Among the most troublesome complications of Chiari surgery is spinal fluid leak. A persistent leak can lead to a collection of spinal fluid, sometimes quite large, within the tissues of the neck. This poses two problems:

1. 1.If large enough, the fluid collection, called pseudomeningocele, pushes the dura membrane and patch onto the neural tissue and crowds the foramen magnum. The Chiari symptoms recur. Even more seriously, the patch may adhere to the neural tissues and obstruct spinal fluid flow.
   
   

2. 2.If the spinal fluid collection within the neck tissues breaks through the skin, meningitis can occur. This serious infection can result in scarring (adhesions) of the subarachnoid space.
    
   

Adhesions in this area are difficult, if not impossible, to treat and can lead to life-long symptoms. Thus, one goal of Chiari surgery, in addition to obtaining adequate decompression of the neural tissues and re-establishing spinal fluid flow, is to keep the surgical risks as low as possible.

In 1999, I had several cases of spinal fluid leak following duraplasty with synthetic dural materials. After consideration of the issues involved and review of the literature, I became convinced that the graft tissue of choice for the duraplasty, whenever possible, was pericranium.

Pericranium, also called the external periosteum, lines the outside of the skull. When you move your scalp, the scalp slides between the inner layer of the scalp (the galea)  and the pericranium. Pericraniun has been used in neurological surgery for many years to repair defects in the dural membrane. In the occipital area, the pericranium is hardy and resilient.

Pericranium can be obtained through a separate incision in the scalp. However, I prefer to extend the linear midline incision used for the decompression a few more centimeters superiorly to expose the pericranium.

It is crucial to obtain enough pericranium to cover the opening in the dura. To this end, silastic templates were developed and are available from Biomet Microfixation. An appropriate size template is laid on the exposed pericranium and needle-tip monopolar cautery is used to cut the pericranium along the edge of the template. The precisely trimmed graft is then elevated with a periosteal elevator.

The graft is sutured to the open edges of dura. My own preference is 5-0 polypropylene suture (Prolene by Ethicon); a suture of small caliber, yet good strength. More importantly, it stretches to hold the edges tightly together. (I first encountered this suture when performing carotid endarterectomy where it has to sustain arterial pulsations.)

The suture line is closed in a running fashion. If the arachnoid membrane has been opened, the subarachnoid space is gently filled with saline before completing the closure. Following closure, a valsalva maneuver (to 35 cm) and the suture line is evaluated for leak.

If a leak is identified, the involved suture line is oversewn. At times, especially at the upper-outer corners where the patient’s dura is usually thin, a secondary patch may be needed. A dime-size or smaller piece of cervical fascia is obtained from the wound and carefully oversewn at the site of concern. Another valsalva maneuver if performed to assess for leak.

Once closure has been completed, an absorbable hemostatic agent is placed on the dura and graft and coated with a small amount of the patients own blood. The blood may be obtained from the wound, most commonly, aspirated from the area in which the graft was taken. Or, it can be withdrawn from an arterial line if present. This blood patch is to further seal the suture line.

Instead of a blood patch, another option is to coat the duraplasty with a synthetic absorbable dural sealant. Each of these sealing techniques seems to work well and the type used depends on surgeon preference.

By using the pericranial duraplasty technique described above in persons without previous Chiari surgery, the rate of pseudomeningocele has decreased from 5% in my first 100 cases, to 2% currently. (The percent is calculated from the most recent 100 CM-I previously un-operated cases and has varied from 0-2% since 1999). When I have mentioned these figures at medical meetings, I usually see a few neurosurgeons raise their eyebrows.

Let’s be clear. The first post-operative MRI is performed 2-3 months after surgery. When a scan has been needed sooner, a small amount of fluid is often seen within the neck tissues. However, these small, non-distending collections clear within a few weeks or months. They are not palpable on exam and do not cause problems.

The fluid collections I am referring to, the pseudomeningoceles, are distending collections that causes clinical problems, either as palpable expanding mass, or by compression of the patch graft. Put another way, a pseudomeningocele is a collection that one should worry about and for which treatment may be needed.

In summary, I recommend, whenever possible, the use of pericranium as the tissue of choice in Chiari surgery. This wonderful tissue sews and seals well. As the patients own tissue, abnormal reactivity is not a concern. Its harvest is straightforward. The only downside, if you can call it that, is that the scalp does not slide in the area where the tissue has been taken. In over a decade, I have yet to hear a complaint about this.

Comments and suggestions welcome.

Posted by John Oro’, MD

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