Tuesday, August 12, 2008

Skin and Subcutaneous Fasciae

To minimize scarring, incisions of the anterior abdominal wall and flank should follow Langer's lines of cleavage. These lines parallel dermal collagen fibers and are oriented along lines of stress. They correspond to the segmental thoracic and lumbar nerves. The skin is backed by Camper's fascia, a loose layer of fatty tissue that varies in thickness with the nutritional status of the patient. The superficial circumflex iliac, external pudendal, and superficial inferior epigastric vessels branch from the femoral vessels to run in this layer (Figs. 2-3 and 2-4 [3] [4]). The superficial inferior epigastric vessels are encountered during inguinal incisions and can cause troublesome bleeding during placement of pelvic laparoscopic ports.

Figure 2-4 Muscles, vessels, and nerves of the anterior abdominal wall. The rectus abdominis muscles are semitransparent to demonstrate the vessels posteriorly.

Figure 2-3 Left, Anterior view of the deep fasciae of the abdomen, perineum, and thigh. Note the superficial inferior epigastric artery passing superiorly in Camper's fascia. Right, Midline sagittal view of the pelvic fasciae and their attachments.

Scarpa's fascia forms a distinct layer deep to this Camper's fascia, although it may be difficult to discern in older patients. Superiorly and laterally, it blends with Camper's fascia. Inferiorly, it fuses with the deep fascia of the thigh 1 cm below the inguinal ligament along a line from the anterior superior iliac spine to the pubic tubercle. Medially, it is continuous with Colles' fascia of the perineum (see Fig. 2-3 ). Colles' fascia attaches to the posterior edge of the urogenital diaphragm and the inferior ischiopubic rami. It is continuous with the dartos fascia of the penis and scrotum. These fasciae can limit both the spread of infec-tion in necrotizing fasciitis of the scrotum (Fournier's gangrene) and the extent of urinary extravasation in an ante-rior urethral injury. For instance, blood and urine can accumulate in the scrotum and penis deep to the dartos fascia after an anterior urethral injury. In the perineum, their spread is limited by the fusions of Colles' fascia to the ischiopubic rami laterally and to the posterior edge of the perineal membrane; the resulting hematoma is therefore butterfly shaped. They will not extend down the leg or into the buttock, but they can freely travel up the anterior abdominal wall deep to Scarpa's fascia to the clavicles and around the flank to the back.

Abdominal Musculature

The abdominal musculature lies immediately below Scarpa's fascia. The origins of the external oblique, internal oblique, and transversus abdominis muscles and the orientation of their fibers are presented in Chapter 1 , Surgical Anatomy of the Retroperitoneum, Kidneys, and Ureters. These muscles terminate on the anterior abdominal wall as broad, tough aponeurotic sheets that fuse in the midline (linea alba) and form the rectus sheath (see Fig. 2-4 ). The linea alba is avascular and is a convenient point of access to the peritoneal and pelvic cavities. In its upper portion, the anterior rectus sheath is formed by the aponeurosis of the external oblique muscle and a portion of the internal oblique muscle ( Fig. 2-5 ). The posterior sheath is derived from the remaining internal oblique aponeurosis and the transversus abdominis aponeurosis. Two thirds of the distance from the pubis to the umbilicus, the arcuate line is formed, as all aponeurotic layers abruptly pass anterior to the rectus abdominis, leaving this muscle clothed only by transversalis fascia and peritoneum posteriorly.

Figure 2-5 Cross section of the rectus sheath. Top, Above the arcuate line, the aponeurosis of the external oblique muscle forms the anterior sheath and the transversus aponeurosis forms the posterior sheath. The internal oblique muscle splits to contribute to both the anterior and the posterior sheaths. Bottom, Below the arcuate line, all aponeuroses pass anterior to the rectus.

The rectus abdominis arises from the pubis medial to the pubic tubercle and inserts on the xiphoid process and adjacent costal cartilages. The muscle is crossed by three or four tendinous intersections that are firmly attached to the anterior rectus sheath; thus, the muscle can be divided transversely without significant retraction. It is supplied by the last six thoracic segmental nerves that enter it laterally. Paramedian incisions lateral to the rectus divide these nerves, cause atrophy of the rectus, and predispose to ventral hernia. Anterior to the rectus and within its sheath, the triangle-shaped pyramidalis muscle arises from the pubic crest and inserts into the linea alba (see Fig. 2-4 ). It is supplied by the subcostal nerve (T12).

Inguinal Canal

The inguinal canal transmits the spermatic cord in the male, the round ligament in the female, and the ilioinguinal nerve in both sexes ( Fig. 2-6 ; see also Fig. 2-4 ). Its anterior wall and floor are formed by the external oblique muscle, which folds over at its inferior edge as the inguinal ligament. Above the pubic tubercle, the fibers of the external oblique aponeurosis split to form the lateral edges (crura) of the external inguinal ring. Transverse (intercrural) fibers bridge the crura to form the superior edge of the external ring. By dividing the intracrural fibers, the external oblique can be separated along its fibers to gain access to the cord. The posterior wall of the canal is formed by transversalis fascia, which lines the inner surface of the abdominal wall. The cord structures pierce this fascia lateral to the inferior epigastric vessels at the internal inguinal ring ( Fig. 2-7 ). The internal inguinal ring lies midway between the anterior superior iliac spine and the pubic tubercle, above the inguinal ligament, and 4 cm lateral to the external ring. Fibers of the internal oblique and transversus abdominis arise from the iliopsoas fascia and inguinal ligament lateral to the internal ring and arch over the canal to form its roof. They fuse as the conjoint tendon, pass posterior to the cord, and insert into the rectus sheath and pubis. The conjoint tendon reinforces the posterior wall of the inguinal canal at the external ring. With contraction of the internal oblique and transversus muscles, the roof of the canal closes against the floor. Hernias into the canal may occur medial (direct) or lateral (indirect) to the inferior epigastric vessels (see Figs. 2-6 and 2-7 [6] [7]).

Figure 2-6 Deep structures of the left inguinal canal, viewed from the front.

Internal Surface of the Anterior Abdominal Wall

Approached laparoscopically, three elevations of the peritoneum, referred to as the median, medial, and lateral umbilical folds, are visible on the anterior abdominal wall below the umbilicus ( Fig. 2-8 ). The median fold overlies the median umbilical ligament (urachus), a fibrous remnant of the cloaca that attaches the bladder to the anterior abdominal wall. The obliterated umbilical artery in the medial umbilical fold serves as an important landmark for the surgeon. It may be traced to its origin from the internal iliac artery to locate the ureter, which lies on its medial side. During transperitoneal laparoscopic pelvic lymph node dissection, the obturator packet is accessed by incising the peritoneum lateral to the obliterated umbilical artery. The lateral umbilical fold contains the inferior epigastric vessels as they ascend to supply the rectus abdominis.

Figure 2-8 Male pelvis and anterior abdominal wall viewed from behind. The sacrum and ilia have been removed. (From Anderson JE: Grant's Atlas of Anatomy, 7th ed. Baltimore, Williams & Wilkins, 1978.)

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