Anterior Abdominal Wall

The anterior abdominal wall is anatomically delineated as a hexagonal area defined superiorly by the xiphoid process, laterally by the midaxillary lines, and inferiorly by the pubic symphysis. From the superficial to deep order, the anterior abdominal wall consists of the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, subcutaneous tissue, muscle, transversalis fascia, and peritoneum Peritoneum The peritoneum is a serous membrane lining the abdominopelvic cavity. This lining is formed by connective tissue and originates from the mesoderm. The membrane lines both the abdominal walls (as parietal peritoneum) and all of the visceral organs (as visceral peritoneum). Peritoneum and Retroperitoneum. The lateral abdominal muscles include the external and internal obliques and the transversus abdominis. Anterior abdominal muscles include the rectus abdominis and pyramidalis muscles. The abdominal wall is primarily supplied by epigastric arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries and innervated by thoracoabdominal nerves.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

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Introduction

Surface landmarks

  • Superior border:
    • Xiphoid process
    • Costal cartilages of the 7th–10th ribs
  • Middle: Umbilicus is at the midline between the L3 and L4 vertebrae.
  • Inferior border:
    • Inguinal ligament:
      • Created by the inferior border of the external oblique muscle and its aponeurosis
      • Extends between the anterior superior iliac spine and pubic tubercle
    • Pubic crest and pubic symphysis

Abdominal planes

The abdomen can be divided into 4 quadrants with the transverse and sagittal planes.

  • Transverse (transumbilical) plane: crosses the abdomen at the level of the umbilicus
  • Sagittal (vertical) plane: crosses the body at the level of the umbilicus
  • The intersection of these 2 planes defines 4 quadrants:
    • RUQ
    • LUQ
    • RLQ
    • LLQ

The abdomen can also be divided into 9 regions using the following planes:

  • Midclavicular planes: vertical planes extending from the midclavicular lines to the midinguinal points
  • Upper horizontal (subcostal) plane: inferior to the costal margin at the level of L3
  • Lower horizontal (transtubercular) plane: courses between the 2 tubercles of the iliac crest at the level of L5
  • The planes define 9 regions:
    • On the left and right sides (superior to inferior):
      • Hypochondrium
      • Lateral abdominal region
      • Inguinal region
    • Centrally (superior to inferior):
      • Epigastric region
      • Umbilical region
      • Pubic region or hypogastrium
The 9 regions of the abdomen

The 9 regions of the abdomen created by the vertical midclavicular and horizontal subcostal and transtubercular planes:
Note that the hypochondrium, lateral abdominal region, and inguinal region are present on both the left and right sides of the abdomen.

Image by Lecturio.

Muscles

Layers of the abdomen

The layers of the anterior abdominal wall from superficial to deep are:

  • Skin
  • Superficial fascia:
    • External layer of adipose tissue Adipose tissue Adipose tissue is a specialized type of connective tissue that has both structural and highly complex metabolic functions, including energy storage, glucose homeostasis, and a multitude of endocrine capabilities. There are three types of adipose tissue, white adipose tissue, brown adipose tissue, and beige or "brite" adipose tissue, which is a transitional form. Adipose Tissue (Camper fascia):
      • Contains superficial epigastric veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins that drain the anterior abdominal wall
      • Superficial epigastric veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins drain into the femoral and paraumbilical veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins.
    • Internal layer of dense connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue (Scarpa fascia)
  • Muscles:
    • Lateral abdominal muscles:
      • External oblique
      • Internal oblique
      • Transversus abdominis
    • Anterior abdominal muscles:
      • Rectus abdominis
      • Pyramidalis muscle
  • Transversalis fascia
  • Extraperitoneal fat
  • Peritoneum
Layers of anterolateral abdominal wall

Layers of the anterolateral abdominal wall

Image by Lecturio.

Lateral abdominal muscles

External oblique:

  • Origin: outer surface of ribs 5–12
  • Insertion: linea alba (rectus sheath), pubic tubercle, and iliac crest
  • Nerve supply:
    • Intercostal nerves (T7–T11)
    • Subcostal nerve (T12)
    • Iliohypogastric nerve
  • Action:
    • Flexes and rotates the trunk
    • Compresses and supports the internal viscera
    • Assists with expiration
External oblique muscle

External oblique muscle

Image by BioDigital, edited by Lecturio

Internal oblique:

  • Origin: anterior iliac crest, thoracolumbar fascia, and lateral 3rd of the inguinal ligament
  • Insertion: inferior borders of ribs 10–12 and linea alba (rectus sheath)
  • Nerve supply:
    • Intercostal nerves (T7–T11)
    • Subcostal nerve (T12)
    • Iliohypogastric nerve
  • Action:
    • Flexes and rotates the trunk
    • Compresses and supports internal viscera
    • Assists with expiration
Internal oblique muscle

Internal oblique muscle

Image by BioDigital, edited by Lecturio

Transversus abdominis:

  • Deepest of the 3 lateral abdominal muscles
  • Fibers run horizontally.
  • Transversalis fascia lies underneath the transversus abdominis.
  • Origin: inner surface of costal cartilages of ribs 7–12, iliac crest, thoracolumbar fascia, and lateral 3rd of the inguinal ligament
  • Insertion: linea alba (rectus sheath)
  • Nerve supply:
    • Intercostal nerves (T7–T11)
    • Subcostal nerve (T12)
  • Action:
    • Flexes and rotates the trunk
    • Compresses and supports internal viscera
    • Assists with expiration
Transversus abdominis

Transversus abdominis

Image by BioDigital, edited by Lecturio

Anterior abdominal muscles

Rectus abdominis:

  • Pair of long, straight muscles running vertically
  • Left and right parts are separated by the central linea alba.
  • Each muscle consists of 4 parts separated by 3 bands of tendon → tendinous intersections
  • Origin: pubic symphysis and crest
  • Insertion: xiphoid process and costal cartilage Cartilage Cartilage is a type of connective tissue derived from embryonic mesenchyme that is responsible for structural support, resilience, and the smoothness of physical actions. Perichondrium (connective tissue membrane surrounding cartilage) compensates for the absence of vasculature in cartilage by providing nutrition and support. Cartilage of ribs 5–7
  • Nerve supply:
    • Intercostal nerves (T7–T11)
    • Subcostal nerve (T12)
  • Action:
    • Flexes trunk
    • Compresses internal viscera
    • Assists with expiration
  • Enveloped by the rectus abdominis sheath:
    • Created by the aponeurosis of the 3 lateral abdominal muscles
    • Above the arcuate line, the rectus abdominis is enclosed within the sheath.
    • Below the arcuate line, the sheath is entirely anterior to the muscle, placing the muscle in direct contact with the transversalis fascia.
Rectus abdominis muscle

Rectus abdominis muscle

Image by BioDigital, edited by Lecturio

Pyramidalis muscle:

  • Small muscle contained within the rectus abdominis sheath
  • May be absent in 20% of the population
  • Origin: pubic symphysis and pubic crest
  • Insertion: linea alba
  • Nerve supply: subcostal nerve (T12)
  • Action: tenses linea alba
Pyramidalis muscle

Pyramidalis muscle

Image by BioDigital, edited by Lecturio

Inguinal Canal

The inguinal canals are bilateral canals in the lower lateral anterior abdominal wall that run obliquely and superolaterally to inferomedially. Each inguinal canal Inguinal canal The inguinal region, or the groin, is located in the RLQ and LLQ of the anterior abdominal wall, bordered by the thigh inferiorly, the pubis medially, and the iliac crest superolaterally. The inguinal canal is a tubular structure that runs in a straight line from the anterior superior iliac spine to the pubic tubercle. Inguinal Canal and Hernias has 4 walls and 2 openings (inguinal rings), 1 at each end.

  • Anterior wall is formed by the external oblique aponeurosis.
  • Posterior wall is formed by:
    • Tendon of the internal oblique muscle
    • Tendon of the transverse abdominis muscle
    • Transversalis fascia
  • Roof is formed by:
    • Internal oblique muscle
    • Transversus abdominis muscles
  • Floor:
    • Formed by the inguinal ligament and the aponeurosis of the lower border of the external oblique muscle
    • Extends from the pubic tubercle medially to the anterior superior iliac spine
  • Deep inguinal ring:
    • Origin of the inguinal canal Inguinal canal The inguinal region, or the groin, is located in the RLQ and LLQ of the anterior abdominal wall, bordered by the thigh inferiorly, the pubis medially, and the iliac crest superolaterally. The inguinal canal is a tubular structure that runs in a straight line from the anterior superior iliac spine to the pubic tubercle. Inguinal Canal and Hernias
    • Formed by an opening in the transversalis fascia
    • Located superior to the inguinal ligament halfway between the pubic bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones and the anterior superior iliac spine
  • Superficial inguinal ring:
    • Termination point of the inguinal canal Inguinal canal The inguinal region, or the groin, is located in the RLQ and LLQ of the anterior abdominal wall, bordered by the thigh inferiorly, the pubis medially, and the iliac crest superolaterally. The inguinal canal is a tubular structure that runs in a straight line from the anterior superior iliac spine to the pubic tubercle. Inguinal Canal and Hernias
    • Formed by an opening in the external oblique aponeurosis
    • Located 1 cm superiorly and medially to the pubic tubercle
  • Contents of the inguinal canal Inguinal canal The inguinal region, or the groin, is located in the RLQ and LLQ of the anterior abdominal wall, bordered by the thigh inferiorly, the pubis medially, and the iliac crest superolaterally. The inguinal canal is a tubular structure that runs in a straight line from the anterior superior iliac spine to the pubic tubercle. Inguinal Canal and Hernias include:
    • Genital branch of the genitofemoral nerve (L1–L2)
    • Ilioinguinal nerve (L1)
    • Spermatic cord in men
    • Round ligament of the uterus in women
Inguinal canal

Schematic representation of the location of the inguinal canal Inguinal canal The inguinal region, or the groin, is located in the RLQ and LLQ of the anterior abdominal wall, bordered by the thigh inferiorly, the pubis medially, and the iliac crest superolaterally. The inguinal canal is a tubular structure that runs in a straight line from the anterior superior iliac spine to the pubic tubercle. Inguinal Canal and Hernias in the anterior abdominal wall

Image by Lecturio.

Neurovasculature

Arterial supply

The arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries of the anterior abdominal wall are divided into superficial and deep layers.

  • Superficial layer:
    • Musculophrenic artery:
      • Branch of the internal thoracic artery
      • Supplies the superior anterolateral abdominal wall
    • Superficial epigastric artery:
      • Branch of the femoral artery
      • Supplies the inferior anterolateral abdominal wall
    • Superficial circumflex iliac artery:
      • Branch of the femoral artery
      • Supplies the inferior anterolateral abdominal wall
  • Deep layer:
    • Superior epigastric artery:
      • Direct continuation of the internal thoracic artery
      • Runs inside the rectus sheath behind the rectus muscle
      • Supplies the superior part of the abdominal wall
    • Inferior epigastric artery:
      • Branch of the external iliac artery
      • Courses through the rectus sheath and anastomoses with the superior epigastric artery
      • Supplies the inferior part of the abdominal wall
    • The 10th and 11th intercostal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries and the subcostal artery supply the lateral abdominal wall.
Arteries of anterior and lateral abdominal wall

Arteries of the anterior and lateral abdominal wall

Image by Lecturio.

Venous drainage

  • Venous drainage follows the arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries of the same name.
  • The superficial veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins around the umbilicus anastomose with the deep veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins through the paraumbilical veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins.

Innervation

  • The skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, abdominal muscles, and peritoneum Peritoneum The peritoneum is a serous membrane lining the abdominopelvic cavity. This lining is formed by connective tissue and originates from the mesoderm. The membrane lines both the abdominal walls (as parietal peritoneum) and all of the visceral organs (as visceral peritoneum). Peritoneum and Retroperitoneum are innervated by:
    • Thoracoabdominal nerves (T7–T11) that run within the internal oblique and transversus abdominis muscle layers
    • Subcostal nerve (T12)
    • Iliohypogastric nerve (L1)
    • Ilioinguinal nerve (L1)
  • Sensory distribution:
    • Series of transverse dermatomal bands from T7 to L1
    • Skin around the umbilicus is innervated by T10.
Innervation of abdominal wall

Innervation of the abdominal wall

Image by Lecturio.

Clinical Relevance

  • Inguinal hernias: The superficial and deep inguinal rings represent 2 weak points in the abdominal wall and create a pathway for inguinal hernias. Several risk factors have been implicated in the development of inguinal hernias, including obesity Obesity Obesity is a condition associated with excess body weight, specifically with the deposition of excessive adipose tissue. Obesity is considered a global epidemic. Major influences come from the western diet and sedentary lifestyles, but the exact mechanisms likely include a mixture of genetic and environmental factors. Obesity, pregnancy Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-hCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care, and aging. Affected individuals will present with a burning sensation or dull ache at the groin, and a mass that may fluctuate in size based on time of the day and preceding activity. Classically, coughing or straining leads to the appearance of the hernia. Treatment is surgical and usually performed on an outpatient basis with excellent results.
  • Caput medusae: a sign of portal hypertension Portal hypertension Portal hypertension is increased pressure in the portal venous system. This increased pressure can lead to splanchnic vasodilation, collateral blood flow through portosystemic anastomoses, and increased hydrostatic pressure. There are a number of etiologies, including cirrhosis, right-sided congestive heart failure, schistosomiasis, portal vein thrombosis, hepatitis, and Budd-Chiari syndrome. Portal Hypertension that manifests by the appearance of dilated superficial epigastric veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins radiating from the umbilicus. The name caput medusae (Latin for “head of Medusa”) originates from the apparent similarity to Medusa’s head, who, according to Greek Mythology, had venomous snakes instead of hair. Treatment is geared toward controlling portal hypertension Portal hypertension Portal hypertension is increased pressure in the portal venous system. This increased pressure can lead to splanchnic vasodilation, collateral blood flow through portosystemic anastomoses, and increased hydrostatic pressure. There are a number of etiologies, including cirrhosis, right-sided congestive heart failure, schistosomiasis, portal vein thrombosis, hepatitis, and Budd-Chiari syndrome. Portal Hypertension.
  • Cullen sign: hemorrhagic discoloration and edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema of the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin around the umbilicus. A similar finding involving the flank is called Grey Turner sign. Both signs are due to intraperitoneal hemorrhage due to acute hemorrhagic pancreatitis, intra-abdominal trauma, or conditions that lead to hemorrhage into the abdominal cavity. Discoloration of the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin is due to blood collection in the subcutaneous fascial planes.

References

  1. Cheuck, L. (2017). Inguinal region anatomy. Medscape. Retrieved September 8, 2021, from https://reference.medscape.com/article/2075362-overview
  2. Flynn, W., Vickerton, P. (2021). Anatomy, Abdomen and Pelvis, Abdominal Wall. StatPearls. Treasure Island (FL). https://pubmed.ncbi.nlm.nih.gov/31869113/
  3. Rather, A.A. (2021). Abdominal hernias. Medscape. Retrieved September 8, 2021, from https://reference.medscape.com/article/189563-overview

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