From the North Penn Hernia Institute
Hernias are, by definition, a defect in the muscle container of the abdominal wall. That is, they are a gap, hole or defect in the abdominal wall. As a result of this hole or defect, the contents of the abdominal cavity, such as intestine, fat and other organs, may tend to be push through this hole by the normal pressure that occurs within the abdomen. As this material pushes through the hernia defect, a bulge or localized area of swelling will become evident beneath the skin of the abdominal wall. Since there are many Types of hernias, the site of this bulge will vary according to the type of hernia and location of the hole or defect. With activity such as exercise, coughing, lifting and straining etc., the pressure within the abdomen increases. As a result, more abdominal contents tend to push through the hernia defect, and the bulge gradually increases in size.
Pain occurs from hernias for several reasons, and can and does often vary in character (sharp, dull, burning etc.) and severity from patient to patient. Pain can occur because the tissue at and around the hole is being stretched or torn and therefor in some fashion damaged. This usually will cause pain directly at the site of the hernia and is Localized Pain. Pain may also occur as a result of irritation of or damage to area nerves as a result of the hernia and its contents pushing into or pinching the nerves. This too may cause localized pain, or may cause pain at a more distant area and is called Referred Pain. If the abdominal contents have become trapped or damaged within the confines of the hernia, as is the case with hernia Incarceration or Strangulation, the pain may well become more generalized in location and may even involve the entire abdomen if secondary peritonitis develops.
Pain, localized to the area of the hernia defect itself is usually the result of stretching and tearing of the abdominal wall tissue such as the area muscle and tendon.As the bulge increases, this pain tends to be more intense. As the bulge reduces, and the contents of the hernia fall back into the abdominal cavity itself, the pain reduces or perhaps even disappears, only to recur again as the hernia once again protrudes. The character of the pain varies. It may be a severe, intense and sharp type pain, or it may be only a dull ache in the area. Other potential characteristics include burning, stinging and "raw sensation" type of pain.
If the contents of the hernia become trapped or Incarcerated, the intestine's blood supply may become compromised or shut off. Tissue within a hernia who's blood supply is pinched off is said to be Strangulated. As a result of Strangulation, because of a lack of blood and oxygen, this tissue will progressively die. This may, in addition to causing localized pain, cause a more Generalized pain throughout the abdomen. This pain is relatively severe and unremitting, but at times also has 'colicky' over-current episodes of discomfort. Unlike the pain associated locally with the hernia, this pain is not at all relieved by rest.
If the hernia irritates, inflames or damages nearby nerves, the pain felt from the hernia may not be at the site of the hernia, but rather at the area to which these nerves are traveling. For example, pain from an Inguinal Hernia may be felt as discomfort in the scrotum of men or the labia of women, or the back, upper leg and /or hip area. This is because nerves that supply sensation to these remote areas travel through the inguinal canal (site of the hernia) and may therefore be irritated or inflamed by the hernia itself.
When intestine becomes trapped within the hernia (Incarceration), the normal flow of food through the intestine becomes blocked. This creates a progressive back-up within the intestine and may result in nausea and vomiting. If, as a result, the intestine is only partially blocked, nausea (without vomiting) and poor appetite may be the result.
If any portion of the intestine is contained within the hernia, the normal flow of food contents and subsequently feces can becomed slowed or even completely blocked. When this occurs, the patient may develop constipation.. Severe cases of intestinal blockage within a hernia can occur when a hernia becomes incarcerated. This often necessitates urgent or emergent surgery.
If the bladder becomes entrapped within a hernia (usually an Inguinal Hernia, but also possibly a Femoral Hernia), urinary symptoms such as hesitancy, frequency, urinary burning, frequent infections, bladder stones etc., may all occur.