Lab Manual - Abdominal Wall

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Recall the basic terminology used to define the surface representations of the regions of the abdomen. (explanation)
  2. Identify the major skeletal landmarks of the abdominopelvic cavity. (explanation)
  3. Define the innervation, blood supply, and lymphatic drainage of the anterior abdominal wall. (explanation)
  4. Describe the formation of the rectus sheath. (explanation)
  5. Describe the layers of the anterolateral abdominal wall. (explanation)

Readings and Modules:

Procedure:

1. Review the bony landmarks. (Play movie; View images: N 185, 248, 268, 486A, 486B; TG 3-04A, 3-04B, 4-04, 5-01A, 5-01B, 5-01C, 5-03)

Read about the surface characteristics of the anterior abdominal wall and the topographic regions of the abdominal wall (nine regions and four quadrants) and cavity used for clinical descriptions. What are their names?

Identify on the skeleton: iliac crest, anterior superior iliac spine, pubic crest, pubic tubercle, pecten pubis (pectineal line), iliopectineal line. Review rib cage and costal margins.

2. Remove the skin from the anterior abdominal wall and examine its subcutaneous tissue and cutaneous nerves. (Play movie; View images: N 249, 250, 256, 257, 258, 266, 267, 387, 390, 497, 498, 500, 546; TG 3-14, 3-22, 3-25, 5-02, 5-04, 5-37, 5-38, 6-31)

Remove the skin from the anterior abdominal wall (cut around the umbilicus and leave it in place) and scrotum in the male and labia majora in the female. In the thigh remove the skin to about two inches below the inguinal ligament (which lies along a line projected from the anterior superior iliac spine to the pubic tubercle). In the labia majora the subcutaneous tissue is fatty. In the scrotum, the subcutaneous tissue contains no fat, so care must be taken to remove only the skin in the male.

Within the subcutaneous tissue of the abdominal wall and groin region locate the superficial epigastric, superficial circumflex iliac, superficial external pudendal veins and arteries. Do not trace them into the thigh at this time. In the thigh, observe the large superficial inguinal lymph nodes (afferent and efferent channels) below the plane of the inguinal ligament. What regions do they drain?

Examine the subcutaneous tissue. Distinguish between the fatty layer and the membranous layer of superficial fascia . What is the extent of the membranous layer? Cut through the subcutaneous tissue at the level of the umbilicus and elevate it as a sheet from the deep fascia. Place your hand under the sheet and explore the attachment of this fascia to the linea alba, pubic crest, pubic tubercle, fascia lata (deep fascia of the thigh), and the iliac crest. In the female, trace the subcutaneous tissue into the labia majora. In the male trace the subcutaneous tissue into the scrotum as the tunica dartos scroti. What are its characteristics and extent?

As you elevate the subcutaneous fascial sheet, locate examples of anterior and lateral cutaneous branches of the segmental nerves to the abdominal wall. What is their source? Which segmental nerves supply the abdominal wall? Do they run horizontally or follow the slope of the ribs? Locate lateral cutaneous branches of the subcostal and iliohypogastric nerves crossing the iliac crest.

Remove the subcutaneous tissue completely, being careful to preserve the nerves and vessels found in it.

3. Clean and examine the external abdominal oblique and its parts. (Play movie; View images: N 249, 250, 257, 259, 260, 267, 387A, 387B, 390, 497, 498; TG 3-14, 3-25, 5-02, 5-04, 5-08, 5-10, 5-38, 6-31)

Trace the thin deep (investing) fascia on the surface of the external abdominal oblique muscle. In the male this fascia evaginates over the spermatic cord as the external spermatic fascia, which is extremely delicate. In the female this same layer evaginates for a short distance over the continuation of the round ligament of the uterus into the labia majora, but has no specific name. As the round ligament traverses the inguinal canal it is gradually replaced by fat, and it is this cylinder of fat which extends into the labia and is covered by the fascia of the external oblique. Take great care to see this layer extending from the margin of the superficial (external) inguinal ring. Clear the muscular fascia from the external abdominal oblique muscle, exposing its muscular and aponeurotic parts. Note its free posterior border, its midline aponeurotic insertion into the linea alba, and its other aponeurotic specializations: medial crus, lateral crus, intercrural fibers (variably developed), and the inguinal ligament. Define the superficial inguinal ring and locate it on the anterior abdominal wall using anatomical landmarks.

Identify the anterior labial or scrotal branch of the ilioinguinal nerve perforating the external spermatic fascia at the superficial inguinal ring and distributing into the scrotum in the male and into the labia majora in the female. Consider its sources and extent of distribution. Carefully examine the aponeurotic fibers of the external oblique muscle to see how the inguinal ligament is formed. What does the superficial inguinal ring transmit in the female? In the male? Examine external spermatic fascia completely.

Starting posteriorly, reflect the external abdominal oblique muscle from its costal attachment and the iliac crest, stopping at the anterior superior spine. How do you differentiate it from the internal abdominal oblique? Along a horizontal line just above the level of the anterior superior iliac spine, cut through its aponeurosis from the anterior superior spine to a point vertically above the midpoint of the superficial inguinal ring. This line of incision will leave the inguinal ligament intact for future study; it will be extended through other layers of the anterior abdominal wall as the dissection proceeds in order to obtain a full view of both superficial and deep surfaces of the inguinal region. Lift the external abdominal oblique aponeurosis from the underlying internal abdominal oblique, noting that its aponeurosis fuses with that of the underlying internal abdominal oblique muscle medially. Probe carefully beneath the external abdominal oblique aponeurosis and demonstrate the continuity with the delicate fascia over the round ligament and spermatic cord (as external spermatic fascia). In order to see the internal oblique surface adequately in the region of the inguinal ligament, it is necessary to mobilize the intact portion of external oblique aponeurosis a bit more by a vertical cut through its aponeurosis down to the margin of the superficial ring. Do this on one side only. Reflect the external abdominal oblique fascia from the deeper layers of the coverings of the spermatic cord or round ligament.

4. Clean and examine the internal abdominal oblique and transversus abdominis, their parts and specializations. (Play movie; View images: N 174, 250A, 250B, 251A, 251B, 252, 253, 255, 257, 258, 259, 260, 267, 387, 390; TG 1-13, 5-02, 5-04, 5-05, 5-06, 5-07, 5-10, 5-38, 6-31)

With the external oblique lifted, identify the iliohypogastric and ilioinguinal nerves lying on the internal abdominal oblique muscle and running roughly parallel to the inguinal ligament. These nerves may be difficult to find since they may be hidden in folds of muscular tissue. They may appear as two distinct nerves throughout the field of dissection or as branches of one common stem that pierces the internal abdominal oblique. Where do these two nerves pierce the internal and external abdominal oblique muscles? Where do they distribute?

Examine the thoracolumbar (aponeurosis) fascia. Trace the course of the internal abdominal oblique, noting its origin and its attachment to the inguinal ligament. Differentiate between its muscular and aponeurotic parts, and note the direction of its fibers. Identify the falx inguinalis (conjoint tendon) and the delicate cremaster muscle that is evaginated along the round ligament or spermatic cord as one of its covering layers. Where does the cremaster muscle lie in relation to the external spermatic fascia? Compare male and female in terms of its relative development.

Reflect the internal abdominal oblique muscle from its origin along the thoracolumbar fascia and the iliac crest. Do not remove the part arising from the anterior superior iliac spine and the inguinal ligament. At the level of the umbilicus, cut through the muscle on a horizontal line from above the anterior superior iliac spine to the lateral border of the rectus sheath as you did for the external abdominal oblique. Be careful, since this muscle is not easily separated from the underlying transversus abdominis muscle . Identify the ascending branch of the deep circumflex iliac artery, a large muscular branch lying on the transversus abdominis muscle, which runs superiorly in the region of the anterior superior iliac spine. (Note: if the internal oblique and transversus abdominis prove extremely difficult to separate, it might be possible to do a better job of separating them by first finding this artery, which immediately puts you on the correct plane between the muscular parts of these two muscles.) Note also that the segmental nerves and vessels are in the plane of separation that you are now attempting to open. How do the iliohypogastric and ilioinguinal nerves differ in this respect? Find the segmental vessels and nerves on the surface of the transversus abdominis muscle and consider their level, origin, areas of distribution, oblique orientation (why oblique? ), and the manner in which they enter the rectus sheath.

5. Open the rectus sheath and examine it and the rectus abdominis. (Play movie; View images: N 191, 250, 251, 253, 255, 256, 257; TG 4-09, 5-02, 5-04, 5-05, 5-07)

Open the rectus sheath of each side by a vertical incision through its mid-length. Elevate the borders and separate from the rectus abdominis muscle, cutting the attachments of the tendinous intersections to the deep surface of the anterior wall of the sheath as you go. At the level of the umbilicus, divide the rectus muscle and reflect both ends toward their respective attachments, noting the manner in which segmental vessels and nerves enter the sheath and the muscle, and then continue to the skin. Locate superior and inferior epigastric arteries. What are their sources? Do they anastomose?

Follow the posterior wall of the rectus sheath caudally until the aponeurotic sheath disappears. At this level an arching border - the arcuate line - is formed. At what level (relative to the umbilicus) do you find it? Is it distinct? What tissue is left on the posterior side of the rectus muscle caudal to this line? Note how each muscle layer contributes to the sheath. What muscles contribute aponeurotic fibers to the posterior wall of the sheath at each level?

Surface anatomy of the abdomen Surface anatomy of the inguinal region

 

 

Updated: 21 November 2011