The acute abdomen

The abdominal survey

 

Technique of examination

No special preparation for the study is necessary but the patients will commonly already have a gastric tube and a urinary catheter in situ. The survey, preferably using full-size images includes:
A. vertical beam images with the patient in the supine (Fig. 2), left
(Fig. 3) and right lateral oblique (Fig. 4) positions, including the diaphragmatic and inguinal regions (Fig. 5), and

a	Figure 1. a) AP plain film in a patient with vomiting, showing gas in the gastric antrum to the left of the vertebral column, in the bulb to the right of the vertebral column, in distal loops of the ileum and in the left colonic flexure. b) Follow-through study 90 minutes after the ingestion of 200 ml of diluted barium suspension. The distended, proximal duodenal loop and the gastric retention indicate a mid-duodenal obstruction. c) Abdominal CT of the same patient verifies a large duodenal carcinoma which has almost obliterated the lumen. d) Abdominal ultrasound of the same tumour prior to a fine needle puncture. The carcinoma is seen as an hypoechoic mass lesion.
b
c
d

 

Figure 2. Frontal, supine, abdominal film showing a normal distribution of gas and normal haustra in the large bowel. The ilio-psoas muscles (1) and the kidneys (2) are outlined by fatty tissue.

 

Figure 3. Left oblique vertical beam plain film of the left hypochondrium in a patient with numerous areas of pancreatic calcification. The left ilio-psoas muscle and left kidney are clearly outlined.

 

Figure 4. Right oblique vertical beam plain film of the lateral abdominal wall showing fat between the abdominal wall muscles (white arrow) and around the lower border of the right lobe of the liver (arrowheads). Benign rib calcification is seen underneath the right breast.

 

Figure 5. Frontal pelvic survey in a patient with a left inguinal hernia (1) with signs of obstruction in a dilated proximal loop of ileum with swollen mucosal folds, often compared to fingerprints (2). The urinary bladder (arrows) is delineated by fat.

Figure 6. Frontal, horizontal beam plain film in an erect patient with a collection of free gas lInderneath the right hemi-diaphragm. In order to disclose even smaller amounts of subphrenic air, a spot film with tight con ing should be centred at the diaphragmatic level.

B. horizontal beam images with the patient erect, to demonstrate the subphrenic spaces (Fig. 6), or in the right and left decubitus positions, to demonstrate the paracolic and parahepatic and spaces. In patients with acute colitis one supine view usually suffices, which can be enhanced if necessary by minimal air insufflation of the large bowel (pneumocolon, see below).

Image interpretation

In order to recognize pathology, a knowledge of normal abdominal anatomy is essential. Areas of calcification, soft-tissue mas ses and fluid collections have to be interpreted with the full knowledge of the patient's history and in close collaboration with the referring clinician.

Fat spaces

As fat is more radiolucent than blood, muscle and solid organs such as the liver, spleen and kidney, it is depicted as dark grey areas on the radiograph. Fat is found along the abdominal wall and ilio-psoas muscles, in the paracolic spaces (Fig. 4), in the retroperitoneum and in the mesentery. It also envelopes the kidneys, urinary blader and rectum, thereby delineating these structures and the displacement or abolition ofthese fat spaces may indicate the presence of pathology.

Gas collections

Gas is seen as dark black areas on the radiograph, and is normally present in the stomach, large bowel (Fig. 2) and rectum. Gas may also be
found in small bowel loops if the patient is suffering from pain or is under mental stress. Deviations from the normal appearances are seen as abnormally distributed or abnormally large collections of gas either within the lumen, indicating obstruction (Fig. 5), or outside the bowel as a result of perforation (Fig. 6).

 

Normally, there is some saliva and gastric juice, as well as gas in the stomach and this results in an air-fluid level which is seen on horizontal beam films lying just underneath the left hemi-diaphragm close to the midline. Every other air-fluid level found may signify an abnormality, see below under "obstruction".

Calcification

The chondromatous part of the ventral thoracic cage may already contain are as of calcification in healthy, young adults (Fig. 4). If there is any doubt an oblique view will disclose the extra-abdominal location of such calcification.

Intra-abdominal, well-defined, shell-like, benign areas of calcification may be found along the midline representing calcified lymph nodes or, lying centrally in the true pelvis, may be seen in the myomatous uterus.

Punctate calcification may be found in the prostatic gland in elderly men, or in phleboliths, often symmetrically distributed in the true pelvis. The latter may be difficult to differentiate from a stone in the ureter; as a general rule, however, phleboliths are doughnut-like whereas urinary tract stones are oval in shape and homogeneous. In the elderly a varying amount of calcification may be seen in the aorta and in the iliac and splenic arteries.

Bowel content

Bowel content is recognized by its rich content of tiny air bubbles. It is seen as amorphous masses in the right side of the colon and more formed collections in the left colon and rectum. It has to be differentiated from an abscess which may have the same feature of multiple, tiny air bubbles.

The small and large bowel

The diameter of the colon is in general greater than that of the small bowel which is located in the mid-abdomen and surrounded by the colon. When the small bowel is air fille d it is recognized by its 1-2 mm folds running spirally from one side to the other (Fig. 1 b), while the large bowel folds are broken, forming the typical haustra (Fig. 2). The outer contour of the normal gut is convex.

The parenchymal organs
The liver is seen as an homogeneous soft-tissue structure beneath the right hemidiaphragm. Its right lower tip stretches down to the iliac crest and is demarcated by fat (Fig. 4).

In most patients the kidneys are outline d by pararenal fat. The right kidney is usually located somewhat caudad to the left. The spleen is situated laterally just under the left hemi-diaphragm but is sometimes obscured by the stomach and colonic flexure. The normal pancreas, adrenal and prostate are invisible on the plain film as is the normal uterus, but calcified myomata are often present. The normal gallbladder is not seen on plain films whereas the urinary bladder is delineated by fat in the perineum and lateral pouches of Retzius (Fig. 5). 

 

David J. Allison, Olle Ekberg and Frans-Thomas Fork