The Operation for Chiari Malformations in Children
Head: The authors prefer to use a Mayfield head holder. The head is carefully held in a flexed position.
Scalp incision: A straight vertical linear incision is made midline from mid-occiput to upper C2.
Bony exposure: A linear incision is made just below the inion and extending down to level of C2. Dissection is carried out through the avascular plane of the midline, and the occipital musculature is dissected away from the suboccipital bone and C1.
Craniotomy: A suboccipital craniectomy is performed at the foramen magnum using a drill. Dimensions of the craniectomy are measured on the preoperative MRI.
Laminectomy: A C1 laminectomy can then be performed if the tonsils extend to that level (common). If the tonsils extend to C2 (rare), a partial or complete C2 laminectomy is performed.
Dural opening: Occasionally, only a bony decompression may be sufficient. However, in most cases with significant tonsillar herniation, especially when a syrinx is also present, dural opening is warranted as described below. Some centers also shrink the tonsils.
Chiari I malformation
Controversy about dural opening and intradural work: Approximately 5–10% of surgeons choose to stop after bony decompression of the craniocervical junction (some of these procedures are also accompanied by duropexy, i.e., stripping the outer layer of the dura); 45% open the dura and perform a duraplasty, leaving the arachnoid intact; and the other 45% open the arachnoid, lyse arachnoidal adhesions, and often shrink or resect the cerebellar tonsils (58).
Decision-making: The decision to open the dura and perform duraplasty has not been evaluated in randomized studies, and therefore the best evidence available in favor of performing either procedure is still based on retrospective data. It seems that there is some benefit of duraplasty over bony decompression alone in terms of symptom improvement and the need for reoperation for recurrent symptoms. In experienced hands, the rate of CSF-related complications related to duraplasty is not significant. The overwhelming majority agree to perform a duraplasty in cases associated with syringomyelia (59, 60).
Opening the arachnoid: Some surgeons advocate opening the arachnoid to explore for veils and adhesions. Similarly, no data are available to support such an approach.
Tonsil reduction: Despite the high rate (45%) of tonsillar reduction after duraplasty among North American pediatric neurosurgeons, no data are available to support this practice over tonsil-sparing duraplasty.
Use of ultrasound: Visualization of movement of tonsils through the dura or intraoperative ultrasound is used at some centers to determine the need for dural opening.
Autograft for duroplasty: In an effort to minimize the use of synthetic grafts, the authors recommend harvesting nuchal ligament or pericranium to create a dural graft for the duraplasty. A duraplasty is performed to keep the sac capacious, and the dura is closed in a watertight fashion. In the authors’ practice, the preferred dural graft is the patient’s own nuchal ligament. If it is not possible to harvest the nuchal ligament, commercially available dural substitutes can be used.
Craniotomy left open and bone discarded
Tight fascial closure: The resection cavity is closed with a meticulous approximation of muscle, fascia, and skin.