(YNRF) Intradural Pathology in Posterior Fossa Decompression with Duraplasty for Chiari Type 1 with and Without Syringomyelia: Vascular, Tonsillar, and Arachnoid Abnormalities at the Craniocervical Junction

Introduction: Definitive management of Chiari Malformation Type 1 (CM1) requires the functional restoration of an obstructed cisterna magna. In posterior fossa decompression with duraplasty (PFDD), various intradural pathologies are suggested to alter CSF flow at the craniocervical junction and require surgical correction. However, reports of specific intraoperative intradural pathologies and their nuances are scarce, especially those characterizing rarer findings such as compressive vascular structures.

Methods: We conducted a retrospective cohort analysis of adults and children undergoing first-time PFDD for CM1 (2011-2021), with and without syringomyelia. We characterized a wide variety of intradural microsurgical findings and outcomes, with intraoperative images.

Results: All 180 patients (aged 1-72 years; median (IQR) 24 (14-38); 37% children < 21 years) exhibited multiple intradural pathologies, with a median of 7 distinct pathologies concurrent in each patient. Novel findings not previously reported included blood vessels at the cervicomedullary junction compressing neural elements (26.7%) and PICA obstruction of the foramen of Magendie (FoM) (17.2%). Other common findings included arachnoid adhesions (92.8%), thickening (90.6%), and webs at the obex (52.2%); tonsillar gliosis (57.2%), hypertrophy (18.3%), and adhesions obstructing the FoM (62.2%); and dural scarring (87.8%). Tonsillar gliosis and intertonsillar adhesions obstructing the FoM were more common in children than adults. Tonsillar gliosis and arachnoid webs were more common among syringomyelia patients. After multivariable adjustment, no pathologies were found to be independently associated with syringomyelia or pre-operative symptoms. The vast majority of patients improved post-operatively. The complication rate was low: 1.2% of patients required revision PFDD, 3.6% experienced other operative complications, and 0% had CSF leaks.

Conclusion : Intradural pathologies may be more common than previously reported among all CM1 patients both with and without syringomyelia, especially compressive vascular structures. Further study may determine how these contribute to CM1 symptomatology. Such findings were microsurgically addressed with a favorable safety and efficacy profile in our cohort.