7.15: Abdominal wall pathologies and hernias

Amandeep Singh

Introduction

The abdominal wall surrounds the anterolateral aspect of the abdominal cavity, where many important organs are located.

The abdominal wall is made up of:

• Skin.
• Superficial fascia – thin single layer above the umbilicus and two layers below the umbilicus (superficial fatty layer of Camper’s fascia and deep layer of Scarpa’s fascia with neurovascular bundle running between them).
• Muscles.
1. 1) Flat muscles: External oblique, internal oblique, transversus abdominis.
2. 2) Vertical muscles: Rectus Abdominis and Pyramidalis.
3. 3) The rectus sheath: An aponeurosis of five muscles of the anterior abdominal wall. The anterior wall is formed by the external oblique and outer fibres of internal oblique whereas the posterior wall is formed by inner fibres of the internal oblique and transversus abdominis. Only the anterior wall of the rectus sheath present about midway between the umbilicus and pubic symphysis where the rectus abdominis muscle is in direct contact with the transversalis fascia. Arcuate line forms the area of transition at which the posterior wall disappears (Fig. 7.15.1).
• Fascia transversalis.
• Parietal peritoneum.

Fig. 7.15.1 Pictoral representation showing layers of anterior abdominal wall.

Blood supply

Superior epigastric artery, inferior epigastric artery, deep circumflex iliac vessels, superficial epigastric vessels and superficial circumflex iliac vessels supply the anterior abdominal wall.

Nerve

Nerves of the anterior abdominal wall include subcostal nerve, iliohypogastric and ilioinguinal nerves.

Hernias

Types of abdominal hernias:

• External hernias
• Internal hernias

The diagnosis of hernia can be made with plain radiographs, barium studies and CT.

External hernias

They consist of a peritoneal sac which protrudes through a weakness/defect in the muscular layers of the abdominal wall (mainly in transversalis fascia below the conjoined tendon). Preperitoneal fat, greater omentum and viscera may protrude into the sac (Fig. 7.15.2).

• The complications of abdominal hernias include bowel obstruction, incarceration (nonreducible) and strangulation (absence of blood supply). The transition point of obstruction at the level of the hernia can be detected with CT which shows dilated bowel loops proximal to the hernia and collapsed loops distal to it. Incarceration can be seen in cases where the hernia sac has a narrow neck. CT findings in case of strangulation include free fluid within the sac, bowel wall thickening and hypoattenuating or hyperattenuating bowel wall enhancement with proximal bowel dilatation.

Fig. 7.15.2 Schematic representation of abdominal wall hernias.

Inguinal hernias

Types: Indirect or direct (depending on their relationship to the inferior epigastric vessels).

Indirect hernia: They occur in infants and children. The peritoneal sac passes through the internal ring into inguinal canal, lateral to the inferior epigastric vessels and anterior to the spermatic cord. In women, it goes along the round ligament into the labium. Rarely, the herniated sac instead of leaving the external inguinal ring continues along with the abdominal wall muscles. This is called interparietal hernia (Fig. 7.15.3).

Fig. 7.15.3 Left inguinoscrotal hernia: Herniation of small-bowel loops and omentum into the left inguinal canal is seen with entrapment at neck causing proximal bowel dilatation.

Direct hernia: It is always acquired. The herniated sac is medial to the inferior epigastric vessels and does not pass through the inguinal canal. Hence, they do not reach up to scrotum.

Femoral hernias

Femoral hernias are less common than inguinal hernias. They are more common in paediatric age groups and women. The predisposing feature is the empty space between the lacunar ligament medially and the femoral vein laterally. Physical changes of pregnancy dilate this space.

The herniated sac is below the inguinal ligament and lateral to the femoral vessels. Strangulation is a common complication.

In femoral hernia, the sac lies below and lateral to the pubic tubercle as it emerges from the femoral canal. It can be differentiated from an inguinal hernia which lies above and medial to the pubic tubercle (Fig. 7.15.4).

Fig. 7.15.4 **Femoral hernia:** Localized sac (arrow) is located lateral to pubic tubercle (arrow).

Incisional hernias

Incisional hernias occur as a result of complication of laparotomy. Risk factors include old age, obesity, postoperative wound infection, chronic pulmonary disease, cirrhosis, malignant tumour, steroids and malnutrition. Most of these hernias develop during the first few months after surgery but may remain silent for up to a period of 5 years. Incisional hernia are more likely to occur as a result of vertical incisions than transverse incisions. They may occur following incisions as small as a puncture site for laparoscopic surgery. A common variation is the parastomal hernia, in which bowel and omental fat protrude through a defect immediately adjacent to an ileostomy or colostomy opening. Bowel loops may be incorporated into the hernia and become incarcerated or strangulated, if the hernia is not treated (Fig. 7.15.5).

Fig. 7.15.5 **Incisional hernia:** Localized sac (arrow) through a defect in right paramedian location in supraumbilical region.

Richter’s hernias

Richter’s hernia is a rare type of hernia which includes only a part of the bowel wall. Because only a portion of the intestinal wall is included into the hernia, therefore, the lumen remains patent and does not result in obstruction. However, incarceration is not common.

Littre hernias

Any hernia which contains a Meckel’s diverticulum is known as Littre hernia. They may occur due to the presence of inflammatory adhesions that cause confinement of the Meckel’s diverticulum within the hernia sac. Approximately 50% of Littre hernias develop in the inguinal region, 20% in the femoral, 20% in umbilical and 10% in other sites.

Spigelian hernias

Spigelian hernia is a rare acquired ventral hernia that occurs through the linea semilunaris, the line where lateral rectus sheath is formed by fusion of sheaths of lateral abdominal muscles. They are almost always found just above the point where posterior wall of the rectus sheath is pierced by the inferior epigastric vessels. It occurs at midpoint between the umbilicus and symphysis pubis, which is a weak point along the lateral border of the rectus muscle. They are rare but have a high frequency of incarceration and strangulation. It may be mistaken for an abdominal wall lipoma, if it contains only peritoneal fat. CT can be quite beneficial to confirm the diagnosis (Fig. 7.15.6).