Dural Tears: Should a Minimally Invasive Complication Such as a Dural Tear Routinely Be Opened for Adequate Repair or Are There Safe and Reliable Minimally Invasive Techniques for Dural Closure?

14 Dural Tears: Should a Minimally Invasive Complication Such as a Dural Tear Routinely Be Opened for Adequate Repair or Are There Safe and Reliable Minimally Invasive Techniques for Dural Closure?

MIS: John E. O’Toole
Open: Michelle J. Clarke

14.1 Introduction

The reported incidence of unintended durotomy during spine surgery in general ranges from 1.6 to 17.4%.1,2,3,4,5,6,7,8,9 Minimally invasive surgery (MIS) techniques do not appear to increase this incidence, particularly when reported beyond surgeons’ early learning curve with MIS.^{6,10,11,12,13,14,15} The intra-operative management of unintended durotomy in traditional open spine surgery has been well explored, including the use of various methods of primary repair, fibrin glue, cerebrospinal fluid (CSF) diversion, epidural blood patch, and prolonged bed-rest.^{1,2,3,5,6,7,8,16,17,18,19,20} During MIS, however, primary dural closure using standard surgical instruments can be challenging due to the limited surgical corridor and working angles encountered using tubular retractors.

Concurrently, the evolution of and growing familiarity with MIS techniques have led to an increasing number of intradural pathologies addressed via MIS approaches, including intradural neoplasms, vascular malformations, syringomyelia, and tethered spinal cord.^{21,22,23,24,25,26,27,28,29,30,31,32} In contrast to unintended durotomies, intended durotomies are often larger and thus may be more prone to cause postoperative complications if not properly closed. This chapter reviews the evidence concerning the management of both unintended and intended durotomies during MIS spinal surgery.

14.2 Indications for Repair of Durotomy during Minimally Invasive Surgery

A failure to achieve adequate dural closure after durotomy can lead to persistent CSF leak, pseudomeningocele, or CSF-cutaneous fistula with attendant headache, nausea, vomiting, and back pain. More severe complications including wound infection, meningitis, and even intracranial hemorrhage can be seen after insufficiently repaired durotomy.1,3,6,33,34 A range of intraoperative dural injuries may occur including partial thickness (e.g., arachnoid intact), linear, stellate, root-sleeve, or avulsion. Each of these may be amenable to different strategies or techniques to manage them, but in each case, appropriate efforts should be made to control the egress of CSF to avoid postoperative complications.

14.3 Advantages of Minimally Invasive Surgery

By utilizing tissue dilation rather than subperiosteal dissection with a circumferentially solid retractor of a typically small diameter, multiple potential benefits are gained. The smaller working corridor and preservation of the normal paraspinal soft tissues allow the tissues to reapproximate at the end of the procedure, thereby obliterating potential dead space in which CSF might accumulate. Moreover, normal amounts of postoperative blood products layer over the dura and are contained just within the confines of the bony opening without significant extension into the paraspinal muscles, effectively functioning as a native “blood patch.” Similarly, any muscle/fat graft or fibrin sealant placed over the dural defect is tightly contained. Finally, the solid tubular retractor and limited skin opening prevent introduction of skin flora that might impair wound healing or even produce a wound infection, either of which might perpetuate a CSF leak.

14.4 Advantages of Open Surgery

The advantage to open dural repair is access. By extending the incision, the surgeon is able to function without the constraints of the MIS retractor. This allows better visualization as the surgeon is able to simultaneously view a larger area. Thoroughly exposing the dural defect ensures the surgeon is able to safely tuck any herniated nerve roots back into the thecal sac to prevent further injury. Dural repair is made easier with unfettered access to the dural tear and without the need of special equipment for oversewing the rent within a narrow tube. Muscle and fat pledgets are easily harvested should the surgeon desire these to reinforce a primary repair of an unapposable tear. A tight, multilayered closure can then eliminate dead space and promote wound healing, and is the main line of defense against pseudomeningocele formation, transcutaneous CSF leak, and wound infection.

14.5 Case Illustration

A 63-year-old woman is undergoing an L4–L5 minimally invasive transforaminal interbody fusion via a 26-mm diameter tubular retractor. While removing the ligamentum flavum to expose the thecal sac and disc space, an unintended durotomy is created with a Kerrison rongeur. The durotomy is approximately 5 mm in length with CSF briskly emanating. Options for repair of the durotomy are considered.

14.6 Surgical Technique in Minimally Invasive Surgery

For the purposes of this discussion, standard access to the posterior spinal canal via a tubular retractor system is assumed.35 Once a durotomy is created, either incidentally or intentionally for intradural access, efforts should be made to avoid excessive influx of blood products intradurally to limit the extent of inflammation and possible postoperative arachnoiditis.

Partial-thickness durotomies with intact arachnoid are typically treated with fibrin glue alone or with an additional tiny piece of Gelfoam (Pfizer, Kalamazoo, MI) soaked in local blood placed over the defect. For full-thickness unintended durotomies, the possibility of primary repair is assessed on a case-by-case basis. If the durotomy is not amenable to primary suture repair (e.g., located at the edge or undersurface of the bony opening or the ventral surface of the dura), a small blood-soaked piece of Gelfoam or dural substitute is laid over the dural defect (often gently tucked under the bony edge to secure it in place), followed by fibrin glue. For those durotomies that are amenable to primary repair (i.e., those more dorsally located), a variety of suture is available on appropriately sized needles, including 4–0 Nurolon, 5–0 Prolene, or 6–0 Gore-Tex sutures (Ethicon, Somerville, NJ). The latter suture has the advantage of the needle diameter being smaller than the suture diameter, resulting in fewer “stitch-hole leaks.” The dura can be routinely closed using a commercially available, specialized set of dural repair instruments that includes two modified needle drivers, a bayoneted Chitwood Knot Pusher, and suture-cutting scissors (Scanlan International, St. Paul, MN).⁷ These instruments have a bayoneted offset that allows proper microscopic visualization during needle driving and also allow the knots to be thrown outside the tubular retractor and seated down to the dura using the knot pusher. If the repair is not watertight to Valsalva’s maneuver, a small piece of locally harvested paraspinal muscle can be sutured in as a buttress graft over the leak site. Fibrin glue is then routinely applied over the defect as well. After allowing the fibrin glue to congeal, the tubular retractor is slowly removed while obtaining hemostasis in the paraspinal musculature. The wound is then closed in layers using interrupted sutures for fascia and subcutaneous tissues followed by an adhesive sealant for the skin. No subarachnoid or subfascial drains are used. The patients are kept on bedrest overnight only and are allowed to fully mobilize on the morning of postoperative day 1.

14.7 Surgical Technique in Open Surgery

Upon noting the CSF leak, an initial attempt should be made to repair the dural defect and complete the surgery through the MIS approach as described above. However, in the rare case in which the surgical access limits the ability to repair the defect or there are other complicating factors, one can consider transitioning to open surgery. Examples of situations in which open repair should be considered include nerve roots herniated from the defect that are difficult to reinsert into the thecal sac or a defect that extends beyond the area visualized by the retractors.

Once the decision has been made to convert to an open approach to aid in the dural repair, the wound is extended and retractors swapped to ensure excellent visualization. Of note, based on the original surgical trajectory (often a Wiltse or transmuscular approach), exposure will likely be more lateral than a standard open midline approach. While a standard open procedure involves stripping the muscular attachments to the posterior elements, opening laterally entails a less familiar transmuscular approach. The surgeons should take pains to separate the muscles longitudinally and take advantage of the natural plane between the multifidus and longissimus components of the sacrospinalis muscle as in the Wiltse approach.36 The surgeon may also choose to close the original MIS incision and perform a true midline open approach and resection of appropriate bony elements for a broader exposure as the remaining spinous process and muscle mass medial to the MIS incision may continue to hinder visualization.

To complete an adequate repair the surgeon must completely define the durotomy edges. Often, durotomies occur under the laminectomy defect or near the insertion of the yellow ligament.³⁷ This is an awkward location to visualize, and further bone removal may be necessary. Care is taken to avoid injuring any herniated nerve roots. Nerve roots should be reduced and held in place with a surgical patty to prevent reherniation and minimize further CSF egress while the area around the defect is prepared. If the nerve roots are not reducible and are being strangulated in the defect, the durotomy may be enlarged and CSF drained to allow the roots to be safely tucked into the thecal sac.

Once the durotomy margins are defined, suture is used to close the defect in a watertight fashion as above. In most cases, a simple figure-of-eight or running suture will completely occlude the leak site. However, in cases where a portion of dura is missing, a dural patch graft can be used, or a muscle pledget can be oversewn without pulling the dural leaves together completely. At this point, a Valsalva maneuver is used to confirm the watertight repair. A dural sealant may be added as well.

The most important component of the open repair is watertight wound closure. Once the surgery is completed, a tight, multilayer closure is required to reduce dead space and the potential for pseudomeningocele formation. If a subfascial drain is required, instructions should be relayed to floor and house staff to be mindful of the possibility of ongoing CSF leak, and to remove the drain from suction should that be suspected. A tight fascial closure is performed with interrupted suture. This is followed by a running suture over the interrupted suture line to ensure this layer is watertight. The remainder of the incision is closed in standard fashion. The patient is kept on bedrest overnight and mobilized the morning following surgery.