Plain Abdomen & Gastrointestinal Tract (OESOPHAGUS)

By: Khashayar Cyrus

The standard plain film of the abdomen is a supine anteroposterior

Free intraperitoneal air can be seen on an erect chest radiograph (CXR), which is usually performed at the time of the abdominal x-ray. Rarely, in patients who are unable to sit or stand, a lateral decubitus view (i.e. an AP film with the patient lying on his or her side) is performed using a horizontal x-ray beam as a means of detecting free intraperitoneal air

looking at a plain abdominal film: • Analyze the intestinal gas pattern and identify any

dilated portion of the gastrointestinal tract. • Look for gas outside the lumen of the bowel. • Look for ascites and soft tissue masses in the abdomen

and pelvis. • If there are any calcifications, try to locate exactly

where they lie. • Assess the size of the liver and spleen.

Intestinal gas pattern: Relatively large amounts of gas are usually present in

the stomach and colon in a normal patient. The stomach can be readily identified by its location above the transverse colon, by the band-like shadows of the gastric rugae in the supine view. The duodenum often contains air and there may be some gas in the normal small bowel, but it is rarely sufficient to outline the whole of a loop. If the bowel is dilated it is important to try and decide which portion is involved.

Dilatation of the bowel: Dilatation of the bowel is the cardinal plain film sign of

intestinal obstruction, and the pattern of dilatation is the key to the radiological distinction between small and large bowel obstruction. In small bowel obstruction, the small intestine is dilated down to the point of obstruction and the bowel beyond this point is either empty or of reduced calibre.

In large bowel obstruction, the large bowel is dilated down to the level of obstruction. If the ileocaecal valve, where the ileum joins the colon, is incompetent, there will also be small bowel dilatation. Making the distinction between large and small bowel obstruction depends on the ability to recognize which portions of bowel are dilated.Dilated small bowel usually lies in the centre of the abdomen within the ‘frame’ of the large bowel (but the sigmoid and transverse colon may be redundant and may also lie in the centre of the abdomen, particularly when dilated). When the proximal and mid small intestine are dilated, the valvulae conniventes (plica circulares) can be identified. The valvulae conniventes are always closer together and cross the width of the bowel (the colonic haustra do not), often giving rise to an appearance known as a ‘stack of coins’The distal small intestine has a relatively smooth outline and it may be difficult to distinguish the lower ileum and the sigmoid colon because both may be smooth in outline. The radius of curvature of the loops is sometimes helpful: the tighter the curve, the more likely the loop is to be dilated small bowel.The colon is recognized by its haustra, which usuallyform incomplete bands across the colonic gas shadows.Haustra are always present in the ascending and transverse colon, but may be absent distal to the splenic flexure. The presence of solid faeces is a useful and reliable indication of the position of the colon.

A. B.

If the cause or site of the obstruction is not evident from plain films, and immediate exploratory surgery is not indicated,then computed tomography (CT) or a contrast study(either a follow-through for small bowel obstruction or instant enema for large bowel obstruction) is helpful. CT can demonstrate the site of obstruction by showing the location of the transition from dilated to collapsed bowel, and can confirm or exclude a mass at the site of obstruction

Dilatation of the bowel occurs in a number of conditions. In remembering causes of mechanical bowel obstruction it is often easiest to think of conditions that: (i) obstruct the lumen (e.g. gall stone ileus); (ii) affect the bowelwall and cause a narrowing (e.g. Crohn’s disesase; or (iii)cause extrinsic compression of the bowel (e.g. adhesions).Bowel dilatation, however, occurs in conditions other than mechanical bowel obstruction, notably: paralytic ileus,acute ischaemia and inflammatory bowel disease. The radiologicaldiagnosis of these phenomena depends mainly onthe pattern of distribution of the dilated loops

paralytic ileus Mechanical obstruction of the small bowel

Mechanical obstruction of Closed loop obstruction the large bowel

Toxic dilatation of the colon

Pneumoperitoneum The radiological diagnosis of perforation of the

gastrointestinal tract is based on recognizing free gas in the peritoneal

cavity (pneumoperitoneum) The most common cause of spontaneous pneumoperitoneum is a perforated peptic ulcer and two-thirds of such cases are recognizable radiologically. The largest quantities of free gas are seen after colonic perforation, and the smallest amounts with leakage from the small bowel. A pneumoperitoneum is very rare in acute appendicitis even if the appendix has perforated.Free intraperitoneal air is a normal finding after laparotomy or laparoscopy. In adults, all the air is usually absorbed within 7 days. In children, the air absorbs much faster, usually within 24 hours. An increase in the amount of airon successive films indicates continuing leakage of air.

Pneumoperitoneum under the right hemidiaphragm is usually easy to recognize on an erect CXR as a curvilinearcollection of gas between the line of the diaphragm and the opacity 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 the colon. Gas in these organs may mimic free intraperitonealair when none is present.

Gas in an abscess Gas in an abdominal or pelvic abscess produces a very variable

pattern on plain films. It may form either small bubbles or larger collections of air, both of which could be confused with gas within the bowel. Fluid levels in abscesses may be seen on a horizontal x-ray film. As abscesses are mass lesions, they displace the adjacent structures; for example, the diaphragm is elevated with a subphrenic abscess, and the bowel is displaced by pericolic and pancreatic abscesses. A pleural effusion or pulmonary collapse/ consolidation are very common in association with subphrenic abscess. Ultrasound and CT are extensively used to evaluate abdominal abscesses

Gas in the wall of the bowel Numerous spherical or oval bubbles of gas are seen in

the wall of the large bowel in adults in the benign condition known as pneumatosis coli. Linear streaks of intramural gas have a more sinister significance as they usually indicate infarction of the bowel wall. Gas in the wall of the bowel in the neonatal period, whatever its shape, is diagnostic of necrotizing enterocolitis a disease that

is fairly common in premature babies with respiratory problems.

Gas in the biliary system Gas in the biliary system is seen on plain films following

sphincterotomy or anastomosis of the common bile duct to the bowel (Fig. 5.10). It is also seen with a fistula from erosion of a gall stone into the duodenum or colon, or following penetration of a duoden al ulcer into the common bile duct.Gas may be seen, very occasionally, in the wall or lumenof the gall bladder in acute cholecystitis from gas-forming organisms

Ascites Small amounts of ascites cannot be detected on plain

films. Larger quantities separate the loops of bowel from one another and displace the ascending and descending colon from the fat stripes, which indicate the position of the peritoneum along the lateral abdominal walls The loops of small bowel float to the centre of the abdomen In practice, plain films are of very limited value in the diagnosis of ascites as the signs are so difficult to interpret confidently except when a large amounts of ascites is present. Ascites is readily recognized at ultrasound or CT

Abdominal calcification An attempt should always be made to determine the

nature of any abdominal calcification. The first essential is to localize the calcification, as once the organ of origin is known the pattern or shape of the calcification will usually limit the diagnosis to just one or two choices The most common calcifications are of little or no significance to the patient; most are phleboliths, calcified lymph nodes, costal cartilages and arterial calcification. Calcifications in the abdomen are likely to be one of the following:

Pelvic vein phleboliths:

Calcified mesenteric lymph nodes:

Vascular calcification:

Uterine fibroids

Malignant ovarian masses:

Adrenal calcification

Liver calcification Splenic calcification

Pancreatic calcification

Faecoliths

Liver and spleen Substantial enlargement of the liver has to occur before

it can be recognized on a plain abdominal film. As the liver enlarges it extends well below the costal margin, displacing the hepatic flexure, transverse colon and right kidney downwards and displacing the stomach to the left. The diaphragm may also be elevated Occasionally, there is a tongue-like extension 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 generalized liver enlargement.As the spleen enlarges, the tip becomes visible in the left

Abdominal and pelvic masses Attempting to diagnose the nature of an abdominal mass on a

plain film is notoriously difficult, and ultrasound, CT or magnetic resonance imaging (MRI) are the appropriate imaging modalities. The site of the mass, the displacemen of adjacent structures and the hpresence of calcification are important diagnostic signs but plain films are unable to distinguish between solid and cystic masses.An enlarged bladder can be seen as a mass arising from the pelvis, displacing loops of bowel. In females, uterine and ovarian enlargements also appear as masses arising from the pelvis. Ovarian cysts can become very large, almost filling the abdomen and displacing the bowel to the sides of the abdomen (Fig. 5.19). An ovarian dermoid cyst can be readily identified on a plain film due to its content of low attenuation fat and often the presence of other mesenchymal structures within it, such as teeth.Retroperitoneal tumours and lymph nodes, when large,become visible on plain films. Renal masses, especially cysts and hydronephrosis, can become large and appear as masses in the flank. With retroperitoneal masses the outline of the psoas muscle may become invisible.

Gastrointestinal TractImaging techniques: general

principlesContrast examinationsComputed tomographyUltrasound examinationsMagnetic resonance imagingNuclear medicine

OESOPHAGUSPlain films: Plain films do not normally show the oesophagus unless it is very

dilated (e.g. achalasia), but they are of use in demonstrating an opaque foreign body such as a bone lodged in the oesophagus Plain films are also used to check the position of a nasogastric tube, to ensure that thetube travels down through the oesophagus and into the stomach, rather than down into one of the main bronchi or an oesophageal pouch

Barium swallow examination The patient swallows a gas-producing agent to distend

theoesophagus, followed by barium, and its passage down the oesophagus is observed on a television monitor. Films are taken with the oesophagus both full of barium to show the outline, and following the passage of the barium to show the mucosal pattern.The oesophagus has a smooth outline when full of barium. When empty and contracted, barium normally lies in between the folds of mucosa, which appear as three or four long, straight, parallel lines Peristaltic waves can be observed during fluoroscopy.They move smoothly along the oesophagus to propel the barium rapidly into the stomach. It is important not to confuse a contraction wave with a true narrowing: a narrowing is constant whereas a contraction wave is transitory.Sometimes the contraction waves do not occur in an orderly fashion but are pronounced and prolonged, giving the oesophagus an undulated appearance (Fig. 6.6). These socalled tertiary contractions usually occur in the elderly, and in most instances they do not give rise to symptoms.Occasionally, tertiary contractions cause dysphagia.Endoscopy is the primary investigation in patients with dysphagia.

Normal oesophagus barium has passed Tertiary contractions

Computed tomograpphy Computed tomography is used in the staging of

carcinoma of the oesophagus. The primary function of CT is to detect distant disease (e.g. lung, liver or bone metastases), and although it does give information on local staging, this is more accurately performed by endoscopic ultrasound

Fluorodeoxyglucose positron emission tomography/computed tomography

In patients with oesophageal carcinoma who have potentially curable disease, an FDG-PET/CT study is performed to identify any occult metastases prior to undertaking either surgery or definitive chemoradiotherapy.

Oesophageal abnormalitiesStrictures of the oesophagusDilatation of the oesophagus

Strictures of the oesophagus: Oesophageal carcinoma

Peptic strictures

Achalasia

Corrosive strictures

Benign tumoursOther medistinal masses

Anomalous right subclavian artery

Dilatation of the oesophagus

There are two main types of oesophageal dilatation –obstructive and non-obstructive:

Dilatation due to obstruction is associated with a visible stricture. The patient with a carcinoma usually presents with dysphagia before the oesophagus becomes very dilated.On the other hand, a markedly dilated oesophagus indicates a very longstanding condition, usually achalasiaor occasionally a benign stricture.

Dilatation without obstruction occurs in scleroderma.The disease involves the oesophageal muscle, resulting in dilatation of the oesophagus, which resembles an inert tube with no peristaltic movement so that barium does not flow from the oesophagus into the stomach unless the patient stands upright.

Other abnormalities of the oesophagus

oesophageal web

Oesophageal diverticula

oesophageal atresia