible, avoid a leak in the first place. This can be done by avoiding sharp bone edges along the margins of a decompressive laminectomy.
Make good use of your assistant. In the lumbar spine, have your assistant use a blunt nerve hook or a no. 4 Penfield to gently displace the dura away from the bone edge while you are doing your decompression.
Most midline durotomies lend themselves to primary dural repair.
Durotomies which occur in the lateral recess or overlying the exiting nerve root sheath are more difficult to repair.
When a CSF leak occurs in the lateral recess, first obtain wider bone exposure. A primary dural repair should then be attempted.
Large dural defects that cannot be repaired primarily should be grafted (eg, with bovine pericardial graft or dural substitute). These grafts should be sewn in place in a watertight manner when possible.
For dural tears that cannot be repaired primarily or patched, consider an onlay dural substitute graft reinforced with a dural sealant.
When CSF leaks occur over the nerve root sheath, these are often difficult to repair primarily and can be treated successfully with dural sealant or fibrin glue.
Occasionally, one can face a fairly small lumbar durotomy through which multiple rootlets of the cauda equina can herniate. In this situation, it may be necessary to enlarge the durotomy and even to drain some spinal fluid to allow for safe reduction of the rootlets back into the spinal canal followed by primary repair of the dura.
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Durotomies during Revision Lumbar Surgery
Patients with a history of CSF leak with previous surgery should be counseled preoperatively that they are likely at a higher risk of recurrent CSF leak.
During exposure of the spine, sharp curettes can be used to define normal facet and bone anatomy. The use of a diamond drill around the margins of a previous laminectomy may help prevent a leak. When scar is densely adherent to the underlying dura, it may be prudent to leave areas of adherent scar attached to avoid a CSF leak.
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Durotomies during Posterior Thoracic Surgery
Many of the same principles as outlined in repair of CSF leaks during posterior lumbar surgery apply in the posterior thoracic spine.
If a leak occurs over a thoracic nerve root sheath, the root itself can be ligated and sacrificed to prevent further leakage of CSF.
With CSF leak in the setting of posterior lumbar or thoracic surgery, we will often recommend a period of flat bed rest for the first 48 hours to allow for short-term healing of the repair.
After 48 hours, we will mobilize the patients ad lib.
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Durotomies during Posterior Cervical Surgery
Durotomies during posterior spinal surgery normally are midline or paramedian in location and lend themselves to primary dural repair.
This can be supplemented with dural sealant.
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Durotomies during Anterior Cervical Spinal Approaches
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CSF leaks are not as common in anterior cervical approaches as they are in lumbar spinal procedures.
Most leaks that we have observed during anterior cervical discectomy and fusion (ACDF) have been in association with the use of high-powered drills.
These leaks normally occur at the site of the takeoff of the cervical root sheath. In this location, the dura takes a slight superior course as the nerve root exits the foramen, making the dura more likely to be injured in this location.
Durotomies during ACDF can be extremely difficult to repair primarily.
Most of these durotomies can be treated with an onlay dural substitute and a widely fitting bone graft that occupies the width of the discectomy defect.
Consideration should be given to the placement of a lumbar subarachnoid drain.
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Durotomies during Anterior Thoracic Spinal Approaches
Durotomies that occur during anterior thoracic approaches are of concern because of the large potential space of leak and frequent requirements for postoperative chest tubes.
Attempt should be made to repair the dura primarily if possible.
Often, these leaks can only be repaired with onlay dural substitute and dural sealant together. Attention should be given to the postoperative chest tube output.
If there is a question about whether chest tube fluid represents normal pleural fluid or CSF, a sample of fluid can be collected and sent for beta-2 transferrin testing, which is positive in CSF.
With a persistent CSF leak occurs in the setting of a chest tube with CSF coming out of the chest tube, we recommend taking the chest tube off of negative pressure suction when feasible and continuing the lumbar drain until the chest tube can be removed.
Our experience has been that recurrent CSF leaks in the chest are unusual.
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Placement of Lumbar Subarachnoid Drains
We will most often place a lumbar drain in cases of recurrent CSF leak after primary repair or in cases that are deemed to be high risk for postoperative CSF leak.
Lumbar subarachnoid drains can either be placed surgically at the time of a lumbar decompressive laminectomy or separately through a 14-gauge Tuohy needle.
The purpose of a lumbar drain is to divert spinal fluid and alleviate pressure to allow for the repaired area of CSF leak to heal.
Care should be taken at the time of lumbar catheter placement; do not attempt to reposition the drain catheter while the spinal needle is in place. This can result in inadvertent shearing of the catheter.
Lumbar drains are connected to a sterile drainage system. Most common site of insertion is from L2 to L5.
POSTOPERATIVE MANAGEMENT
Lumbar drains
Careful postoperative orders must be given regarding the management of lumbar drains.
Drainage systems are most commonly placed at the level of the patient's spine, and the height of the drainage collection device is adjusted to maintain a CSF output of approximately 80 mL of spinal fluid per 8-hour shift.
Patients are frequently maintained on intravenous antibiotics while the spinal drain is in place. We use prophylactic Ancef until the drain is removed.
The drain is normally left open for 3 to 7 days to allow time for healing of the durotomy.
The lumbar drainage system is clamped and the patient is observed for signs or recurrent CSF leak.
If there is no further evidence of CSF leak after the drain has been clamped for 24 hours, the lumbar subarachnoid drain is removed.
Overdrainage of CSF through a lumbar drain can result in tearing of cranial bridging veins and acute subdural hematoma formation.
The risk of infection with prolonged indwelling drains can be minimized with good sterile technique. Drains can also be tunneled, which also helps to minimize infection risk. It has been our practice to maintain our patients on intravenous antibiotics while the drain is in place, and we make an effort not to extend CSF diversion through a lumbar drain beyond 7 days.
Wound drains (wound Hemovac)
We will place wound drains in the setting of a repaired CSF leak to help prevent the postoperative occurrence of an epidural hematoma.
Epidural hematoma is of concern due to a loss of turgor pressure within the thecal sac and decompression of the lumbar epidural venous plexus.
These drains can later be removed or taken off of suction if the drain outputs are high or the patient develops a spinal headache.
COMPLICATIONS
Clinical signs of CSF leak
Low-pressure (spinal) headaches will be present when the patient is in the upright position and will resolve or improve when the patient is recumbent.
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New onset cranial nerve palsies (abducens nerve palsy)
As the sixth cranial nerve has the longest intracranial course, this is presumably due to traction on the sixth nerve with excessive CSF drainage.
Nausea and vomiting
For cases of recurrent CSF cutaneous fistulas or recurrent symptomatic CSF leaks that have not resolved with CSF diversion, often, the only option is reexploration and attempted repair of the leak if it can be located.
Pseudomeningocele should be divided according to small or asymptomatic collections and larger, symptomatic, or cosmetically disfiguring collections.
Small, asymptomatic collections can be observed.
Large, symptomatic collections will usually require reexploration and repair with possible CSF diversion through a lumbar subarachnoid drain.
Patients who have symptomatic pseudomeningocele may complain of pain or swelling at the surgical site or symptoms of low CSF pressure. These symptoms include persistent positional headache, nausea, vomiting, or occasionally photophobia. These symptoms are exacerbated in the upright
position (FIG 1).
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