Abdominal Wall

ANATOMY OF ANTERIOR ABDOMINAL WALL & RECTUS SHEATH

By: Dr. Firas Abdullah

Structure of Abdominal Cavity

Superiorly it is formed by diaphragm which separates the abdominal cavity from the thoracic cavity

Inferiorly the abdominal cavity is continuous with the pelvic cavity through the pelvic inlet

Structure of Abdominal Wall

Anteriorly:

The abdominal wall is formed above by lower part of the thoracic cage

Below by the rectus abdominis, external oblique, internal oblique, and transversus abdominis muscles and fasciae


Structure of Ant. Abdominal Wall
It is made up of skin, superficial fascia, deep fascia, muscles, extraperitoneal fascia and parietal peritoneum

The abdominal walls are lined by a fascial envelope and the parietal peritoneum

Superficial Fascia
Fatty layer or fascia of camper is continuous with the superficial fat over the rest of the body and may be extremely thick in obese patients

The membranous layer or scarpa’s fascia is thin and fades out laterally and above

Becomes continuous with the superficial fascia of the back and the thorax

Superficial Fascia

Inferiorly the membranous layer passes onto the front of the thigh, where it fuses with the deep fascia

In the midline inferiorly forms a tubular sheath for the penis or clitoris

Below in the perineum, enters the wall of the scrotum or labia majora

From there it passes to be attached on each side to the margins of pubic arch, here it is called Colle’s fascia

Superficial Fascia

Posteriorly it fuses with the perineal body and the margin of the perineal membrane

The fatty layer is represented as a smooth muscle in the scrotum, the dartos muscle

The membranous layer persists as a separate layer

Deep Fascia

Deep fascia in the anterior abdominal wall is merely a thin layer of connective tissue covering the muscles

It lies immediately deep to the membranous layer of the superficial fascia

Muscles
Consists of Three broad thin sheets that are aponeurotic in front

From exterior to interior they are:

External oblique, internal oblique, and transverse

A wide vertical muscle, the rectus abdominis

They lie on either side of the midline anteriorly

Muscles

As the aponeurosis of three sheets pass forward, they enclose the rectus abdominis to form the rectus sheath

The cremaster muscle which is derived from the lower fibers of internal oblique, passes inferiorly as a covering of the spermatic cord and enters scrotum

External Oblique Muscle

Is a broad, thin, muscular sheet

Origin: Lower 8 ribs

Insertion: Xiphoid process, linea alba, pubic tubercle, iliac crest

Nerve Supply: Lower 6 thoracic nerves, iliohypogastric & ilioinguinal nerves

Action: Supports abdominal contents, assist in forced expiration, micturition, defecation, parturition, vomiting

External Oblique Muscle

A triangular shaped defect in the external oblique aponeurosis lies immediately above and medial to the pubic tubercle, known as superficial inguinal ring

Between the anterosuperior iliac spine and the pubic tubercle, the lower border of the aponeurosis is folded backward on itself, forming the inguinal ligament

Internal Oblique Muscle

Origin: Lumbar fascia, iliac crest, lateral two-thirds of inguinal ligament

Insertion: Lower three ribs and costal cartilages, xiphoid process, linea alba, symphysis pubis

Nerve Supply: Lower six thoracic nerves, iliohypogastric & ilioinguinal nerves

Action: Supports abdominal contents, assist in forced expiration, micturition, defecation, parturition, vomiting

Transversus Abdominis

Origin: Lower six costal cartilages, lumbar fascia, iliac crest, lateral third of inguinal ligament

Insertion: Xiphoid process, linea alba, symphysis pubis

Nerve Supply: Lower six thoracic nerves, iliohypogastric & ilioinguinal nerves

Action: Compresses abdominal contents

Rectus Abdominis

Origin: Symphysis pubis and pubic crest

Insertion: 5th, 6th and 7th costal cartilages and xiphoid process

Nerve Supply: Lower six thoracic nerves


Action: Compresses abdominal contents, flexes vertebral column, accessory muscle of expiration

Lymph Drainage

Lymph drainage of the skin of the anterior abdominal wall above the umbilicus is upward to the anterior axillary (pectoral group of nodes)

Below the level of umbilicus drains downward and laterally to the superficial inguinal nodes

Swelling in the groin is may be due to enlarged superficial inguinal node

Venous Drainage
Venous blood is collected into a network of veins that radiate from the umbilicus

The network is drained above into the axillary vein via the lateral thoracic vein

Below into the femoral vein via the superficial epigastric and the great saphenous veins

Few small veins, the paraumbilical veins form a clinically important portal-system venous anastomosis

Nerves

Nerves of the anterior abdominal wall supply the skin, muscles and the parietal peritoneum

They are derived from the anterior rami of lower six thoracic and the first lumbar nerves

Inflammation of parietal peritoneum causes pain in the overlying skin and also a reflex increase in tone of the abdominal musculature in the same area

Rectus Sheath

Is a long fibrous sheath

Encloses the rectus abdominis and pyramidalis muscle (if present)

Contains the anterior rami of lower six thoracic nerves and the superior and inferior epigastric vessels and lymph vessels


Formed mainly by aponeurosis of three lateral abdominal muscles

Rectus Sheath

For description it is considered at three levels:

Above the costal margin the anterior wall is formed by the aponeurosis of the external oblique and posterior wall is formed by the thoracic wall

That is the 5th , 6th and 7th costal cartilages and the intercostal spaces

Rectus Sheath
Between the costal margin and the level of the anterosuperior iliac spine, the aponeurosis of the internal oblique splits to enclose the rectus muscle

The external oblique aponeurosis is directed in front of the muscle

Transversus aponeurosis is directed behind the muscle

Rectus Sheath

Between the level of the anterosuperior iliac spine and the pubis, the aponeurosis of all three muscles form the anterior wall


The posterior wall is absent

The rectus muscle lies in contact with the fascia transversalis

Rectus Sheath

The posterior wall of the rectus sheath is not attached to the rectus abdominis muscle

The anterior wall is firmly attached to it by the muscle’s tendinous intersections

Linea Alba
The rectus sheath is separated from its fellow on the opposite side by a fibrous band called the linea alba

Extends from the xiphoid process to the symphysis pubis