Anterolateral Abdominal Wall Vocabulary

Anterolateral Abdominal Wall

Introduction

  • The abdominal cavity is inferior to the diaphragm and superior to the pelvic inlet.

  • It consists of fascial and myotendinous soft tissue layers, allowing for greater movement but less protection compared to the thoracic region.

  • Isometric contraction of abdominal muscles provides protection from mechanical trauma.

  • Core exercises increase protection and stabilize the abdominal region by actively contracting these muscles.

Abdominal Quadrants

  • Used in clinical practice to localize pain and injury.

  • Two reference lines divide the abdomen into four quadrants:

    • Median plane: A midsagittal vertical line from the xiphoid process through the umbilicus to the symphysis pubis, dividing the abdomen into right and left sides.

    • Umbilical plane: A horizontal line through the umbilicus, dividing the abdomen into upper and lower sections.

  • Upper Right Quadrant:

    • Liver

    • Gallbladder

    • Head of the pancreas

    • Right kidney

  • Upper Left Quadrant:

    • Majority of the stomach

    • Spleen

    • Body of the pancreas

    • Left kidney

  • Right Lower Quadrant:

    • Vermiform appendix

    • Right ureter

    • In females: right ovary and fallopian tube

  • Left Lower Quadrant:

    • Left ureter

    • In females: left ovary and fallopian tube

Anterolateral Abdominal Wall Layers

  • Composed of muscle, tendon, and fascia

    • Superficial fascial component (loose and dense layers)

    • Three broad muscles that wrap around the lateral aspect

    • A pair of longitudinal muscles anteriorly

    • Inguinal canal inferiorly

Camper's Fascia

  • Superficial, just beneath the skin.

  • Composed of adipose connective tissue (yellow in appearance).

  • Variable thickness (nonexistent in frail elderly, thick in obese individuals).

  • Contributes to android obesity (beer belly).

  • Provides insulation and cushioning to protect internal organs.

Scarpa's Fascia

  • Deep to Camper's fascia.

  • Composed of dense irregular connective tissue (more consistent thickness).

  • Anchors Camper's fascia to the underlying musculature.

Myotendinous Layers

  • Oblique Muscles: Originate posteriorly off the ribs and thoracolumbar fascia, wrapping anterolaterally.

    • External Oblique Muscles:

      • Originate off ribs 5-12.

      • Posterior fibers run vertically to the iliac crest.

      • Anterior fibers run obliquely (hand-in-pocket orientation).

      • Transition to an aponeurotic tendon at the midaxillary line, fusing at the midline.

      • Contraction results in flexion and contralateral rotation of the trunk.

    • Internal Oblique Muscles:

      • Continuous with the thoracolumbar fascia.

      • Fibers project anterolaterally in a radiating pattern.

        • Superior fibers attach to lower ribs.

        • Intermediate fibers transition to an aponeurosis and fuse at the midline.

        • Inferior fibers insert along the pubic crest and contribute to the inguinal canal.

      • Contribute to trunk flexion; unilateral contraction produces ipsilateral rotation.

    • Transversus Abdominis:

      • Originates off the thoracolumbar fascia; fibers run transversely.

      • Fuses along the midline via aponeurosis.

      • Works with internal obliques to compress abdominal contents and provide rigidity to the abdominal wall.

      • Aids in bracing against mechanical trauma and increasing intra-abdominal pressure.

  • Transversalis Fascia: Deepest layer of the anterolateral abdominal wall.

Core Exercises and the Thoracolumbar Fascia

  • Internal obliques and transversus abdominis engagement is at the core of core exercises.

  • Muscles fuse with the thoracolumbar fascia around the erector spinae muscle, generating tension to support the erector spinae.

  • Core training is associated with lower risks of back injury.

Longitudinal Muscles

  • Rectus Abdominis: Extends from the costal margin and xiphoid process to the pubic crest and symphysis pubis.

  • Principal flexor of the trunk.

  • Pyramidalis: Vestigial triangular muscle from the pubic crest to the midline.

  • Minimal contribution to trunk flexion.

Rectus Sheath

  • Internal Oblique Aponeurosis: Bifurcates at the lateral border of the rectus abdominis.

    • Half passes anterior, half passes posterior.

    • Re-fuses past the medial border and fuses at the midline.

  • External Oblique: Passes entirely anterior to the rectus abdominis, interdigitating with the anterior fibers of the internal oblique to form the anterior rectus sheath.

  • Transversus Abdominis: Runs posterior to the rectus abdominis, fusing with the posterior division of the internal oblique to form the posterior rectus sheath.

  • Linea Alba:

    • Midline fusion of anterior and posterior rectus sheaths.

    • Thick, white appearance.

Changes Below the Umbilicus

  • All three aponeuroses run anterior to the rectus abdominis.

  • Transversalis fascia lies immediately posterior to the rectus abdominis.

  • Arcuate Line: Arch between the opaque superior and translucent inferior regions.

Tendinous Intersections

  • Rectus abdominis is segmented by tendinous intersections.

  • These intersections fuse the anterior and posterior rectus sheaths.

  • Account for the "six-pack" appearance.

Inner Surface of the Anterolateral Abdominal Wall

  • Five protrusions are visible through the fascial cover:

    • Median Umbilical Fold: Extends from the apex of the bladder to the umbilicus.

    • Created by the urachus (remnant of the allantois).

    • Medial Umbilical Folds: Lateral to the median umbilical fold.

      • Mark the location of the umbilical ligaments (remnants of the umbilical arteries).

    • Lateral Umbilical Folds: Generated by the inferior epigastric vessels.

      • No embryological remnant.

      • Clinical landmark.

Clinical Significance of Umbilical Folds

  • Lateral to the lateral umbilical folds is the deep inguinal ring (location of indirect inguinal hernias).

  • Medial to the lateral umbilical folds is a thin region (common site of direct inguinal hernias).

  • Inguinal Triangle: Defined by the lateral border of the rectus abdominis, the inguinal canal, and the lateral umbilical fold.

    • Location of direct inguinal hernias.

    • Indirect inguinal hernias occur just lateral to this region.

Blood Supply

  • Superficial:

    • Inferior epigastric arteries (medially)

    • Superficial circumflex iliac arteries (laterally)

    • Both branch off the femoral artery.

  • Deep:

    • Deep circumflex iliac arteries (from the external iliac artery):

      • Supply the superolateral aspects, anastomosing with descending branches off the intercostal arteries.

    • Inferior epigastric arteries (from the external iliacs):

      • Supply the superomedial aspects.

      • Anastomose with the superior epigastric vessels, which are terminal branches off the internal thoracic artery.

    • Musculophrenic artery: Terminal branch off the internal thoracic artery.

      • Supplies blood to the anterolateral thoracoabdominal wall and the anterior portion of the diaphragm.

Surface Anatomy

  • Highly variable based on the individual.

  • Sternal notch and sternal angle important for understanding the location of the great vessels and the insertion of the second rib.

  • In ectomorphic individuals, ribs and intercostal segments are more easily palpated.

  • In well-toned individuals, the rectus abdominis muscles are prominent, separated by tendinous intersections.

  • Linea Semilunaris: Crescent-shaped line that marks the tendinous junction between the oblique musculature and the rectus sheaths.

  • McBurney's Point: Two-thirds of the distance along an imaginary line from the umbilicus to the anterior superior iliac spine.

    • Approximates the location of the vermiform appendix.

    • Tenderness and rebound pain indicate appendicitis.