The history that the groin mass protrudes with straining (Valsalva) and reduces in the supine position is highly suggestive of a hernia. Hernias develop as a result of structural weakness of the abdominal wall in conjunction with increased intra-abdominal pressure. Contributing factors include prior incisions, heredity, multiple pregnancies, obesity, or liver disease with ascites. History should include conditions that lead to chronic straining, as these may provide clues to underlying untreated conditions such as a chronic cough (chronic bronchitis, lung cancer), constipation (colon cancer), or urinary straining (benign prostatic hypertrophy, prostate cancer). It is also important to inquire about work- and activity-related issues such as heavy lifting and physical exertion.

A hernia is a protrusion of tissue or organ(s) through a defect, most commonly in the abdominal wall. In abdominal hernias, peritoneal contents, such as the omentum and/or bowel, protrude through a defect or weakness in the muscle/fascia. Hernias have three components: the abdominal wall defect, the hernia sac which protrudes through the defect, and the contents within the sac. The neck of a hernia is the part of the hernia sac adjacent to the abdominal wall defect. If the neck is narrow, bowel may herniate less frequently, but once it does enter, it has a higher chance of becoming constricted by the narrow neck and incarcerating.

A hernia can be described as reducible if the contents within the sac can be pushed back through the defect into the peritoneal cavity, whereas with an incarcerated hernia, the contents are stuck in the hernia sac. A strangulated hernia is a type of incarcerated hernia in which there is compromised blood flow to the herniated organ (usually the small intestine, but can also be the omentum, large bowel, or ovary). Strangulation more frequently occurs when the hernia defect is narrow. A loop of bowel protrudes through the hernia and becomes entrapped by the narrow neck. This may lead to a closed-loop bowel obstruction whereby both ends of the bowel are blocked with nowhere for fluid and gas to egress. As the bowel continues to produce gas and secrete fluid, the progressive distention leads to a compromise of the blood flow. Strangulation requires prompt surgical intervention since it can lead to intestinal ischemia, sepsis, bowel infarction, and death. The overall incidence of strangulation in inguinal hernias is less than 1 %. This risk is increased in symptomatic patients and those with significant comorbidities. Predisposing risk factors include older age, duration of hernia (shorter is worse), type (femoral), and comorbidities. Some incarcerated hernias (particularly those with large defects) can remain irreducible for years without causing major symptoms. Others (particularly with narrow necks) are at higher risk of progressing to strangulation.

A strangulated hernia leads to a compromise of the blood supply of the bowel and subsequent irreversible ischemia and necrosis. Ischemic bowel typically triggers SIRS. Thus the cardinal signs of a strangulated hernia include fever, tachycardia, and an elevated WBC count, as well as redness of the skin overlying the hernia and pain. The patient described presented with all of these signs. A strangulated hernia is a surgical emergency.

Inguinal hernias are divided into direct and indirect types based upon etiology (Table 1.2) and anatomic location. Femoral hernias occur in the femoral canal (Fig. 1.1), inferior to the inguinal ligament traversing the empty space medial to the femoral vein (recall the mnemonic “NAVEL” {from lateral to medial: femoral nerve, artery, vein, empty space, lymphatic}). Although they appear infrequently in patients (10 % of all hernias), they are much more common in women and have the highest rate of strangulation. Umbilical hernias (Fig. 1.2) are prevalent in the pediatric population and common with congenital hypothyroidism. In children, most are asymptomatic and close spontaneously with no intervention. In adults, umbilical hernias are associated with increased intra-abdominal pressure (pregnancy, ascites, weight gain). Surgery is recommended if symptomatic. Ventral or incisional hernias appear at the site of a previous surgery and can occur weeks, months, or even years after the procedure.

In general, indirect inguinal hernias are congenital, whereas direct hernias are acquired. Indirect inguinal hernias are caused by a persistent (patent) processus vaginalis. During embryologic development, the processus vaginalis, an outpouching of the peritoneum, descends into the scrotum, bringing along the testicle with it. It subsequently closes prior to birth. If the processus remains patent (open), peritoneal fluid can fill the scrotum (communicating hydrocele) or bowel can pass through the patent processus vaginalis into the scrotum (indirect hernia). In men, the indirect hernia sac travels along with the spermatic cord through the internal ring, and into the scrotum. In women, it follows the tract of the round ligament towards the pubic tubercle. Direct inguinal hernias are due to a weakness in the floor (transversalis fascia) of the inguinal canal, directly through Hesselbach’s triangle. They typically manifest after years of chronic straining, causing wear and tear to the abdominal wall musculature. Since they are acquired, it is unusual to find a direct inguinal hernia in a young person. The neck of an indirect inguinal hernia is relatively narrow as it passes through a relatively rigid and inflexible space (the internal ring), whereas direct inguinal hernias typically have a more broad-based neck, making strangulation less likely to occur.