The hernia sac (bulge) is formed by extension of the lining of the abdominal cavity (peritoneum) and may contain part of the small or large intestine. A hernia can be present at birth (congenital), but most of the time appears later in life (acquired). It is generally reducible; in this case the bulge appears intermittently and disappears easily when laying-down.

Acquired hernias may develop as a result of increased pressure within the abdominal cavity, for instance during pregnancy, heavy lifting, obesity, constipation, or chronic cough. Poor nutrition, smoking and past family history of hernia repair are also known predisposing factors.

Abdominal wall hernia can cause symptoms including abdominal pain exacerbated with coughing or exercising, abdominal distension, burning, gurgling or dragging sensation, nausea and vomiting.

Those symptoms are often more pronounced when the hernia becomes non-reducible (incarcerated), prompting the patient to present to the hospital on emergency. On few occasions, intestine can be involved causing bowel obstruction due to strangulation. In this situation urgent hernia surgery is mandatory as any delay can lead to death of the bowel wall due to compromised blood supply, and be potentially life threatening.

Hernia can occur anywhere in the abdomen, but most commonly at weak anatomical points, mainly inguinal (groin) and umbilical (navel).

• Inguinal hernia: is the most common and affects predominantly male patients due to the presence of the spermatic cord structures that cross the lower abdominal wall via the inguinal canal. Sometimes, the hernia sac can extend down to the scrotum.
• Umbilical hernia: often presents as a bulge arising through or beside (para-umbilical) the belly button. Most of the time the hernia sac content is made of intra-abdominal fat (omentum)
• Femoral hernia: is more common in female patients as they have a broader pelvis. The weak point is situated at the level of the femoral canal, just lateral to the pubic bone, where the external iliac (pelvic) vessels pass through to the lower limb. Femoral hernias tend to incarcerate and are often operated on emergency.
• Epigastric hernia: is a defect that develops at the level of the upper and middle part of the abdomen, below the xiphoid process (breastbone).

• Incisional hernia: always occurs following previous abdominal surgery and is caused by incomplete healing and residual weakness of the scar tissue. This condition is fairly commonly following a previous median vertical incision (midline laparotomy) as it may develop in more than 35% of the cases.
• Hiatal hernia: A hiatal hernia is when your stomach bulges up into your chest through an opening in your diaphragm, the muscle that separates the two areas. The opening is called the hiatus, so this condition is also called a hiatus hernia. There are two main types of hiatal hernias: sliding and paraesophageal.
• Spigelian hernia: (or lateral ventral hernia): is uncommon and occurs lateral to the rectus abdominis muscles, at the level of the umbilicus.
• Obturator hernia: Is a rare condition that generally develops in older female patients, particularly following recent weight loss or after a fall. It is situated in the pelvis (obturator foramen) and is often diagnosed intra-operatively following emergency surgery.