The gastrointestinal tract Stomach and duodenum
Imaging techniques
Contrast studies
The routine contrast examination for gastroduodenal disease is the double-contrast barium meal (DCBM); this has been found consistently superior to single contrast studies. There are many variations in technique for performance of the DCBM, but a frequently used method is a biphasic one that incorporates elements of the single contrast examination. The single contrast barium meal is occasionally justified in very elderly, sick or immobile patients and can be used to answer specific questions, such as determining the presence of gastric outlet obstruction. Water-soluble iodinated contrast media are used where there is suspected perforation or where a recent anastomosis is being tested. The commonest such contrast is 76% sodium methylglucamine diatrizoate ("Gastrografin"). However, this is contra-indicated if there is a risk of airway aspiration or suspicion of an oesophago-tracheal fistula, since its hyperosmolality can precipitate pulmonary oedema. Non-ionic iodinated contrast media are then used (or, alternatively, low-density dilute barium, with caution).
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Figure 18.
Supine double contrast view of gastric body and antrum showing mosaic-like areae gastricae.
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The aim of the DCBM is to see, by appropriate positioning, all parts of the
oesophagus, stomach and proximal
duodenum in double contrast with good mucosal
barium coating, adequate gaseous distension and hypotonia. A measure of good coating is the visualisation of the areae gastricae, which are seen as a mosaic-like pattern in the stomach (Fig. 18). These represent the areas about 1-4 mm in diameter, in the centre of which, the gastric glands open. Their visualisation depends on
radiographic technique,
barium density and the amount of mucus in the stomach. They are most often seen in the gastric antrum and body. Although controversial there is a suggestion that an increase in size of the areae and their presence in the proximal stomach are associated with increased acid production.
Focal abnormalities of the areae are more important; distortion or enlargement may be seen in
gastritis around an ulcer or due to superficial
infiltration by
carcinoma, and may be the only subtle c1ue to this. Other anatomical features seen in the stomach on DCBM include the rugal folds and the cardia. The folds in the antrum are effaced with distension by gas; if they persist this suggests antral gastitis. The rugae in the fundus and proximal body should be smooth and relatively straight in the distended stomach. The appearance of the cardia is variable; it may appear en face as a rosette which may be flat or have elevated margins; it may possess a hooded fold - the "burnaus sign"; or it may be seen as a crescentic line.
The modem biphasic barium meal should inc1ude double and single contrast oesophagograms, compression views of the gastric antrum and duodenal cap as well as double contrast images of the stomach and duodenum, and an assessment of oesophageal motility. As part of the DCBM it is important to ensure that the second and third parts of the duodenum have been outlined. It is possible to obtain good double-contrast distended views of the descending duodenum. It is rarely necessary nowadays to perform a hypotonic duodenogram using a tube method.
If the examination is being performed for suspected gastroduodenal perforation, a water-soluble contrast is used. Profile views of the filled stomach are obtained. The patient is then turned onto the right side to allow duodenal filling and turned through 360°. If no obvious extravasation of contrast is seen, the patient should remain on the right side for ten minutes or so and then re-fluoroscoped. If no perforation is seen but is still strongly suspected clinically, delayed films may show contrast excreted through the urinary tract, since Gastrografin is absorbed from the peritoneal cavity. However, this sign is not specific for perforation since inflamed or ischaemic mucosa can allow absorption and thus renal excretion.
Computed tomography (CT)
CT is useful in gastroduodenal disease for staging of neoplasms and assessment of extramural disease. The patient should be fasted so that solid food in the lumen does not cause confusion with pathological filling defects. Distension of the gut with oral contrast medium is essential. Dilute (3 %) Gastrografin or dilute barium sulphate suspension is used. As well as positive contrast, a gas- forming agent can be given to distend the stomach and duodenum. Sometimes this can be given in lieu of the final cup of contrast. A hypotonic agent may also be administered if gas is used. This distension allows recognition of wall thickening and intraluminal filling defects. If there is a suspicion of wall thickening the patient can be rescanned in a decubitus or prone position as appropriate to show the distended non-dependent wall of the viscus, for example right-side up for lesions at the cardia. Normally, a dynamic sequential scan following intravenous bolus administration of contrast is used to show vascular structures and for the identification of liver metastases. Recent CT technological advances allow helical (spiral) CT images of the upper abdomen to be obtained with a single breath-hold.
CT is also a useful technique in suspected gastroduodenal perforation, being able to detect very small volumes of free intraperitoneal gas or iodinated contrast.
Ultrasonography (US)
Conventional US has little place in gastroduodenal disease in adults, although wall thickening due to gastric carcinoma and inflammatory disease in the antrum can often be seen. Real-time US can also be used to study antropyloric emptying and motility non- invasively. Endoscopic ultrasound (EUS) is accurate in the T and N staging of gastric adenocarcioma and the confirmation of linitis plastica. It may also be used to detect and stage gastric lymphoma, and image submucosal tumours such as smooth muscle lesions and distinguish them from extrinsic impressions seen at endoscopy or barium studies.
Nuclear medicine scintigraphy
Applications of nuclear medicine techniques in the gastroduodenal region include gastric emptying studies and, occasionally, detection of duodenogastric bile reflux. The former is performed with either a solid or liquid phase test meal or both. Serial imaging is performed with computer acquisition and time-activity curves are generated to calculate gastric emptying rate. Bile reflux into the stomach is assessed by injecting intravenously a Technetium-labelled iminodiacetic acid derivative (e.g. HIDA). This tracer is excreted by the liver into the bile duct and thence the duodenum. If there is significant retrograde passage of tracer into the stomach this can be quantitated.
Investigation of dyspepsia
Dyspepsia means different things to different individuals. It has been carefully defined as intermittent or continuous pain, discomfort or nausea that is referable to the upper gastrointestinal tract, which is present for at least a month, is not precipitated by exertion and is unrelieved within five minutes by rest. This definition will include patients with organic gastroduodenal disease, GOR disease, various forms of non-ulcer dyspepsia and biliary tract disease. If one considers patients with gastroduodenal dyspepsia of age greater than, say, 45 years or with symptoms that include one or more of constant daily pain, weight loss, vomiting, a past history of gastric ulcer or gastric surgery, then these patients by virtue of their age and/or symptoms, may be expected to have an increased probability of gastric pathology - either benign or malignant compared to younger patients whose symptoms do not have any of the above features. If endoscopic and radiological services are of equal availability it is reasonable for endoscopy to be the primary investigation in the former group (since all of this group require investigation and are likely to need biopsies). Where endoscopic services are limited, a careful biphasic barium meal should be performed. A barium study may be the initial examination in the latter group. It has been suggested that this latter group may not require initial investigation at all, and that it is acceptable to treat empirically for dyspepsia and to reserve investigation for those with refractory symptoms. In patients with barium-negative dyspepsia consideration should be given to other causes of symptoms such as biliary or pancreatic disease (and US should be performed.) The relationship of non-uIcer dyspepsia to Hehobacter pylori gastric infection remains to be finally clarified. Some patients will respond to eradication of these organisms.
Pathology
Hiatus hernias and gastric rotations
Sliding hernias
The gastro-oesophageal junction is above the diaphragm (Figs. 11, 19). The size of the herniated proximal stomach is variable. Small sliding hiatus hernias are a very common finding and are often asymptomatic. The major association of sliding hiatus hernias is gastro-oesophageal reflux (see above).
Para-oesophagueal hernias
These are much less common (about 5%). In this case the gastro-oesophageal junction lies below the diaphragm but all or part of the gastric fundus is above the diaphragm and lies adjacent to the distal oesophagus - usually to the left. Most para-oesophageal hiatus hernias are non-reducible. They may be recognised on a chest radiograph by an air fluid level behind the heart, the nature of which may be confirmed by repeating the radiograph after the patient takes a few mouthfuls of barium. Most patients with paraoesophageal hernias are asymptomatic, but
 | Figure 19.
Sliding hiatus hernia. Area of narrowing is arrowed at level of diaphragmatic hiatus. There is a benign gastric ulcer (small arrow) on the lesser curve, presumed due to recurrent mechanical trauma at the hiatus. |
complications are mechanical. Dysphagia may occur when the intrathoracic portion of the stomach fills during a meal and obstructs the distal
oesophagus.
Obstruction of the herniated portion of the stomach may cause strangulation and perforation. An acute torsion may occur.
Mixed hernias
In this case the oesophagogastric junction is in the thorax but much of the rest of the stomach also lies in the chest adjacent to the distal oesophagus. A variant of this is the intrathoracic stomach. This is associated with partial twisting of the stomach so that the fundus lies behind the heart, the greater curvature is cranial, and the antrum passes through the diaphragm (Fig. 20). When the fundus lies at a level inferior to the body, distension of the former with food may cause obstruction to the antrum. Similarly obstruction may occur when a herniated fundus returns into the abdomen (Fig. 21). Other viscera, particularly the transverse colon, may also be herniated. Although the intrathoracic stomach is prone to volvulus, chronic volvulus usually only causes mild symptoms. However, acute torsion presents as an emergency.
The stomach can undergo two main types of rotation and these are often associated with herniation of the stomach. Organo-axial rotation is a
 | Figure 20.
lntrathoracic stomach. The GOJ is in the thorax (curved arrow), the gastric fundus lies behind the heart, the greater curve is upper-most, due to organo-axial rotation and the antrum passes through the diaphragm (straight arrow). |
 | Figure 21.
Intrathoracic stomach with axial rotation, but fundus has returned to infradiaphragmatic position with resulting partial obstruction. The nasogastric tube demonstrates the position of the GOJ (arrowed). |
twist along the long organic axis of the stomach - that is the line drawn from the fundus to pylorus. The resulting configuration depends on the original orientation of the stomach. If the stomach was horizontally orientated, then the result is a reversal of the normal lesser and greater curves (Fig. 20). When the stomach is more vertically orientated the fundus lies to the right and the antrum points to the left - so called "mirror-image" stomach. Organo-axial rotation is only rarely associated with severe symptoms. Mesentero-axial rotation is less common but much more often
 | Figure 22.
Varioliform erosive gastritis. Multiple punctate erosions are seen in the gastric antrum and body, each surrounded by a halo of oedema. |
associated with obstruction and strangulation. The stomach rotates around an axis joining greater and lesser curves and perpendicular to its long organic axis so that the resulting configuration is an "upside-down" stomach. Total volvulus is a rotation greater than 180? with obstruction at GOJ and/or gastric outlet. The patient has sudden epigastric pain, retching without vomitus and collapse. Ischaemia and necrosis of the stomach result. A chest radiograph may show air-fluid levels in the upper abdomen and the mediastinum. A contrast study shows tapering obstruction of the distal oesophagus.
Gastritis
Radiology is limited in the diagnosis of gastritis and other superficial mucosal disease, but certain patterns are recognisable based on the presence of erosions, thickening or atrophy of folds, hyper -rugosity and wall thickening. Disturbance of the areae gastricae pattern is a further indication of mucosal disease.
Erosive gastritis may be acute or chronic and may be asymptomatic or accompanied by dyspeptic symptoms or bleeding. Causes include alcohol, aspirin and other non-steroidal anti-inflammatory drugs, but many are idiopathic. Two patterns of erosive gastritis are seen. The so-called varioliform gastritis comprises multiple aphthous erosions surrounded by a mound of radiolucent oedema, usually orientated along the longitudinal folds and tending to be concentrated in the antrum (Fig. 22). A similar appearance may be seen in Crohn's disease affecting the stomach. The second pattern is of flat erosions without a halo of oedema, but tending to have the same distribution of varioliform gastritis. This variety is more difficult to diagnose on DCBM. Distinction must be made from barium precipitates.
Hypertrophic gastropathy is a group of entities characterised radiologically by hyper-rugosity of the stomach. Such conditions include hyperacidity states such as Zollinger-Ellison syndrome and chronic renal failure, Menetrier's disease and hypertrophic gastritis, and are mimicked by infiltration with lymphoma or submucosal spread of carcinoma.
Gastric atrophy, such as occurs in pernicious anaemia, is associated with loss of folds on the greater curvature and in the fundus and reduction of the areae gastricae.
Eosinophilic gastritis is a condition characterised by peripheral eosinophilia, a history of allergy and protein-losing enteropathy. The stomach only is involved in about half the patients with eosinophilic gastroenteritis. The usual site is the antrum and in the acute stage demonstrates enlarged rugal folds. In the chronic phase there is a contracted nodular antrum.
Corrosive gastritis
Corrosive damage to the stomach is usually due to acid ingestion, but sometimes alkalis can affect the stomach as well as, more typically, the oesophagus. The radiological findings depend on the stag e of damage. Acutely there is gastric atony, rugal swelling, ulceration, pneumatosis or perforation. These may be visible on plain radiographs. Gradually scarring occurs with resultant deformity and contraction of the stomach (Fig. 23).
Gastric ulceration
On double-contrast barium meal (DCBM), gastric ulcers are seen as niches or collections of barium. When viewed en face, ulcers on the posterior (dependent) wall are apparent as barium collections when full of contrast, or ring shadows when empty, with or without radiating folds (Fig. 25 a). On the non-dependent (anterior) surface they are seen en face
 | Figure 23.
Stomach of a young man approximately 3 weeks after Formalin ingestion. The stomach is contracted with sacculation and ulceration and antral narrowing. There is also narrowing and spiculation of the proximal duodenum. GOJ and pylorus are arrowed.
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 | Figure 24.
Benign gastric ulceration. Two ulcers (arrowed); that on the lesser curve is empty of barium and seen almost in profile as a curvilinear outpouching - note that the edges (and those of the ulcer in Fig. 19) do not protrude into the lumen - compare with Fig. 26. The posterior antral ulcer contains barium. |
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 a | Figure 25.
a) Benign posterior wall gastric ulcer showing radiating folds extending to ulcer crater.
b) Malignant antral ulcer with thickened margin and folds amputated short of the ulcer crater. |
 b | |
as ring shadows.
Anterior wall lesions may not be easily se en without erect and prone compression views. In profile ulcers are seen as barium-filled collections extending beyond the lumen or, if empty, curvilinear lines of barium (Figs. 19, 24). The majority of benign gastric ulcers occur on the lesser curve or in the antrum (usually posterior wall). Greater curve ulcers are more suggestive of malignancy, but even benign ulcers in this site may have a malignant appearance. There appears to be an association between non-steroidal anti-inflammatory drug therapy and benign greater curve ulcers which may progress to gastrocolic fistulae. Pyloric and prepyloric ulcers are usually
 | Figure 26.
Gastric diverticulum just distal to the cardia. Note the gastric folds running into the lesion aiding the distinction from gastric ulceration. |
small and
benign. Size is not a good indicator of
benign or
malignant nature; giant ulcers are often
benign. Features on
barium meal that help distinguish
benign and
malignant gastric ulcers are listed in Table 4. As ulcer healing occurs the crater diminishes in size and the oedematous edges disappear. The radiating folds become more apparent as scarring progresses. As re-epithelialisation occurs the crater may end up as a small residual depression (an ulcer scar) or as an area of flat
mucosa with radiating folds.
Gastric diverticula are not-infrequently misdiagnosed as gastric ulcers. These true (congenital) lesions occur on the posteromedial wall just distal to the cardia (Fig. 26). The typical site and often the demonstration of gastric folds running into them will help distinguish these non-consequential lesions from ulcers.
 | Figure 27.
Malignant gastric ulcer. Although a typical site (lesser curve, incisural) for a benign ulcer, note the margins protruding into the lumen, characteristic of a malignant lesion (arrowed). |
 | Figure 28.
Malignant gastric ulcer seen en face. The ulcer crater is empty of barium and the raised margins typical of malignancy are clearly shown (arrows). |
Table 4. Benign versus malignant gastric ulcers (Figs. 19, 24-28)
Feature Benign Malignant
| Size | Not a good indicator | Not a good indicator
|
| Site | majority lesser curve or antrum | variable |
| Shape | round, oval, linear | irregular |
| Areae gastricae | extend to crater* | cease away from crater |
| Edges | +/- ulcer mound/ collar
with central and
symmetrical niche.
Margins of mound form
obtuse angle with
normal wall.
Hampton line | raised edges protruding into lumen |
| Radiating folds | smooth, radiate to ulcer* | clubbed, nodular
amputated, fused |
* but not necessarily when the ulcer is surrounded by significant gastritis
If a gastric ulcer is diagnosed on barium meal the question of further investigation prior to treatment will depend on a) the degree of radiological confidence that it is benign, and b) the prevalence of gastric cancer and, particularly, "early" gastric cancer in that community. Laufer introduced the concept of confidence levels in relation to radiological diagnosis of a benign gastric ulcer and found that, if the radiologist is confident of the benign nature of an ulcer then he/she is rarely wrong. Subsequent studies have confirmed the reliability of a radiological diagnosis of a benign gastric ulcer by DCBM and have suggested that endoscopy and biopsies can be reserved for equivocal or malignant-appearing ulcers or those that do not completely heal on follow-up imaging after ulcer therapy. However, partly due to the oft-quoted ability of malignant ulcers to heal on modem ulcer therapy, many gastroenterologists prefer to perform endoscopy on all radiologically diagnosed gastric ulcers. In communities where "early" gastric cancer is common, it is prudent to follow this policy. It must be remembered that malignant change may be patchy and, therefore, multiple biopsies from all areas of the ulcer rim and crater and, preferably, cytological brushings should be obtained. Where "early" gastric cancer is not prevalent a reasonable costeffective policy for a radiographically benign gastric ulcer is to perform endoscopy/biopsy where available prior to therapy and follow-up (if confirmed benign) to complete healing by subsequent DCBM examinations.
Gastric carcinoma
Diagnosis
The diagnosis of gastric carcinoma is usually made by endoscopy or barium meal. "Early" gastric cancers (EGC), i.e. those limited to mucosa +/- submucosa regardless of the presence of lymph node metastases) are prevalent in some communities, such as Japan, but are relatively uncommon in most Western societies. They can appear as Type I (polypoid), Type II (superficial; Type IIa elevated; Type IIb flat; Type IIc depressed), or Type III (excavated). Mixed types occur. The surface of early polypoid lesions on DCBM is lobular or granular and simulates the areae gastricae. Differentiation is required from adenomas and hyperplastic polyps (see below). Type H lesions are seen as flat mucosal elevations. Where a central depression is present (i.e. superficial erosion) this is irregular in outline with an uneven surface. Folds radiating towards
the
lesion may show evidence of
infiltration such as nodularity, amputation or fusion. Type III lesions demonstrate deeper excavations.
Advanced gastric cancers are more common than EGC in Western societies. These involve the muscularis propria or deeper layers. They may be classified on gross radiological appearances as polypoid, ulcerative with raised margins (Figs. 25 b, 27, 28), a larger infiltrative and ulcerating type, and a diffuse infiltrative type (often se en as a constricting tumour in the antrum) (Fig. 29). These correspond to Borrman types 1-4, respectively. Linitis plastica is a diffuse infiltration, predominantly submucosal, which is manifest on contrast studies as a poorly distensible so-called "leather bottle"-stomach. This not infrequently may be overlooked endoscopically and, to a lesser extent, radiographically. Advanced ulcerative or raised cancers are often large and obvious radiologically. All lesions need endoscopic biopsy for confirmation.
Staging
The need for staging of gastric carcinoma is less obvious than for oesophageal lesions. However, in communities where EGC is prevalent, it is useful to help determine therapy and prognosis, particularly where non-surgical endoscopic treatment is contemplated. Where advanced lesions are more prevalent it could be argued that surgery, whether for attempted cure or palliation, is the treatment of choice and that pre-operative staging does not influence management. However, surgeons' practices differ; if staging is required then this is best achieved by CT or EUS for local staging, and dynamic enhanced or helical CT (or conventional US) for distant metastases. EUS has been shown consistently superior to CT for local staging, but is of limited availability. CT visualises the thickened gastric wall and its relationship to adjacent structures, but is unable to determine the depth of wall invasion. CT can detect lymph node enlargement but is non-specific, unable to distinguish reactive from malignant nodes. The criterion for enlargement is usually taken as > 10 mm. Since metastases can also be present in non-enlarged nodes, CT is not very sensitive. When performed optimally CT, using either a dynamic sequential technique with bolus contrast enhancement or the newer spiral (helical) techniques, is relatively accurate (probably in the region of 90%) at showing whether the patient has liver metastases or nor, but is significantly less sensitive at demonstrating all lesions in an individual patient. Moss has suggested a CT staging scheme for gastric carcinoma (Table 5).
Table 5.CT Staging of gastric carcinoma (after Moss et al)
Stage IIntraluminal mass without wall thickening (i.e. < 10 mm thick). No metastases.
Stage IlWall thickening > 10 mm without
tumour extension or metastases.
Stage IIIThickened wall with adjacent organ involvement but no distant metastases.
Stage IV
Distant metastases with thickened wall.
The accuracy of EUS in T and N staging of gastric carcinoma is similar to its accuracy in oesophageal carcinoma and significantly better than dynamic CT, being 80-90% for T and 75% + for N in most series. Once again, there is difficulty in distinguishing benign from malignant nodes although positive and negative predictive values of87.5 % and 82 % have been achieved for nodal metastasis. EUS is highly accurate in distinguishing EGC from advanced cancer. In linitis plastica EUS demonstrates a diffuse thickening of the submucosa and muscularis propria layers.
 | Figure 30.
Submucosal smooth muscle tumour of the gastric body (seen in single contrast) exhibiting central ulceration (arrowed). Note otherwise smooth surface and right angled conjunction with gastric walls. |
Other gastric tumours
Submucosal tumours
Although many cell types can give rise to submucosal tumours in the stomach, the vast majority are smooth muscle lesions - leiomyomas, leiomyoblastomas and the malignant leiomyosarcomas. Radiology essentially cannot distinguish these three lesions. Most smooth muscle tumours are fundal, rounded and often exhibit central ulceration (Fig. 30). The latter accounts for the frequent presentation of bleeding. Size is variable. As for all submucosal lesions they appear on DCBM as smooth surfaced with normal overlying mucosa. In profile the margins are at right angles or obtuse to the line of the gastric wall. Much of the bulk of the tumour may be exophytic to the stomach - an "iceberg" phenomenon. EUS is useful for confirming the origin of the tumour from muscularis propria and distinguishing between a submucosal and an extrinsic mass (Fig. 31). For larger lesions where malignancy is suspected, EUS or CT are helpful in assessing infiltration of adjacent structures.
Haematogenous metastases from malignant melanoma, breast and lung carcinoma, phaeochromocytoma and, in recent times, Kaposi sarcoma, may give rise to small submucosal tumours. These are usually multiple and have a "bull's eye" or target appearance due to central ulceration. Breast carcinoma may spread submucosally like scirrhous carcinoma.
 | Figure 31.
EUS image of submucosal smooth muscle gastric |