Spinal Dural Injuries

Anatomy and Pathophysiology

The meninges cover the brain and spinal cord. They consist of dura mater, arachnoid, and pia mater. The dura has three distinct layers: a fibroelastic outer layer, a fibrous middle layer, and a cellular inner layer. Although there is controversy regarding the orientation of dural fibers, there is substantial evidence that they run longitudinally, as evidenced by their higher ultimate stress in this plane. Cerebrospinal fluid (CSF) is produced by the choroid plexus in the lateral third and fourth ventricles of the brain. CSF formation occurs at a rate of 0.3 to 0.6 mL/min, which is the daily equivalent of 500 mL ( Fig. 96.1 ).

Incidence

High-energy thoracolumbar spinal trauma can lead to dural tears. Several authors have reported an incidence of dural tears between 10% and 19% in patients sustaining lumbar or thoracic burst fractures. In a retrospective review of 45 patients with lumbar burst fractures, Ozturk et al. reported a 19% rate of traumatic dural tears. Similarly, in an analysis of 60 patients with a surgically treated thoracic or lumbar burst fractures, Cammisa et al. found an 18% rate of traumatic dural tears. Ozturk et al. assessed their outcomes for L3–L5 burst fractures with associated greenstick lamina fractures and found a 25% rate of dural tears ( Fig. 96.2 ). The authors recommended exploring the greenstick lamina fractures to avoid potential injury to neural elements. Other authors have also commented on the important association between traumatic dural tears and neurologic deficits due to nerve root avulsion or entrapment within the fracture.

Dural tears can occur during elective spine surgery for degenerative spine disorders, with a higher rate reported during revision surgery. Incidental durotomies occur due to dural laceration during dissection of adherent, fibrotic, or calcified tissue. The dura in revision surgeries is more likely to tear because of adhesions in the epidural space, scarring, fibrosis, and loss of surgical landmarks. Dural tears are also more likely because of absence of dural lining due to prior injury or compression. Risk factors for durotomy in primary surgery include severe spinal stenosis (in these patients, the dura can be very thin or frankly eroded), adhesions, fibrosis, or redundancy.

The reported incidence of incidental durotomy varies. In a retrospective review of 2144 patients, Cammisa et al. reported a 3.1% rate of incidental durotomy, with a higher incidence (8.1%) in revision surgeries. Stratifying by levels, authors have reported a 1% rate of dural tears with cervical surgeries compared with a 7.6% rate for primary lumbar surgeries and a 15.9% rate for revision lumbar surgeries. Overall, revision spine procedures have a higher incidence of durotomy, with reported rates between 8.1% to 15.9%.

The risk of incidental durotomy varies depending on the type of spine surgery; in the Spine Patient Outcomes Research Trial, Weinstein et al. found that the rate of durotomy increased from 4% for patients undergoing lumbar discectomy to 8% for patients undergoing decompression for lumbar stenosis to 11% for patients undergoing lumbar decompression and fusion for spondylolisthesis.