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==Description==
==Description==
A hernia is defined as the displacement of an organ through a normal aperture (a true hernia) or pathological aperture (false hernia or rupture). The mobile organs of the abdomen are most commonly displaced through hernias involving the abdominal wall, diaphragm, inguinal canal or femoral canal.
[[Image:hernial sac.jpg|thumb|right|150px|Diagram of a hernial sac (Courtesy of Elspeth Milne)]]
A hernia is defined as the displacement of an organ through a normal aperture (a '''true hernia''') or pathological aperture ('''false hernia''' or '''rupture'''). The mobile organs of the abdomen are most commonly displaced through apertures in the abdominal wall, diaphragm, inguinal canal or femoral canal.
In a true abdominal hernia, the displaced organs are contained within a hernial sac which consists of the parietal peritoneum together with any overlying soft tissues. In an external hernia, the skin would form the outermost layer and the hernial sac and its contents would be palpable. Since the parietal peritoneum is torn when ruptures occur, these do not have defined hernial sacs.
In a true abdominal hernia, the displaced organs are contained within a '''hernial sac''' which consists of the parietal peritoneum together with any overlying soft tissues. In an '''external hernia''', the skin forms the outermost layer and the hernial sac and its contents are be palpable. '''Internal hernias''' involve an aperture within the abdominal cavity. Since the parietal peritoneum is torn when ruptures occur, these do not have defined hernial sacs.
Hernias may be congenital or acquired. Congenital hernias usually result from a failure of physiological apertures (such as the umbilical canal) to close fully during embryonic or neonatal development whereas acquired hernias may be related to trauma, wounds or to physiological weakening of tissues with age, pregnancy or chronic straining.
Hernias may be '''congenital''' or '''acquired'''. Congenital hernias usually result from a failure of physiological apertures (such as the umbilical canal) to close fully during embryonic or neonatal development whereas acquired hernias may be related to trauma, wounds or to physiological weakening of tissues with age, pregnancy or chronic straining.
==Pathogenesis==
==Pathogenesis==
The sequelae of a hernia depend on whether the hernia is reducible and if the herniated organs are incarcerated or strangulated.
The sequelae of a hernia depend on whether the hernia is reducible and if the herniated organs are incarcerated or strangulated.