Pseudomeningocele (PM) is one of the more common complications following posterior fossa decompression for the Chiari I malformation (CM-I). A leak of spinal fluid through the duraplasty creates a pocket of CSF in the posterior cervical muscles. If the fluid collection enlarges, it pushes the duraplasty membrane into the foramen magnum region causing crowing and recurrence of the Chiari symptoms. In a few cases, spinal fluid leaks through the incision and, if untreated, leads to infection.
While a number of Chiari centers have been able to keep the risk of pseudomenigocele very low, rates as high as 18% patients have been reported.
If the PM is small, it can be observed with follow-up MRI scans and may resolve on its own. However, large persistent PMs pose difficulties. The duraplasty can become adherent to the underlying cerebellar tonsils and block CSF flow. Once adherent, surgical revision is difficult.
Dr. Scott Parker and colleagues at the Department of Neurological Surgery at Vanderbilt University studied the effects of symptomatic PMs on the 1-year postoperative “pain, disability, and quality of life” in patients undergoing Chiari decompression.
The researchers found that “a postoperative symptomatic pseudomeningocele has lingering effects at 1 year, which significantly diminishes the overall benefit of suboccipital decompression for CM-related symptoms.”
While the authors use this finding to argue for a “less invasive approach,” I have a different view. The less invasive approaches, such as thinning of the dura by stripping its outer layer, have a higher a risk of failure than the duraplasty approach.
The goal of surgery for the Chiari malformation is adequate posterior fossa decompression with minimal surgical risks. Thus, the key is to use a duraplasty technique that markedly decreases the risk of pseudomeningocele. This is possible through the use of autologous pericranium harvested from a separate small incision in the midline occiput just above the main incision.
Using triangular silastic templates, the appropriate size of graft can be obtained. The pericranial graft is sutured in place with a monofilament running suture in a watertight fashion. Two Valsalva maneuvers to 35 cm are performed following the repair and if any leak is visualized under microscopic magnification, the area is oversewn or a secondary patch is used.
Durplasty using a patient’s own pericranial tissue has been effective in posterior fossa decompression for patients with CM-I. The leak rate can be reduced to a minimal level: 2% or less. The use of a duraplasty results in greater expansion of the subarachnoid space at the foramen magnum than possible in non-duraplasty procedures and allows the patient the best opportunity to improve.
If a leak does develop, it is followed closely and if it enlarges, treated with lumbar drainage or surgical revision. Fortunately, the likelihood is low in centers experienced with the pericranial duraplasty technique.
Follow Chiari Medicine on Twitter.