There are types of extra-abdominal hernias such as reducible, intractable, incarcerated, and strangulated. reducible hernia: A hernia in which the contents of the hernia can be easily retracted into the abdominal cavity is called a reducible hernia. Irreducible hernia: A hernia in which the contents cannot be retracted or completely retracted into the abdominal cavity but do not cause serious symptoms is called an irreducible hernia. Repeated protrusion of the hernia contents, resulting in damage to the hernia sac neck by friction and adhesions are the common causes of failure to retract the hernia contents. Most of the contents of this type of hernia are the greater omentum. In addition, some huge hernias with long duration and large abdominal wall defects are often difficult to retract because the abdominal wall has completely lost its role in resisting the protrusion of the contents due to the large number of contents. In a few other hernia with long duration of disease, the downward force generated when the contents keep entering the hernia sac gradually pushes the peritoneum on the neck of the sac into the sac, especially in the iliac fossa area where the retroperitoneum is extremely loosely combined with the posterior abdominal wall, making it easier to be pushed, and the appendix (including the appendix), sigmoid colon or bladder then moves down and becomes part of the wall of the hernia sac. This type of hernia is called a sliding hernia and is also considered a refractory hernia. As with easy-to-recover hernias, the contents of a refractory hernia are not obstructed by blood flow and there are no serious clinical symptoms. Incarcerated hernia: When the neck of the hernia sac is small and the intra-abdominal K is suddenly increased, the contents of the hernia can forcibly expand the neck and enter the hernia sac, and then the elastic contraction of the neck can jam the contents and prevent them from retracting, which is called an incarcerated or clamping hernia. If the contents of the hernia are intestinal tubes, the intestinal wall and its mesentery may be compressed at the neck of the hernia sac, which first obstructs the venous return and leads to stasis and edema of the intestinal wall, and the intestinal wall and its mesentery gradually thicken and change color from normal light red to dark red, and yellowish exudate may accumulate inside the sac. As a result, the intestinal canal becomes more difficult to retract due to increased pressure. The pulsation of the mesenteric artery can be detected when the intestine is embedded, and if the intussusception can be released in time, the diseased intestine can return to normal. stranggulanted hernia: If the intussusception is not released in time, the increasing pressure on the intestinal wall and its mesentery may reduce the arterial blood flow. Finally, it leads to complete blockage, which is called strangulated hernia. At this time, the mesenteric artery pulsation disappears, and the intestinal wall gradually loses its luster, elasticity and peristaltic capacity, and eventually becomes black and necrotic. The fluid inside the hernia sac becomes light red or dark red. In case of secondary infection, the exudate in the hernia sac becomes purulent. If the infection is severe, it may cause cellulitis of the tissue covered by the hernia. Pus accumulation in the hernia sac can be self-perforated or mistakenly drained by incision and fecal fistula (enterocutaneous fistula) can occur. An incarcerated hernia and a strangulated hernia are actually two stages of a single pathological process, and it is difficult to distinguish them clinically. In cases of intussusception or strangulation, acute mechanical intestinal obstruction can result. However, sometimes the embedded contents are only part of the intestinal wall and the mesenteric side of the intestinal wall and its lining do not enter the hernia sac and the intestinal cavity is not completely obstructed; this hernia is called an intestinal wall hernia or a Richter hernia; if the embedded small intestine is a small intestinal diverticulum (usually a Meckel diverticulum), it is called a Littre hernia. The contents of the intussusception are usually a segment of the intestinal canal, and sometimes the intussusception can include several intestinal collaterals shaped like a W. The intestinal canal between the intussusception collaterals within the hernia sac can be hidden in the abdominal cavity, a condition known as a retrograde intussusception hernia or Maydl hernia (Figure 34-3). This is because once retrograde intussusception occurs, not only the intestinal canal in the hernia sac can be necrotic, but also the intermediate intestinal collaterals in the abdominal cavity, and sometimes even the intestinal canal in the hernia sac is still alive while the intestinal collaterals in the abdominal cavity are already necrotic. Therefore, in the surgical management of intussusception or strangulated hernia, the vitality of the intestinal canal should be accurately judged, especially to alert for retrograde intussusception, and the relevant intestinal collaterals in the abdominal cavity must be pulled out for inspection during surgery to prevent the necrotic intermediate intestinal collaterals hidden in the abdominal cavity from being missed. In children, because the hernia ring tissue is generally soft, strangulation rarely occurs after impaction.