Thirty-day outcomes for suboccipital decompression in adults with Chiari malformation type I: a frailty-driven perspective from the American College of Surgeons National Surgical Quality Improvement Program
Authors: Kassicieh Alexander J. , Estes Emily M. , Rumalla Kavelin , Kazim Syed Faraz , McKee Rohini G. , Schmidt Meic H. , Bowers Christian A. 
Published: March 2023

OBJECTIVE
When indicated, patients with symptomatic Chiari malformation type I (CM-I) may benefit from suboccipital decompression (SOD). Although SOD is considered a lower-risk neurosurgical procedure, preoperative risk assessment and careful surgical patient selection remain critical. The objectives of the present study were twofold: 1) describe 30-day SOD outcomes for CM patients with attention to the impact of preoperative frailty and 2) design a predictive model for the primary endpoint of nonhome discharge (NHD).

METHODS
There were 1015 CM-I patients who underwent SOD in the 2011–2020 American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) database, as specified by diagnostic and procedural codes (Current Procedural Terminology code 61343). Descriptive statistics were used to analyze total cohort baseline demographics, preoperative comorbidities, and postoperative outcomes within 30 days of surgery. Univariate cross-tabulation was used to compare baseline demographics and preoperative characteristics across the NHD and home discharge (HD) cohorts. Receiver operating characteristic (ROC) curve analysis was used to assess the discriminative ability of the revised Risk Analysis Index (RAI-rev) on NHD.

RESULTS
The study cohort had a median age of 36 years, and 80.6% of patients were female. Race distribution was categorized as White (69.9%), Black (16.6%), and other groups (13.6%). The most common preoperative comorbidities were active smoking (24.4%), hypertension (19.2%), and diabetes mellitus (4.7%). The primary outcome of NHD occurred in 4.6% of patients (n = 47). Increasing frailty (measured by the RAI-rev) was associated with a stepwise increase in the rate of NHD: 2.3% for RAI-rev scores 0–10, 5.8% for RAI-rev scores 11–15, 7.6% for RAI-rev scores 16–20, 18.2% for RAI-rev scores 21–25, and 77.8% for RAI-rev scores ≥ 26 (p < 0.001). Other preoperative factors associated with NHD included older age, nonelective surgery, diabetes, hypertension, and elevated creatinine (all p < 0.01). The other most common 30-day complications included unplanned readmission (9.3%), unplanned reoperation (5.3%), return to the operating room (5.8%), Clavien-Dindo grade IV (life-threatening) (1.5%), organ space surgical site infection (SSI) (1.5%), superficial SSI (1.4%), and reoperation for a CSF leak (1.1%). Surgical mortality (within 30 days) was extremely rare (1/1015, 0.1%). ROC curve analysis demonstrated that RAI-rev predicted NHD with significant discriminatory accuracy among CM-I patients who received SOD treatment (C-statistic 0.731, 95% CI 0.648–0.814).

CONCLUSIONS
This decade-long analysis of a multicenter surgical registry provides internationally representative, modern rates of 30-day outcomes after suboccipital decompression (with or without duraplasty) for adult CM-I patients. Preoperative frailty assessment with the RAI-rev may help identify higher-risk surgical candidates.