Gastrointestinal tract

Published on 12/06/2015 by admin

Filed under Radiology

Last modified 12/06/2015

Print this page

rate 1 star rate 2 star rate 3 star rate 4 star rate 5 star
Your rating: none, Average: 0 (0 votes)

This article have been viewed 1910 times

3

Gastrointestinal tract

Introduction to contrast media

Barium

Barium suspension is made up from finely ground barium sulphate (the contaminant barium carbonate is poisonous). The particles of barium must be very small (in the range of 1 µm) to make them more stable in suspension. To prevent the particles clumping a non-ionic suspension medium is used. The resulting solution has a pH of 5.3 which makes it stable in gastric acid.

There are many varieties of barium suspensions in use. Ingredients are designed to optimise mucosal coating and to make it palatable. In most situations the preparation will be diluted with water to give a lower density (Table 3.1) and must be shaken well immediately before use.

Table 3.1

Barium suspensions and dilutions with water to give a lower density

Proprietary name Density (w/v) – use
Baritop 100 100% – all parts gastrointestinal tract
EPI-C 150% – large bowel
E-Z-Cat 1–2% – computed tomography of gastrointestinal tract
E-Z HD 250% – oesophagus, stomach and duodenum
E-Z Paque 100% – small intestine
Micropaque DC 100% – oesophagus, stomach and duodenum
Micropaque liquid 100% – small and large bowel
Micropaque powder 76% – small and large bowel
Polibar 115% – large bowel
Polibar rapid 100% – large bowel

Examinations of different parts of the gastrointestinal tract require barium preparations with differing properties:

1. Barium swallow, e.g. Baritop® 100% w/v or E-Z HD® 200–250% 100 ml (or more, as required).

2. Barium meal, e.g. E-Z HD® 250% w/v. A high-density, low-viscosity barium is required for a double-contrast barium meal to give a good thin coating that is still sufficiently dense to give satisfactory opacification. It also contains simethicone (an anti-foaming and coating agent) and sorbitol (a coating agent).

3. Barium follow-through, e.g. E-Z Paque® 60–100% w/v 300 ml (150 ml if performed after a barium meal). This preparation contains sorbitol, which produces an osmotic hurrying and is partially resistant to flocculation.

4. Small bowel enema, e.g. either one 300 ml can of Baritop 100% w/v or two tubs of E-Z Paque made up to 1500 ml (60% w/v). N.B. As the transit time through the small bowel is relatively short in this investigation, there is a reduced chance of flocculation. This enables the use of barium preparations which are not flocculation-resistant. Gastrografin can be added to the mixture as this may help reduce the transit time still further.

5. Barium enema, e.g. Polibar 115% w/v 500 ml or more, as required. Reduced density between 20% and 40% w/v for single contrast examinations.

Complications

1. Perforation. The escape of barium into the peritoneal cavity is rare. If large amounts enter the peritoneal cavity it is extremely serious and will produce pain and severe hypovolaemic shock. Treatment should consist of aggressive intravenous fluid resuscitation, emergency surgery with copious washout and antibiotics. A 50% mortality rate is quoted and of those that survive, 30% will develop granulomata and peritoneal adhesions. Intramediastinal barium also has a significant mortality rate. It is imperative that a water-soluble contrast medium be the initial agent used for any investigation in which there is a risk or suspicion of perforation.

2. Aspiration. Aspirated barium is relatively harmless. Sequelae include pneumonitis and granuloma formation. Physiotherapy is the only treatment required (for both aspirated barium and low osmolar contrast material (LOCM)), and should be arranged before the patient leaves hospital.

3. Intravasation. This very rare complication may result in a barium pulmonary embolus, which carries a mortality of 80%.

For further complications (e.g. constipation and impaction), see the specific procedure involved.

Water-soluble contrast agents

There are numerous water-soluble contrast agents available. Two agents of particular note are Gastrografin® and Gastromiro®. Gastrografin is an aniseed-tasting, high osmolarity contrast agent (sodium amidotrizoate and meglumine amidotrizoate) containing a wetting agent for oral or rectal use. Although primarily used in diagnosis, its high osmolarity is exploited to help achieve bowel catharsis in CT colonography, to diagnose and treat meconium ileus and also in adhesive small bowel obstruction. Its use needs to be especially carefully monitored in the frail and the very young owing to potential profound fluid and electrolyte disturbance. It should be diluted 4–5-fold for rectal administration.

Low osmolar contrast agents may be given orally but taste unpleasant. Gastromiro, a low osmolarity contrast agent (containing iopamidol), is a more palatable orange-flavoured alternative.

Gases

1. Oesophagus, stomach and duodenum – Carbon dioxide and, less often, air are used in conjunction with barium to achieve a ‘double contrast’ effect. For the upper gastrointestinal tract, CO2 is administered orally in the form of gas-producing granules/powder (sodium bicarbonate) which when mixed with fluid (citric acid) produces gas. The requirements of these agents are as follows:

2. Large bowel – For the large bowel, room air is administered per rectum via a hand pump attached to the enema tube. Carbon dioxide can also be administered by hand pump and is said to be resorbed more quickly, cause less abdominal pain, but produce inferior bowel distension when compared to air.1 CO2 insufflating pumps are in common usage in CT colonography.

Pharmacological agents

Hyoscine-N-butylbromide (Buscopan®)

This is an antimuscarinic agent thus inhibiting both intestinal motility and gastric secretion. It is not recommended in children.

Adult dose

20 mg i.v.

The advantages of hyoscine include its immediate onset of action, relatively short duration of action (approx. 5–10 min) and its relatively low cost. Disadvantages include short-lived antimuscarinic side effects which include blurring of vision, a dry mouth, transient bradycardia followed by tachycardia and rare side effects said to include urinary retention and acute gastric dilatation. A particular side effect is that hyoscine can precipitate acute-angle closure glaucoma (AACG) in those patients who are susceptible to this because it dilates the pupil. In the UK patients who have AACG are almost always treated surgically in both eyes to prevent any recurrence. Pupillary dilatation has no role to play in the most common sort of glaucoma, open angle glaucoma, which accounts for 90% cases. Denying patients hyoscine on the basis of previous history of glaucoma is now not thought justified. Instead the following precautions are thought sufficient for the administration of hyoscine.1

Glucagon

This polypeptide hormone produced by the alpha cells of the islets of Langerhans in the pancreas has a predominantly hyperglycaemic effect but also causes smooth muscle relaxation. It is used in USA as an alternative to hyoscine which is not licensed there.

Contrast swallow

Technique

1. Start with the patient in the erect position, right anterior oblique (RAO) position to project the oesophagus clear of the spine. An ample mouthful of barium is swallowed and this bolus is observed under fluoroscopy for dynamic assessment to assess the function of the oesophagus. Then further mouthfuls with spot exposure(s) to include the whole oesophagus with dedicated AP views of the gastro-oesophageal junction.

2. Coned views of the hypopharynx should be obtained with a frame rate of 3–4 per second to include AP, lateral and oblique views whilst the patient swallows contrast.

3. The patient is placed semi-prone in a ‘recovery position’ in a left posterior oblique (LPO) position with their right arm by their side behind their back and the left arm used to support the cup containing contrast. One further swallow with a single bolus is observed under fluoroscopy to assess motility with the effect of gravity eliminated. A distended single-contrast view should be obtained as the patient rapidly sips and swallows contrast as this best identifies hernias, subtle mucosal rings and varices.

4. Modifications may be required depending on the clinical indication.

(a) If dysmotility is suspected barium should be mixed with bread or marshmallow bolus and observed under fluoroscopy correlating symptoms with the passage of the bolus in the erect position.

(b) If perforation is suspected a control film may be useful to identify pneumomediastinum and ideally the patient should be examined in four positions (prone/supine/left lateral/right lateral) with water-soluble contrast first, and if this is negative then with barium contrast.

(c) To demonstrate a tracheo-oesophageal fistula in infants, a ‘pull back’ nasogastric tube oeosphagogram may be performed if the standard oesophagogram is negative.1 This technique is particularly useful in patients known to aspirate or in ventilated patients. Suction and nursing support should be available should aspiration occur. The patient is positioned prone with the arms up and the table may be tilted slightly head down. A nasogastric tube is introduced into stomach and then withdrawn to the level of the lower oesophagus under lateral screening guidance. Ten to 20 ml of LOCM is syringed in to distend the oesophagus which will force the contrast medium through any small fistula which may be present. The process is repeated for the upper and mid oesophagus. It is important to watch for aspiration into the airway from overspill which can lead to diagnostic confusion.

Barium meal

Technique

The double contrast method (Fig. 3.1):

1. A gas-producing agent is swallowed.

2. The patient then drinks the barium while lying on the left side, supported by their elbow. This position prevents the barium from reaching the duodenum too quickly and so obscuring the greater curve of the stomach.

3. The patient then lies supine and slightly on the right side, to bring the barium up against the gastro-oesophageal junction. This manoeuvre is screened to check for reflux, which may be revealed by asking the patient to cough or to swallow water while in this position (the ‘water siphon’ test). The significance of reflux produced by tipping the patient’s head down and simultaneously drinking water is debatable, as this is non-physiological – 24-hour pH probe monitoring is the best current investigation. If reflux is observed, images are taken to record the level to which it ascends.

4. An i.v. injection of a smooth muscle relaxant (Buscopan 20 mg or glucagon 0.3 mg) may be given to better distend the stomach and to slow down the emptying of contrast into duodenum. The administration of Buscopan has been shown not to affect the detection of gastro-oesophageal reflux or hiatus hernia.

5. The patient is asked to roll onto the right side and then quickly over in a complete circle, to finish in an RAO position. This roll is performed to coat the gastric mucosa with barium. Good coating has been achieved if the areae gastricae in the antrum are visible.

Images

There is a great variation in views recommended. One scheme is:

1. Spot exposures of the stomach (lying):

From the left lateral position the patient returns to a supine position and then rolls onto the left side and over into a prone position. This sequence of movements is required to avoid barium flooding into the duodenal loop, which would occur if the patient were to roll onto the right side to achieve a prone position.

2. Spot image of the duodenal loop (lying):

An additional view to demonstrate the anterior wall of the duodenal loop may be taken in an RAO position.

3. Spot images of the duodenal cap (lying):

4. Additional views of the fundus in an erect position may be taken at this stage, if there is suspicion of a fundal lesion.

5. Spot images of the oesophagus are taken, while barium is being swallowed, to complete the examination.

Modification of technique for young children

The main indication will be to identify a cause for vomiting. The examination is modified to identify the three major causes of vomiting – gastro-oesophageal reflux, pyloric obstruction and malrotation, and it is essential that the position of the duodeno-jejunal flexure is demonstrated:

1. Single-contrast technique using 30% w/v barium sulphate and no paralytic agent.

2. A relatively small volume of barium – enough to just fill the fundus – is given to the infant in the supine position. An image of the distended oesophagus is exposed.

3. The child is turned semi-prone into a LPO or RAO position. An image is taken as barium passes through the pylorus. The pylorus is shown to even better advantage if 20–40° caudocranial angulation can be employed with an overhead screening unit. Gastric emptying is prolonged if the child is upset. A dummy coated with glycerine is a useful pacifier.

4. Once barium enters the duodenum, the infant is returned to the supine position, and with the child perfectly straight a second image is taken as barium passes around the duodenojejunal flexure. This image should just include the lower chest to verify that the child is straight.

5. Once malrotation has been diagnosed or excluded, a further volume of barium is administered until the stomach is reasonably full and barium lies against the gastro-oesophageal junction. The child is gently rotated through 180° in an attempt to elicit gastro-oesophageal reflux.

In newborn infants with upper intestinal obstruction, e.g. duodenal atresia, the diagnosis may be confirmed if 20 ml of air is injected down the nasogastric tube (which will almost certainly have already been introduced by the medical staff). If the diagnosis remains in doubt, it can be replaced by a positive contrast agent (dilute barium or LOCM if the risk of aspiration is high).

Complications

N.B. It must be emphasized that there are many variations in technique, according to individual preference, and that the best way of becoming familiar with the sequence of positioning is actually to perform the procedure oneself.

Small bowel follow-through

Contrast medium

E-Z Paque 100% w/v 300 ml usually given divided in 10–15-min increments, although some radiologists give the full 300 ml at once. The transit time through the small bowel has been shown to be reduced by the addition of 10 ml of Gastrografin to the barium. In children, 3–4 ml kg−1 is a suitable volume.

In general water-soluble small bowel contrast studies are avoided as contrast becomes diluted in small bowel fluid resulting in poor mucosal detail compared with barium. An exception is in adhesional small bowel obstruction where conservative investigation and ‘treatment’ with water-soluble contrast agents, frequently Gastrografin, may reduce the need for surgical intervention.1 In this case limited images are usually acquired at 1, 4 and 24 h, stopping once contrast is seen in the colon.

Small-bowel enema

Technique

1. The patient sits on the edge of the X-ray table. If a per-nasal approach is planned, the patency of the nasal passages is checked by asking the patient to sniff with one nostril occluded. The pharynx is anaesthetized with lidocaine spray or Xylocaine gel instilled into a nostril. The Silk tube should be passed with the guidewire pre-lubricated and fully within the tube, whereas for the Bilbao-Dotter tube the guidewire is introduced after the tube tip is in the stomach.

2. The tube is then passed through the nose or the mouth, and brief lateral screening of the neck may be helpful in negotiating the epiglottic region. The patient is asked to swallow with the neck flexed, as the tube is passed through the pharynx. The tube is then advanced into the gastric antrum.

3. The patient then lies down and the tube is passed into the duodenum. Various manoeuvres may be used alone, or in combination, to help this part of the procedure, which may be difficult:

4. When the tip of the tube has been passed through the pylorus, the guidewire tip is maintained at the pylorus as the tube is passed over it along the duodenum to the level of the ligament of Treitz. The tube is ideally passed beyond the duodenojejunal flexure to diminish the risk of aspiration due to reflux of barium into the stomach.

5. Barium is then run in, ideally with a controllable mechanical pump, or by gravity. Initially start at 50 ml min−1 and, with regular initial screening, aim to ‘chase’ the leading edge of the barium distally to maintain an unbroken column of contrast within the small bowel. The infusion can usually be increased rapidly to 100 ml min−1 depending on the progress of the barium through the bowel. If methylcellulose is used, it is infused continuously, after an initial bolus of 500 ml of barium, until the barium has reached the colon.

Buy Membership for Radiology Category to continue reading. Learn more here