Abdominal Wall Anatomy and Vascular Supply

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Chapter 1 Abdominal Wall Anatomy and Vascular Supply

Harvey Chim, MD, Karen Kim Evans, MD, Christopher J. Salgado, MD, Samir Mardini, MD

1 Clinical Anatomy

1 Overview

image The anterior abdominal wall (Figs. 1-1 to 1-3) is a hexagonal area defined superiorly by the costal margin and xiphoid process; laterally by the midaxillary line; and inferiorly by the symphysis pubis, pubic tubercle, inguinal ligament, anterior superior iliac spine, and iliac crest.
image Layers of the anterior abdominal wall include skin, subcutaneous tissue, superficial fascia, deep fascia, muscle, extraperitoneal fascia, and peritoneum.
image

Figure 1-1

image

Figure 1-2

image

Figure 1-3

2 Superficial Fascial Layers (see Figs. 1-1 and 1-2)

image The superficial fascia of the abdominal wall consists of a single layer above the umbilicus, consisting of the fused Camper and Scarpa fasciae.
image Below the umbilicus the superficial fascia consists of a fatty outer layer (Camper fascia) and a membranous inner layer (Scarpa fascia).
image Camper fascia is continuous inferiorly with the superficial thigh fascia and extends inferiorly to the scrotum in males and labia majora in females.
image Scarpa fascia fuses inferiorly with the fascia lata of the thigh and continues posteriorly to the perineum, where it is called Colles fascia.

image Pearls and Pitfalls

Scarpa fascia is usually a visible and durable structure and is closed separately during various surgeries on the abdominal wall to achieve optimal scar result.

3 Deep Fascial Layers (see Figs. 1-1 and 1-2)

image The rectus sheath is found in the midline.
image Laterally, layers of the abdominal wall deep to superficial fascia include external oblique, internal oblique, transversus abdominis, and parietal peritoneum.
image The arcuate line (see Fig. 1-3) is located midway between the umbilicus and symphysis pubis and is a transition point where the posterior rectus sheath transitions from being the fusion of part of internal oblique fascia and transversalis fascia superiorly to only transversalis fascia inferiorly.
image Above the arcuate line, the anterior rectus sheath consists of external oblique fascia and part of internal oblique fascia. The posterior rectus sheath consists of internal oblique fascia and transversalis fascia. The anterior and posterior layers of the rectus fascia therefore invest the rectus abdominis muscles.
image Below the arcuate line, the external oblique and internal oblique fasciae merge to form the anterior rectus sheath. The posterior rectus sheath consists of transversus abdominis fascia, making this only a thin layer with minimal strength.
image The linea alba results from fusion of the anterior and posterior rectus sheaths and lies in the midline, extending cranially from the xiphoid process to the pubic symphysis caudally Figure 1-4 shows the anterior wall fascia after dissection of the abdominal wall skin and subcutaneous tissue, showing the linea alba and linea semilunaris.
image

Figure 1-4

image Pearls and Pitfalls

Incision, release, and dissection of the anterior external oblique fascia can be done for repair of ventral hernias. This technique is called the components separation (Fig. 1-5). The incision in the external oblique fascia is made 1 to 2 cm lateral to the linea semilunaris, and the fascia is released to attain primary closure. Incisions also can be made in the posterior rectus sheath to gain additional length.

image

Figure 1-5

4 Abdominal Wall Musculature (see Figs. 1-1 to 1-3)

image The paired rectus abdominis muscles are the principal flexors of the anterior abdominal wall. They function to stabilize the pelvis while walking. They also protect the abdominal organs and help in forced expiration.
image The rectus abdominis muscles originate from the pubic symphysis and pubic crest and insert on the anterior surfaces of the fifth, sixth, and seventh costal cartilages and the xiphoid processes. Laterally, the rectus sheath merges with the aponeurosis of the external oblique muscles to form the linea semilunaris (Fig. 1-4).
image Three to four tendinous inscriptions, which are adherent to the anterior rectus sheath, interrupt the rectus abdominis along its length (Fig. 1-6).
image The external oblique muscle is the most superficial and thickest of the three lateral abdominal wall muscles. It originates from the lower eight ribs and courses in an inferomedial direction. Inferiorly it folds back on itself and forms the inguinal ligament, which extends between the anterior superior iliac spine and pubic tubercle. It is attached medially to the pubic crest.
image The internal oblique muscle is deep to the external oblique muscle, and its aponeurosis splits medially above the arcuate line to form part of the anterior rectus sheath and part of the posterior rectus sheath. Below the arcuate line, the inferior oblique aponeurosis does not split and fuses with the external oblique fascia to form the anterior rectus sheath. The internal oblique muscle runs in a superomedial direction, perpendicular to the external oblique muscle. It originates from the thoracolumbar fascia, anterior two thirds of the iliac crest, and lateral half of the inguinal ligament. It inserts on the inferior and posterior borders of the tenth through twelfth ribs superiorly. Inferiorly, the internal oblique inserts on the pectineal line with fibers from the transversus abdominis, forming the conjoint tendon, which inserts on the pubic crest.
image The transversus abdominis muscle is the deepest of the three lateral abdominal wall muscles and courses in a horizontal direction. It originates from the anterior three fourths of the iliac crest; lateral third of the inguinal ligament; and inner surface of the lower six costal cartilages, interdigitating with fibers of the diaphragm. The muscle ends medially in a broad flat aponeurosis, merging above the arcuate line with the posterior lamella of the internal oblique aponeurosis and the linea alba. Below the arcuate line, it inserts into the pubic crest and pectineal line, forming the conjoint tendon with the internal oblique.
image The pyramidalis is a small triangular muscle found anterior to the inferior aspect of the rectus abdominis; it is absent in about 20% of the population. It originates from the body of the pubis and inserts into the linea alba inferior to the umbilicus.
image The semilunar lines are formed by fusion of the external oblique, internal oblique, and transversus abdominis aponeuroses at the lateral border of the rectus abdominis.
image

Figure 1-6

image Pearls and Pitfalls

Of all the muscles in the abdominal wall, the rectus abdominis muscle is the most versatile and useful for flap procedures. The rectus muscle can be harvested as a free flap for microsurgical transfer of tissue to various defects. It also can be harvested as a pedicled flap, based on the superior or inferior epigastric arteries and rotated to fill groin, chest wall, mastectomy defects, vaginal, and perianal wounds.

It is also important to note the functional loss that results if the rectus abdominis muscle is harvested. Using isometric dynamometry, studies have shown that there is at least a 20% functional loss in trunk flexion. Bilateral harvest of the rectus abdominis muscles can be debilitating for patients who are very active because there is a 40% functional loss in trunk flexion, which may infringe upon activities of daily living.

5 Neurovascular Supply of the Abdominal Wall

image Pearls and Pitfalls

image The blood supply of the abdominal wall can be divided into three zones (Huger, 1979).
image Zone I consists of the upper and midcentral abdominal walls and is supplied by the vertically oriented deep superior (Fig. 1-7, A).and deep inferior epigastric arteries (Fig. 1-7, B).
image Zone II consists of the lower abdominal wall and is supplied by the epigastric arcade, superficial inferior epigastric, superficial external pudendal, and superficial circumflex iliac arteries. Perforators from the deep circumflex iliac arteries also supply a region of skin posterior and cephalad to the anterior superior iliac spine along the axis of the iliac crest.
image Zone III consists of the lateral abdominal wall (flank region) and is supplied by the musculophrenic, lower intercostals (Fig. 1-8, A), and lumbar arteries (Fig. 1-8, B).
image image

Figure 1-7

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