Importance of C1 laminectomy in foramen magnum decompression surgery: A technical note

Arnold-Chiari malformations (ACM) of the brain result from aberrations in the development of the posterior fossa resulting in its smaller volume leading to tonsillar herniation. The most common type includes Type I ACM where tonsillar descent reaches up to either C1 or C2 along with cervico-dorsal syringomyelia. The surgery (foramen magnum decompression, [FMD]) is usually straight forward and includes sub-occipital craniectomy and cervical laminectomy based on the level of descent. Rarely inadequate cervical laminectomy of C1 arch may result in residual compression at the level of obex even after "lax" duraplasty. A cervico-dural angle (angle between the neo-dura and cervical dura) at level foramen magnum can be observed in these patients. This angle is usually obtuse in imaging of cranio-vertebral junction (CVJ) of normal people and in postoperative patients of Chiari malformations where normal anatomy is restored. Inadequate C1 laminectomy may result in an acute cervico-dural angle with residual compression at the level of CVJ. Therefore, C1 laminectomy becomes a key step in FMD surgery that is often underemphasized, and neurosurgeons should be careful in doing it adequately.