The recurrence of radiating pain after spinal surgery has many causes. Recurrent disc herniation, remnant herniated disc material, postoperative epidural hematoma, and nerve root inflammation can all cause recurrence of this radiating pain. A few studies have reported rare causes of postoperative recurrence of radiating pain, such as the presence of a pseudomeningocele and posttraumatic spinal cord or nerve root herniation through a dural defect site2,3,9,11-13,15,17)
. However, only a few cases of nerve root entrapment in the intervertebral space after lumbar disc surgery have been reported17)
. In most cases, the occurrence of a pseudomeningocele and posttraumatic spinal cord or nerve root herniation after spinal surgery is due to the presence of a dural tear that arises from the dorsal aspect. However, in the case of nerve root entrapment in the intervertebral space, the iatrogenic dural tear is located on the ventral side.
The incidence of unintended intraoperative durotomy is between 0.3% and 17.4% and varies depending on the type of surgical procedure1,4,5,8,10,12-14,16)
. Because many patients do not show symptoms, the exact incidence of postoperative pseudomeningocele is not known, but the overall incidence is reported to be less than 2%1,5,9,11,15)
. An iatrogenic pseudomeningocele can also occur after a lumbar puncture7)
. However, iatrogenic entrapment of the nerve root in the intervertebral space through a ventral dural defect is extremely rare. One article reported 2 cases of nerve root entrapment in the intervertebral space after lumbar disc surgery17)
. The author noted that a small dural defect, particularly one that was located at the level of the intervertebral space, could lead to transdural root herniation and root entrapment in the intervertebral space. This is the only article reporting nerve root entrapment in the intervertebral space after lumbar disc surgery.
The mechanism postulated for nerve root entrapment in the intervertebral space is a water-hammer effect resulting from the difference between the intradural pressure and the intervertebral space pressure7,12)
. Intradural pressure may increase while standing or straining12)
. This increased intradural pressure may cause compression of the spinal cord leading to widening of small unrepaired dural defects. Increased intradural pressure forces the dura and the nerve rootlet into the intervertebral space. The nerve rootlet can become entrapped in the intervertebral space through the dural defect, causing rootlet irritation, leading to severe radiating pain.
Rootlet entrapment can be diagnosed by MRI. The typical appearance of rootlet entrapment is a beak-like appearance of the ventral dura and rootlet in the sagittal view. In the axial view, the entrapped rootlets are located in the intervertebral disc space. A magnetic resonance myelogram can also show CSF leakage into the involved disc space. However, the diagnostic value of myelography is limited if the subarachnoid space does not extend outside the dural space. Before exploration, it is important to obtain a radiographic image to confirm the location of the dural defect.
An iatrogenic dural tear causes a poor clinical outcome16)
. It may cause fistula formation, meningitis, arachnoiditis, or an epidural abscess. In addition, a pseudomeningocele may entrap nerve roots or the spinal cord and cause radicular symptoms1,9,13,15,16)
. One study reported that of 6 patients with a dural defect that was not repaired during the first operation, 5 developed psuedomeningocele, and all 6 patients eventually underwent dural repair because of failure of conservative therapy4)
. Another study reported a case of cauda equina syndrome resulting from a pseudomeningocele; the cauda equina syndrome was caused by herniation of the cauda equina roots through the dural defect1)
. Another study reported that patients with incidental durotomy had poorer outcomes after surgery; in this 10-year follow-up study, a significant number of patients with incidental durotomy complained of headaches after surgery16)
. In addition, patients with incidental durotomy tended to undergo repeat operations and were unable to work for a longer duration. These patients also had increased back pain and functional limitations related to back pain.
Surgically accessing the ventral or lateral side of the dura is difficult5)
. CSF leakage does not usually occur in these cases, particularly in the cases of small dural tears on the ventral side. Therefore, a surgeon may neglect the risk of complications. Although conservative treatments such as bed rest and closed subarachnoid drainage have been attempted, midline durotomy and meticulous surgical dural repair remain the definitive treatment. Treatment with gelfoam and fibrin glue alone may not prevent persistent CSF leakage17)
. One study reported that bed rest is not a definitive treatment; in this study, the patients who did not undergo dural repair developed complications6)
. These patients eventually underwent dural repair. Another study reported that the Valsalva maneuver may help identify the dural tear in suspected cases10)
. The authors also reported that prompt identification and careful closure of the dural tear during the first surgery leads to a successful outcome.
In our four cases, prompt diagnosis and operation were performed in all cases except case number 2. In case 2, correct diagnosis was delayed and the patient suffered from radiating pain for several months. However, postoperatively, there was no neurologic deficit, and there was good improvement in all cases. If a patient presented with recurrent pain after brief improvement, the surgeon must cautiously watch the operated level first.