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External oblique muscle

The external oblique muscle is the largest and most superficial of the anterolateral abdominal wall muscles. It originates from the outer surfaces of ribs 5–12 and runs inferiorly and medially in a “hands-in-pockets” orientation.

The muscle fibers insert into the linea alba, pubic tubercle, and anterior half of the iliac crest. Its broad aponeurosis forms part of the rectus sheath and contributes to the inguinal ligament (inferior margin of the aponeurosis folding between the anterior superior iliac spine and pubic tubercle).

The external oblique works synergistically with the internal oblique and transversus abdominis to form the abdominal wall, provide core stability, and assist in respiration. It is also critical in the formation of the inguinal canal, and thus is important in hernia pathology.

Synonyms

  • Musculus obliquus externus abdominis

  • External abdominal oblique

  • Outer oblique muscle

Function

  • Bilaterally: flexes the trunk, compresses abdominal contents, stabilizes pelvis and core

  • Unilaterally: bends trunk laterally to the same side, rotates trunk to the opposite side

  • Aids in forced expiration, coughing, defecation, and childbirth

  • Provides anterior abdominal wall support and posture maintenance

Nerve Supply

  • Thoracoabdominal nerves (T7–T11)

  • Subcostal nerve (T12)

  • Iliohypogastric and ilioinguinal nerves (variable contribution)

Arterial Supply

  • Lower six posterior intercostal arteries

  • Subcostal artery

  • Superior epigastric artery

  • Inferior epigastric artery

  • Deep circumflex iliac artery

Venous Drainage

  • Parallels arterial supply:

    • Intercostal and subcostal veins → azygos and hemiazygos systems

    • Superior and inferior epigastric veins → internal thoracic and external iliac veins

    • Deep circumflex iliac vein → external iliac vein

MRI Appearance

T1-weighted images:

  • Normal muscle shows intermediate signal intensity with fascicular structure

  • Fat planes along rectus sheath and inguinal canal appear hyperintense

T2-weighted images:

  • Normal muscle: intermediate-to-low signal

  • Muscle injury or edema: hyperintense areas within muscle fibers

STIR:

  • Fat suppression highlights muscle edema, inflammation, and hematoma as hyperintense regions

  • Useful for detecting sports-related injuries (e.g., oblique strains in athletes)

T1 Post-Gadolinium (Gd-enhanced MRI):

  • Normal muscle enhances mildly and uniformly

  • Abnormal enhancement in myositis, tumors, or post-traumatic inflammation

  • Highlights vascularity in inguinal canal hernia sac walls

MRI Non-Contrast 3D Imaging:

  • Provides 3D reconstruction of muscle thickness, fiber orientation, and relationship with rectus sheath and inguinal canal

  • Valuable in hernia repair planning and core muscle injury evaluation

CT Appearance

Non-contrast CT:

  • External oblique appears as a thin muscular sheet on the lateral abdominal wall

  • Detects muscle atrophy, hematomas, or calcification

CT Post-Contrast:

  • Enhances differentiation of muscle, fascia, and abdominal viscera

  • Useful in evaluating hernia contents, muscle tears, or infections

  • 3D reconstructions assist in surgical planning for abdominal wall reconstruction and hernia repair

MRI images

External oblique muscle anatomy MRI axial image -img-00000-00000

MRI images

External oblique muscle anatomy MRI coronal image -img-00000-00000

CT image

External oblique muscle CT anatomy Location and Imaging Appearance -img-00000-00000