2024 Volume 49 Issue 3 Pages 88-95
Introduction: Although various surgical methods are performed to treat Chiari malformation (CM) type 1 and achondroplasia, foramen magnum decompression (FMD) and C1 laminectomy are common surgical techniques that require sufficient bone resection of the foramen magnum. Since the structure of the craniocervical transition region in both CM type 1 and achondroplasia differs from the normal structure, bone resection in FMD may sometimes be difficult. We verified surgery for CM type 1 and achondroplasia using intraoperative computed tomography (CT) at our hospital.
Materials and methods: Cases of CM type 1 and achondroplasia that were younger than 18 years and underwent surgery using intraoperative CT at our hospital between 2010 and 2022 were analyzed. We examined the number of intraoperative CT scans performed, whether additional bone resection was required after CT scans, and improvements in postoperative images and symptoms.
Results: Six cases of CM type 1 (mean age 11 years) and four of achondroplasia (mean age 7.5 years) underwent FMD and C1 resection using intraoperative CT. Although intraoperative CT was performed only once in all cases of CM type 1, additional bone removal after intraoperative CT was required for one case with an occipital bone anomaly at the foramen magnum. Intraoperative CT was performed once in two cases of achondroplasia; however, additional bone removal after intraoperative CT was required in one case. Intraoperative CT was conducted twice in two cases of achondroplasia to confirm that FMD was sufficient. The decompression width expanded by an average of approximately 4.1 mm after the first CT scans. All cases showed the attenuation of symptoms and/or a reduction in syringomyelia.
Discussion: At the craniocervical junction in achondroplasia, the thickened occipital bone invaginates perpendicularly into the foramen magnum, causing narrowing. Some cases of CM type 1 have bone abnormalities at the craniocervical junction. Due to the above reasons, the bone resection of the foramen magnum may be inadequate in these patients; however, intraoperative CT can visualize the occipital bone of the foramen magnum with easy-to-understand 2D and 3D images, allowing surgeons to confirm the extent of bone resection during surgery. Considering the risk of radiation exposure to children, it is recommended that intraoperative CT be used only in cases of Chiari malformation and achondroplasia in which FMD is difficult.
Conclusion: Although careful consideration must be given to radiation exposure in the case of children, intraoperative CT may be useful for FMD in cases of CM type 1 with abnormalities at the craniocervical junction and achondroplasia.
