Clinical Cases - Abdominal Wall

A 28-year-old woman in her 36th week of pregnancy arrived in the emergency room following an automobile accident. Immediately following the accident she went into labor. The accident had broken her pelvis such that the emergency room physician deemed a vaginal delivery would be hazardous. An obstetrician was called, and she agreed with the ER physician's initial assessment. A Cesarian section was performed, resulting in the delivery of a healthy baby girl. During the operation, the obstetrician used a Pfannenstiel incision to open the abdomen. This incision involves making a transverse, slightly convex cut large enough to deliver a child at approximately the pubic hairline.

Questions to consider:

1. What abdominal wall layers must be incised at the pubic hairline (near the midline) in order to access the abdominal cavity?

   The Pfannenstiel incision is made below the arcuate line, so the layers incised are as follows: skin, superficial fascia (fatty and membranous), deep fascia, anterior rectus sheath, rectus abdominis muscle, transversalis fascia, extraperitoneal connective tissue, and peritoneum.

2. Why is the incision made in a convex manner instead of straight across?

   The segmental nerves of the anterior abdominal wall follow a superior to inferior course as they progress medially, so by making an incision that approximately parallels the course of the nerves, the surgeon can minimize the number of nerves that are damaged, thus reducing post-operative muscle paralysis and skin paresthesia. In addition, a convex incision parallels the lines of cleavage in the skin of the inferior abdominal wall, resulting in less scarring. A truly horizontal linear incision may cut more than one segmental nerve, depending on the size and location of the incision.

3. What vascular structures might be cut during a Pfannenstiel incision?

   The vascular structures that may be at risk include the inferior epigastric artery and vein, as well as their branches (especially the pubic artery and vein), and the superficial epigastric vessels.

4. Where in the abdomen could a surgeon make a large vertical incision with minimal detrimental effect?

   Vertical abdominal incisions may be made at the midline, through the linea alba, as well as within about 2.5 cm on either side of the midline (paramedian). If a paramedian incision is chosen, the rectus abdominis muscle can be retracted laterally after incision of the anterior rectus sheath. This exposes the posterior rectus sheath and prevents damage to the rectus abdominis muscle and its innervation.

A twenty-five year-old female medical student presents to the emergency room with a complaint of "colicky" periumbilical pain which has intensified over the last 6-8 hours and now has started to migrate to the right lower quadrant. The patient reports some initial nausea, and as the pain has increased she has had increasing emesis and anorexia. Physical exam demonstrates the patient has no distension, auscultation reveals hyperactive bowel sounds, and on palpation the patient demonstrates abdominal guarding and rebound tenderness, and the muscles of the anterior wall in the right lower quadrant are rigid. In addition, the patient has a low-grade fever, and laboratory tests reveal a rising white blood cell count. The attending determines that the patient has acute appendicitis and prepares to take the student to the O.R. for an appendectomy. The surgeon asks you the following questions regarding the surgery.

Questions to consider:

1. What signs and symptoms revealed to the physician that the patient had an acute abdominal problem - potentially appendicitis?
   

   Abdominal pain (periumbilical shifting to the right lower quadrant) followed by anorexia, nausea, and vomiting.

2. How would you distinguish between gastroenteritis and appendicitis?
   

   Gastroenteritis usually causes vomiting before pain and is associated with diarrhea. The patient will also present with a less acute history of abdominal discomfort.

3. What is McBurney's point?
   

   It is the point within the right lower quadrant which can be defined as: one-third the distance from the anterior iliac spine to the umbilicus on a line connecting the two.

4. What is McBurney's sign?
   

   Tenderness at McBurney's point in patients with appendicitis.

5. What types of incisions can be made in the abdominal wall?
   

   Surgeons choose each of the following based on their ability to provide access to the desired organ:
   
   Median or midline: Cut through the linea alba, superior or inferior to the umbilicus. Benefit: minimal blood loss, avoids major nerves, and easy access for exploration.
   
   Paramedian incisions: Cut to the right or left of the midline. Benefit: Avoid nerves, frees the rectus abdominal muscle which decreases tension to the muscle. Gives access to the peritoneal cavity.
   
   Gridiron (muscle splitting)/McBurney incisions: Incision of the external oblique aponeurosis in the direction of its fibers. The internal oblique and transversus abdominis are then incised and split in the direction of their fibers which are then retracted. Benefit: Provides good access with almost no muscle damage and it avoids damage to local nerves.
   
   Pfannenstiel (suprapubic incision): This transverse, slightly convex cut transects the linea alba and anterior layer of the rectus sheath at the pubic hairline. Separate the underlying rectus muscles via the tendons (to allow better reattachment) and identify the surrounding nerves. Benefits: Use for most gynecologic surgeries.
   
   Transverse incision: Cuts through the anterior rectus sheath and the rectus abdominis. Benefits: Causes the least amount of nerve damage, the muscular segments can be rejoined, they are incredibly useful for dissection above the level of the umbilicus.

6. Which of these incisions would be the most ideal for an appendectomy?
   

   Transverse incisions have become increasingly more popular replacing the traditional McBurney's incision. Transverse incisions are less likely to cause nerve injury.

7. When placing an incision in the abdominal wall, what nerves have to be identified? What would be a consequence of damage to the nerves?
   

   The inferior thoracic spinal nerves (T11 and T12), the iliohypogastric nerve and the ilioinguinal nerve innervate abdominal muscles and skin inferior to the umbilicus. The iliohypogastric nerve perforates the posterior part of the transversus muscle; it further divides between the transversus muscle and the internal oblique via cutaneous branches both anteriorly and laterally. In addition these branches provide muscular branches to both the transversus abdominis and internal oblique muscles. Therefore, damage to these nerves can lead to muscle weakness with a potential for herniation and pain/altered sensation due to both these muscular and cutaneous branches.

8. Suppose that the surgeon, in the process of the appendectomy, is unable to locate the appendix through the small incision he made in the right lower quadrant, so he decides to extend his incision several inches superiorly toward the rib cage. What is likely to result from such a procedure?
   

   A vertical incision at approximately the right mid-clavicular line, as would occur if McBurney's incision was extended superiorly, would cut several segmental nerves, resulting in loss of sensation and paralysis of the muscles on the right side, which would in turn cause bulging of the abdominal wall and might necessitate the use of a support belt.

9. Why were the muscles of the anterior abdominal wall rigid?
   

   The ruptured appendix caused peritonitis. Inflammation of the parietal peritoneum causes pain and reflex spasm of the abdominal wall over that area--the peritoneum, abdominal muscles, and overlying skin are all supplied by the same segmental nerves (T11, T12, L1). Spasm apparently occurs to immobilize that region of the abdomen in order to minimize spread of the infection.

10. What nerve is at risk when an incision is made at McBurney's point? What would be the long-term effects of damage to this nerve?
    

    Ilioinguinal and iliohypogastric nerves. Damage to the nerve could cause partial paralysis of the internal oblique and transversus abdominis muscles resulting in laxity of the conjoint tendon and possibly inguinal hernia. Sensation in the anterior scrotal and lateral part of the penis might also be affected.

11. If the appendix is not immediately visible, what features of the cecum could the surgeon use to locate it?
    

    The teniae coli muscles can be traced along the cecum to locate the base of the appendix.

12. Fortunately for the patient, she was treated before her infection became life-threatening; however, if she had waited to seek treatment or if the physicians had not acted quickly on their suspicions, her infection may have continued to spread in the peritoneal cavity and the blood stream. Which organ is particularly at risk for secondary infection in appendicitis and why?
    

    The liver. The vast majority of blood from the GI tract drains into the portal vein and then filters through the liver before entering the inferior vena cava and passing into the general circulation. As a result, the liver is particularly susceptible to secondary infection in appendicitis.

References:

Advanced Surgical Recall
Surgery Scientific Principles and Practices (Greenfield's) pp. 1246-1261.
Moore's Clinical Anatomy pp. 175-191.
Woodburne & Burkel, p. 421-31