Incidence and Prevalence

Dural tears with CSF leaks are well-documented common complications of spinal surgeries. However, the incidence rate is hypothesized to be underreported because of the lack of associated morbidity with most dural tears. Thus, the prevalence is largely debated, but has been reported to be 0.5% to 18%.^1,2 The prevalence of CSF leaks is higher in patients undergoing revision surgery. The occurrence and management of CSF leaks are specific to the region and the surgical approach.

Specific Regions and Surgical Approaches

The lumbosacral region is noted as the most common location for dural injuries due to the region anatomy as well as its common location for spinal surgeries.^1,2 Many conditions facilitate dural tears including thinned dura, prior spinal surgery, dural fibrosis, spinal stenosis, and spinal bifida.^3,4 Additionally, ossifications of spinal ligament, high-speed drill, and synovial cysts have been associated with dural tears.^4,5 Numerous mechanisms such as trauma, disc fragments, bone spikes, excessive dural traction and iatrogenic laceration by sharp instruments or intradural explorations have led to CSF leaks with several dramatic consequences.^3,6 Potentially, leaks can lead to pseudomeningocele formation, intracranial hypotension, neural element herniation with pain and neurologic deficits, wound dehiscence, fistula formation, and infection.^1,7,8 Therefore, any CSF leak warrants immediate repair.

CSF leakage in extradural operation frequently happens during a severe spinal cord stenosis decompression or reoperation with associated scar tissue. In a virgin spine without prior surgery, the bony structures should be removed initially with a Leksell rongeur and a high-speed drill superficial to the ligamentum flavum for further dural protection. Ideally the drill should be used in a medial to lateral fashion to reduce incidence of slippage and tear. Proper and adequate dural separation from the overlaying fascia and lamina must be performed to reduce the incidence of any dural tear, which is most commonly caused by dura being caught between the Kerrison rongeur footplate and the bone. Therefore, a fine dissecting instrument such as angled curette or Woodson dissectors should be utilized before placement of a cutting instrument in the epidural space. This exercise becomes even more important in a reoperation case as there is associated scar formation and it can be adherent to dura. A 3% to 5% higher rate of duratomy has been reported in a revision case.^1,2,9 It is recommended that the laminectomy be extended to obtain a nonoperated segment of dura and operate from normal to abnormal (scar) anatomy. If the scar is easily dissected from the dura then a blunt dissector may be utilized, otherwise sharp dissection may be needed for safe exploration.

Use of spinal instruments as well as bony spikes are reported causes of delayed CSF leaks.¹⁰ Medial placement of pedicle screws or deep placement of anterior spinal fusion plating screws can lead to dural injures with late presentation of CSF leak symptoms. In these scenarios, CSF leaks may not be noted during the surgery or may not even exist in the case of injury with bony spikes. Special attention must be made to proper length and placement of screw and prevention of bony spicule by smoothing the bony edges. In case of a surgical repair, extension of bony decompression may be warranted in order to directly expose the dural injury for adequate visualization and repair. Also, intraoperative Valsalva maneuver and tilting of the table to increase the depended position of durotomy can help in direct evaluation of the dura.

The relative risk of developing an intraoperative inadvertent dural tear using an anterior procedure has been reported to be increased in patients undergoing corpectomy, fusion, surgical management of ossification of the posterior longitudinal ligament (OPLL) and revision. Dural injuries during anterior spinal operations follow the same principles as previously mentioned. Proper and careful dural dissection in addition to adequate bony exposure is essential to prevent and repair leaks in these approaches. However, special attention must be given to cases involving ossification of posterior longitudinal ligaments, as dural injuries in the cervical spine are most prevalent in the presence of OPLL.⁴ These patients are 13.7 times more likely to have CSF leak during their spinal surgeries.⁵ If a laceration occurs and warrants a suture repair, dura should be carefully dissected parallel to its fiber. However, following the removal of the posterior longitudinal ligament, a dural gap is most often created which requires a patch. Occasionally, this gap may not be completely covered in which case it can be sewn onto the dura as much as possible with the remainder of the defect being sealed with fat, muscle, and fibrin glue.

The transoral approach has a deep surgical field and it is particularly susceptible to penetration by instruments and injury to the dura. CSF leaks during transoral approaches can have significant mortality; thus many neurosurgeons recommend a preoperatively placed lumbar drain to reduce the hydrostatic pressure on the wound. If the dural tear is significant, then the lumbar drain may need to be converted to a shunt to maintain a low pressure for at least 1 month postoperatively.

In an intradural case, dura may be opened in a midline or paramedian fashion. These cases mostly involve spinal tumors or biopsies for which dura can be easily repaired by watertight dural suturing under a microscope. With meningiomas and a dural defect that is under tension, if dorsally located and adequate exposure is obtained, a dural patch may be used for sealing of the dura. However, with far lateral approaches to spine or ventral defects, dura may not be easily repaired. In this situation further treatments as described later may be necessary to prevent CSF leakage.

Signs and Symptoms

Signs and symptoms of an incidental durotomy can manifest in many ways. Typically, they are asymptomatic, but commonly are reported to present with postural headaches, wound swelling, and drainage of CSF through the incision. Other symptoms include nausea, emesis, photophobia, dizziness or vertigo, cranial nerve palsies, axial pain, radiculopathy, and/or myelopathy. The symptoms have been postulated to be a result of intracranial hypotension leading to tension on the meninges and other intracranial structures. Patients with unrecognized CSF leaks are also at risk for acute or chronic meningitis.

Diagnosis

Typically, inspection of the wound would be the first step in assessing a CSF leak. The classic target sign is often a clear discharge that produces a halo surrounding a central pink stain on the patient’s pillow or sheets. Many clinicians advocate for the analysis of the fluid for B2-transferrin—a polypeptide that is highly sensitive to CSF. This test typically can be performed within 3 hours.

Magnetic resonance imaging (MRI) remains the gold standard to diagnose a CSF leak. The only difficulty may be in distinguishing between CSF and seroma fluid. Overall, MRI helps to delineate the location, extent, and characteristics of the lesion. Specifically, CSF is hypointense on T1-weighted images and hyperintense on T2-weighted images. Fluid collections in this pattern that seem to be extravasating from the spinal canal should raise suspicion of a pseudomeningocele (Fig. 194-1). In lieu of a MRI, computed tomography (CT), myelography, and radionuclide myelography may be adjunctive imaging modalities (Fig. 194-2).