Dural tears represent a serious challenge for the spine surgeon as well as the patient. Nerve injury, spinal fluid leak and meningitis are all possible complications of a dural tear. Dural tears usually occur in re-operation where the dura is adherent to perineural and peridural scar tissue. This situation as well as dura adherent to periosteum is usually evident on adequate pre-operative MRI scans.
Dural tears are less likely to occur in a primary operative (virgin spine) procedure. They may actually exist prior to surgery where a freely sequestered fragment of disc material has torn a nerve axilla and produced its own tamponade. In this circumstance the removal of the fragment may remove the tamponade and spinal fluid leakage is then seen. The appropriate repair of dural tears requires skill and the right surgical tools and well as appropriate assistive devices.
When a linear tear occurs in the dura optimal closure involves the placement of sutures for a water tight closure. The most secure closure is with interrupted sutures rather than a “running” stitch as shown on the left. Silk is the best material for dural suture as it enhances fibroblast proliferation.
Poor quality dural closure or failure to use adequate magnification and illumination makes it difficult for the surgeon to differentiate nerve root from the dura itself. This can result in nerves being injured by the suture process or to have nerves herniating through the closure site. Significant patient disability can result from this.
When dural tears are amenable to suture repair but patching is required the surgeon has a number of dural substitutes to chose from:
- Autogenous- tensor facia lata
- Allograft- cadaver dura
- Synthetic- Goretex
An important tool in avoiding or controlling dural problems is the appropriate utilization of autogenous free fat grafts. The use of this autogenous tissue is not only valuable in preventing excessive post-operative scarring but also in sealing dural tears not amenable to
primary repair with sutures.
This illustration by Mayfield shows the incorporation of an autogenous fat graft with a suture as a means of closing a dural defect. Free fat grafts applied properly can often serve to tamponade and seal dural defects without associated sutures (particularly in situations where suturing is not possible).
If dural repair is not water-tight it is important to keep the patient flat in bed for at least 24 hours. If cerebrospinal fluid leakage then occurs spinal drainage should be instituted (as well as prophylactic antibiotic coverage). Shown here is a spinal drainage system in use. It is important to maintain the system at a proper height. If placed too low excessive fluid can be drawn from the subarachnoid space causing patient injury, and even death.
The control of spinal fluid leaks requires a plan of action. This may also include decreasing normal spinal fluid production by the use of steroids or drugs such as Diamox. Enforced bed rest carries with it the added risk of thrombophlebitis, deep vein thromboses and pulmonary emboli. All of these factors must be taken into consideration for proper problem management.