Inguinal Hernia

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Also known as: Scrotal hernia

Introduction

Inguinal hernias occur when abdominal organs move into the inguinal canal where they may become incarcerated or strangulated. The herniated organs may be within the tunica vaginalis (an indirect hernia) or they may be beside the tunica but within the inguinal canal (a direct hernia). In both cases, a true hernial sac is formed by either the tunica vaginalis or parietal peritoneum, respectively. Scrotal hernias occur in male animals when indirectly herniated organs pass along the tunica vaginalis to the level of the scrotum. Organs in a scrotal hernia are much more likely to become strangulated. The organs most commonly involved in the hernia are the omentum, small intestine, bladder and uterus and these may become incarcerated or strangulated within the relatively narrow inguinal canal.

Signalment

In small animals, inguinal hernias may be congenital (often in male entire dogs) or acquired, often in older females. West Higland white terriers, Pekingese and Cairn terriers are known to be predisposed to congenital hernias but it is not currently known whether the disease is heritable. In male dogs, both testes have usually descended within a few weeks of birth but, if this descent is delayed, the inguinal canals are held open by the testes. It is suggested that the widening of the canals increases the chance of another abdominal organ entering the canal and becoming incarcerated there. These congenital inguinal hernias are therefore often associated with cryptorchidism and they may also occur with concurrent umbilical herniation.

Acquired hernias occur with any condition that causes the diameter of the inguinal canal to increase. In pregnant bitches, it is suggested that hormones cause the inguinal rings to widen allowing abdominal organs (including the gravid uterus) to herniate. Fat may also be deposited in the canal in obese animals and this is thought to effectively hold the canal open. Inguinal hernias may occur after blunt abdominal trauma, either due to an increase in intra-abdominal pressure or due to congenital weakness of the muscles forming the inguinal rings.

In horses, inguinal hernias occur most commonly after stallions have recently been castrated. In such cases, it is likely that the sudden removal of part of the mature spermatic cord provides more space in the inguinal canal for the herniation of abdominal organs.

Diagnosis

Clinical Signs

In small animals, clinical signs are most likely to be noticed if part of the small intestine becomes strangulated, causing:

  • Vomiting
  • Anorexia, depression and lethargy
  • Septic peritonitis may develop if the intestine ruptures

The hernia may be palpable in the inguinal region and over the scrotum of male dogs. The hernia may be externally reducible, especially if the animal is in dorsal recumbency and the hind limbs and caudal abdomen are elevated.

In horses, entrapment of the small intestine in the hernia may cause obstruction and/or strangulation. Affected horses show signs of severe colic, including rolling, flank watching, belly kicking, flehmus, bruxism and scraping. Rectal palpation will reveal the presence of multiple loops of distended small intestine (which feel similar to bicycle inner tubes) and intestine may be palpable within the scrotum. See here for more details.

Laboratory Tests

There are no specific tests for diagnosis of inguinal hernias but animals with incarcerated intestine may show changes on haematological and biochemical blood profiles.

Diagnostic Imaging

Plain radiographs of the abdomen show that the normally distinct border of the caudal ventral abdomen is disrupted by the presence of structures within the inguinal canal. If the hernia contains small intestine, gas lucencies may be evident within the canal.

Ultrasonography may be used to identify the contents of the inguinal canals. It is important that both canals are scanned and palpated as the contralateral side may be subclinically affected. This modality is also useful in cases of suspected scrotal herniation to assess testicular blood flow and to ascertain whether the spermatic cord is torsed.

Treatment

The condition should be managed surgically and, although the exact surgical approach and procedure may vary, the aim is to relocate the herniated organs to the abdomen and to completely or partially close the inguinal canal(s) to prevent the condition from recurring. An incision can be made directly over a simple unilateral inguinal hernia and the contents of the hernial sac milked back into the abdomen. The sac may be twisted to empty it and the hernial ring extended if necessary. In a female dog, the hernial sac is then amputated at its neck but in males this is not possible because the inguinal canal contains the spermatic cord. Since castration is recommended (to prevent recurrence and because the condition may be heritable), the testes may be removed and the tunica vaginalis closed at the level of the internal inguinal ring. A scrotal ablation may also be performed if this tissue is compromised. If the testes are to be retained, the herniated organs are relocated to the abdomen as before and the hernial sac (which is the parietal tunica vaginalis) is partially closed with transfixing sutures. Care should be taken not to compromise the neurovascular structures of the spermatic cord when these sutures are placed. In female dogs in which bilateral inguinal herniation is suspected, a caudal midline coeliotomy may give access to both inguinal canals through a single incision.

If an area of intestine is strangulated, this should be resected and an anastomosis created between the orad and aborad portions. It is advisable to move the affected section of intestine into the abdominal cavity (by enlarging the hernial ring) before attempting this.

Prognosis

The prognosis is good after surgical correction of the hernia but is poorer if intestinal strangulation or rupture have occurred. A mortality rate of 3% has been recorded for surgical management of inguinal hernias [1].


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References

  1. Waters DJ, Roy RG, Stone EA. A retrospective study of inguinal hernia in 35 dogs. Veterinary Surgery. 1993 Jan-Feb;22(1):44-9.

Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition) Mosby Elsevier




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