ABDOMINAL IMAGING
PLAIN FILMS:
The routine projection is the supine abdominal film. This should include the diaphragms and the symphysis pubis. Other projections may sometimes be useful for diagnosis such as:
1.Erect abdomen
2.Erect CXR
3.Left Lateral Decubitus
4.Supine decubitus
5.Lateral abdomen
Erect Abdomen:
This is taken to look for fluid levels and free gas. However, fluid levels are non- specific and free gas (pneumoperitoneum) is better shown on an erect CXR. An erect film is helpful when obstruction is suspected and a diagnosis cannot be made from the supine film.
Erect CXR
An erect CXR should be part of a routine abdominal series because:
- It shows a small pneumoperitoneum more clearly than an erect abdomen. This is because in an erect abdominal film the divergent rays pass obliquely at the level of the diaphragm, which is projected to the top of the film. This part is also often over exposed. In a chest X-ray the top of the diaphragm is almost tangential to the beam.
-An acute abdomen may be complicated by chest pathology: For example:
pleural effusions in acute pancreatitis
aspiration pneumonia following prolonged vomiting
basal inflammatory changes with inflammation below the diaphragm
basal atelectasis in post operative patients and following a pulmonary embolus
heart failure especially in elderly patients
-Conversely chest pathology may mimic an acute abdomen:
Myocardial infarction
Pulmonary embolus
Pericarditis
Lower lobe pneumonia
Pneumothorax
Dissecting aortic aneurysm
Heart failure
Decubitus views
These may be useful instead of an erect film if the patient is unfit to stand. A left lateral decubitus view is taken with the patient lying on the left side. The film is placed behind the patient and the tube aimed to the centre of the abdomen. This shows fluid levels and small amounts of free air will be seen between the liver and the diaphragm. If the patient is unable to turn onto the side, a supine decubitus film may (rarely) be necessary. It will show free air but is less useful.
In babies with imperforate anus, a prone decubitus film with the buttocks elevated is sometimes taken. This however may be misleading and many centres are now using ultrasound to show the level of rectal atresia.
Lateral abdomen
This is seldom necessary but may occasionally be useful for suspected aortic aneurysm (if ultrasound is not immediately available).
An abdominal X-ray is seldom helpful in the diagnosis of chronic abdominal pain. It is of no help in the diagnosis of acute appendicitis or certain other acute conditions such as ruptured ectopic pregnancy. A normal abdominal X-ray does not exclude serious pathology and is often unhelpful. Bearing this in mind abdominal X-ray should be reserved for patients in whom it is likely to be helpful in diagnosis.
Indications:
-suspected intestinal perforation
-suspected intestinal obstruction
-renal colic ?calculus
-foreign body
Plain films are NOT indicated for the following:
-non specific abdominal pain
-gastro-enteritis
-constipation
-acute appendicitis
-urinary retention
-pancreatitis
-acute urinary tract infection
-diarrhoea
-acute peptic ulceration
-haematemesis/malaena
-biliary disease
NORMAL FEATURES:
When assessing an abdominal film, a study of three areas will cover the majority of abnormal findings: bowel gas pattern, areas of calcification, and skeletal abnormalities.
1.) The small bowel lies centrally. There should be no more than 3 short fluid levels on an erect film. There should only be small amounts of gas in the small bowel. After being swallowed air reaches the colon within 30 minutes. The jejunum is recognised by valvulae conniventes, folds which traverse the full width of the bowel. The distal ileum is smoother in appearance.
2.) The large bowel lies peripherally. There may be longer fluid levels and the maximum diameter is variable. The large bowel often contains faeces & has a speckled appearance due to gas trapped in the faeces. The haustra may be outlined by gas. It is quite common to see gas outlining much of the large bowel normally. The haustra can be recognised by the fact that they do not cross the full width of the bowel and they are not regular.
3.) The bladder may be seen as a soft tissue density arising from the pelvic floor.
4.) The stomach is normally outlined with air below the left hemidiaphragm.
5.) Calcifications may be seen that are not significant.
-Phleboliths in the pelvis – these may mimic lower ureteric stones but are more rounded in appearance. Often multiple.
-Mesenteric nodes. These are often confused with renal or ureteric calculi but they are mobile and move with posture.
-Costal cartilages. These may cast confusing shadows in the upper abdomen and may be confused with renal calculi. They can easily be distinguished by taking an oblique film.
-Prostate. Calcification is often seen in the prostate and is a normal finding. It should not be confused with a bladder calculus. It lies below the bladder, centrally.
-Seminal Vesicles. These occasionally calcify. They are serpiginous in appearance, lying behind the bladder. Calcification is commoner in diabetic patients
6.Fat lines. It is only because of the fat surrounding the internal solid organs that they are visible. The renal outlines can usually be seen, as can the psoas shadows. A fat line lying adjacent to the parietal layer of peritoneum in the flanks can sometimes be seen. This is called the properitoneal fat line
ABNORMAL FINDINGS:
1.) Pneumoperitoneum – free air within the peritoneal cavity is seen in bowel perforation and post operatively. Air rises to the highest part of the diaphragm on an erect film The stomach is distinguished from free air by the fact that it usually has a fluid level. It should not be mistaken for a pneumoperitoneum, which does not usually show a fluid level unless there is secondary infection (abscess). A pneumoperitoneum is seldom symmetrical and may be unilateral but usually there is a small one visible on the other side. When there is doubt on the erect film or if a perforation is strongly suspected and the film appears normal, a L lateral decubitus film is helpful. Small amounts of free air will rise to lie between the liver and the diaphragm and are more readily seen. It is important to wait for a few minutes after positioning the patient to allow any free air enough time to rise to the highest point.
The commonest cause of intestinal perforation in Ghana is typhoid fever. In the Western world, it is more likely to be either a peptic ulcer or diverticular disease.
Occasionally a pneumoperitoneum may be suspected on a supine film. Collections of gas may be seen in areas where the bowel does not normally lie such as overlying the liver. Also, the outer wall of the bowel may be visible in addition to the inner wall. The double wall sign. Normally the outer bowel wall is not seen as it lies against other soft tissues of similar density.
2.Excessive intestinal gas – This may be physiological - children have more gas in the bowel than adults as a result of air swallowing. Patients with dyspnoea and severe pain swallow more air and if marked the bowel may be full of gas, a condition known as “meteorism” which is most commonly seen in renal colic. Bowel gas pattern should be evaluated with particular reference to dilatation. Excessive gas and dilatation occur in ILEUS and OBSTRUCTION. The small bowel is considered to be dilated if the width exceeds 3cm. The diameter of the colon is more variable but a width of 5.5cm is definitely abnormal.
Causes of ileus include:
Post operative
Peritonitis
Inflammation of:
Pancreas
Gallbladder
Appendix
Fallopian tubes
Bowel (gastro-enteritis)
Trauma
Renal colic
Ruptured aortic aneurysm
Low serum potassium
Drugs e.g. morphia
General debility
Vascular occlusion
Uraemia
Meningitis, malaria, any acute severe infection
Features that may help in differentiation are:
-ILEUS : both large and small bowel are usually dilated
There is more gas than fluid with few fluid levels
Decreased bowel sounds on clinical examination
-OBSTRUCTION: Proximal bowel is dilated with collapsed distal bowel beyond the obstruction
More fluid levels and bowel diameter greater
Increased bowel sounds on clinical examination
Differentiation between large and small bowel obstruction can be difficult but things to look for are:
-Valvulae conniventes are seen in the jejunum
-Number of loops; small bowel obstruction usually shows many distended loops, large bowel obstruction few
-Distribution; small bowel lies central, large bowel peripheral
-Haustra : folds which as asymmetrical and not traversing the full width of the bowel indicate large bowel
-Diameter: large bowel has a greater width. In general if 3 - 5cms in diameter = small bowel. Over 5cm = large bowel.
-Radius of curvature. Small bowel has a smaller radius of curvature
-Solid faeces are seen only in large bowel.
Small bowel obstruction is often lower than suspected on plain films as the lower ileum may fill with fluid and become invisible. Gas will be seen at a higher level than the obstruction.
The large bowel signs depend on the competency of the ileocaecal valve. If the valve is competent there is a danger of caecal perforation due to ischaemia. Critical diameter is 9cm. If the valve is incompetent, the small bowel will also dilate with excess gas and the appearances look similar to ileus. Clinically obstruction of the large bowel is more insidious in onset than that of the small bowel. Sigmoid volvulus is a common cause and shows as a dilated loop of large bowel in the shape of an inverted “U” with the open end pointing towards the pelvis or left iliac fossa.
In practice, it can be very difficult to differentiate ileus from obstruction and also to correctly identify the site of an obstruction on plain films.
3. Calcification:
Abnormal intra-abdominal calcifications are common in the kidneys. Other calcifications may also occur as shown in the diagram.
-Gallstones - only 20% calcify and a plain abdomen is not indicated in cholecystitis. Ultrasound is the imaging method of choice.
-Renal tract calcification – a ureteric stone is a common cause of acute abdominal pain. Many calculi are visible on plain films, especially if over 3mm in diameter. There may be bladder wall calcification in Schistosomiasis.
-Pancreatic calcification - seen in the central upper abdomen in chronic or relapsing pancreatitis.
-Adrenal calcification – is less common but may be seen secondary to tuberculosis or in adrenal tumour.
-Tumours, fibroids – fibroids commonly calcify and show a rather mottled appearance in the pelvis, in contrast to a bladder calculus which is laminated. Ovarian tumours rarely calcify except for dermoids, which may contain recognisable teeth.
-Calcification in the liver may occur following a successfully treated amoebic liver abscess, or in a tuberculous granuloma.
-Calcification in the spleen is rare but may follow infarction in sickle cell disease.
4.Gasless abdomen:
Occasionally there will be a paucity of gas in the bowel on a plain abdominal film. Often this will be normal but other causes to consider are:
-High intestinal obstruction – gas not passing beyond to outline the bowel lumen
-Ascites
-Excessive vomiting e.g. in severe pancreatitis
-Fluid filled bowel – this may occur in small bowel obstruction and the diagnosis missed unless an erect film is taken which will show multiple very small fluid levels.
-Large abdominal mass – compressing and displacing bowel
-Normal
5.Abnormal gas shadows – gas lucencies lying outside the bowel lumen (excluding pneumoperitoneum). They are difficult to interpret but important diagnostically.
-Retroperitoneal gas - gas streaking in the retroperitoneal tissues along the psoas muscle and around kidneys. May be due to perforation of a part of bowel which is lying retroperitoneally (caecum, rectum) or be postoperative.
-Gas in the biliary tract. This has several causes:
- Gas in the bowel wall – due to ischaemia, gangrene, and impending perforation.
- Gas in the bladder lumen – vesico-colic fistula such as may occur in diverticular disease.
- Gas in the bladder wall - anaerobic infection
- Gas in the portal veins- necrotising entercolitis. Can be distinguished from gas in the biliary tree by the fact that the veins are seen extending out to the periphery of the liver whereas the bile ducts are more central.
- Abscess collections may occur anywhere. If subphrenic, they cause elevation of the diaphragm, basal lung changes, and usually show a fluid level beneath the diaphragm. Collections occurring elsewhere in the abdomen are usually missed on plain films but they may cause a mottled appearance, which looks very much like faeces in the large bowel.
7.Displaced bowel by masses. Hepatosplenomegaly is a common cause of abdominal mass. An enlarged spleen pushes the stomach gas shadow medially and displaces the left kidney downwards. Similarly, an enlarged liver displaces the hepatic flexure downwards. Other masses will also displace bowel and this is a clue as to their presence. Plain abdominal films are not indicated however for abdominal masses and ultrasound is the examination of choice
8.Abnormal bowel mucosa – this may show as “thumbprinting” due to bowel wall oedema or inflammation. The bowel outline shows indentations (scalloping) instead of having a smooth outline.
9.Fat lines – these may be displaced or lost. A bulging psoas shadow is of more significance than an absent one because they may be obscured by bowel gas and not always seen. The psoas outline is bulging or lost in rupture of an aortic aneurysm and psoas abscess.
10.Elevation of a diaphragm – this may be associated with changes below the diaphragm such as liver or splenic abscess. Liver tumour, ascites, or other abdominal masses, subphrenic abscess and rupture of the diaphragm.
11.Bony abnormality – areas of abnormality may be seen in the spine, which may be relevant to the abdominal symptoms e.g. sclerotic areas due to prostatic metastases. There may be collapse of a vertebral body or changes in the spine or hips due to sickle cell disease.
PLAIN FILMS ARE NOT ALWAYS DIAGNOSTIC AND MAY BE CONFUSING. THE NEXT IMAGING INVESTIGATION OF CHOICE IS ULTRASOUND. Ultrasound may also be the first investigation of choice rather than plain films in certain cases.
2. ULTRASOUND
Ultrasound is a first line investigation for:
1.The biliary tract
2.The liver and spleen
3.Renal Tract
4.Masses
5.Abscess
6.Intussusception
7.Ectopic pregnancy/ ovarian pathology/fibroids
8.Ascites
9.Infantile pyloric stenosis, if local expertise available
10.Aortic aneurysm
11.Pancreas (if no CT)
12.Trauma – if no CT or patient very ill
Ultrasound is also useful in:
-Inflammatory bowel disease – shows as bowel wall thickening
-Appendicitis
3. CONTRAST STUDIES OF THE GIT
These are usually performed using Barium but if perforation is suspected water -soluble contrast medium must be used. Gastrografin is the most readily available but must not be used if there is a danger of lung aspiration. In these cases, non-ionic contrast should be used.
Barium Swallow/Meal
Single contrast study
Double contrast study
Single contrast studies are performed in acutely ill patients and children. Barium sulphate is given by mouth and the patient turned into various positions to demonstrate any abnormality. Fluoroscopy should be used for all contrast investigations of the gastrointestinal tract. Double contrast examinations are now the standard for other patients. In double contrast barium meal a smaller amount of high- density barium solution is swallowed followed by granules, which release gas in the stomach. The patient is laid supine and turned through 360 degrees, to coat the gastric mucosa with barium. Buscopan may be given intravenously to allow the stomach to distend adequately making visualisation of small mucosal lesions easier.
Gastroscopy has now replaced barium studies for many disorders of the stomach and oesophagus. Gastroscopy allows a biopsy to be taken if indicated and when readily available should be used in preference to a barium study in:
-Haematemesis
-Oesophagitis
-Dyspepsia -gastric ulcer?
-Carcinoma
-Chronic duodenal ulcer for assessment of continuing activity
-Previous non recent surgery
Barium studies should still be performed initially in preference to gastroscopy in:
-Dysphagia
-Hiatus Hernia
-Complications of recent surgery
However, a properly performed double contrast examination is a very good imaging test and can replace endoscopy if the latter is not readily available. The only exception to this is haematemesis for which endoscopy should always be the first line investigation. Whether barium studies or endoscopy are used will very much depend on the local circumstances and expertise available.
Barium Swallow:
Dysphagia
This is a common symptom and a barium swallow is a simple and effective screening test. Commonly encountered conditions are:
- Pharyngeal pouch. This is a posterior mucosal protrusion arising in the upper neck just above the cricopharygeus muscle. The patient presents with dysphagia and regurgitation of food on lying down. Plain films may show a fluid level in the pouch but barium swallow is diagnostic with barium filling the pouch which is seen best in the lateral projection when the “neck” connecting it to the oesophagus can be seen.
- Hiatus Hernia - a protrusion of a portion of the stomach through the oesophageal hiatus of the diaphragm into the chest may range in size from a very small transient hernia to a thoracic stomach. They may be classified as “sliding” or “paraoesophageal”. A sliding hernia is the commonest type and occurs when the gastro-oesophageal junction (cardia) and part of the stomach slip upwards above the diaphragm. It is associated with reflux and is usually reducible unless very large. If small, it may only be demonstrated in certain positions. When transient it may not be demonstrated on barium meal at all. With a paraoesophageal hernia, the cardia remains in the normal position and part of the stomach herniates alongside it. Reflux is not a feature and this type of hernia is often irreducible (incarcerated) in which case the hernia remains permanently above the diaphragm and may show as a mass on the chest X- ray containing a fluid level.
- Oesophagitis. Inflammation of the oesophageal mucosa may be secondary to reflux, infections such as monilia, or due to accidental ingestion of a caustic solution. It causes mucosal irregularity with erosions and sometimes ulcers. Strictures may form. Benign strictures usually has smooth, tapering edges in contrast to a malignant stricture which shows an abrupt change in calibre (shouldering).
- Carcinoma. This causes a range of appearances depending on the tumour size and degree of malignancy. It is commonest in the distal third presenting as progressive dysphagia with weight loss. On barium swallow, it may present as a mass resulting in a filling defect in the lumen. If infiltrative, it results in narrowing of the lumen initially. Later there is also mucosal destruction and irregularity of the lumen.
- Functional disorders. A wide range of functional disorders occur in elderly patients. There may be disordered contractions resulting in a “corkscrew” appearance. There may be swallowing difficulties due to neuromuscular inco- ordination as a result of stroke. There is a danger of barium aspiration in these patients during the investigation. This does not usually cause any serious problems unless the patient is very debilitated or the barium of large amount. Physiotherapy is given if a significant amount of barium is aspirated into the smaller bronchi.
- Oesophageal varices: are venous anastomotic collateral veins, usually resulting from portal venous hypertension or portal vein obstruction. They commonly develop as a result of liver cirrhosis and are usually confined to the lower two thirds of the oesophagus. Endoscopy is the investigation of choice but a barium swallow can delineate the large submucosal veins in many cases. If the oesophagus is distended with barium the bulging varices may flatten against the wall and be hidden by the barium. Varices are best shown on films when the barium has passed but coated the oesophageal mucosa in its collapsed state. They show as serpiginous (worm-like) filling defects.
Barium Meal:
Abnormalities seen on barium meal examinations:
- Gastric ulcer: most commonly seen on the lesser curve but may arise anywhere. Barium collects in the ulcer crater & when seen en face on a double contrast examination shows as a pool of barium surrounded by radiating mucosal folds to the ulcer crater. In profile, it shows as an out pouching of barium from the gastric wall. Ulcers can be benign or malignant. It is not always possible to distinguish a benign from malignant ulcer on barium meal and biopsy is always recommended.
Benign ulcer: smooth radiating folds reaching the edge of the ulcer crater. In profile the ulcer crater protrudes
beyond the wall of the stomach.
Malignant ulcer: shallow, irregular in contour, thick irregular mucosal folds. In profile it does not protrude beyond the normal confines of the gastric wall. Be suspicious of ulcers on the greater curvature.
There may be surrounding mucosal destruction or a mass.
- Carcinoma of the stomach. This may present in several ways on barium meal
1. A polypoidal soft tissue mass protruding into the lumen as a filling defect
2. An ulcer which usually lies within the outline of the stomach
3. Diffuse infiltration: submucosal infiltration over a wide area leads to narrowing and rigidity of the stomach with loss of folds – a small rigid stomach. Called linitis plastica or “leather bottle stomach”
4. Local infiltration: mucosal destruction & irregularity at the site of the tumour with focal narrowing and rigidity.
- Caustic stricture of the stomach. Ingestion of caustic often results in stricture of the oesophagus, which may be extensive.
Occasionally it causes stricture in the stomach, which radiologically looks very similar to a scirrhous carcinoma.
-Gastric outlet obstruction: may be caused by
Ulcer or carcinoma of the gastric antrum
Ulceration or scarring of the duodenal cap
Pancreatic carcinoma or duodenal carcinoma involving the duodenal loop
Infantile pyloric stenosis
The stomach is distended and often grossly enlarged with resting juice and food residue. A barium meal shows a mottled appearance of the barium as it mixes with the food residue and there is either no gastric emptying or marked delay. The cause of the obstruction is often difficult to demonstrate due to the large amount of food residue present in the stomach.
Infantile pyloric stenosis is now commonly diagnosed by ultrasound but if local expertise or the correct probe frequency is not available barium meal may be necessary.
- Polyps are relatively uncommon in the stomach compared to the large bowel. They are usually benign but if in the gastric antrum may be pre-malignant. Occasionally a leiomyoma is seen in the stomach. This is a benign tumour arising from the muscle layers. On barium meal, there is a smooth well- defined mass projecting into the stomach lumen. It may ulcerate with a central ulcer crater.
-Lymphoma may affect the stomach showing as very thickened folds or a large filling defect.
-Duodenal deformity/ulceration. The most frequent site for a duodenal ulcer is the proximal part, the cap or bulb. Post bulbar ulcers may occur but are less common. Diagnosis depends on demonstration of a crater or niche, into which the barium pools. The crater may be anterior or posterior and chronic ulceration heals by scarring. This causes deformity of the cap, which often has a tri-lobed appearance if the ulcer crater is central. The scarring is permanent and reactivation of the ulcer, or ulcer healing is very difficult to detect on barium studies. Follow up of a duodenal ulcer is best done by endoscopy.
The small Intestine:
Preferably the small bowel should be targeted for a single study with suitable barium mixture rather than done as a continuation of a barium meal (a “follow through”). The high- density barium used for a satisfactory barium meal is not suitable for study of the small bowel where a larger volume of a relatively low -density barium solution is more appropriate. It is better to do this as a separate study and the examination is now referred to as a “small bowel meal”. In some patients a small bowel enema may be necessary. In this examination, a tube is placed in the 3rd part of the duodenum and barium injected followed by air or water for double contrast. It shows the small bowel in greater detail but fluoroscopy is necessary
Abnormalities which may be seen in the small bowel:
- Obstruction. Occasionally a small bowel obstruction is not obvious on plain films. This is especially likely if the obstruction is very high or if the loops are filled with fluid rather than air. A small bowel study may localise the site and cause of an obstruction. Sometimes it is preferable to use water contrast such as gastrografin rather than barium. If surgery is needed immediately, it is easier if grossly distended loops of bowel are NOT full of barium, which will cause a serious peritonitis if spilled into the peritoneal cavity.
- Malabsorption syndromes. These are best diagnosed clinically rather than by barium study although specific causes for the malabsorption may be demonstrated, such as Crohns disease. Coeliac disease causes non-specific dilatation of small bowel loops in severe cases but small bowel biopsy is much more specific. Jejunal diverticulosis, blind loops, fistulae and strictures may all cause malabsorption and are detectable on contrast studies. The features which may be seen in malabsorption are:
Dilation of the small bowel
Thickening of the valvulae conniventes
Clumping of the barium (flocculation) which does not maintain a continuous column.
- Inflammatory bowel disease e.g. Crohns disease. Inflammatory disease causes mucosal oedema with thickening of the folds, There may be strictures, and dilated loops especially in Crohns disease.
- Lymphoma may involve the small bowel. There is usually mucosal oedema together with displacement and distortion of bowel loops. Primary carcinoma of the small bowel is rare but can occur and usually presents as an obstruction.
Large bowel
Symptoms such as altered bowel habit, rectal bleeding, abdominal pain, weight loss, and anaemia may indicate colonic disease. Colonoscopy and barium studies are complementary and equally useful but the method of investigation used depends on the local circumstances. In many countries, a double contrast barium enema is combined with a flexible sigmoidoscopy in all patients with symptoms suggestive of large bowel pathology.
Barium studies require full bowel preparation and a double contrast technique is routine, unless the patient has acute inflammatory bowel disease or obstruction. In the latter two cases, the use of water soluble contrast is preferred.
A fairly high-density barium is run into the bowel per rectum as far as the hepatic flexure. Buscopan is given intravenously and most of the barium drained back. Air is then introduced by means of a Higginsons syringe causing the remaining barium to reach the caecum, the colon to fully distend with air while the mucosa is coated with barium.
Abnormalities seen on barium enema examination:
-Redundant loop of sigmoid: this is a normal variant and is common in Ghana. It predisposes to volvulus, when the loop rotates about its axis becoming obstructed. Unrelieved it may lead to bowel infarction and perforation. On barium enema, the colon is obstructed at the level of the volvulus and the contrast column tapers to give a birds beak or twisted ribbon appearance.
- Carcinoma: can occur anywhere in the colon but is commonest in the rectosigmoid area. It may develop from a polyp and present as a filling defect or it may infiltrate the bowel wall appearing as a stricture. The first presentation may be large bowel obstruction. Occasionally it may penetrate into adjacent structures such as the bladder and present as a vesico-colic fistula.
- Polyp: polyps are localised mass lesions arising from the colonic mucosa. They protrude into the lumen and may have a flat broad base (sessile) or be pedunculated on the end of a stalk. They occur anywhere in the colon. The majority are benign, especially the small or pedunculated ones. Sessile polyps are pre-malignant and the object of a double contrast study is to detect polyps before malignant transformation has occurred. Multiple polyps occur in the hereditary conditions of familial polyposis coli and Peutz-jeghers syndrome. The polyps of the former have malignant potential whereas the polyps in the latter are always benign. Pseudo-polyps may occur in long- standing inflammatory bowel disease due to areas of mucosal hypertrophy.
- Diverticular disease. Relatively uncommon in Africa, it is very common in the Western world and often leads to complications. The smooth muscle hypertrophies with pouch like protrusions between the thickened fibres. The mucosa and submucosa herniate through sites of weakness in the bowel wall. The sigmoid is the most frequently involved area but diverticulae may arise anywhere and are not uncommon in the caecum. Complications include acute inflammation with pericolic abscess, colonic perforation, fistula formation especially into the bladder and haemorrhage.
- Inflammatory bowel disease: is characterised by diffuse mucosal changes due to oedema and ulceration. It may affect the whole colon or only part of the colon. If due to Crohns disease, the distal ileum and caecum are commonly involved. A barium enema in the acute setting is seldom indicated and may be contraindicated because of the danger of perforation. A plain abdominal film may show a dilated colon outlined by air, toxic dilatation, which is an absolute contraindication to barium enema. Ulcerative colitis and Crohns disease are common in the Western World but in Africa an infective aetiology, such as Salmonella, Shigella, or Amoebiasis is more common. In the acute phase, the large bowel will show mucosal irregularity and small ulcers projecting from the wall. In the chronic stage there may just be generalised narrowing of the lumen and loss of haustration giving a “pipestem” appearance.
- Intussusception - occurs when part of the bowel invaginates on itself. The proximal bowel becomes invaginated into the lumen of the distal bowel. This may occur because of a localised lesion such as a polyp or carcinoma, which is carried by peristalsis along the bowel. As it is attached to the wall, it carries the proximal bowel with it. Most commonly however it occurs in infants between the ages of 3 months and 2 years when an inflamed Peyers (lymphoid) patch in the distal ileum is often the cause. As the bowel is carried down within the distal lumen the blood supply becomes impeded, oedema occurs and the bowel may become necrotic. It is nowadays usually diagnosed by ultrasound but if local expertise is not available, a barium enema can be performed. Sometimes it is possible to reduce an early intussusception in children by barium enema if fluoroscopy and local expertise are available. The appearances on barium enema show either as an abrupt filling defect with complete obstruction to flow, or a “coil spring” appearance with a little barium outlining oedematous folds.
- Hirschsprungs disease presents in children. The patient gives a history of severe constipation from an early age due to an aganglionic segment of large bowel, which will not distend. There may be considerable abdominal distension. The aganglionic segment may occur anywhere but is usually in the distal large bowel, in the sigmoid region. Sometimes it is very low, in the rectum. If this is the case, it may not be demonstrated on barium study as the enema tube will be inserted beyond it. The appearance on imaging is that of a distal small calibre lumen with narrowing which suddenly changes to a very dilated proximal colon loaded with faeces. This is now more commonly diagnosed by rectal biopsy, as the aganglionic segment may be too low to demonstrate on barium enema. It is important not to fill the proximal dilated bowel with barium as impaction may occur. Water soluble contrast may be used instead of barium. Only a limited examination is necessary, just to show the transition in calibre and confirm the diagnosis.
- Pseudo obstruction of the large bowel: distension of the large bowel may occur in the absence of obstruction. Plain films show progressive dilatation of the colon, resembling a mechanical obstruction. It may occur in-patients who are severely ill from diseases such as pneumonia or in elderly patients who are bed ridden. It may also occur in patients with myxoedema or patients on antidepressant drugs. A barium or water-soluble enema may be necessary to exclude an obstruction.
Complications of Barium examinations:
Although barium is a much safer contrast agent than the iodine based contrast media given intravenously, complications occasionally occur.
Contraindications to performing a barium enema
OTHER METHODS OF IMAGING THE ABDOMEN:
1.COMPUTED TOMOGRAPHY:
Computed tomography is not as readily available as ultrasound and is often a second line investigation. It is however the imaging of choice in abdominal trauma and for staging tumours.
It is used for the following conditions:
2. NUCLEAR MEDICINE:
Nuclear medicine, when available, is useful for the following:
3. Magnetic Resonance Imaging
The role of MRI is still being evaluated. It is little used for general abdominal conditions but good for specific conditions such as liver haemangiomas, staging tumours involving the uterus, bladder, and prostate. It is also good for imaging the bile ducts and pancreatic duct. It is unlikely to be available in a third world setting.