The role of tonsillar manipulation in posterior fossa decompression for Chiari I malformation: a 26-year...

Despite many years of research and advanced technology aiding in the diagnosis and treatment of Chiari 1 malformation (CM1), ideal surgical techniques remain controversial. When duraplasty is necessary, tonsillar coagulation is often performed to restore cerebrospinal fluid (CSF) pathways, though its benefits are unclear. Extensive intradural manipulation may increase surgical risk and reoperation rates secondary to arachnoid adhesions. The objective of our study is to delineate whether tonsillar manipulation is safe and ultimately necessary for adequate posterior fossa decompression in CM1 surgery.

A retrospective review of all patients who underwent initial posterior fossa decompression and duraplasty for CM1 at a single institution from 1997 to 2024 was performed with IRB approval. Fourth ventricular stents were excluded. Indications for surgery included intractable occipital headache, neurological deficits, and/or syringomyelia. Demographics, radiographic details, and surgical outcomes were compared between patients with (PFDD + TM) and without (PFDD) tonsillar manipulation.

A total of 151 patients met inclusion criteria, with 73% undergoing PFDD + TM and 27% undergoing PFDD alone. The only significant difference in baseline characteristics was extent of tonsillar herniation, with all patients with > 20 mm herniation undergoing PFDD + TM (p = 0.01). Attending surgeon preference was also significantly associated with surgical approach (p < 0.0001). Thirty-day complication rates were similar between groups (PFDD 29.3% vs. PFDD + TM 14.5%, p = 0.06). Over a mean follow-up of 49.8 months, reoperation rates were 7.3% in PFDD and 4.5% in PFDD + TM (p = 0.68). Symptomatic improvement occurred in > 70% of patients across all symptom categories without significant differences between surgical approaches, with syrinx improvement in 85.2% of PFDD and 75.8% of PFDD + TM patients (p = 0.51).

There were no significant differences between CM1 patients that underwent duraplasty with or without tonsillar manipulation regarding complications, reoperations, or symptomatic outcomes. Thus, there is no significant advantage to performing tonsillar manipulation nor any meaningful disadvantage. Multi-institutional studies are needed to uncover potential statistical differences in outcomes that may identify a superior surgical technique, especially over longer periods of follow-up.