Anatomical Variation of Abdominal Wall Musculature: An Objective Assessment Using Cross-Sectional Imaging.

Abstract

Purpose: To determine normal anatomical variation of abdominal wall musculature. Methods: A retrospective analysis of CT scans was performed on adults (>18years) with normal abdominal wall muscles. Two radiologists analysed the images independently. Distances from three fixed points in the midline were measured. The fixed points were; P1, mid-way between xiphoid and umbilicus, P2, at the umbilicus, and P3, mid-way between umbilicus and pubic symphysis. From these three fixed points the following measurements were recorded; midline to lateral innermost border of the abdominal wall musculature, midline to lateral edge of rectus abdominis muscle, and midline to medial edges of all three lateral abdominal wall muscles. To obtain aponeurotic width, rectus abdominis width was subtracted from the distance to medial edge of lateral abdominal wall muscle. Results: Fifty normal CT scan were evaluated from between March 2023 to August 2023. Mean width of external oblique aponeurosis at P1 was 16.2mm (IQR 9.2mm to 20.7mm), at P2 was 23.5mm (IQR 14mm to 33mm), and at P3 no external oblique muscle was visible. Mean width of the internal oblique aponeurosis at P1 was 32.1mm (IQR 17.5mm to 45mm), at P2 was 10.13 (IQR 1mm to 17.5mm), and at P3 was 9.2mm (IQR 3.0mm to 13.7mm). Mean width of the transversus abdominis aponeurosis at P1 was -25.1mm (IQR 37.8mm to -15.0mm), at P2 was 29.4mm (IQR 20mm to 39.8mm), and at P3 was 20.3mm (IQR 12mm to 29mm). Conclusion: In this study we describe normal anatomical variation of the abdominal wall muscles. Assessing this variability on the pre-operative CT scans of ventral hernia patients allows for detailed operative planning and decision making.