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Imaging in GI Surgery
Julie F.C. Olliff and Peter J. Guest
Aims
To explain the indications for and types of imaging available.
Introduction
Imaging is playing an increasingly important role in the investigation and work-up of patients who present to GI surgeons. The choice of the appropriate investigation can be one of the most crucial decisions in the patient work-up. This chapter discusses the commonly used imaging methods with indications, contraindications and some discussion about technique and inter- pretation. Recent Ionising Radiation (Medical Exposure) Regulations (IRMER) regulations (EU) require the justification of imaging inves- tigations that use ionising radiation. Investiga- tions such as MRI or ultrasound that avoid the use of ionising radiation should always be con- sidered. This becomes especially relevant in young people because of the increased risk of a lifetime cancer from ionising radiation or in patients who are going to undergo repeated imaging examination throughout the course of their illness. Examination involving ionising radiation of the lower abdomen and pelvis is not advised in patients who may be pregnant.
Plain Radiology
Lateral Soft Tissue Neck
Indications: Suspected radio-opaque foreign body, suspected perforation with or without retropharyngeal abscess.
Chest
Indications. Suspected oesophageal perfora- tion, suspected aspiration, suspected foreign body; perforated abdominal viscus, perforated oesophagus, achalasia.
The erect chest x-ray with the beam centred at the level of the diaphragm is the investigation of choice for detecting extraluminal intra-abdom- inal air (Figure 22.1). If the patient is not well enough to have an erect film, then a left lateral decubitus film of the abdomen can be per- formed. These films can demonstrate as little as 1–2 ml of free air (Figure 22.2).
It may take some time for small amounts of gas to collect either just below the diaphragm or lateral to the liver so ideally the film should be obtained with the patient having been in the erect position for 10 minutes or more.
Mediastinal air and/or pleural fluid should be looked for in patients suspected of oesophageal perforation following ingestion of a foreign body or instrumentation.
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2 311 Figure 22.3.a Achalasia: A chest X-ray showing dilated viscus
forming an extra border to the right side of the mediastinum with evidence of an aspiration pneumonia in the left lower lobe.
b Barium swallow showing the dilated oesophagus with much food residue and the characteristic “bird beak” of the gastro- oesophageal junction.
Figure 22.2. Erect chest X-ray demonstrates a small amount of free gas (arrowed).
Figure 22.1. Erect chest X-ray demonstrates a large amount of free gas below the diaphragms following caecal perforation.
b a
Established achalasia may be diagnosed by the presence of a dilated oesophagus projecting beyond the normal mediastinum and contain- ing copious fluid residue (Figures 22.3a and 3b).
Plain Abdominal Film
Indications. Intestinal obstruction, detection of calcification or other radio-opaque material, suspected ischaemia, inflammatory bowel disease, intestinal transit studies.
Contraindications. Pregnancy.
The plain abdominal film is most helpful for detecting intestinal obstruction although the site of obstruction can be difficult to judge because of fluid-filled loops of bowel interposed between the actual obstruction and distal air- filled loops.
The normal calibre of the proximal jejunum should be less than 3.5 cm, of the mid small bowel less than 3 cm and of the ileum less than 2.5 cm (Figure 22.4a ,b and c).
Extraluminal air can also be assessed on a supine film of the abdomen. All collections of gas should be assessed for a possible extralumi- nal location. Triangular air collections may be extraluminal (Figure 22.5). Air may be seen in the hepatorenal space (Morrison’s pouch) or outlining the fissure of the ligamentum teres (Figure 22.6). If large amounts of air are present, both sides of the bowel wall may be seen (Rigler’s sign) (Figure 22.7). Retroperitoneal free gas will cause the renal outlines to appear unusually sharp (Figure 22.8).
Focal collections of air within abscesses will appear as areas of mottled gas lying outside the normal distribution of bowel or as a collection 111
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Figure 22.4.a Plain film of the abdomen demonstrating small bowel obstruction b and c Coned view of the abdomen (b) and a CT (c) in small bowel obstruction to illustrate the origin of the
“string of beads” sign. The abdominal X-ray shows a line of gas bubbles corresponding to gas (arrowheads) trapped between the small bowel folds in dilated fluid-filled small bowel.
b
c a
of gas seen within an abscess with an air fluid level. These may only be identified if they lie outside the normal distribution of bowel gas.
Bowel wall thickening may be seen in condi- tions such as ischaemia, inflammatory bowel disease, etc.
An erect abdominal film is not needed either to assess the presence of extraluminal gas (as an erect chest X-ray is preferable) or to diagnose intestinal obstruction. Rather than fluid levels on an erect abdominal X-ray, the physician should evaluate the film for dilated bowel, or if fluid filled for linear bubbles of gas (“string-of- beads” sign) (Figures 22.4b and c) correspond- ing to air trapped between the small bowel folds.
Gas may be seen within the biliary tree in patients who have had sphincterotomy, have a biliary enteric anastomosis or who have recently passed a gallstone. Biliary gas appears as branching linear lucencies lying centrally. Gas in the portal veins in an adult appears as gas shadows which extend to the periphery of the liver (Figure 22.9). Gas may also be seen as splenic or mesenteric veins and within the bowel wall (Figure 22.10). This is seen in necro- tising enterocololitis following umbilical vein catheterisation and in erythroblastosis fetalis.
In adults it is a grave prognostic sign most 1111 2 3 4 5 6 7 8 9 1011 1 2 3 4 5 6 7 8 9 2011 1 2 3 4 5 6 7 8 9 3011 1 2 3 4 5 6 7 8 9 4011 1 2 3 4 5 6 7 8 9 5011 1 2 311 Figure 22.7. Close-up of an abdominal X-ray to demonstrate air on both sides of the bowel wall (Rigler’s sign) as an indicator of free intra-abdominal gas.
Figure 22.6. Plain film of the abdomen shows the falciform ligament outlined by free gas.
Figure 22.5. Supine abdominal radiograph showing extensive free air as manifest by non-anatomical or triangular collections of air (arrows) and air on both sides of the bowel wall (Rigler’s sign – arrowheads).
commonly seen in critically ischaemic bowel.
Rarely it may, however, be seen in patients with severely ulcerated large bowel following embolus of air during a double contrast barium enema.
Calcification should be looked for on a plain film within the gall bladder, pancreas and renal tract. Gall bladder stones are visible on a plain abdominal film in about 10% of cases, and are characteristically laminated and polygonal.
Curvilinear calcification lateral to the lumbar spine raises the possibility of an aortic aneurysm which can be further assessed using ultrasound or CT.
Free intra-abdominal fluid leads to medial displacement of the colonic gas shadows from the properitoneal fat line (Figure 22.11). It also leads to a ground glass appearance.
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Figure 22.8. The right renal outline is very clearly seen due to retroperitoneal gas.
Figure 22.9. Portal vein gas seen on CT in a patient with ischaemic bowel.
Contrast Radiography
Oral Cholecystography
Indications. Suspected cholelithiasis. This method has almost completely been replaced by ultra- sound. It may occasionally be needed in patients in whom ultrasound has failed usually due to obesity. It may also be used if ultra-sound is doubtful in the diagnosis of a small chronically contracted gall bladder and is useful to assess gall bladder function although this may also be done by ultrasound.
Barium Swallow
Indications. Dysphagia, pain, possible motility disorder.
Barium should never be used as the oral con- trast agent if there is any possibility of aspira- tion or leak into the peritoneum. The use of Gastrografin, which is a hyper-osmolar water- soluble contrast agent, is also contraindicated if there is any risk of aspiration because this may lead to pulmonary oedema which can be fatal.
Isotonic water-soluble contrast agents should be used in these patients.
Double contrast spot films assess morphology better. The presence of gastro-oesophageal reflux may be assessed by tipping the patient head down or by asking him to cough. A double contrast barium swallow has a sensitivity of 75 to 90% in diagnosing reflux oesophagitis depending on the severity. It may also be used to diagnose infectious and drug-induced oesophagitis. Aspiration occurs when contrast medium enters the laryngeal vestibule or between swallows during normal respiration.
Aspiration is associated with stasis in the pharynx. This may be due to neuromuscular disorders, tumour, pharyngeal pouch or diver- ticulum. Aspiration can also occur during gastro-oesophageal-reflux or may be due to an obstruction in the lower oesophagus. A
1111 2 3 4 5 6 7 8 9 1011 1 2 3 4 5 6 7 8 9 2011 1 2 3 4 5 6 7 8 9 3011 1 2 3 4 5 6 7 8 9 4011 1 2 3 4 5 6 7 8 9 5011 1 2 311 Figure 22.10. Coned view of a radiograph of the right flank
showing gas (arrowheads) within the mesenteric arcades and the portal venous system in the liver in this patient with ischaemic gut.
Figure 22.11.
prominent cricopharyngeus (Figure 22.12) is also often seen in patients with gastro- oesophageal reflux or oesophageal obstruction.
It may also be due to abnormal pharyngeal peri- stalsis. Pharyngeal diverticulum or pouch can be demonstrated by barium swallow.
Malignant pharyngeal and oesophageal tumours may be differentiated from benign strictures by irregular narrowing of the lumen associated with mucosal destruction, ulceration and mass effect. Narrowing of the oesophagus by mediastinal tumours causes an extrinsic mass effect unless there is direct invasion.
Benign strictures appear as smooth areas of
oesophageal narrowing and may be due to pre- vious radiotherapy, caustic ingestion, dermato- logical disorders and gastro-oesophageal reflux.
High strictures or ulceration may be seen in Barrett’s oesophagus.
An oesophageal web (Figure 22.12)appears as a narrow shelf-like band usually in the cervical oesophagus. Oesophageal varices may be missed if the oesophagus is distended.
Barium swallow may also be used to evaluate motility disorders of the oesophagus. These are preferably recorded as video clips or digital movie clips. Tongue movement, soft palate elevation, epiglottic tilt, laryngeal closure, 111
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Figures 22.12. Anteroposterior view of a barium swallow (a) demonstrating a narrow linear filling defect which is shown on the lateral view (b) to be a well-defined shelf-like defect anteriorly consistent with a web. A prominent cricopharyngeus is noted posteriorly.
b
a
pharyngo-oesophageal segment (cricopharyn- geal opening) and pharyngeal peristalsis may all be assessed.
Aspiration should be looked for early as the examination may need to be terminated.
Peristalsis should be assessed in the prone or supine position to eliminate the effects of gravity. Oesophageal peristalsis is normally rapid with a primary stripping wave propelling a liquid or solid bolus through the oesophagus.
Early dysfunction is manifest as failure of this wave which may dissipate in the mid oesopha- gus. Secondary peristalsis may then clear the oesophagus. More advanced dysmotility is manifest as tertiary contractions which are inef- fective in terms of propulsion and may be manifest as a “corksrew oesophagus”. Elderly patients usually have minor dysmotility which may be asymptomatic. Patients may demon- strate a normal liquid swallow, in which case the examination should be continued with a solid bolus (bread or marshmallows if available).
Achalasia is a specific motility disorder of the gastro-oesophageal junction characterised radi- ologically by a dilated oesophagus, failure of relaxation of the gastro-oesophageal junction, with intermittent opening and passage of barium into the stomach (a “bird beak” appear- ance (Figure 22.3b)).
Water-soluble Contrast Swallow
Indications. Possibility of aspiration, assess- ment of integrity of anastomoses.
As discussed above, water-soluble contrast agents should be used if there is any risk of aspi- ration. They are routinely used to assess integrity of anastomoses post surgery. Barium within the peritoneum is extremely irritant and should not be used in this instance.
Unfortunately, mucosal detail is poorly seen with water-soluble contrast agents and there- fore barium is the contrast agent of choice for routine examination of the gut mucosa.
Barium Meal
Indications. Dyspepsia, weight loss, GI haem- orrhage, high GI obstruction.
Contraindications. Complete large bowel obstruction, suspected site of perforation.
Complications. Side effects of muscle relaxants.
This investigation has been almost completely replaced by upper GI endoscopy. It is now only used on those patients who are not suitable for upper GI endoscopy or in instances where upper GI endoscopy is not available. A gas-pro- ducing agent is swallowed. The patient then drinks barium. The patient is turned to achieve adequate coating of the stomach and double contrast views are obtained. An intravenous injection of a smooth muscle relaxant (Buscopan or glucagon) is given and views of the duodenum are taken.
A barium meal may be used to diagnose gas- tritis and peptic ulceration. Ulcers greater than 5 mm in size are more likely to be detected on barium study than smaller ones. Imaging cannot confidently distinguish between benign and malignant ulcers but may be very suggestive (Figure 22.13). Atrophic gastritis, eosinophilic gastritis and involvement of the stomach by Crohn’s disease may also be shown. Benign tumours such as hyperplastic polyps and adenomatous polyps may be demonstrated.
Congenital conditions such as ectopic pancre- atic rests and duplication cysts can also be seen.
Barium Follow Through/Small Bowel Meal
Indications. Pain, diarrhoea, bleeding, partial obstruction.
Contraindications. Complete obstruction, sus- pected perforation unless a water-soluble con- trast medium is used rather than barium sulphate.
Small bowel contrast studies are better per- formed as a dedicated study rather than a study following a barium meal. The relaxant given for a barium meal will hinder the passage of barium through the small bowel. An optimal study is dynamic and involves regular fluoroscopy to assess mobility of small bowel loops and take spot views of possible pathologies with com- pression or palpation.
Although direct enteroscopy is developing, barium radiology of the small bowel remains the main method for evaluation of this segment of bowel. It demonstrates the mucosal ulceration,
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Figure 22.13. Gastric ulcers on barium meal: Classic gastric ulcer pre-treatment (a) and post-treatment (b). It is typically benign with smooth folds extending up to the ulcer crater although endoscopy would generally be advised for biopsy confirmation.
(c) Obviously malignant gastric ulcer – deeply penetrating irregular lesion with associated extensive infiltration through a thickened stomach wall.
a
b
c
strictures, fistulas and obstructive elements of Crohn’s disease (Figure 22.14) Characteristic appearances are seen in coeliac disease, sys- temic sclerosis, radiotherapy change etc.
Malignancies such as adenocarcinoma or lym- phoma are rare but usually well shown.
Obstruction can be demonstrated and the cause identified although computed tomography (CT) is a competitive modality here.
Small Bowel Enema
Indications. As for small bowel meal. Possible Meckel’s diverticulum.
Contraindications. Complete obstruction, sus- pected perforation.
A nasojejunal tube with a guide-wire is intro- duced into the duodenum and advanced to beyond the duodenojejunal flexure (the level of the ligament of Treitz). Diluted barium is then run in quickly or barium followed by methyl- cellulose for a double contrast effect. Spot films are taken of the barium column and its leading edge at regions of interest until the colon is reached.
It is more time-consuming for the radiologist, more unpleasant for the patient but it allows better visualisation of the small bowel.
Radiologists are divided, however, as to which technique is the best.
It is a more sensitive technique than a small bowel meal for the demonstration of obstruct-
ing lesions as a result of proximal distention but may demonstrate the terminal ileum less well.
Complications. Aspiration, perforation of the bowel by the guide-wire.
Sinogram
Indications. Investigation of a sinus/fistula.
Water-soluble contrast medium is used. A fine catheter is inserted into the orifice of the sinus or fistula and contrast medium injected with screening. Films are taken as required.
Retrograde Ileogram and Colostomy Enema
Indications. To investigate the bowel proximal to a colostomy or ileostomy.
The tip of a Foley catheter is introduced a few centimetres into the appropriate stoma and the balloon inflated carefully. Barium is run into the bowel and spot films are taken as required.
Water-soluble contrast medium should be used if an anastomotic leak is suspected.
Cross-sectional Imaging
Ultrasound
Indications. Abdominal pain, weight loss, unexplained pyrexia post surgery.
Ultrasound (US) does not use ionising radiation and is therefore a safe technique. It is readily available in most hospitals and can be portable and therefore used to examine patients who are too ill to travel to the imaging department. It is very operator dependent. The US beam will not penetrate gas or bone well and is attenuated (weakened) as it passes through the tissues. It may therefore have a limited use in the obese patient, in patients who have free gas within the abdomen or who have gaseous distension of bowel loops. It is a useful initial investigative tool in patients who present with upper abdom- inal pain, being able to image the liver, biliary tree, renal tract pancreas and spleen before upper endoscopy or after a negative upper endoscopy.
1111 2 3 4 5 6 7 8 9 1011 1 2 3 4 5 6 7 8 9 2011 1 2 3 4 5 6 7 8 9 3011 1 2 3 4 5 6 7 8 9 4011 1 2 3 4 5 6 7 8 9 5011 1 2 311 Figure 22.14. Terminal ileal mucosal Crohn’s ulceration
optimally demonstrated with a small bowel meal.
Bowel wall thickening (Figure 22.15a and b) may be detected on US in patients with inflam- matory or neoplastic conditions.
It is very useful to detect fluid within the chest and abdomen. It may be used to differentiate between pleural effusions and underlying pul- monary parenchymal collapse and consolida- tion. It is to able to distinguish between fluid collections above and below the diaphragm and to guide diagnostic tap. If necessary US can then be used to guide pigtail catheter placement. It thus has an important role to play in the inves- tigation of the pyrexial postoperative patient. It may not identify collections lying between gas- containing bowel loops and therefore a negative US scan in a patient suspected of having a post- operative abscess or collection needs to be inter- preted with caution. In these patients it may be necessary to proceed to CT. It can be used to obtain diagnostic cytology in patients with upper GI cancers who are found to have ascites and suspected peritoneal disease.
Endoscopic Ultrasound (EUS)
Indications. Local staging of oesophageal and gastric cancer, assessment of the pancreatic head and bile duct for malignancy and stone.
EUS is the most accurate method of assessing early T-stage GI tumours (Figure 22.16) and for predicting local organ invasion. Currently it is not widely available but is likely to become increasingly required to direct conservative
surgery such as endoscopic submucosal resection.
Computed Tomography
Indications. Staging upper GI cancer, investiga- tion of abdominal pain, postoperative pyrexia.
Computed tomography (CT) uses ionising radi- ation. X-rays are attenuated by the tissues that they pass through. This attenuation is propor- tional to the atomic number of the tissue.
Images are displayed as a grey scale with air conventionally displayed as black and bone as white. The development of spiral CT and more recently multi-slice CT enables a volume of data to be collected during a breathhold. This data may be displayed as axial slices or multiplanar reformats may be made. Upper GI CTs should use water to distend the stomach (hydro CT).
The normal oesophageal and gastric walls are thin. Abnormal thickening may be due to benign or malignant causes and therefore his- tology (usually from endoscopy) is needed before a diagnosis can be made. CT can, however, stage local and distant disease (Figure 22.17a, b and c), being able to image not only the extent of the local tumour but also local and distant nodal involvement, hepatic metastatic disease and peritoneal disease.
Aortic invasion by oesophageal cancer is rare (Figure 22.18) but is a contraindication to surgery. CT and MRI have similar accuracy in the assessment of aortic involvement.
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311 Figures 22.15. Gastric cancer manifest as irregular hourglass-type stricture on barium meal (a) and marked wall thickening on ultrasound (b).
b a
1111 2 3 4 5 6 7 8 9 1011 1 2 3 4 5 6 7 8 9 2011 1 2 3 4 5 6 7 8 9 3011 1 2 3 4 5 6 7 8 9 4011 1 2 3 4 5 6 7 8 9 5011 1 2 311 Figure 22.17. a CT showing a large lesser curve gastric cancer extending into the gastrohepatic ligament which is nevertheless operable. b Local direct liver invasion from gastric cancer on CT. c Advanced gastric cancer with extensive peritoneal carcinomatosis as seen on CT. Note wall thickening and a non- distensible stomach, and marked peritoneal infiltration and nodularity.
Figure 22.16. Endoscopic ultrasound is the most accurate method of local staging of oesophageal and gastric tumours. a An EUS showing a T3 tumour on the basis of the irregular external contour indicating invasion into the perioesophageal fat. b An enlarged local node. Involved nodes are typically round and hypoechoic. (Images courtesy of Dr Alison Maclean.)
b a
a
b
c
Nodal abnormality is assessed using size cri- teria with para-aortic nodes and mediastinal nodes being considered abnormal if they measure greater than 1 cm in diameter. CT can be used to diagnose and stage other small bowel tumours such as carcinoid (Figure 22.19)
CT can be used to investigate the acute abdomen in patients with suspected upper GI
pathology. It can be used to determine the site and probable cause of obstruction (Figures 22.20 and 22.21). It will demonstrate not only the abnormal wall thickening seen in Crohn’s disease (Figure 22.22) but will elucidate whether bowel separaration seen on barium studies is due to fibro-fatty proliferation, lymph node enlargement or to abscess/phlegmon formation.
In the postoperative patient it can be used not only to identify collections but also to guide diagnostic aspiration and drainage procedures.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) has a rela- tively limited role in the upper GI tract. MRI staging of oesophageal and gastric cancer has no advantage over CT.
Magnetic resonance cholangio-pancreatogra- phy (MRCP) uses a heavily T2-weighted sequence usually with fat suppression to provide images of the water content of the biliary and pancreatic ducts. It is non-invasive, uses no con- trast and is therefore no risk. It provides good images, particularly in the dilated system, and is increasingly used for diagnosis rather than endoscopic retrograde cholangiopancreatogra- phy (ERCP). However, ERCP remains essential for therapeutic manoeuvres.
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Figure 22.18. CT of a large oesophageal cancer subtending an angle of greater than 90 degrees on the descending aorta which is deformed. This tumour is likely to be inoperable therefore.
Figure 22.19. Carcinoid tumour as seen on a small bowel meal with barium and a CT. a The barium study shows irregular nodularity and fold thickening of the distal small bowel but with a normal terminal ileum. b The CT shows indrawing of small bowel loop by a spiculate irregular cicatrizing mesenteric nodal mass, typical of carcinoid nodal metastases.
a
b
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a
b
Magnetic resonance enteroclysis is currently undergoing evaluation for the assessment of small bowel pathology. Technique is as for a small bowel enema, i.e. a nasojejunal tube is placed and up to 2 litres of an isotonic solution infused directly into the small bowel. As for MRCP the water content of the bowel is the basis for the images. It involves no ionising radiation
and because it is a cross-sectional technique has advantages over the X-ray projection images, by taking out the effect of overlying bowel loops. It demonstrates the bowel lumen but also the wall and extraluminal disease unlike barium studies.
It does not, however, demonstrate mucosal detail (Figure 22.23).
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Figure 22.21. Intussusception due to melanoma metastatic to small bowel as shown by CT. a CT showing fat and mesenteric contents within the bowel lumen, and a layered appearance as a result of invagination of the bowel. b CT at a lower level showing the intraluminal bowel and the lead point, a picture corresponding well to the intraoperative photograph (c).
b a
c
Radionuclide Imaging
There are a number of radiopharmaceuticals tailored for specific purposes in the investiga- tion of the gastrointestinal tract. Radionuclide
imaging is best not regarded as a structural investigation as the anatomical resolution is of the order of 10 times worse than cross-sectional imaging such as US or CT. However, it provides a unique functional map of physiological processes in the body. For example, white cell scanning directly images inflammation and enables an assessment of disease activity in Crohn’s disease, but does not provide good images of the morphology such as ulceration or strictures.
White Cell Scanning Using Radiopharmaceuticals
Separated white cells taken from the patient can be labelled with one of two radionuclide agents:
technetium-99m HMPAO or indium-111. The technetium agent is usually preferred as the isotope with a gamma ray energy of 140 keV is ideally suited for gamma camera imaging, is associated with a lower radiation dose to the patient and can be used to reach diagnostic images by 1–4 hours. It has the disadvantage, however, of being excreted by the biliary tract and hence bowel activity on the later images can
1111 2 3 4 5 6 7 8 9 1011 1 2 3 4 5 6 7 8 9 2011 1 2 3 4 5 6 7 8 9 3011 1 2 3 4 5 6 7 8 9 4011 1 2 3 4 5 6 7 8 9 5011 1 2 311 Figure 22.22. CT study of a patient with Crohn’s. Note how the
wall thickening is well seen, as with MR enteroclysis or ultrasound, but in contrast to barium studies where far more information about mucosal integrity is obtained.
Figure 22.23. New techniques such as MR enteroclysis (MRE) demonstrate mural disease of the bowel to good effect as in this case of Crohn’s disease (a) with the corresponding barium examination (b). Mucosal detail is not, however, seen with the MRE although the extraluminal effect, e.g. loop separation, is apparent.
b
a
cause diagnostic difficulties. Indium-111, on the other hand, may be more helpful if lower grade or chronic infection is suspected. Because of the longer half-life of the agent imaging is usually undertaken at 4–24 hours but can be extended for longer.
Indications. The main GI tract indication is the diagnosis and assessment of inflammatory bowel disease (Figure 22.24a and b), as the dis- tribution of the disease and disease activity are shown.
Other indications are the investigation of unexplained pyrexia or suspected abdominal collections, but this has largely been superseded by ultrasound supplemented by CT where necessary.
Biliary Imaging Using Radiopharmaceuticals
The usual radiopharmaceuticals are iminodi- acetic acid (IDA) derivatives, e.g. HIDA or T- BIDA. These are labelled to technetium-99m and have the property of being excreted by the hepatocytes into the biliary system.
They can therefore be used for the following indications:
• bile leaks and fistulae (extraluminal col- lections or abnormal drainage pathways)
• bile reflux (Figure 22.25) into the stomach as a cause of biliary gastritis (gastric activity)
• afferent loop obstruction (activity retained)
• congenital anomalies, e.g. choledochal cysts, biliary atresia (delayed drainage)
• acute cholecystititis (gall bladder shows no uptake)
• suspected functional disorders of the gall bladder or sphincter of Oddi (delayed or absent gall bladder contraction or biliary drainage in response to a fatty meal or pharmacological agents such a cholecys- tokinin or morphine)
• characterisation of hepatic masses (e.g.
follicular nodular hyperplasia character- istically shows retention of IDA deriva- tives).
Meckel’s Scan
A Meckel’s diverticulum as a cause of unex- plained gastrointestinal bleeding will always contain ectopic gastric mucosa. It will therefore show as an isolated focus of activity in the right 111
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Figure 22.24. Technetium-99m-labelled white cell scan (a) showing activity in pelvic small bowel loops but with an associated non-anatomical branching pattern that can only be explained by fistula formation as shown on the corresponding small bowel meal study (b).
b
a
iliac fossa on a radionuclide scan using free technetium-99m pertechnetate.
Octreotide Imaging
Octreotide is an analogue of somatostatin and hence when attached to an appropriate radionuclide such as indium-111 can be used to image tumours (Figure 22.26) that express somatostatin receptors – in particular neuoren- docrine tumours such as carcinoids and gastri- nomas.
Transit Studies
Oesophagus
Technetium-labelled colloid mixed with 10 ml liquid food such as tomato soup is used to obtain a dynamic assessment of oesophageal motility in patients with oesophagitis, dyspha- gia or atypical chest pain. The results are dis- played as time activity curves for each third of
the oesophagus, with combined curves for the whole oesophagus and the stomach. Transit in the upper third is about 1 second, middle third 2 seconds and the lower third 4–6 seconds.
There are a number of drugs which affect motil- ity such as metoclopramide and domperidone, and opiates, and these should generally be stopped before the test if possible.
Total and sectional transit time, ineffective peristalsis, retrograde peristalsis and gastro- oesophageal reflux can be assessed. A barium swallow dedicated to function provides similar data but is not quantitative.
Gastric Emptying
Gastric function in response to both solid and liquid agents can be shown using technetium- 99m colloid mixed with scrambled egg or orange squash respectively. This may be helpful in patients with dumping syndromes, unex- plained nausea or vomiting, autonomic dys- function or oesophagitis.
1111 2 3 4 5 6 7 8 9 1011 1 2 3 4 5 6 7 8 9 2011 1 2 3 4 5 6 7 8 9 3011 1 2 3 4 5 6 7 8 9 4011 1 2 3 4 5 6 7 8 9 5011 1 2 311 Figure 22.25. Radionuclide imaging: T-BIDA scan demonstrating activity excreted by the biliary tract refluxing into the stomach.
Dynamic images are obtained for up to 60 minutes and gastric emptying curves calculated.
Normal T1⁄2 for liquids is 10–20 minutes, and for solids 30–60 minutes. As for oesophageal studies, it may be necessary to withhold certain drugs.
Small Bowel Transit
The solid gastric emptying study can be contin- ued by taking further images at 30 minute inter- vals to allow calculation of the stomach to caecum transit time. There is a wide normal range and difficulties may be encountered in defining the position of the ileocaecal junction.
Questions
1. Give indications for plain chest X-ray.
2. What contrast radiology is available?
3. What techniques should be used to stage gastro-oesophageal neoplasms?
4. Outline functional investigations.
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Figure 22.26. Radionuclide imaging: indium-111 labelled octreotide scan showing somatostatin-receptor positive tumour in the left iliac fossa, confirmed on CT (not shown). Necrotic tumour in the liver is manifest as cold lesions in the superior segments. Activity in the right flank is normal renal activity.
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