Hernias 

As defined in 1804 by Astley Cooper, a hernia as a protrusion of any viscus from its proper cavity. The protruded parts are generally contained in a sac-like structure, formed by the membrane with which the cavity is naturally lined.^[1]

Since that time, several different types of abdominal wall hernias have been identified, along with a larger number of associated eponyms. This article reviews the pathophysiology, evaluation, and treatment of most of these hernias from an emergency medicine perspective. Hernias are brought to the attention of an emergency physician either during a routine physical examination for other medical complaints or when the patient has developed a complication associated with the hernia.

See Medscape's Hernia Resource Center.

Types of Hernia - Location

Indirect hernia

An indirect inguinal hernia follows the tract through the inguinal canal. This results from a persistent process vaginalis. The inguinal canal begins in the intra-abdominal cavity at the internal inguinal ring, located approximately midway between the pubic symphysis and the anterior iliac spine. The canal courses down along the inguinal ligament to the external ring, located medial to the inferior epigastric arteries, subcutaneously and slightly above the pubic tubercle. Contents of this hernia then follow the tract of the testicle down into the scrotal sac.^{[2, 3, 4]}

Direct hernia

A direct inguinal hernia usually occurs due to a defect or weakness in the transversalis fascia area of the Hesselbach triangle. The triangle is defined inferiorly by the inguinal ligament, laterally by the inferior epigastric arteries, and medially by the conjoined tendon.^[5]

Femoral hernia

The femoral hernia follows the tract below the inguinal ligament through the femoral canal. The canal lies medial to the femoral vein and lateral to the lacunar (Gimbernat) ligament. Because femoral hernias protrude through such a small defined space, they frequently become incarcerated or strangulated.^[6]

Umbilical hernia

The umbilical hernia occurs through the umbilical fibromuscular ring, which usually obliterates by 2 years of age. They are congenital in origin and are repaired if they persist in children older than age 2-4 years.^{[2, 5]}

Richter hernia

The Richter hernia occurs when only the antimesenteric border of the bowel herniates through the fascial defect. The Richter hernia involves only a portion of the circumference of the bowel. As such, the bowel may not be obstructed, even if the hernia is incarcerated or strangulated, and the patient may not present with vomiting. The Richter hernia can occur with any of the various abdominal hernias and is particularly dangerous, as a portion of strangulated bowel may be reduced unknowingly into the abdominal cavity, leading to perforation and peritonitis.^[6]

Incisional hernia

This iatrogenic hernia occurs in 2-10% of all abdominal operations secondary to breakdown of the fascial closure of prior surgery. Even after repair, recurrence rates approach 20-45%.

Spigelian hernia

This rare form of abdominal wall hernia occurs through a defect in the spigelian fascia, which is defined by the lateral edge of the rectus muscle at the semilunar line (costal arch to the pubic tubercle).^{[7, 8]}

Obturator hernia

This hernia passes through the obturator foramen, following the path of the obturator nerves and muscles. Obturator hernias occur with a female-to-male ratio of 6:1, because of a gender-specific larger canal diameter. Because of its anatomic position, this hernia presents more commonly as a bowel obstruction than as a protrusion of bowel contents.^[1]

Types of Hernia - Condition

• Reducible hernia: This term refers to the ability to return the contents of the hernia into the abdominal cavity, either spontaneously or manually.
• Incarcerated hernia: An incarcerated hernia is no longer reducible. The vascular supply of the bowel is not compromised. Bowel obstruction is common.
• Strangulated hernia: A strangulated hernia occurs when the vascular supply of the bowel is compromised secondary to incarceration of hernia contents.

Frequency

United States

• Over 1 million abdominal wall hernia repairs are performed each year, with inguinal hernia repairs constituting nearly 770,000 of these cases.^{[9, 10, 11]}
• Approximately 25% of males and 2% of females have inguinal hernias in their lifetimes; this is the most common hernia in males and females.^{[11, 12]}
• Approximately 75% of all hernias occur in the groin; two thirds of these hernias are indirect and one third direct.^[2]
• Indirect inguinal hernias are the most common hernias in both men and women; a right-sided predominance exists.
• Incisional and ventral hernias account for 10% of all hernias.^[4]
• Only 3% of hernias are femoral hernias.
• The incidence of inguinal hernias in children ranges up to 4.4%, while umbilical hernias occur in approximately 1 out of every 6 children.^{[10, 2]}
• The incidence of incarcerated or strangulated hernias in pediatric patients is 10-20%; 50% of these occur in infants younger than 6 months.^[10]

International

• Data from developing countries is limited, therefore, an accurate occurrence value is unavailable. Current epidemiologic assessments postulate that gender and anatomic distribution are similar.

Mortality/Morbidity

Morbidity is secondary to missing the diagnosis of the hernia or complications associated with management of the disease.

• A hernia can lead to an incarcerated and often obstructed bowel.
• The hernia also can lead to strangulated bowel with a compromised blood supply. Reduced strangulated bowel leads to persistent ischemia/necrosis with no clinical improvement. Surgical intervention is required to prevent further complications such as perforation and sepsis.
• Ensuing surgery to repair the hernia or its complications may leave the patient at risk for infection, future hernias, or intra-abdominal adhesions.

Race

• Umbilical hernias occur 8 times more frequently in black infants than in white infants.^[12]

Sex

• Approximately 90% of all inguinal hernia repairs are performed on males.^[11]
• Reduction of hernias in females may be complicated by inclusion of the ovary in the hernia.
• Femoral hernias (although rare) occur almost exclusively in women because of the differences in the pelvic anatomy.
• The female-to-male ratio of obturator hernias is 6:1.^[12]

Age

• Indirect hernias usually present during the first year of life, but they may not appear until middle or old age.
• Indirect hernias occur more frequently in premature infants compared to term infants. Indirect hernias develop in 13% of infants born before 32 weeks' gestation.^[10]
• Direct hernias occur in older patients as a result of relaxation of abdominal wall musculature and thinning of the fascia.
• Umbilical hernias usually occur in infants and reach their maximal size by the first month of life. Most hernias of this type close spontaneously by the first year of life, with only a 2-10% incidence in children older than 1 year.^[13]