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 inguinal and femoral hernia. However, there are a number of less common abdominal hernia that require identification and suitable management.
An epigastric hernia occurs in the midline through the fibres of the linea alba.
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 where the linea alba becomes widened. This results in a palpably increased distance between the rectus muscles and a subsequent midline bulge.
A paraumbilical hernia occurs through the linea alba around the umbilicus (not through the umbilicus itself). They are typically secondary to raised chronic intra-abdominal pressure – such as with obesity, pregnancy, or ascites.
They present as a painful lump around the umbilicus and will worsen with an increased intra-abdominal pressure, such as with standing or coughing.
Note: In infants, umbilical hernias can form as ventral wall abnormalities, either as an omphalocele or gastroschisis.
A spigelian hernia is a rare form of abdominal hernia that occurs at the semilunar line around the level of the arcuate line.
The rectus abdominis muscle is enclosed by the rectus sheath, with the arcuate line at the lower limit of the posterior layer of the rectus sheath (around 1/3 of the distance between umbilicus and pubic symphysis). The semilunar line is the tendinous lateral border of the rectus, where the aponeuroses fuse.
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.
One study has shown cryptorchidism is also present in 75% of cases of Spigelian hernia in male infants; this is likely associated with a failure in gubernaculum development.
An obturator hernia is a hernia of the pelvic floor, occurring at the obturator foramen, into the obturator canal. They are more common in women (due to a wider pelvis), typically in middle-aged patients and more often occur on the right side.
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.
Obturator hernias are often diagnosed intra-operatively in patients presenting with bowel obstruction.
Patients will classically present with a mass in the upper medial thigh. 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)
The Obturator Canal
The obturator canal is formed in the obturator foramen (the large opening between the ischium and pubis bones), by the gap through the obturator membrane, passing into the medial thigh. It contains the obturator nerve, obturator artery, and obturator vein.
A Littre’s hernia is a very rare form of abdominal hernia, whereby there is herniation of Meckel’s diverticulum. This most commonly occurs at the inguinal canal and many will become strangulated.
Lumbar hernias are rare posterior hernias occurring spontaneously* through an area of weakness, or iatrogenically following surgery. They present with a posterior mass and often with associated back pain.
*One case report suggests the congenital form should prompt consideration of lumbo-costo-vertebral syndrome, a disorder with a spectrum of symptoms which may be due to a single somatic mutation during development
The lumbar posterior wall has two common areas of physiological weakness where lumbar hernia most often occur:
- Superior lumbar triangle – termed Grynfeltt’s quadrangle.
- Inferior lumbar triangle – termed Petit’s triangle.
However, most lumbar hernias are incisional, classically following renal surgery.
A Richter’s hernia is a partial herniation of small bowel, whereby only the anti-mesenteric border becomes strangulated, therefore only part of the lumen of the bowel is within the hernia.
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 quick surgical intervention. Care must be taken during hernia repair to identify a Richter’s Hernia so as to not damage the bowel during the surgery.