Lumbar Skeletal Muscle Index (SMI) Based on Skeletal Muscle Area in an Abdominal CT Scan

Description

The area of skeletal muscle in an abdominal CT scan correlates with a patient’s total skeletal muscle mass. The muscle area can be standardized by dividing it by the body height squared. Measuring lumbar skeletal muscles can be helpful in oncology patients since so many of these patients have CT imaging studies.

NOTE: The term Skeletal Muscle Index is also used in 02.19.02 and 02.19.22 with the muscle mass in kilograms indexed to body height squared.

Method:

(1) An abdominal CT scan is performed.

(2) Two adjacent axial images at the third lumbar vertebra are selected.

(3) The total area of skeletal muscle in each image is measured in square centimeters. This includes the rectus abdominis, abdominal (lateral and oblique), psoas, quadratus lumborum and erector spinae.

average total muscle area in square cm =

= ((area in image 1) + (area in image 2)) / 2

lumbar skeletal muscle index =

= (average total muscle area) / ((height in meters)^2)

Units: (square cm) / (square meters)

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