Colorectal cancer is the third most common cancer among men and women in the United States, and roughly 55,000 patients are expected to die of the disease by the end of 2026. Surgery remains the most common primary treatment, but it carries a substantial burden: postoperative complications occur in about 35 percent of patients, mortality ranges from 1 to 16.4 percent, and adverse outcomes prolong hospitalization. Identifying who is at highest risk before the first incision is made has therefore become a pressing clinical goal, and the skeletal muscle has emerged as an unexpected prognostic organ, thanks to its secretory and metabolic properties.

The technique at the heart of the study is opportunistic imaging analysis. Using preoperative abdominal CT scans, the researchers measured two quantities at the level of the third lumbar vertebra. The skeletal muscle index, or SMI, quantifies muscle quantity by dividing the cross-sectional area of muscle by the square of the patient’s height. The skeletal muscle density, or SMD, expressed in Hounsfield units, captures the average radiation attenuation of the muscle—essentially a proxy for how much fat has infiltrated the tissue. Healthy muscle attenuates more radiation; fat-invaded muscle reads darker and lower. Segmentation was performed with semi-automated software integrated into the hospital’s picture archiving system, using the standard Hounsfield unit window of −29 to +150, and the measurements proved remarkably repeatable, with an intraclass correlation coefficient of 0.99.

What distinguishes this study from much of the prior literature is its treatment of these variables. Most earlier work dichotomized patients into low versus normal muscle categories using fixed cutoffs, which is clinically convenient but obscures how graded changes in muscle characteristics translate into graded changes in risk. Here, the team modeled SMI and SMD both as continuous predictors, expressed per 5-unit decrease, and as binary variables using two widely applied definitions drawn from Martin and colleagues and from Xiao and colleagues. The cohort of 415 patients had a mean age of 63.7 years, a mean body mass index of 28.2 kilograms per square meter, and underwent laparoscopic, robotic-assisted, or open resection in roughly equal measure.

The results were strikingly one-sided. Each 5-unit decrease in SMD was associated with a 6 percent higher incidence of hospital days after surgery, an association that held whether muscle density was modeled continuously or through clinical cutoffs. Muscle quantity, by contrast, lost its apparent univariate association with length of stay once age, sex, comorbidity burden, tumor stage, neoadjuvant treatment, and surgical approach were adjusted for. A similar pattern emerged for severe complications, defined as grade 3 or higher on the Clavien–Dindo classification: each 5-unit drop in SMD raised the odds by 25 percent, while SMI showed no significant adjusted association. These findings persisted in sensitivity analyses restricted to patients scanned within two months of surgery, a window that best captures muscle status closest to the operation.

Perhaps the most consequential findings concerned where patients went after leaving the hospital. Of 409 patients with discharge data, 30 were sent to a skilled nursing facility, inpatient rehabilitation, or long-term care rather than home. Each 5-unit decrease in SMD was associated with 40 percent greater odds of non-home discharge, and patients classified as having low SMD faced roughly three-and-a-half to eight-and-a-half times the odds of institutional discharge depending on the cutoff definition used. Non-home discharge matters beyond convenience: it is linked to diminished quality of life and higher healthcare costs across surgical populations, making it a meaningful marker of functional recovery.

Mortality data reinforced the same hierarchy. Twelve patients died within 90 days of surgery, and although the small number of events precluded multivariable analysis, each 5-unit decrease in SMD was associated with a 36 percent higher hazard of early death in univariate analysis. Over a median follow-up of 31.6 months, 75 patients—18.1 percent of the cohort—died of any cause. In adjusted Cox regression, each 5-unit decrease in SMD carried a 26 percent higher risk of overall mortality, and low SMD per the Martin criteria was associated with a 93 percent higher risk compared with normal density. Kaplan–Meier curves confirmed significantly worse survival for patients with low values of either measure, but only SMD survived full statistical adjustment.

Why would fat inside muscle outpredict muscle size? The authors point to the biology of myosteatosis, which appears to compound age-related declines in muscle strength and function more aggressively than simple atrophy. Across studies of older adults and patients with cancer, muscle density correlates more strongly than muscle quantity with strength, physical performance, frailty, and comorbidity burden. Myosteatosis is also entwined with systemic inflammation and insulin resistance, mechanisms plausibly relevant to surgical stress, wound healing, and immune defense. Encouragingly, the condition may be modifiable: meta-analytic evidence shows that aerobic and resistance training improve SMD in adults, raising the prospect that prehabilitation programs before cancer surgery could measurably densify muscle and blunt operative risk, though such trials in surgical oncology remain scarce.

The study has limits the authors acknowledge. The cohort was modest, and events for complications, discharge location, and early mortality were few, forcing cautious interpretation and simplified models. Nearly all scans were contrast-enhanced, which modestly overestimates SMD and may underdiagnose myosteatosis, and the researchers lacked data on physical activity, nutrition, and frailty over time. Still, the central message is hard to dismiss: a measurement already sitting inside nearly every preoperative CT scan, requiring no extra radiation, cost, or patient burden, may identify the colorectal surgery patients most likely to struggle. The authors argue that preoperative SMD could guide risk stratification, treatment decisions, and perioperative care, and they call for trials testing whether prehabilitation can improve muscle density before the operating room doors swing open.

Subject of Research: CT-derived skeletal muscle density and mass as predictors of postoperative outcomes after colorectal cancer surgery

Article Title: Associations of CT‐Derived Skeletal Muscle Index and Density With Postoperative Outcomes Following Colorectal Cancer Surgery

Article References: Papadopoulos, E., Irving, B. A., Spielmann, G., Lin, M., & Finan, K. R. (2026). Associations of CT‐Derived Skeletal Muscle Index and Density With Postoperative Outcomes Following Colorectal Cancer Surgery. Journal of Cachexia, Sarcopenia and Muscle, 17(5), Article e70384. https://doi.org/10.1002/jcsm.70384

Image Credits: AI Generated

DOI: 10.1002/jcsm.70384

Keywords: colorectal cancer, skeletal muscle density, myosteatosis, sarcopenia, CT imaging, postoperative complications, length of stay, mortality, prehabilitation, surgical oncology, body composition, risk stratification