Anterior abdominal wall

Summary

The anterior abdominal wall extends from the xiphoid process and costal margins cranially to the pubic and iliac bones inferiorly and to the mid-axillary lines on either side. The abdomen is divided into regions or quadrants to more precisely describe abdominal symptoms and signs and help identify underlying organs. The muscles of the anterior abdominal wall are flat muscles and include the rectus abdominis, the external and internal obliques, the transversus abdominis, and the pyramidalis. These muscles allow the trunk to bend either forward or laterally, maintain abdominal tone, and help increase intra-abdominal pressure. The main arteries of the anterior abdominal wall are the inferior and superior epigastric arteries. The abdominal wall is innervated by the intercostal nerves, the subcostal nerves, and, to a lesser extent, the iliohypogastric and ilioinguinal nerves.

Overview

Boundaries of the anterior abdominal wall

Functions

  • Protects abdominal viscera
  • Assists in forceful expiration
  • Decreases risk of herniation
  • Enables the trunk to bend forward or laterally

Planes of the anterior abdominal wall

  • Transverse abdominal planes
    • Subcostal plane
    • Transtubercular plane
      • Lies midway between the transpyloric plane (see below) and the pubic symphysis
      • Passes through the iliac tubercles and the L5 vertebral body
    • Transpyloric plane
      • Passes through the 9th costal cartilage
      • Lies at the level of the inferior border of L1 vertebral body.
  • Vertical abdominal lines: the right and left midclavicular lines that extend from the midpoint of the clavicle cranially to the midinguinal point caudally

Divisions of the abdomen

The regions or quadrants of the abdomen are used in clinical contexts to describe abdominal symptoms and signs and help identify underlying organs.

Regions

  • There are 9 abdominal regions
    • Upper regions: right hypochondriac (1), epigastric (2), left hypochondriac (3)
    • Middle regions: right lumbar (4), umbilical (5), left lumbar (6)
    • Lower regions: right inguinal (7), hypogastric or suprapubic (8), left inguinal (9)
  • They are divided by:
    • Two transverse planes
      • Subcostal plane
      • Transtubercular plane
    • Two vertical lines: right and left midclavicular lines

Quadrants

Components of the anterior abdominal wall

A defect in the upper linea alba can cause an epigastric hernia.

Herniation of intra-abdominal contents through the linea semilunaris is known as a Spigelian hernia.

Inguinal canal

Transitions to
Transversalis fascia Internal spermatic fascia
Internal oblique muscle and fascia Cremaster muscle and cremasteric fascia
External oblique fascia and superficial fascia External spermatic fascia
Scarpa fascia Dartos fascia of the scrotum, Colles fascia, superficial fascia of the clitoris and penis

References:[1][2][3][4]

Musculature

Muscle Characteristics Origin Insertion Vascular supply Innervation Function

Anterior muscles

(vertical muscles)

Rectus abdominis
  • Intercostal nerves (T7–11)
  • Flexes the trunk
  • Maintains abdominal wall tone and helps increase intra-abdominal pressure (e.g., forced expiration, coughing, Valsalva maneuver)
Pyramidalis
  • Small triangular muscle
  • Absent in 10–25% of the population
  • Subcostal nerve (T12)

Anterolateral muscles

(flat muscles)

External oblique

  • Largest abdominal muscle and the most superficial anterolateral muscle
  • Its fibers are oriented in an inferomedial direction (“hand-in-pocket”).
  • Lower 8 ribs (5–12)
  • Lower intercostal, subcostal, and deep circumflex iliac arteries
  • Intercostal nerves (T7–11)
  • Subcostal nerve (T12)
  • Ipsilateral lateral flexion of the trunk
  • Contralateral rotation of the trunk
  • Maintains abdominal wall tone and helps increase intra-abdominal pressure

Internal oblique

  • Lies deep to the external oblique
  • Its fibers are oriented in a superomedial direction.
  • Lower intercostal, subcostal, and deep circumflex iliac arteries
  • Intercostal nerves (T7–11)
  • Subcostal nerve (T12)
  • Iliohypogastric and ilioinguinal nerves (L1)
  • Ipsilateral lateral flexion of the trunk
  • Ipsilateral rotation of the trunk
  • Maintains abdominal wall tone and helps increase intra-abdominal pressure

Transversus abdominis

  • The deepest muscle of the anterolateral abdominal wall
  • Its fibers are oriented transversely.
  • Maintains abdominal wall tone and helps increase intra-abdominal pressure

The conjoint tendon forms the medial portion of the posterior inguinal canal. A weakness of the conjoint tendon can result in a direct inguinal hernia.

References:[1][2][5]

Vasculature and innervation

Arteries

The inferior epigastric artery forms the lateral boundary for the Hesselbach triangle, which helps in distinguishing between direct and indirect inguinal hernias intra-operatively.

Veins

Lymphatics

Cutaneous innervation and dermatomes


Clinical significance

  • 1. Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences; 2016.
  • 2. Chung KW, Chung HM. Gross Anatomy. Philadelphia, PA: Lippincott Williams & Wilkins; 2012.
  • 3. Wyatt M. Oxford Textbook of Fundamentals of Surgery. Oxford University Press; 2016.
  • 4. Mahadevan V. Anatomy of the anterior abdominal wall and groin. Surgery (Oxford). 2003; 21(2): pp. 25–27. doi: 10.1383/surg.21.2.25.14667.
  • 5. Knipe H. Conjoint Tendon. https://radiopaedia.org/articles/conjoint-tendon. Updated January 1, 2019. Accessed January 3, 2019.
  • Gray JE, Mizell JS. Anatomy of the Abdominal Wall. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/anatomy-of-the-abdominal-wall. Last updated September 27, 2017. Accessed January 3, 2019.
last updated 12/05/2019
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