Preoperative Posterior Paraspinal Fatty Infiltration and an Exploratory Axial Muscle Imaging Phenotype in Surgically Treated Metastatic Epidural Spinal Cord Compression: A Retrospective Cohort Study

Abstract

Background and Objectives: Prognostic assessment in metastatic epidural spinal cord compression (MESCC) requires estimation of survival, systemic condition, and the likelihood of early functional improvement. We evaluated whether posterior paraspinal fatty infiltration and an exploratory routine-imaging axial muscle phenotype derived from preoperative L3 CT/MRI were associated with overall survival and early neurological improvement after surgery for MESCC. Materials and Methods: Consecutive adults who underwent surgery for MESCC (Bilsky grade 1C–3) between June 2020 and November 2025 were retrospectively analyzed. Psoas quantity was measured on preoperative L3 computed tomography using the psoas-to-vertebral-body ratio (PVR) and psoas muscle index. Posterior paraspinal muscle quality was graded on axial T2-weighted L3 magnetic resonance imaging using a Goutallier-style scale in the multifidus/erector spinae compartment. The primary exposure was high-grade posterior paraspinal fatty infiltration, defined as patient-level maximum Goutallier grade 3–4. An exploratory secondary phenotype combined lower PVR by sex-specific cohort median with Goutallier grade 3–4. Results: Among 133 eligible patients, PVR measurements were available in 119, Goutallier grading in 112, and complete combined phenotyping in 109. Median survival was 383 days for Goutallier 0–2 and 144.5 days for Goutallier 3–4. In the primary clinical/Katagiri-adjusted Cox model, Goutallier 3–4 was associated with worse overall survival (hazard ratio [HR] 1.80, 95% confidence interval [CI] 1.06–3.07; p = 0.029). The exploratory both-abnormalities subgroup comprised 21 patients, with median survival of 73 days, and among patients with a preoperative Frankel deficit, early Frankel improvement occurred in 2/15 (13.3%); the adjusted overall-survival HR was 2.64 (95% CI 1.15–6.03; p = 0.021), whereas binary-outcome estimates were imprecise. Conclusions: High-grade posterior paraspinal fatty infiltration was associated with inferior survival and lower early neurological improvement after surgery for MESCC. The combined phenotype identified a small high-risk subgroup but should be regarded as hypothesis-generating. These routine-imaging markers require external validation and should not be used as stand-alone surgical selection criteria.