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Rectus abdominis muscle

The rectus abdominis muscle is a long, paired, vertically oriented strap muscle located on the anterior abdominal wall. It extends from the pubic symphysis and pubic crest inferiorly to the xiphoid process and the 5th–7th costal cartilages superiorly.

It is enclosed within the rectus sheath, which is formed by the aponeuroses of the external oblique, internal oblique, and transversus abdominis muscles. The two rectus abdominis muscles of each side are separated in the midline by the linea alba, a tendinous raphe extending from the xiphoid process to the pubic symphysis.

The rectus abdominis is characterized by tendinous intersections (usually three or more), which give rise to the segmented "six-pack" appearance. The muscle functions as a major flexor of the trunk, compressor of the abdominal viscera, and contributes to postural stability, forced expiration, and increased intra-abdominal pressure during actions such as defecation, micturition, childbirth, and heavy lifting.

Clinically, the rectus abdominis is important in abdominal wall hernias (especially at the linea alba and linea semilunaris), rectus sheath hematomas, and post-surgical abdominal wall reconstructions.

Synonyms

  • Abdominal rectus muscle

  • Six-pack muscle

  • Musculus rectus abdominis

Function

  • Flexes the trunk at the lumbar spine (as in sit-ups)

  • Compresses abdominal viscera to aid in forced expiration, defecation, micturition, and childbirth

  • Helps stabilize the pelvis during walking and postural adjustments

  • Works with other abdominal wall muscles to maintain core stability

Nerve Supply

  • Innervated by the thoracoabdominal nerves (T7–T11, continuation of intercostal nerves)

  • Subcostal nerve (T12)

  • Motor and sensory innervation for muscle and overlying skin

Arterial Supply

  • Superior epigastric artery (continuation of internal thoracic artery)

  • Inferior epigastric artery (branch of external iliac artery)

  • Small contributions from lower intercostal arteries

Venous Drainage

  • Superior epigastric vein → internal thoracic vein → brachiocephalic vein

  • Inferior epigastric vein → external iliac vein

  • Intercostal veins → azygos system

MRI Appearance

T1-weighted images:

  • Normal rectus abdominis appears as intermediate signal intensity with visible fascicular architecture

  • Fat between rectus sheath and muscle appears hyperintense

T2-weighted images:

  • Normal muscle: intermediate-to-low signal

  • Muscle edema (injury, strain, hematoma) appears hyperintense

STIR:

  • Suppresses fat signal, highlighting muscle edema, inflammation, or hematomas

  • Sensitive for detecting acute trauma or infection

T1 Post-Gadolinium (Gd-enhanced MRI):

  • Normal muscle shows mild homogeneous enhancement

  • Pathologies such as myositis, abscess, or tumor show abnormal heterogeneous enhancement

  • Enhances vascular supply to detect rectus sheath hematoma margins

MRI Non-Contrast 3D Imaging:

  • Provides 3D view of rectus abdominis thickness, attachments, and symmetry

  • Useful in preoperative abdominal wall reconstruction planning

CT Appearance

Non-contrast CT:

  • Muscle appears as a soft tissue density bounded by the rectus sheath

  • Detects rectus sheath hematomas, muscle atrophy, calcification, or asymmetry

CT Post-Contrast:

  • Shows vascular supply and pathology

  • Rectus sheath hematomas appear as hyperdense collections, with possible active extravasation after contrast

  • Enhances detection of tumors, infections, or vascular lesions

  • 3D reconstructions used in abdominal wall reconstruction and hernia repair planning

MRI images

Rectus abdominis muscle anatomy MRI axial image -img-00000-00000

MRI images

Rectus abdominis muscle anatomy MRI coronal image -img-00000-00000

CT image

Rectus abdominis muscle anatomy CT axial image -img-00000-00000