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Abdominal swelling is a manifestation of numerous diseases. Patients may complain of bloating or abdominal fullness and may note increasing abdominal girth on the basis of increased clothing or belt size. Abdominal discomfort is often reported, but pain is less frequent. When abdominal pain does accompany swelling, it is frequently the result of an intraabdominal infection, peritonitis, or pancreatitis. Patients with abdominal distention from ascites (fluid in the abdomen) may report the new onset of an inguinal or umbilical hernia. Dyspnea may result from pressure against the diaphragm and the inability to expand the lungs fully.

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The causes of abdominal swelling can be remembered conveniently by the six Fs: flatus, fat, fluid, fetus, feces, or a “fatal growth” (often a neoplasm).

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Flatus

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Abdominal swelling may be the result of increased intestinal gas. The normal small intestine contains approximately 200 mL of gas made up of nitrogen, oxygen, carbon dioxide, hydrogen, and methane. Nitrogen and oxygen are consumed (swallowed), whereas carbon dioxide, hydrogen, and methane are produced intraluminally by bacterial fermentation. Increased intestinal gas can occur in a number of conditions. Aerophagia, the swallowing of air, can result in increased amounts of oxygen and nitrogen in the small intestine and lead to abdominal swelling. Aerophagia typically results from gulping food; chewing gum; smoking; or as a response to anxiety, which leads to repetitive belching. In some cases, increased intestinal gas is the result of bacterial metabolism of excess fermentable substances such as lactose and other oligosaccharides that can lead to production of hydrogen, carbon dioxide, or methane. In many cases, the precise cause of abdominal distention cannot be determined. In some persons, particularly those with irritable bowel syndrome and bloating, the subjective sense of abdominal pressure is attributable to impaired intestinal transit of gas rather than increased gas volume. Abdominal distention, an objective increase in girth, is the result of a lack of coordination between diaphragmatic contraction and anterior abdominal wall relaxation in response to an increase in intraabdominal volume loads. Occasionally, increased lumbar lordosis accounts for apparent abdominal distention.

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Fat

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Weight gain with an increase in abdominal fat can result in an increase in abdominal girth and can be perceived as abdominal swelling. Abdominal fat may be the result of an imbalance between calorie intake and energy expenditure associated with a poor diet and sedentary lifestyle and also can be a manifestation of certain diseases such as Cushing's syndrome. Excess abdominal fat has been associated with an increased risk of insulin resistance and cardiovascular disease.

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Fluid

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Fluid within the abdominal cavity, or ascites, often results in abdominal distention and is discussed in detail below.

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Fetus

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Pregnancy results in increased abdominal girth. Typically, an increase in abdominal size is first noted at 12 to 14 weeks of gestation, when the uterus moves from the pelvis into ...

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