Layers of the Abdominal Wall

From the outside in, the layers around the abdomen are: 

1. Skin.
2. Subcutaneous fat (which has a very weak upper "Camper" fascia and lower "Scarpa" fascia--not to be confused with the true abdominal-binding fascia).
3. Fascia.
4. Parietal peritoneum.
5. Visceral peritoneum, which are reflections of the peritoneum over the organs.
6. The posterior peritoneum, or the floor of the abdomen, under which are the aorta, vena cava, kidneys, and ureters.

 

The PERITONEAL Cavity

The abdomen is a "package deal." It contains the stomach and the entire lower gastrointestinal tract, which is actually considered external to the other organs, beginning and ending with the mouth of the upper GI tract and the anus, respectively. (In the abdomen, it involves the lower esophagus, down.) Its bacteria-rich lumen contents are sealed away from the rest of the sterile abdomen by the bowel wall.

There is a filmy shroud of tissue around the entire abdomen called the parietal peritoneum, which when it encounters an organ, reflects upon it to cover that organ as serosa, or the visceral peritoneum. (The serosa is typically considered the outermost layer of an organ's wall, but it really is part of the peritoneum.

Peritoneum, therefore, allows for some cross-talk among the organs, which can make a diagnosis confusing and challenging, because it is very rich in nerves that react to distention or inflammation (infection).

The rest of the abdomen contains the reproductive organs (in women), the spleen, the pancreas, the hepatobiliary system (liver, gallbladder, bile duct), and the bladder; and under its floor of the parietal peritoneum, the kidneys and their drainage tubes, the ureters to the bladder.

The Hernia Sac

A hernia sac alone, consisting of just protruding peritoneum, as an empty pouch is a fleeting thing, as it usually is followed by bowel or other abdominal contents to fill it.

 

The Fascia

As a binder, the peritoneum fails. What really holds the organs in is fascia, a tough fibrous layer (the "grizzle") that surrounds the abdomen superior to the peritoneum, separating as pockets to surround the abdominal wall muscles. As such, it flows above and below the abdominal muscles (the anterior and posterior rectus sheaths) and coalesces away from each muscle back into the combined layer--altogether the main layer responsible for holding in all of the abdominal organs.

While the peritoneum is a flimsy but very reactive layer surrounding the abdominal cavity, the fascia is a tough, fibrous fascial layer mechanically holding in the internal organs. Think of a girdle with two layers, fused together except at points of pocketing between them to hold in the abdominal wall muscles.

Hernias are conditions in which part of an organ can push through the fascia, away from the cavity containing it. (The peritoneum offers no barrier at all if the fascia has a weak spot.)

Hernias can be caused by a combination of muscle weakness + strain and can develop either quickly or over an extended period of time. Another cause is congenital, as in the failure of the abdominal wall to close properly in the womb.

 

Hernias

INDIRECT HERNIAS

There are natural defects in the fascia, notably the umbilicus (navel) and the inguinal canals through which blood vessels, lymphatics, nerves, ducts, and ligaments run, from one area of the body to another. Herniation through these natural openings can occur when they widen, called "indirect" hernias. In other words, they follow natural routes of accessibility as an outlet for escape.

EXAMPLES:

• Inguinal hernias can cause protrusion from the abdominal cavity into the inguinal canal.

Through the inguinal canal in men run the testicular suspensory ligaments and through the same canal; in women run the round ligaments, which are part of the support for the uterus, internally. 

• Femoral hernias are located in or near the groin or thigh, where the femoral ring allows passage of the femoral artery, vein, and nerve.

• Umbilical hernias are located just behind the navel. This was the site of insertion of the umbilical cord before birth and never really closes completely. (Everyone has at least a 1-cm natural umbilical hernia that can be felt in the navel.)

DIRECT HERNIAS

Direct hernias are those that bulge/weaken in fascial areas that are not natural, such as in faulty post-operative wound healing.

EXAMPLES:

• Incisional hernias are found in areas of incompletely healed surgical wounds or scars that became infected and opened.
• Herniation through old traumatic scars, such as stab wounds, etc., over time, evoked through the increased pressure of obesity.
• Herniation through tears in the muscles, due to athletic injury.
• Herniation between separation of muscles.

An example is "diastasis recti," when the longitudinal rectus muscles on either side of the midline separate during pregnancy.

• Spigelian hernia: occurs at a defect where the lateral edge of the midline rectus abdominal muscle meets the medial edge of the external oblique muscle, i.e., at the lateral points of the "six-pack."

CONGENITAL HERNIAS

Congenital hernias represent incomplete fusion/reapproximation of separated areas, i.e., failure to properly close during the fetal period.

EXAMPLES:

• Epigastric hernias are located in the abdomen, are usually present at birth, and may heal without treatment as the muscles involved may strengthen as the child ages.
• Hiatal hernias are located in the esophageal opening in the diaphragm. If it widens, portions of the stomach can rise up through it, become trapped, and sit irritated by acid.

These symptoms often spontaneously resolve with gravity, sitting up to allow the stomach to slip back through the area of weakness.

• During fetal development, there is an extension of the parietal peritoneum that precedes through the inguinal area ahead of the testicles in men and the round ligament (supports the uterus) and the ovarian suspensory ligament in women. This closes during the 8th month of gestation, but when it doesn't, can result in migration into the scrotum through the soon-to-close inguinal ring small bowel or cecum, in men; in women, it can allow herniation of the ovary or fallopian tube. This type of hernia is also an indirect hernia.

 

Hernia Complications

INCARCERATED HERNIA: Incarcerated hernias are defined as hernias with entrapped abdominal contents, usually bowel, which will cause severe pain, nausea and vomiting, loss of the ability to have a bowel movement, and even overt bowel obstruction. They are the result of an intestinal loop becoming entrapped by the concentric stricture of the hernial ring. If not corrected, this can cause intestinal ischemia and cell death due to the strangulation of the blood supply to the tissue trapped.

Reducible Hernias:

A hernia can sometimes be "reduced," applying gentle pressure against it to allow the trapped contents to fall back in. In this case, it is not an incarcerated hernia, because this won't work when the contents are truly incarcerated. 

 

Signs and Symptoms

• Pain or discomfort in the affected area (usually, inguinal or umbilical); this is especially evoked with coughing, lifting, or straining, as this increases the intra-abdominal pressure thrusting the bulge out even more. ? Weakness, pressure or a feeling of heaviness in the abdomen.
• Burning, gurgling, or aching sensation at the site of the bulge.
• With strangulation of the blood supply to the entrapped loop of bowel, signs of an acute abdomen may occur: rigidity/guarding and rebound tenderness.

 

In the Field

With reducible hernias, especially with an umbilical hernia, when entrapped bowel can be gently pushed back through this hole in the fascia, this may make the problem less of a time-urgency, but transport is still necessary.

The bottom line is whether a hernia is an incarcerated hernia, whether the contents are "reducible" by your being able to GENTLY push the abdominal contents back in, assisted by gravity (supine position).

Hernia pain severe enough to warrant an EMS call, however, should be enough to justify transport to decrease any possible jeopardy to the bowel.

Pre-hospital management should focus on

• strict attention to BSI and PPE,
• airway and circulatory support (ABC),
• IV fluid replacement,
• medication administration, and
• transport to definitive care.