A hernia is defined as the protrusion of part or whole of an organ or tissue through the wall of the cavity that normally contains it.
There are numerous types of abdominal hernia, the most common of which are hiatus, inguinal, femoral, and incisional hernia. However, there are a number of less common abdominal hernia that require identification and suitable management.
An epigastric hernia occurs in the upper midline through the fibres of the linea alba (Fig. 1). They are typically secondary to raised chronic intra-abdominal pressure, such as with obesity, pregnancy, or ascites.
They are relatively common with a prevalence up to 10%, mostly affecting middle-aged men. Whilst typically asymptomatic, they may present as a midline mass that disappear when lying on the back.
An important differential diagnosis is divarication of the recti, a cosmetic condition caused by the weakening and widening of the linea alba. The key difference is that in divarification the linea alba is stretched and weakened but is intact (i.e. there is no discrete defect, and therefore by definition no hernia).
A paraumbilical hernia is a herniation occurring through the linea alba around the umbilical region* (not through the umbilicus itself).
They are also typically secondary to raised chronic intra-abdominal pressure and present as a lump around the umbilical region. They are extremely common, with risk factors including obesity and pregnancy.
Generally they contain pre-peritoneal fat although they can occasionally contain bowel. Whilst they are a fairly common presentation in general surgery, they do not commonly strangulate.
*Umbilical hernias can also occur, commonly in children (congenital in aetiology), either omphalocele or gastroschisis, caused by a failure of abdominal contents to return back to the abdominal cavity during intrauterine development
A spigelian hernia is a rare form of abdominal hernia that occurs at the semilunar line (the tendinous lateral border of the rectus, where the aponeuroses fuse), around the level of the arcuate line.
Clinically, they present as a small tender mass at the lower lateral edge of the rectus abdominus*. They have a high risk of strangulation, and so should be repaired urgently.
*One study has shown cryptorchidism is also present in 75% of cases of Spigelian hernia in male infants, likely associated with a failure in gubernaculum development
An obturator hernia is a hernia of the pelvic floor, occurring through the obturator foramen, into the obturator canal (Fig. 3). They are more common in women (due to a wider pelvis), typically in elderly patients*.
Patients will classically present with a mass in the upper medial thigh and often patients will have features of small bowel obstruction.
In around half of cases, compression of the obturator nerve passing through the obturator canal will result in a positive Howship-Romberg sign (hip and knee pain exacerbated by thigh extension, medial rotation, and abduction).
*Due to the substantial amount of fat that is contained within the obturator canal, many obturator hernias also present in those who have undergone rapid weight loss; losing the fat located in the canal results in a larger space for potential herniation to develop
A Littre’s hernia is a very rare form of abdominal hernia, whereby there is herniation of a Meckel’s diverticulum. This most commonly occurs in the inguinal canal and many will become strangulated.
Lumbar hernias are rare posterior hernias, that typically occur spontaneously or iatrogenically following surgery (classically following open renal surgery). They present as a posterior mass, often with associated back pain.
A Richter’s hernia can occur at any of the above sites and is a partial herniation of bowel, whereby the anti-mesenteric border becomes strangulated, therefore only part of the lumen of the bowel is within the hernial sac (Fig. 4).
Patients will present with a tender irreducible mass at the herniating orifice and will have varying levels of obstruction (purely dependent on how much bowel circumference is involved). Due to obstruction, these are often surgical emergencies that need urgent surgical intervention.
- Epigastric herniae occur in the upper midline through the fibres of the linea alba
- Paraumbilical herniae occur through the linea alba around the umbilical region
- Spigelian herniae occur at the semilunar line around the level of the arcuate line
- Obturator hernia occur through the obturator foramen into the obturator canal
- Richter’s herniae are partial herniation of bowel involving the anti-mesenteric border