Plain X-rays of the chest and abdomen are chiefly used in the investigation of an acute abdomen including patients presenting with acute colitis. Analysis of gas shadows gives information about the bowel. Areas of calcification can be seen in chronic pancreatitis. Faecal loading is seen in constipation.

Ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI)

These techniques are used to define the intra-abdominal organs (e.g. liver, spleen, pancreas) but also to detect thickened bowel, masses, abscesses or fistulae. Ultrasound is often performed first as it is cheap and easy to perform although very operator dependent.

• Ultrasound. This involves no exposure to radiation and is the first-line investigation for the liver, gall bladder, spleen and pancreas. It will show dilated fluid-filled loops of bowel where there is obstruction, and thickening of the bowel wall when inflamed or infiltrated. It is valuable when ascites is suspected or when there is suspicion of abscess when it can be used to guide percutaneous drainage. In the acute abdomen, ultrasound can diagnose cholecystitis, appendicitis, enlarged mesenteric glands and other inflammatory conditions.
• Endoscopic ultrasound (EUS). A gastroscope incorporating a high-frequency ultrasound probe at the tip is used to assess abnormalities arising in the oesophageal or gastric wall. It is particularly valuable in the detailed staging of oesophageal/gastric cancer, including detection of local lymph nodes. It is also a sensitive technique for detection of small pancreatic tumours.
• Endoanal ultrasonography involves the passage of a transducer into the rectum. It is used to define the anatomy of the anal sphincters, to detect perianal disease and to stage rectal carcinomas.
• Computed tomography. CT, particularly thin-section spiral CT, gives excellent anatomical definition. Modern multi-slice fast scanners are also able to evaluate the vascularity of an abnormality using intravenous contrast. The bowel wall and mesentery are well seen, together with the retroperitonal structures. It is used as a first-line investigation for the acute abdomen in many centres. Small volumes of gas from a perforated viscus can be detected as well as leakage of contrast from the gut lumen. Abscesses, appendicitis, diverticulitis, Crohn’s disease and its complications can be demonstrated as well as the presence and cause of high-grade bowel obstruction. It is widely used in cancer staging and as guidance for fine-needle biopsy of tumour or lymph nodes. CT pneumocolon/CT colonography (virtual colonoscopy) involves air insufflation into the colon after colon preparation and provides a valuable alternative for evaluation of colon mass lesions. It is being used as a screening test for colon cancer with sensitivities of over 90% for > 10 mm polyps
• Magnetic resonance imaging. MRI has the advantage of using no ionizing radiation. It is particularly useful in the evaluation of abscesses and fistulae in the perianal region and its use is evolving in the evaluation of luminal gut disease. MRI is used more in hepatobiliary and pancreatic disease.
• Positron emission tomography (PET) after fludeoxyglucose F18 is used for staging oesophageal, gastric and colorectal cancer and in the detection of metastatic and recurrent disease.

A general examination is performed, with particular emphasis on the examination of all lymph nodes and noting the presence of anaemia or jaundice. Detailed examination of the gastrointestinal tract starts with the mouth and tongue, before examining the abdomen with the patient lying flat.

Examination of Abdomen

Inspection

Abdominal distension, whether due to flatus, fat, fetus, fluid or faeces, must be looked for. Lordosis may give the appearance of a distended abdomen; it is a common feature of the ‘abdominal distension’ seen in functional bowel disorders.

Palpation

The abdominal organs may be felt in some normal subjects but this is not common and such organs are usually only just palpable. A Reidel’s lobe is an extension of the lateral portion of the right lobe of the liver and can occasionally be palpated.

Any palpable mass is carefully felt to decide which organ is involved and also to evaluate its size, shape and consistency and whether it moves with respiration. The hernial orifices should be examined if intestinal obstruction is suspected.

A succussion splash suggests gastric outlet obstruction if the patient has not drunk for 2-3 hours; the splash of fluid in the stomach can be heard with a stethoscope laid on the abdomen when the patient is moved.

Percussion

This is performed in the usual way to detect the area of dullness caused by the liver and spleen, and possibly bladder enlargement. The presence of fluid in the peritoneal cavity (i.e. ascites) is detected by shifting dullness. The percussion note changes from resonance to dullness when the patient is moved from one side to the other. It is a good physical sign, but 1-2 L of fluid must be present to elicit it. A large ovarian cyst can sometimes produce an enlarged abdomen, but the dullness is more centrally placed than in ascites.

Auscultation

Auscultation is not of great value in gastrointestinal disease, apart from in the evaluation of the acute abdomen. Abdominal bruits are often present in normal subjects, but these are not clinically significant.