The significance of occipitocervical dura angulation in selection of surgery procedures for Chiari malformation type I

At present, the common surgical procedures for the Chiari malformation type I are comprised of posterior fossa decompression, duraplasty and tonsillectomy. Some neurosurgeons prefer these so called minimally invasive surgeries. However, there are still some failures for patients undergoing the above surgeries in clinical practice. Analyzing causes of many surgical failures, the author put forward the anatomical concept of occipitocervical dura angulation (ODA). The ODA is defined as the included angle between the cerebral dura mater and spinal dura mater at the posterior foramen magnum on the median sagittal plane. For Chiari malformation type I without atlantoaxial instability, the selection of appropriate surgeries and accurate evaluation on the effect of the decompression can be realized after the comprehensive analysis both on the severity of tonsil herniation and the ODA. Tonsillectomy may be needed to add to posterior fossa decompression (PFD) and duraplasty for Chiari malformation type I with the ODA being the larger obtuse angle and/or the tonsil herniation to the level of arcus posterior atlantis.