Hernias can be classified according to their anatomical location:
- abdominal hernias,
- diaphragmatic hernias and hiatal hernias (for example, paraesophageal hernia of the stomach)
- pelvic hernias, for example, obturator hernia
- anal hernias
- hernias of the nucleus pulposus of the intervertebral discs
- intracranial hernias
- Spigelian hernia
Each of the above hernias may be characterized by several aspects:
congenital or acquired: congenital hernias occur prenatally or in the first year(s) of life, and are caused by a congenital defect, whereas acquired hernias develop later on in life. However, this may be on the basis of a locus minoris resistantiae (Lat. place of least resistance) that is congenital, but only becomes symptomatic later in life, when degeneration and increased stress (for example, increased abdominal pressure from coughing in COPD) provoke the hernia.
complete or incomplete: for example, the stomach may partially or completely herniate into the chest.
internal or external: external ones herniate to the outside world, whereas internal hernias protrude from their normal compartment to another (for example, mesenteric hernias).
intraparietal hernia: hernia that does not reach all the way to the subcutis, but only to the musculoaponeurotic layer. An example is a Spigelian hernia. Intraparietal hernias may produce less obvious bulging, and may be less easily detected on clinical examination.
bilateral: in this case, simultaneous repair may be considered, sometimes even with a giant prosthetic reinforcement.
irreducible (also known as incarcerated): the hernial contents cannot be returned to their normal site with simple manipulation.
If irreducible, hernias can develop several complications (hence, they can be complicated or uncomplicated):
strangulation: pressure on the hernial contents may compromise blood supply (especially veins, with their low pressure, are sensitive, and venous congestion often results) and cause ischemia, and later necrosis and gangrene, which may become fatal.
obstruction: for example, when a part of the bowel herniates, bowel contents can no longer pass the obstruction. This results in cramps, and later on vomiting, ileus, absence of flatus and absence of defecation.
dysfunction: another complication arises when the herniated organ itself, or surrounding organs, start to malfunction(for example, sliding hernia of the stomach causing heartburn, lumbar disc hernia causing sciatic nerve pain, etc.).