Introduction: Due to differences in severity in patients, there is no one-size-fits-all procedure for every one with Chiari I malformation. To target two facts of Chiari I malformation: disproportion between cerebellum and posterior fossa, and decreased CSF flow at foramen magnum, we designed a new procedure: posterior fossa expansion plus dural patch suspension.
Methods: Key techniques: A 25-30 by 25-30 mm suboccipital bone flap is created. A 25-30 mm C1 laminectomy is done. The dura is opened in the midline about 3 cm long, and the midpoint is at the foramen magnum. While dural edges are reflected laterally at the midpoints, this rhombus-shaped dura opening is covered with a dural patch. In this way, the posterior edge of the foramen magnum is shifted posteriorly 7-10 mm. The circumference of the foramen magnum is increased 10-13 mm. The bone flap is placed so that its upper edge is at its original position, whereas its lower edge is shifted posteriorly to match the position of dural patch. Plates and screws are used to keep the bone flap in the designed position. The dural edges are suspended to the lower edge of bone flap.
Results: Four patients underwent this procedure. Two patients’ suboccipital headaches resolved, and three patients’ dysphagia almost resolved in a 3-month follow-up. No patients had CSF leakage. Three-month post-operative MRI scans show CSF flow at foramen magnum is restored. The shapes of herniated tonsils have improved.
Conclusions: In this procedure, a rigid bone flap is used to expand posterior fossa and to protect CSF space gained from dural patch. This procedure restores CSF flow immediately at foramen magnum. It is safe and effective.
Restoring CSF flow should be primary goal of Chiari decompression.
A normal CSF flow study in post-operative MRI should be the evidence of successful decompression.
Patient Care: This new procedure will significantly increase cure rate of Chiari I malformation.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Describe the advantage and benefits of this new procedure. It resolves two problems at the same time: to expand posterior fossa because disproportion between cerebellum and posterior fossa; to restore CSF flow because decreased CSF flow at foramen magnum;
2) Discuss surgical details of the procedure;
3) Recognize that normal CSF flow study in post-operative MRI is an effective way to prove a successful Chiari decompression.