and Ian A. D. Bouchier2
(1)
Bishop Auckland, UK
(2)
Edinburgh, Midlothian, UK
The function of the small bowel can be evaluated by clinical tests of absorption (Chap. 7). Intestinal biopsy, bacteriology, radiology, radio-isotope studies, enteroscopy and serology provide additional information to enable specific diagnoses to be made.
The diagnosis of coeliac disease is complicated by the need for the patient to be on a normal diet when tests are done, since gluten-free foods are widely available and not taken consistently. It may be difficult to persuade a patient to eat normally before a small bowel biopsy is performed to avoid inconclusive results. It should be easier to repeat the biopsy after 6 months on a true gluten-free diet to show normalisation of the total or subtotal villous atrophy (TVA/STVA) of genuine coeliac disease, but it generally proves impossible or impolitic to take a third biopsy on a resumed normal diet to clinch the diagnosis. By this stage patients are aware of the need for permanent rigorous diets and know of the likelihood of ill-health returning if they lapse, including increased risk of small bowel lymphoma and carcinoma.
6.1 Intestinal Biopsy
6.1.1 Endoscopic Forceps Biopsy
This is the standard procedure since it is rapid and reliable. The best results are obtained by taking multiple biopsies of the distal duodenum with the largest available size of forceps. The duodenal bulb is not ideal for non-targeted biopsy of apparently normal mucosa, but histological confirmation of visible abnormalities may occasionally be required.
The endoscope with the widest available channel should be used, with the largest compatible forceps.
6.1.2 Crosby-Kugler Capsule
The instrument consists of a small capsule (9.5 × 18.5 mm) containing a rotating, spring-activated knife. In the wall of the capsule is a small port through which mucosa is drawn by suction. Suction also serves to trigger the knife which severs the mucosa and closes the port, thereby trapping a portion of the mucosa in the capsule. The capsule is attached to a 2 mm polyethylene catheter which serves both for holding the capsule and for suction.
Various modifications of the capsule have been proposed. If the tubing is replaced by a radio-opaque red arterial catheter the whole tube may be seen on the fluoroscope and loops identified and straightened: in addition this catheter is stiffer and allows progress by pushing the capsule onwards. There are three methods for positioning the capsule.
6.1.2.1 Endoscopic Technique
This is a rapid technique and takes minutes. The tubing should be about 50 cm longer than the endoscope, and it is necessary to check catheter length and diameter before commencing the intubation. The patient is prepared for a normal upper digestive endoscopy. The valve of a forward-viewing instrument is removed, the capsule is loaded and threaded retrogradely through the biopsy channel so that the capsule lies snugly against the distal tip of the endoscope. The endoscope is then passed in the usual way, with slight tension on the biopsy capsule catheter to keep the end closely applied to the endoscope tip. The view is partially obscured, but it can be improved if necessary by advancing the capsule 2 cm from the end of the endoscope. The pylorus is located and the tip of the endoscope is held in position while 30 cm or more of the biopsy catheter is carefully advanced through the biopsy channel. The position of the biopsy capsule may be checked fluoroscopically but this is not necessary with experience. The Luer fitting is reattached. Between 5 and 10 ml of water followed by 10 ml air are flushed through the capsule tubing and the capsule is fired by applying suction: a 30 ml syringe is convenient for both purposes. The biopsy capsule is withdrawn to the tip of the endoscope and both removed together. The biopsy capsule is disassembled, the tissue sample floated in saline, examined using a 10× hand lens or under a dissecting microscope, and quickly immersed in formol saline. If enzyme studies are required the sample must be divided immediately and a portion frozen at once. Formalin inactivates disaccharides.
This method is fast, reliable and does not require fluoroscopy. It is, however, dependent on competent endoscopy. If upper gastrointestinal endoscopy is required in the same patient the instrument must be passed a second time.
6.1.2.2 Fluoroscopic Method
The patient fasts overnight. The capsule is swallowed with the patient sitting forward and about 50 cm of tube passed. The patient then lies on the fluoroscopy bed, and it is confirmed that the tubing is not curving in the fundus of the stomach. If it is the capsule must be withdrawn to the cardia and a further attempt made at passage.
The patient is then asked to lie on the right side and the position of the capsule is checked periodically. Once it is estimated to have passed the pylorus it is advanced to the duodenojejunal flexure and fired. The technique often takes 1 h or more, and various procedures have been proposed to facilitate it. A 100 cm outer polythene tube can be used to make the catheter more rigid until the capsule reaches the pylorus, and internal stiffening wires have been used for the same purpose. Another method is to given an IM injection of 10–20 mg metoclopramide 10 min after the capsule has been swallowed. This agent relaxes sphincters and hurries the passage of the capsule into the stomach and duodenum.
The fluoroscopy method requires either a prolonged intubation or heavy commitment of the investigator’s time with repeated fluoroscopy.
6.1.2.3 Traditional Method
The capsule is swallowed 2 h after the last meal of the day, which should be of light fluids. Thereafter only water is permitted. About 100 cm of tube is passed. The end of the tubing is attached to the cheek of the patient who is instructed to lie on the right side for a few hours. The following morning the patient is taken to the radiology department and the position of the capsule is identified. Sometimes it will be found to have passed well beyond the ligament of Treitz. The capsule is withdrawn into the required position if necessary, biopsies usually being taken just beyond the duodenojejunal junction. If ileal biopsies are required more time and tube must be allowed for the capsule to pass down the intestine, and because the capsule is frequently not in the right position the examination may take days to complete.
6.1.2.4 Complications
The Crosby-Kugler is a safe instrument and complications from its use are very rare. The major hazard is intestinal perforation, which is particularly liable to occur in children. There is occasionally haemorrhage from the biopsy site and failure of the knife to sever a piece of mucosa completely may make it impossible to withdraw the capsule until the mucosal fragment has sloughed off. In the latter event patience is required from clinician and patient: the capsule generally frees itself within a day or two and can be recovered, although the sample is usually too damaged to allow histological interpretation.
6.1.3 Rubin Suction Biopsy Tube
In this instrument a cylindrical knife fits into a capsule which is in turn attached to a flexible tube. Different capsules are available containing one or more ports of different sizes, and special double knives are provided for use with the multi-hole capsules. The knife is attached to a pull wire which runs through the flexible tube and stationary handle, and it is attached to an activator handle. Suction is applied via a lateral arm on the stationary handle thereby drawing mucosa into the port. A vacuum gauge is attached to the handle so that the force of suction is measured: this varies according to the age of the patient, the number of ports and the site of the biopsy. The capsule aperture is opened by pushing the activator handle (and therefore the knife) distally. The tube is passed with the knife positioned so that the port is closed. The procedure is best performed by two operators.
6.1.3.1 Method
After an overnight fast the patient is taken to the radiology department, the pharynx is anaesthetized and the suction tube is swallowed. The tube is positioned in the region of the pylorus under fluoroscopic control, when there may be marked heaving and gastric contractions. The tube is then guided into the duodenum by gentle pressure. Alternatively the patient lies on the right lateral position for about 10 min, is re-screened and the procedure repeated until the tube is seen to have passed into the duodenum.
Once in the duodenum the tube is usually readily positioned at the duodenojejunal flexure. The port is opened by pushing the knife forwards, suction is applied and a biopsy is obtained by traction on the activator handle. It is probably advisable to move the tube slightly and repeat the procedure to ensure that a biopsy is taken. The instrument is withdrawn with the knife in the closed position. The instrument is safe and significant haemorrhage or perforation is rare.
The appreciation that upper small intestinal disease may be patchy has led to the popularity of the hydraulic instrument devised by Flick, which delivers biopsies immediately after they have been cut and allows multiple biopsies to be taken from multiple sites at one intubation.
A steerable catheter with a contoured distal Rubin biopsy capsule has been devised. This requires fluoroscopy for passage, and its advantage is the rapidity with which it can be manoeuvred into position.
The choice of biopsy capsule and technique depends on personal preference. Use of the Crosby capsule allows only one biopsy can be obtained, whereas the hydraulic capsule offers the possibility of an indefinite number. Smaller Crosby capsules are available for use in children.
6.1.4 Interpretation
6.1.4.1 Dissecting Microscope
Normal appearance
The jejunal villi are long and finger-like and the vascular arcades are easily recognized. The height of a villus is about three times its width. Essentially similar features are found in the ileum. A normal variant is the broad, flat or leaf-shaped villus and this is seen particularly in duodenal biopsies where the leaves may even coalesce into ridges. An identical appearance may be seen in jejunal biopsy samples from normal subjects of Middle- or Far-Eastern extraction. These features may be identified with a hand lens.
Abnormalities
In coeliac disease the mucosal biopsy will be ‘flat’ or ‘convoluted’. A ‘flat’ mucosa shows a complete loss of villi and the normal vascular arcades. There may be a mosaic or crazy pavement appearance. The ‘convoluted’ mucosa has no true villi but only ridges and whorls. While examination under the dissecting microscope or hand lens is a rapid and convenient diagnostic procedure it does not replace conventional histology. It is usually easy to recognize an abnormal villous pattern; the difficulty lies in deciding when villi are minimally abnormal. In this situation light microscopy is essential.
6.1.4.2 Light Microscopy
Normal Appearance
Tall thin villi are seen lined by columnar epithelium. There are numerous goblet cells. Paneth and argentaffin cells may be seen at the base of the crypts of Lieberkuhn. Mononuclear cells, plasma cells and eosinophils are seen in the lamina propria, the thickness of which is about one-half to one-third the villous height. Similar features are found in both finger- and leaf-shaped villi. Brunner’s glands are seen in the duodenum occupying the full thickness of the glandular (non-villous) mucosa. Villi may be blunted or absent. In the ileum more goblet cells are found, and the villi are slightly broader and shorter. There are collections of lymphoid cells, and villi overlying such areas are either stubby or absent. Specimens from apparently normal subjects from the Middle- and Far-East show a greater proportion of blunt and branched villi, more abnormal surface cells and slightly more prominent mononuclear cellular infiltration.
It is important to appreciate the variations in the appearance of the normal small bowel biopsy. The suggestion has been made that the ‘finding of four adjacent villi in any section justifies an interpretation of normal villous architecture’.
Abnormalities
A number of diseases may be associated with minor non-specific abnormalities of the intestinal mucosa.
Coeliac disease
This is defined as the presence of total or subtotal villous atrophy which reverts to normal, or at least shows improvement, after the patient adheres to a gluten-free diet. It is important that milder abnormalities (partial villous atrophy) are not diagnosed as coeliac disease, because they are common and nonspecific findings.
Children with coeliac disease characteristically have total villous atrophy. There is virtual absence of the villi, thickening of the lamina propria, increased infiltration by lymphocytes and plasma cell, elongated crypts of Lieberkuhn, increase in the mucosal glands and obvious surface epithelial abnormalities with much increased intraepithelial lymphocytes. In less severe villous atrophy the villi are short, thickened and disorganized, the goblet cells are increased in number and there are lesser changes in the lamina propria. The mucosal changes in coeliac disease are seen maximally in the upper jejunum, but in severe involvement the changes will extend to the ileum. There is no correlation between the histological abnormalities and the absorptive function. A flat biopsy is found in some patients who do not respond to gluten withdrawal, and it is not possible to predict the response from the appearance of the intestinal biopsy. The typical appearance of coeliac disease may be found in the biopsies of patients who have, or will subsequently develop, intra-abdominal lymphomas or cancers of the gastrointestinal tract.
Similar appearances can occur in dermatitis herpetiformis, and these sometimes respond to gluten exclusion. Psoriasis may occasionally be associated with villous atrophy.
Tropical sprue
The distinction between coeliac disease and tropical sprue is difficult morphologically because both demonstrate moderate to severe villous abnormalities. In tropical sprue the extent of the villous loss is marked and there are uniform small lipid droplets in the basement membrane adjacent to the surface epithelium.
Abetalipoproteinaemia (acanthocytosis)
There is normal villous architecture, but the intestinal cells are filled with fat-containing vacuoles.
Whipple’s disease
The lamina propria is virtually replaced by macrophages filled with periodic acid-Schiff-positive glycoprotein granules. The normal villous architecture is distorted, and the lymphatics are dilated and filled with fat. Tiny bacilli can be seen on high-resolution light microscopy or with electron microscopy.
Agammaglobulinaemia
There is a complete absence of plasma cells. The villi may be near normal or totally atrophic, but the condition is readily differentiated from coeliac disease by this absence of plasma cells.
Other diseases
In the five conditions described above jejunal biopsy is invariably helpful. In some others, such as lymphangectasia, lymphoma, giardiasis, amyloidosis and Crohn’s disease, biopsy may be helpful but is not necessarily so. Non-specific changes include mild flattening and broad thickening of the villi, an increase in chronic cellular infiltration and minimal thickening of the glandular epithelium. Such an alteration is to be found in association with hepatitis, Crohn’s disease, jejunal diverticulosis, ulcerative colitis, kwashiorkor, pernicious anaemia, after partial gastrectomy and after neomycin therapy. Similar changes may be found in coeliac disease and cannot be used to substantiate the diagnosis. The mucosal biopsies are normal in disaccharide deficiency, iron-deficiency anaemia, peptic ulcer disease and pancreatic disease. Villous abnormalities have been described in association with certain skin diseases such as eczema and psoriasis. These are usually non-specific changes, but occasionally severe atrophy is indistinguishable from coeliac disease is present.
The biopsy specimen can be stained with special histochemical stains to show various intracellular enzymes such as alkaline phosphatase. The biopsy sample can be frozen to −20 °C and used for enzyme estimation. This technique has been used in the diagnosis of disaccharide deficiency states.
Electron microscopy has been used to identify subtle changes in the mucosa and to search for bacteria in Whipple’s disease.
6.2 Radiology (Figs. 6.1, 6.2 and 6.3)
6.2.1 Barium Contrast
Though the small intestine can be studied after radiological examination of the stomach has been completed, during the course of a barium follow-through series there is unpredictable emptying of the stomach. There may be irregular and excessive filling of the intestine and the barium-filled stomach may obscure parts of the intestine. These difficulties are obviated by the use of the Scott-Harden tube which enables the duodenum to be filled rapidly by a known volume of barium. In this manner a small bowel enema is performed using large volumes of relatively dilute barium.
Fig. 6.1
Normal small bowel enema
Fig. 6.2
Small bowel enema showing terminal ileal Crohn’s disease
Fig. 6.3
Ileo-colo-vesical fistula in Crohn’s disease
The normal small intestinal mucosa demonstrates a feathery pattern. On a follow-through in coeliac disease there is slowing of the transit time, the bowel lumen is dilated, intestinal folds appear thickened, and there is ‘stacking’ and clumping of the barium. Barium sulphate tends to flocculate in the presence of steatorrhoea, whether this is the consequence of intestinal or hepatic or pancreatic disease. The use of non-flocculating barium suspensions enables the radiologist to study the intestinal mucosa in the presence of steatorrhoea and it is of help in the diagnosis of Crohn’ s disease, strictures, diverticula and blind loops. The terminal ileum may be better outlined by a retrograde barium enema than by small bowel series.
Angiographic techniques are available and there is a selective technique in which the catheter is introduced into either the coeliac, or superior or inferior mesenteric artery. It is possible to demonstrate vascular lesions involving the major vessels supplying the gastrointestinal tract. In this way it is possible to demonstrate neoplastic disease of the bowel as well as the site of gastrointestinal bleeding.
Lymphangiography has proved of value in the diagnosis of retroperitoneal lesions and in the demonstration of abnormal intestinal lymphatics such as are found in intestinal lymphangiectasia.
Retrograde ileography via a colonoscopically placed catheter has been described.
6.3 Radio-Isotope Studies (Little Used Nowadays)
6.3.1 WBC Scanning
The patient’ s own white blood cells are labelled with 99mTc-HMPAO (hexamethyl propylene-amine oxime) and re-injected. Abdominal scanning will localize areas of inflammation by increased uptake. This is particularly useful in identifying sites of Crohn’s disease involvement in the small and large bowel. Appearances are not specific and corroborative evidence is necessary before a complete diagnosis is made. An alternative is the use of 111indium-labelled pooled human immunoglobulin. This avoids the need for handling of blood, but involves use of heterologous blood products.
67Gallium citrate localizes in tumours and inflammatory areas. It can be used to delineate ulcerative colitis and also abdominal abscesses in Crohn’s disease and other conditions, though uncomplicated Crohn’s disease usually yields negative scans. The technique is simple, but ultrasonography, radiology and digestive endoscopy probably yield the same information.
6.4 Enteroscopy (See Chap. 9)
This technique will provide visual information and also the possibility of biopsy in the small bowel. Conditions which can be identified are diaphragm disease and ulceration in patients being treated with NSAIDs, angiodysplasia, tumours and Crohn’s disease.
6.5 Protein Loss
Excessive protein loss into the gastrointestinal tract is a non-specific feature in a number of diseases directly or indirectly affecting the gastrointestinal tract. The loss of protein may present as oedema and hypoalbuminaemia, the clinical syndrome being known as protein-losing gastroenteropathy. Thus tests for the loss of protein into the bowel are important in the clinical investigation of a patient with unexplained hypoalbuminaemia and oedema, particularly when associated with gastrointestinal symptoms.
The quantitative evaluation of enteric protein loss has been attempted either using macromolecular substances with radioactive labels such as 131iodine or the inert polyvinylpyrolidine (PVP). However, the development of techniques for quantitating actual protein loss, and of labelling the patient’s own albumin in vivo represent an improvement.
6.5.1 Radio-Iodinated Serum Protein
131I- or 125I-labelled albumin can be used as the test substance. The method cannot be used for accurate quantitation of intestinal protein loss because of the rapid reabsorption of the radio-iodide label after catabolism of the protein in the gut, and also because of the secretion of the labelled iodine in salivary and gastric secretions.
6.5.1.1 Method
Preparations of radio-iodinated serum albumin which may be used to determine volume and cardiac output are not suitable for measuring intestinal protein loss: it is necessary to purchase commercial materials which are specially prepared for this purpose. Each new preparation of iodinated albumin must be tested in a control subject with normal protein metabolism.
The patient is given 0.5 ml aqueous iodine solution orally four times a day from the day before the test until the completion of the study. 2 MBq of radio-iodinated albumin are injected IV and blood samples are collected without a tourniquet 10–20 min later and then daily for 21 days. Quantitative 24-h urine samples are obtained throughout the study. All stools are collected and assayed for radioactivity. The serum albumin concentration is determined weekly.
The data may be analysed in a variety of ways. Isotope dilution measurements are made of the plasma volume and the intravascular and total albumin pools. The albumin turnover (g/day) is calculated and this equals the albumin synthetic rate if the patient is in a steady state. In protein-losing enteropathies the increased intestinal loss is reflected in an increased disappearance of plasma radioactivity, and faecal radioactivity is significantly elevated above normal values. Quantitative evaluation is not possible except where abnormal protein loss is restricted to the stomach when a quantitative study is possible using gastric suction.
This method is complex for routine use, but it provides much information which is of value for research purposes.
6.5.1.2 Other Methods
IV administration of autologous 111indium-labelled transferrin followed by abdominal imaging over 24 h is a useful technique to show protein loss. Tests using 59Fe-labelled dextran and 67Cu-labelled caeruloplasmin also give good results. Less than 1% of 59Fe-labelled dextran is normally found in stools in the 4 days after an IV injection of 0.002–0.004 MBq/kg, and this isotope is attractive because it is relatively cheap and it is stable. Simultaneous administration of 131I-labelled albumin and 125I-labelled IgG followed by differential faecal counting has been advocated as an index of small bowel activity in Crohn’s disease, where the ratio of 1251 to 1311 is >1.60.
6.5.1.3 Alpha1-Antitrypsin Clearance
Gastrointestinal loss of plasma proteins may also conveniently be measured by estimation of the faecal clearances of the endogenous marker alpha1-antitrypsin, which forms the main alpha1-globulin, with a serum level of 1.9–5.0 g/l. In protein loss the level in stools is higher, though the serum concentration is still usually within the normal range. A more sophisticated variant actually calculates alpha1-antitrypsin clearance over 10 days, but has the serious practical drawback of prolonged stool collection.
Indications
The tests are of value in any patient with oedema and low serum albumin concentrations in whom the cause of the hypoalbuminaemia is not apparent. Protein loss into the bowel has been recorded in congestive cardiac failure, giant rugal hypertrophy of the stomach, gastric cancer, intestinal lymphangiectasia, Crohn’s disease, Whipple’s disease, ulcerative colitis and allergic states involving the gastrointestinal tract.
6.6 Intestinal Bacteria
Under normal conditions the small bowel contains only low numbers of microorganisms. Bacterial overgrowth occurs in a number of disease states and the assessment of intestinal bacteria is of great value. Methods for determining the extent of bacterial proliferation in the bowel are:
- 1.
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