Surgical Anatomy Of Anterior Abdominal Wall

Anterior Abdominal Wall Layers

The anterior abdominal wall layers are covered in skin on the outside, but underneath is subcutaneous tissue that is divided into two layers: the membranous Scarpa's fascia and the fatty Camper's fascia. There is not much anatomical difference between Scarpa's and Camper's fascia anteriorly.

A midline or transverse incision may not present the surgeon with two discrete layers of subcutaneous tissue. Compared to transverse scars, vertical scars on the skin of the anterior abdominal wall appear significantly wider. Because the skin's dermal fibers are distributed transversally and are known as Langer's Line, transverse scars have a higher visual appeal.

 Further, abdominal wall consists of -

• Musculoaponeurotic layer
• Rectus sheath
• Transversalis fascia [fibrous connective tissue layer lining abdominopelvic cavity]
• Preperitoneal fat
• Peritoneum

Musculoaponeurotic Layer

The rectus abdominis and pyramidalis muscles in the midline, the external, internal, and transversus abdominis muscles on the lateral flank, and the layers of oblique muscles enclosing the rectus abdominis form the musculoaponeurotic layer.

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Keylanders Of Pelvis

Pelvis bone is made up of sacrum, coccyx, and innominate bone [ilium, ischium, pubis]. Key landmarks of pelvis are:

• Iliac crest
• Anterior superior iliac spine [ASIS]
• Sacral promontory
• Pubic symphysis
• Pubic tubercle
• Pectineal line
• Arcuate line [Linea terminalis]

External Oblique [EO]

The purpose of the external oblique is to compress and support the abdominopelvic viscera. It arises from the lower ribs [5–12] and inserts into the pubic tubercle, iliac crest, and linea alba. Poupart's ligament, an inguinal ligament formed by the posterior edge of the lower border of the EO muscle, flattens down in the medial aspect to produce the lacunar ligament, also known as Gimbernat's ligament.

The pectineal ligament, also known as Cooper's ligament, is the ligament that extends from the pubic tubercle onto the pectineal line. The superficial inguinal ring is the opening in the external oblique aponeurosis above the pubic crest.

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Internal Oblique

The thoracolumbar fascia, the lateral portion of the inguinal ligament, and the anterior two thirds of the iliac crest are the origins of the internal oblique. It is affixed or inserted into the linea alba, pectineal line, and inferior border of 10–12 ribs.The abdominopelvic viscera are supported and compressed by it.

Transversus Abdominis

The transversus abdominis muscle attaches to the pubic crest, pectineal line, and linea alba. Its origins are the costal cartilages of the lower six ribs, the thoracolumbar fascia, the iliac crest, and the lateral one-third of the inguinal ligament. Its functions are identical to those of the external and internal oblique.

Rectus Abdominis

It flexes the trunk and supports the abdominopelvic viscera. It comes from the sternum and the cartilages of the fifth through seventh ribs. It connects to the anterior surface of the pubic bone.  In certain people, the rectus abdominis may seem posterior to the pyramidalis muscle. 

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Rectus Sheath

The rectus sheath is formed by the aponeurotic insertions of the flank muscles.The rectus sheath surrounds the rectus abdominis muscle, fusing at the linea alba midline and the linea semilunaris laterally.

·         S/C: Subcutaneous tissue

·         EO:External oblique

·         IO: Internal oblique

·         TA: Transversus abdominis muscle

·         f.Tr: Transversalis fascia

·         RA: Rectus abdominis muscle

·         LA: Linea alba

·         LS: Linea semilunaris

Anteriorly: EO aponeurosis and split aponeurosis of IO o Posteriorly: TA aponeurosis and split aponeurosis of IO comprise the rectus sheath above the arcuate line. The rectus sheath beneath the arcuate line is composed of the following anteriorly: EO, IO, and TA aponeurosis and split aponeurosis. Transversalis fascia on the back.

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Neurovascular Plane

Subcostal nerves [T12], anterolateral abdominal wall-supplying arteries, and branches of the intercostal nerves [T7–T11].The lateral cutaneous branch originates from intercostal nerves that travel between the transversus abdominis muscle and the internal oblique muscle.

In certain individuals, they may puncture the rectus sheath near the lateral border of the rectus muscles, giving rise to the anterior cutaneous branch. Prior to separation from the rectus muscle, anterior cutaneous branches may become strained, ripped, or damaged as the rectus sheath is elevated.

The transverse orientation of the muscle fibers in the rectus sheath might produce stress, which reduces the strength of the vertical incision relative to the transverse incision.

Transversalis Fascia & Peritoneum 

In the midline, a single peritoneal fold known as the median umbilical fold is seen. Surgically, the umbilicus is the defect in the front abdominal wall. The remainder of the urachus, the median umbilical ligament, is what forms this.  The lateral umbilical ligament raises the lateral umbilical folds, which in turn signify an obliterated umbilical artery. The medial umbilical fold is elevated as a result of the medial umbilical ligament.

The deep inguinal ring is where the round ligament enters.
The inferior epigastric artery and vein pass beneath the lateral umbilical fold and toward the umbilicus, medial to the round ligament.Hesselbach's triangle is formed by the lateral rectus border, inferior epigastric artery and veins, and inguinal ligament.  A vertical incision should be made somewhat away from the midline to prevent any bladder damage.

Inguinal Canal

It transmits the round ligament, ilioinguinal nerve, and genital branch of the genitofemoral nerve. It extends from the deep to the superficial inguinal ring. The inguinal canal's boundaries are:  Inguinal ligament on the floor, Roof: Transversus abdominis and internal oblique arched fibers Skin, superficial fascia, internal and external oblique aponeurosis on the anterior wall. Transversalis fascia, conjoint tendon, and reflected portion of the inguinal ligament on the posterior wall.

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