RADIOLOGY

PRISCILLA MOREIRA SODRÉ, MD

Plain Abdome



The standard plain films of the abdomen are the supine and erect Ap views. An alternative in patients unable to sit or stand is to take a lateral decubitus. This views, like the erect views, utilises ahorizontal X-ray beam. The main purpose of horizontal beam is to detect air-fluid levels and free intraperitoneal air.

How to Look at a Plain Abdominal Film

  • Look for the normal amounts of gas usually present in the stomach and colon in a normal patient. The stomach can be readly identified by it's location above the transverse colon, by the band like shadows of the gastric rugae in the supine view, and by the gas fluid level beneath the left hemidiaphragm in the erect view. The duodenum often contains air and shows a fluid level. There may be some gas in the small bowel, but it is rarely suficient to outline a whole of a loop. Short fluid levels become abnormal when they are seen in dilated loops of the bowel or when they arevery numerous. If the bowel is dilated it is important to try and decide which portion is involved.

    The colon can be recognised by its haustra, which usually form incomplete bands across the colonic gas shadows. When the duodenum is dilated, the valvulae conniventes can be identified. They are closer together than the colonic haustra and across the width of the bowel, often give rise to the appearance known as "a stack of coins".

    The small bowel usually lies on centre of the abdomen with in the "frame" of the large bowel, but the sigmoid and the transverse colon are frequently very redundant and may also lie in the centre of the abdome ,particularly when dilated. Dilatation of the bowel occurs in mechanical obstruction, paralytic ileus, acute ischaemia and inflammatory bowel disease.

  • Look forany gas outside the lumen of the bowel. Its location and pattern often give valuable diagnostic information:

    Gas in The Peritoneal Cavity is most always due to perfuration of the gastrointestinal tract or follows surgical intervention in the abdomen. Air under the right hemidiaphragm is usually easy to recognise on a erect abdominal or chest film as a curvilinear collection of the gas between the line of the diaphragm and the oppaccity of the liver. Free gas under the left hemidiaphragm is more difficult to identify because of the overlapping gas shadows of the stomach and the splenic flexure of colon. Gas under the diapragm is much easier to diagnose on a erect chest film than on an upright abdominal film. If there is doubt about the presence of a pneumoperitoneum, a lateral decubitus film will show the air collected beneath the flank.

    Gas in The Abscess poduces a very variable pattern of the plain films. It may form either small bubbles or larger collections of air, both of which coud be confused with gas within the bowel. Fluid levels in abscesses may be seen on a horizontal ray film. Pleural or pulmonary shadows are very commonin association with subphenic abscesse.

    Gas in The Wall of Bowel: numerous spherical or oval bubbles of the gas are seen in the wall of the large bowel in adults in the benign condition known as pneumatosis coli. Linear streaks of intra mural gas have a more sinister significance as they usually indicate infartaction of the bowel wall. Gas in thewall of the bowel in the neonatal period, whatever its shape, is diagnostic of necrotising enterocolitis.

    Gas in The Biliary System is seen on plain films following sphincterectomy or anastomosis of the common bile duct to the bowel. It is also seen with a fistula due to erosion of a gallstone into the duodenum or colon, or following penetration of a duodenal ulcer into the common bile duct. Gas may be seen, very occasionally, in the wall or lumen of the gall bladder in acute cholecystitis due to gas-forming micro organisms.

  • Look for ascites and any soft tissue masses in the abdome and pelvis; small amounts of ascites cannot be detected on a plain films. Larger quantities separetethe loops of the bowel from one another and displace the ascending and descending colon from the fat stripes which indicates the position of the peritoneum along the lateral abdominal walls. The loops of small bowel float to the centre of the abdomen. In practice, ascites is readily recognized at ultrasound or computed tomography. Attempting to diagnose the nature of an abdominal masses on a plain film is very difficult, and resourse to ultrasound and CT is invariably necessary. The site of the mass, displacement of adjacent structures and presence of calcification are important diagnostic singsbut plain films are unable to distinguish between cystic or solid masses.

  • Look for calcification and try to locate exactly where it lies; an attempt should always be made to determine the nature of any abdominal calcification. The first essential is to localise the calcification; for this, a lateral or oblique view may be necessary. Once the organ of the origin is known, the pattern or shape of the calcification will usually limmit the diagosis to just one or two alternatives. The most common calcifications are of the little or no significance to patient. These include phleboliths calcifield lamph nodes, costal cartilages and arterial calcification. However, abdominal calcification may be associated with severe diseases; pancreatic calcification occurs in chronic pancreatitis, malignant ovarian masses occasionally contain visible calcium.

  • Identify the liver and spleen. The liver is seen as a homogeneous opacity in the right upper quadrant, usually extanding into the left upper quadrant. Occasinally, there is a tongue-like extention of the right lobe into the right iliac fossa. This is a normal variant known as a Reidl's lobe and should not be confused with generalised liver enlargement. The lower border of the liver is often difficult to see but its position can be predicted by the position of the gas in the hepatic flexure and transverse colon. Following the trauma, rupture of the spleen occurs more frequently than the liver. Ashaematoma forms the plain films may show a mass in the upper abdomen displacing adjacent structures. There may be paralytic ileus and fractures of the lower ribs may also be present. These signs, though helpful if present, are often not seen ever with significant lacerations of the liver and spleen. For this reason, ultrasound or CT is usually carried out in cases os suspected internal abdominal injury.

  • Identify the borders of the kidneys, bladder and psoas muscle: an enlarged bladder can be seen a mass arising from the pelvis displacing loops of bowel. Retro peritoneal tumours and lymph nodes, when large, become visible on plain films. Renal masses, especially cysts and hidronephrosis, can become large and appear as masses in the flank. With retroperitoneal masses the outline of the psoas muscle may become invisible.

    If you have suggestions or comments send an e-mail to Priscilla Moreira Sodré

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