Sarcopenia as a prognostic factor in gastric cancer patients undergoing gastrectomy: Implications for postoperative and long-term outcomes

Table 1 Computed tomography-based body composition parameters

Parameter	Clinical meaning	Assessment method	Common diagnostic cut-off	Prognostic role	Strengths	Limitations
SMI	Muscle quantity, normalized for body size	Cross-sectional skeletal muscle area at L3 (cm2), indexed to height2 (cm2/m2)	Sarcopenia: < 52.4 cm2/m2 (men), < 38.5 cm2/m2 (women); BMI-adjusted cut-offs also used	Overall survival; predicts chemotherapy toxicity, postoperative complications	Well-validated; single L3 slice correlates strongly with whole-body muscle mass; widely used across cancer/surgical literature	No universal cut-off (varies by ethnicity, population, scanner protocol); requires dedicated software/manual segmentation; height2 normalization may under/overcorrect in obese or very short/tall patients
PMI	Surrogate for muscle mass using a single muscle	Cross-sectional area of bilateral psoas muscles at L3 or L4, indexed to height2 (cm2/m2)	No consensus; commonly cited thresholds approximately < 5.0 cm2/m2 (men), < 3.4 cm2/m2 (women), varies widely by study	Postoperative complications, morbidity	Fast to measure (small, discrete structure); minimal manual tracing needed; feasible even on lower-quality/Limited-slice scans	Poorly correlates with total skeletal muscle mass; high inter-study variability in cut-offs; psoas size affected by positioning and vertebral level chosen; less validated than SMI
SMD	Muscle quality (myosteatosis/fatty infiltration)	Mean CT attenuation (HU) of skeletal muscle at L3	Myosteatosis: < 41 HU (BMI < 25) or < 33 HU (BMI ≥ 25)	Overall survival, independent of muscle quantity	Captures muscle quality, not just size - adds prognostic information beyond SMI; low cost (same CT slice as SMI)	Attenuation affected by CT protocol/reconstruction settings and contrast phase; BMI-stratified cut-offs complicate use; less intuitive for clinicians
VFA	Adiposity, visceral fat burden	Cross-sectional visceral adipose tissue area at L3 (or umbilicus level), cm2	Visceral obesity: ≥ 100 cm2 (women), ≥ 130-163 cm2 (men), varies by study/ethnicity	Postoperative and infectious complications	Strong correlate of metabolic risk and surgical complication risk; reproducible measurement	Cut-offs not standardized across populations; requires accurate delineation from subcutaneous fat; single-slice VFA may not reflect total visceral fat volume
IMAC	Poor muscle quality (fat infiltration within/around muscle)	Ratio of CT attenuation of intramuscular/paraspinal fat to that of paraspinal muscle (using psoas or paraspinal muscles)	No universal threshold; typically defined by cohort-specific median or tertile split	Mortality	Complements SMD; useful when psoas is the only reliably visualized muscle group; correlates with frailty	Lacks standardized cut-off; formula/muscle group varies between studies, limiting comparability; less widely validated than SMI/SMD

SMI: Skeletal muscle index; BMI: Body mass index; CT: Computed tomography; PMI: Psoas muscle index; SMD: Skeletal muscle density; HU: Hounsfield units; VFA: Visceral fat area; IMAC: Intramuscular adipose content.