Introduction
Over the past 30 years and despite significant progress, intensive scientific and clinical research efforts have failed to develop convincingly efficient therapies to reverse the devastating paralysis of traumatic spinal cord injury [1]. The maintenance of adequate vascular perfusion and the decompression of the spinal cord are two important aspects of the clinical management of the acutely spinal cord injured patient. Both have received considerable attention in the past two decades, largely due to the belief that they have an influence on neurological recovery [2–4]. Durotomy, defined as an incision of the dura mater and in most cases of the arachnoid, has been described as an adjunctive method to relieve increased subdural pressure in case of intervertebral disc herniation. It had been suggested that the incision of the meninges decompresses the swollen spinal cord parenchyma, permits CSF drainage, and improves spinal cord perfusion pressure.
Effects of durotomy on outcome
The surgical role of durotomy in both spinal cord decompression and improvement of medullary blood flow dates back to the battlefields of the First World War and has always been a topic of controversy [4–7]. It is clear that for some specific lesions (i.e., subdural tumor, hemorrhage, and arachnoidal cyst), durotomy is mandatory to evaluate and treat the intradural and intramedullary lesions [8, 9]. However, in cases of spinal cord injury, the relative risks and benefits of durotomy are still unclear and controversial [9, 10]. After acute intervertebral disc herniation and spinal cord injury, focal swelling of the spinal cord may lead to a kind of “spinal compartment syndrome” due to the poor elasticity of the surrounding meningeal layers. An increase in intracranial pressure following head injury plays a central role in limiting brain perfusion and compounding secondary damage. CSF shunting and durotomy are both effective at controlling intracranial pressure and improving outcome [11, 12]. Accordingly, it would be logical to think that performing a durotomy following spinal cord injury would decrease submeningeal pressure and restore normal spinal cord perfusion.
In a nonpublished study of the evolution of subdural pressure during surgical treatment of intervertebral disc herniation, subdural pressure at the site of herniation before decompression was constantly below 10 mm Hg in all dogs. A catheter was inserted through a small durotomy opening created one segment distal to the compression site. During measurement, CSF drainage occurring at the insertion site elicited a steady drop in subdural pressure in all patients, confirming the hypothesis of subdural pressure relief [13]. It has been hypothesized that CSF drainage might play a role in controlling intraspinal cord pressure in the same manner as intracranial pressure and might improve outcome after spinal cord injury by maintaining spinal cord perfusion [14, 15]. Indeed, a preliminary study in humans demonstrated the safety of the technique and the ability of CSF drainage to improve spinal cord perfusion in the postoperative period [14]. However, a recent study that assessed the effect of durotomy on spinal cord blood flow in dogs with intervertebral disc herniation failed to demonstrate an increase in spinal cord perfusion [16]. Directly after decompression and durotomy in dogs with incomplete spinal cord lesions, an increase in spinal cord blood flow at the site of herniation was seen. In these dogs, no spinal cord swelling was observed after durotomy. After 15 min, the spinal cord blood flow decreased again and returned to almost initial or even lower values in all dogs. In contrast, a study on the evolution of spinal cord blood flow in dogs with intervertebral disc herniation treated by hemilaminectomy without durotomy showed a steady increase in blood flow after decompression [17]. However, getting accurate measurements of spinal cord blood flow is difficult, and additional work needs to be done to confirm these observations.
