Endoscopy and Endosurgery

BSAVA Manual of Canine and Feline

Endoscopy and Endosurgery

Edited by Philip Lhermette and David Sobel

5

Flexible endoscopy: lower

gastrointestinal tract

James W. Simpson

Introduction

The lower gastrointestinal (GI) tract of the dog and cat is much simpler in its anatomical structure compared with many other species, comprising a simple tube which is divided into the caecum, colon, rectum and anus (Figure 5.1). As a result of this simple structure and the accessibility of the lower bowel, it is particu-larly well suited to examination by flexible endoscopy, which is fortunate because disease of the colon is very commonly seen in small animal practice. Previously, radiographs, barium studies and possibly laparotomy to obtain biopsy samples were required, which was time-consuming and expensive. Endoscopy provides a simple and readily available method of

examining the entire mucosal surface of the lower bowel and permitting collection of biopsy samples to ensure a definitive diagnosis is obtained, which has revolutionized the diagnosis of lower bowel disorders in most patients.

For those clinicians considering the use of endo-scopy, examination of the lower bowel is relatively easy to carry out and offers the best site to develop the necessary skills needed and build confidence, whilst at the same time obtaining diagnostic informa-tion which will benefit the patient.

Indications

Clinical signs of lower GI disease are generally those of diarrhoea with or without fresh blood (haemato-chezia) and mucus, tenesmus, dyschezia and/or con-stipation. None of these clinical signs are pathognomonic of any individual disorder of the lower bowel (Figure 5.2). Although many of these condi-tions can be diagnosed endoscopically, it is very important to start the investigation with collection of a detailed history and to carry out a thorough physical examination. The physical examination must include a rectal examination to assess anal sphincter func-tion, check for disease of the anal sacs and to exam-ine the rectal tissue for strictures, obstruction and deviation. The clinical examination will help to rule out systemic disease and will support the presence of a primary lower bowel problem.

Transverse colon Ascending colon Ileum Caecum Descending colon Rectum Anus

Anatomical structure of the lower GI tract.

5.1 5.2 Disorders of the large intestine.

Disorder Comments

Colitis Lymphocytic–plasmacytic; eosinophilic; histiocytic; granulomatous

Infection Salmonella spp.; Campylobacter spp.; Yersinia

spp.; Clostridium spp.; Trichuris vulpis; Giardia;

Uncinaria spp.

Caecal disorders Typhlitis; caecal inversion; caecal abscessation; perforation; neoplasia

Intussusception Ileocaecal; caecocolic; colocolonic

Neoplasia Adenocarcinoma; lymphoma; leiomyosarcoma Rectal disorders Stricture; adenomatous polyps;

Where the patient’s primary clinical signs include rectal tenesmus and dyschezia associated with the passage of formed faeces or ribbon-like faeces, this suggests a partial obstruction in the distal colon, rec-tum or anus. A rectal examination will help determine if anal sac disease or an anal sphincter problem exists, whilst flexible endoscopy will permit visualiza-tion of the rectal and distal colonic mucosa in order to observe the cause of the obstruction. Where a mass is found, biopsy samples should be collected in order to determine whether benign or malignant neoplasia is present. Similarly, where a stricture is detected, biopsy samples should be collected as these lesions can have an underlying neoplastic aetiology.

Many patients with lower bowel disease present with chronic diarrhoea (± blood and mucus), tenesmus and dyschezia. The starting point in this investigation should be a faecal analysis to look for pathogenic bacteria and parasites. Where infection is detected, suitable treatment should be provided and the patient reassessed at a later date. In addition, diet should be carefully scrutinized and where this is found to be inappropriate, dietary corrections should be made.

In those patients where systemic disease, dietary factors and infection have been ruled out and clinical signs have persisted, the most likely cause of the lower GI signs is colitis. Endoscopic examination of the rectum, colon and caecum should now be considered. If there is significant faecal blood loss consideration should be given to assessing a clotting profile, which should include: manual platelet count; prothrombin time; and activated partial thromboplastin time to rule out any clotting defect. Pre-anaesthetic blood tests can be carried out at the same time.

Colitis is generally a diffuse disease, which affects the entire colon; however, there are occasions when only part of the colon may be affected. It is therefore wise to examine the entire colon from rectum to ileocaecocolic junction in all patients. Biopsy samples should be collected both from all visually affected tissue and from apparently normal tissue, and submitted for histopathology.

When carrying out lower GI endoscopy it is often possible, with careful preparation of the patient, to reach and then enter the ileum. Where the patient presents with vomiting and diarrhoea, and the char-acter of the faeces does not clearly reflect large intes-tinal disease, it is not uncommon to carry out an upper and lower GI endoscopic examination at the same time. Where a protein-losing enteropathy or inflam-matory bowel disease (IBD) is suspected, this permits both the cranial and distal small bowel to be exam-ined and biopsy samples collected, thus improving the chances of obtaining a definitive diagnosis.

Irritable bowel syndrome (IBS) is a condition that has been identified in the dog but not in the cat. The clinical signs can be identical to those seen with colitis. As there is no definitive diagnostic test for IBS, the only method of obtaining a definitive diagnosis is by ruling out all other causes of the clinical signs, especially colitis. Endoscopic examination of the lower bowel should be used as part of the investigation. In IBS patients, biopsy samples will reveal no evidence of inflammation or neoplasia.

Disease of the caecum (see Figure 5.2) is rare in dogs and cats. Typhlitis is the most common disease, and is usually the result of whipworm infection or severe inflammation often associated with colitis. Endoscopy will assist in the diagnosis of typhlitis and other caecal disorders including caecal inversion, abscessation and neoplasia.

Flexible endoscopy of the lower GI tract is also extremely useful for evaluating the patient’s response to treatment, whether this be associated with inflam-mation or neoplasia. As no surgical intervention is involved and only a light plane of anaesthesia is required, many owners will permit follow-up endo-scopy. Endoscopy also permits evaluation of healing following surgical resection.

Instrumentation

Unfortunately, in small animal practice patients range in size from kittens to Great Danes. Consequently, the size of the large bowel varies considerably both in diameter and in overall length. In large breeds of dog, the entire 1 m length of the endoscope will be required in order to reach the ileocaecocolic junction. The choice of endoscope will also depend on whether upper GI endoscopy is to be carried out in the prac-tice. It is not possible to have a single ‘universal’ endoscope which will be suitable for kittens through to Great Danes, and for both upper and lower GI endoscopy. A compromise will normally be made in selecting an endoscope which will be suitable for the majority of patients.

Endoscope specifications for lower bowel exam-ination include an end-viewing flexible endoscope with an outside diameter of less than 9 mm and an insertion tube length of at least 1 m. The biopsy chan-nel must be at least 2 mm in diameter and the endo-scope must have an air and water (wash) facility together with four-way tip deflection (Figure 5.3). Such an endoscope would also be suitable for carry-ing out upper GI examinations, although it is likely to be too large for small breeds of dog and cats, espe-cially when attempting intubation of the duodenum.

For carrying out an endoscopic examination of the large bowel in both dogs and cats, a forward-viewing endoscope should be selected, with an insertion tube length of at least 1 m and an outside diameter of less than 9 mm. There must be a wash and air facility, and a biopsy channel of at least 2 mm in diameter.

In addition to the flexible endoscope, standard accessories required for lower bowel endoscopy include a suitable light source with an air and water facility, and biopsy forceps. A suction unit is useful but not essential.

Rigid endoscopes

Although flexible endoscopes are now routinely used for examination of the large bowel, there is a place for the use of rigid endoscopes in the examination of the rectum and distal colon. It can be very difficult to visualize the rectal mucosa using a flexible endoscope because air used to inflate the rectal lumen escapes through the anus. Rigid endoscopy can allow the rectal mucosa to be examined without need for air inflation, but in some cases this is still required. This in turn allows biopsy sample collection from this region to be carried out more easily.

Care should be exercised in choosing the diameter of the rigid endoscope for this procedure, to ensure adequate visualization without causing tissue damage. Illumination may also be a problem in some cases, as the light beam tends to be small with these units. In general, biopsy forceps used with rigid endoscopes allow a much larger biopsy sample to be obtained because there is no restriction in the size of the biopsy channel, as occurs with flexible endoscopes.

Biopsy

When first starting to collect endoscopic biopsy sam-ples, it is not uncommon to receive reports from the pathologist indicating the samples were undiagnostic due to the size of the samples or due to crush arte-fact. In order to reduce crush artefact when collecting large bowel biopsy samples, forceps with fenestrated cups and no central spike (Figure 5.4) should be used. The fenestrated cups permit a captured biopsy sample to expand through the fenestrations, so reduc-ing tissue damage durreduc-ing collection. To ensure an adequate biopsy sample is obtained it is very impor-tant to direct the biopsy forceps so they open perpen-dicular to the mucosa (Figure 5.5). If the biopsy forceps are used parallel to the mucosa, only the sur-face cells will be harvested and the sample will be non-diagnostic. Directing the biopsy forceps perpen-dicular to the mucosa is relatively easy at the junction between the transverse colon and the ascending or descending colon. However, in the descending colon

Careful selection of biopsy forceps will ensure crush artefact is reduced to a minimum. Forceps with a central spike should not be used; those forceps with fenestrated biopsy cups should be selected.

5.4

No

(a)

Yes

Yes

(a) Method of collecting biopsy samples from the colon. (b) The forceps should be advanced as near perpendicular to the mucosa as possible. This will ensure a good depth of sample is collected.

5.5 (b)

this is more difficult. To assist in sample collection from the descending colon, it is important to ensure that it is not over distended, causing the mucosa to be ‘stretched’. The forceps should be advanced until the mucosa ‘tents’ and then the forceps are closed, in this way much more tissue is collected.

Patient preparation

It cannot be overemphasized how important patient preparation is to carrying out lower GI endoscopy. It is simply not possible to examine the colon of a patient with solid or liquid faecal material present (Figure 5.6). When an endoscope comes into contact with fluid or faeces, light is refracted and ‘red-out’ occurs (see Chapter 3), so the procedure has to be abandoned and the patient recovered from anaesthesia.

Enemas should be administered using a Higginson’s Pump (Figure 5.8); however, prior to use it is extremely important to carry out a rectal examina-tion to ensure it is safe to insert the pump into the rec-tum. It is also important not to induce damage to the rectal mucosa whilst carrying out an enema, as this may be mistaken for pathological change when carry-ing out the endoscopy. Lastly, the solution used must be non irritant, otherwise the mucosa will become hyperaemic and inflamed, resulting in difficulty in vis-ual interpretation of the mucosa. The author finds warm water enemas extremely satisfactory at no more than 15 ml/kg. Individual patients and especially small breeds may require smaller volumes to prevent rupture of the colon. Ideally, the first enema should be given on the day prior to the endoscopy with two fol-low-up enemas given on the morning of the proce-dure. However, it is also acceptable to give two or three enemas on the morning of the procedure until the material voided by the patient is free of faeces.

Laxatives which may be used in the treatment of constipation in dogs and cats. Those in bold are useful in preparation for large intestinal endoscopy.

5.7 Type of

laxative Examples Emollient Liquid paraffin Bulk Sterculia

Ispaghula Wheat bran Osmotic Magnesium sulphate

Lactulose (1–15 ml orally q8h for dogs and 0.2–1 ml for cats)

Sodium citrate (Microlax) 1 x 5 ml tube per rectum Phosphates

Stimulant Bisacodyl (Dulcolax) (5–20 mg/dog or 2–5 mg/cat orally

Polyethylene glycol (Klean Prep) <20 ml/kg o.s.

Careful preparation of the large bowel is essential if the entire mucosal surface is to be thoroughly examined. The presence of faeces severely restricts the ability to carry out this examination.

5.6

Careful preparation of the patient is essential. Food should be withheld for 24 hours prior to the pro-cedure to ensure that the distal small intestine is empty and that the colon, which has been carefully prepared by repeated enema administrations, will not slowly refill. An oral laxative may be given at this time to assist in emptying the small intestine (Figure 5.7). Many references quote the use of polyethylene glycol preparations, such as ‘Klean Prep’, which will rapidly cleanse the bowel. However, in the author’s exper-ience, dogs and cats find these agents distasteful and difficult to administer in the required volume.

Thorough preparation of the large bowel for endoscopy is essential. A Higginson’s pump is a very effective method of administering an enema, although commercial enema preparations may also be used.

5.8

Premedication and anaesthesia

Although lower GI endoscopy is carried out without anaesthesia in humans, this is rarely the case in canine practice and never in feline practice. The author has tried various sedative combinations in dogs and has found the use of acepromazine maleate (ACP) at 20 µg/kg together with buprenorphine at 20 µg/kg i.m. an effective method of restraint where the risk of gen-eral anaesthesia is high. However, in the majority of patients and always in those under going both upper and lower GI endoscopy, a general anaesthetic should be used. Following successful enema administration, the patient should receive a premedicant followed by induction with an intra venous agent before intubation and maintenance on gaseous agents.

Patient positioning

Where flexible endoscopy is used, the patient should always be placed in left lateral recumbency (Figure 5.9) as this ensures the descending colon lies

ventrally, which aids intubation of the transverse and ascending colon and assists in drainage of any fluid from the transverse and ascending colon. However, where rigid endoscopy is used, right lateral recumbency is preferred. It is useful to lightly tie a linen bandage round the tail from its base to the tip, especially in long-haired breeds, as this prevents soiling and aids visualization of the anus.

Procedure

The distal 20 cm of the insertion tube should be lightly lubricated using KY Jelly, taking care to avoid the lens, as this will reduce friction and aid forward movement of the endoscope in the colon. The tip of the insertion tube should be inserted into the rectum for about 10 cm, so long as there is no resistance to movement. The rectum should now be inflated but the endoscope should not be advanced until the mucosa of the descending colon can be clearly seen (Figure 5.10).

Occasionally, air will escape through the anus preventing dilation of the bowel. In this situation it may be necessary to pinch the anus to make the rectum air tight. The descending colon should now be clearly seen directly in front of the endoscope tip. The mucosa should appear pale pink in colour, thin and transparent so that the submucosal blood vessels can be observed (Figure 5.11). Inexperienced

To aid intubation of the transverse and ascending colon, and to ensure that any residual fluid does not interfere with the endoscopy, the patient should always be placed in left lateral recumbency.

5.9

Once the endoscope has been advanced into the rectum, the lumen should be inflated with air. It should now be possible to visualize the descending colon extending in front of the endoscope.

5.10

endoscopists sometimes consider detection of these blood vessels as a sign of inflammation; this is not the case. In fact failure to see these blood vessels often suggests thickening of the mucosa, which may be due to either inflammation or neoplasia.

Once the lumen of the descending colon has been observed, the endoscope can be advanced examin-ing the entire circumference carefully for pathological change. If this is not done, damage to the mucosa caused by passage of the endoscope may later be misdiagnosed as pathological. The junction between the descending and transverse colon will be readily detected as an obvious ‘bend’ at the end of the straight descending colon (Figure 5.12). The tip of the endo-scope should be moved in the direction of the bend and advanced slowly. It is not uncommon to induce ‘red-out’ whilst doing this, as the endoscope brushes along the mucosa. Once in the transverse colon an image of the mucosa should be re-established and the procedure continued as before. The next ‘bend’ marks the junction of the transverse and ascending colon, and the endoscope should be manoeuvred as before to enter the ascending colon. Again visualiza-tion of the luminal circumference should be estab-lished before proceeding. More air may be required whilst carrying out these two procedures. There is lit-tle danger of over-distension so long as the anus is not continually occluded, as it will act as a safety valve to relieve pressure.

As the endoscope is advanced along the descending colon, eventually a ‘bend’ will be observed, which represents the flexure between the

descending and transverse colon. This is a normal anatomical landmark, which will be observed on a second occasion as the endoscope reaches the flexure separating the transverse and ascending colon.

5.12

The ascending colon is short and ends at the ileocaecocolic junction. The ileum appears as a raised red button-shaped structure whilst the caecum is a blind-ending sac.

5.13

The ascending colon is short and ends at the ileocaecocolic junction (Figure 5.13). This is readily identified by the opening into the blind-ended caecum and the raised prominent and usually red ileocolic sphincter.

The mucosa of the colon should appear pale pink in colour and the submucosal blood vessels should be clearly visible through the thin mucosal layer.

5.11

The caecum should be carefully examined as this can become inflamed (typhlitis) or may contain the nematode Trichuris vulpis. If the ileum is to be exam-ined, the tip of the endoscope should be directed towards the ileocolic junction and advanced. However, it is extremely unlikely that the ileum will be intubated unless the insertion tube diameter of the endoscope is less than 7 mm, except in large breeds of dog. Another limiting factor in large dogs is where the entire length of the insertion tube is required to reach the ileocaeco-colic junction, leaving no available length to intubate the ileum. Under these circumstances it is permissible to advance biopsy forceps ‘blindly’ into the ileum and collect biopsy samples. This must be done with care and where any resistance to forward movement is detected, the procedure should be stopped.

Lymphocytic–plasmacytic colitis

Lymphocytic–plasmacytic colitis is the most common form of colitis seen in the dog and cat. It is character-ized by an infiltration of the mucosa with lymphocytes and plasma cells. There appears to be a breed predis-position in the Golden Retriever. Macroscopically, this may be suspected by the presence of hyperplastic lymphoid tissue, which can appear like small ‘dough-nuts’ on the mucosa (Figure 5.14) and where the sub-mucosal blood vessels can no longer be seen. It is very unusual for ulceration to be observed in this form of the disease and the mucosa is not usually friable. Following examination of the entire large bowel, the

endoscope is withdrawn slowly and biopsy samples are collected. In areas where no gross lesions have been found, 2 or 3 biopsy samples should be collected from the ascending and transverse colons and a further 4 or 5 from the descending colon. This will give a good representative sample for the pathologist to judge the health of the colon. Where a specific lesion is detected, biopsy samples should be collected from the ‘lesion’ and from surrounding apparently ‘normal’ tissue. These specimens should be placed in separate pots, so the pathologist can compare tissue samples. The exact location of any lesion should be carefully noted by recording the distance marked on the insertion tube at the anus, which is given in centimetres. This will be useful in any follow-up endoscopy so the exact site of the lesion can be quickly found.

The rectum is difficult to examine as the endo-scope is inserted through the anus. As previously described, air often leaks out through the anus, mak-ing dilation of the rectum extremely difficult. Even quite large tumours can be missed if the rectum is visualized as the endoscope is inserted, due to folds in the rectal mucosa. Therefore, the author has found that inserting the endoscope through the rectum and into the distal descending colon, then inflating the lumen with air and slowly withdrawing the endoscope while maintaining air inflation, allows good visualiza-tion of the rectal mucosa. Retroflexing the endoscope is another method of examining the rectum but can only be successfully carried out in larger dogs.

Where a stricture is detected in the rectum or colon, it is often extremely difficult to advance the endoscope. This is because the stricture forms a ‘lip’ around the circumference, which catches the endoscope and prevents further forward movement. Although most strictures are inflammatory in origin, some may be due to neoplasia, and so collection of biopsy samples from the base of strictures is essential prior to deciding on appropriate treatment.

Pathological conditions

Colitis

Colitis is the commonest form of large intestinal dis-ease seen in the dog and cat. Although bacterial pathogens and parasitic infections can be inciting causes, in the majority of patients the clinical signs are chronic and no underlying aetiology is deter-mined. Colitis is generally a diffuse disease involving the entire colon, and may also occur in conjunction with similar changes in the small intestine. These changes, whether purely large bowel or involving both the small and large bowel, come under the umbrella of inflammatory bowel disease. At this time no aetiological agent has been found for IBD, which is usually classified according to the predominant cell type present: lymphocytic–plasmacytic; eosino-philic; histiocytic.

Rarely, granulomatous colitis is detected, which differs from the other forms of colitis because it is often a focal disease and involves only a small section of the large bowel.

Lymphocytic–plasmacytic colitis results in thickening of the mucosa so submucosal blood vessels can no longer be seen, and in many cases lymphoid hyperplasia will be observed as raised ‘doughnut’-shaped structures.

5.14

The mucosa in some cases, particularly those with a long history of disease, may become much more severely affected, with marked proliferative changes suggestive of a neoplastic disease (Figure 5.15). It is very important not to assume that neoplasia is present

Occasionally, lymphocytic–plasmacytic colitis may be severe. In such cases proliferative changes may be observed suggesting the possible presence of neoplasia. It is essential to collect biopsy samples for histopathology and not to over interpret the visual changes.

and biopsy samples should always be collected for histopathology, in order to confirm which type of disease is present. Biopsy samples reveal this form of colitis is associated with increased numbers of plasma cells and lymphocytes, activation of CD4 T helper cells and an increased production of Th1 cytokines. In some cases, crypt abscessation has also been reported and increased numbers of goblet cells and/ or fibrosis may also be observed, depending on the chronicity of the case.

However, occasionally lymphoma and lymphocytic–plasmacytic colitis may appear grossly and histologically very similar. Where a uniform population of lymphocytes are present and lymphoma is suspected, immunocytochemistry should be carried out to determine the type of cells present. If a monoclonal population of lymphocytes is present then a diagnosis of lymphoma may be made.

Eosinophilic colitis

Eosinophilic colitis is less common than lymphocytic– plasmacytic colitis and is mainly seen in the dog. Cats rarely develop this form of colitis. Macroscopically, eosinophilic colitis is characterized by the presence of mucosal erosion and ulceration, loss of submucosal blood vessels, and the mucosa is much more friable, bleeding easily when the endoscope touches it (Figure 5.16). Histologically, it is quite common for there to be an increased numbers of plasma cells and lymphocytes together with a predominance of eosinophils. Where ulceration is severe it is not uncommon to detect varying numbers of neutrophils in the biopsy samples as well.

Histiocytic colitis may appear very similar to eosinophilic colitis. Ulceration, friability and bleeding are common. Proliferative changes may also be observed.

5.17

Eosinophilic colitis results in destructive changes to the mucosa. There are frequently small erosions and/or ulcers present. The mucosa is more friable and bleeds easily on manipulation.

5.16

Where granulomatous colitis is found, the majority of the colon will appear normal and only a small section of the colon will be affected. The lumen of the bowel may appear occluded by proliferative change and bleeding is not uncommon. This must be differentiated from neoplasia by collection and examination of biopsy samples.

5.18

plasma cells, MHC class II cells and PAS cells in the lamina propria. Neutrophils may also be observed and there is usually a reduction in the number of goblet cells.

Granulomatous colitis

Granulomatous colitis is the rarest form of colitis in the dog and is not seen in the cat. This form of colitis often only involves one small region of the colon. The major-ity of the colon will look grossly normal on endoscopy, but often in the transverse or ascending colon a rela-tively small area of mucosal proliferation will be found, which bulges into the lumen of the colon occluding fur-ther forward viewing. These proliferative changes are often accompanied by ulceration and bleeding. It is not normally possible to pass the endoscope further along the colon in these patients (Figure 5.18). The main differential diagnosis in these cases is neoplasia. Therefore, it is essential to collect biopsy samples to rule out neoplasia, particularly adenocarcinoma.

Histiocytic colitis

Histiocytic colitis is a rare form of colitis in the dog and never seen in the cat. It is most often seen in young adult Boxers and French Bulldogs, although the author has seen histiocytic colitis in other breeds as well. In this form of colitis there are gross and diffuse changes to the mucosa, which can be severe with frank bleeding and marked proliferative changes suggestive of neoplasia (Figure 5.17). Biopsy reveals the presence of a mixed cell population with significantly increased numbers of CD3 T cells, IgG

Irritable bowel syndrome

This is a condition which was first recognized in humans and has subsequently been strongly suspected as occurring in the dog but not the cat. Working dogs in particular appear to be predisposed to this condition and present with clinical signs typical of colitis, namely, chronic small volume diarrhoea often containing mucus and sometimes with accompanying rectal tenesmus. Haematochezia is not a feature of this condition. Some dogs may appear to exhibit abdominal pain, which is thought to be associated with colonic spasm. As the majority of these dogs are working dogs, it has been observed that resting them from their duties results in resolution of the clinical signs. Pet dogs of a highly nervous disposition should also be suspected of having IBS.

Unfortunately, there is no definitive diagnostic test for IBS, so the only way in which a diagnosis can be made is by ruling out all other causes of large intestinal disease. Therefore, a full clinical examination should be carried out to rule out systemic disease, followed by faecal analysis and routine blood haematology and biochemistry. These diagnostic tests will rule out infections and systemic disease.

This should be followed by endoscopy to rule out IBD (colitis), which is the most likely differential diagnosis. In patients with IBS, no gross mucosal lesions will be observed during the endoscopic examination and biopsy samples for histopathology will usually reveal normal mucosa, but in some cases increased numbers of goblet cells may be present. However, at endoscopy it may be noticed that there are large amounts of mucus adhering to the mucosa (Figure 5.19) and the colon itself may be difficult to dilate due to colonic spasm. Both these clinical signs are typical of the IBS patient.

especially in the caecum. Lymphoma is generally a diffuse condition that affects the entire colon and may appear very similar to lymphocytic–plasmacytic colitis. In some cases, pathologists may find the differentiation between lymphocytic–plasmacytic colitis and lymph oma difficult. In such cases, immunocytostaining to determine whether a monoclonal population of lymphocytes is present allows the differentiation to be made. The author has observed cases where lymphocytic–plasmacytic colitis has been diagnosed but on follow-up endoscopy lymphoma has been diagnosed. Such cases may not truly reflect a progression from one disease to another, but difficulty in differentiation. The lumen of the bowel is rarely occluded but thickened, and bleeding is not normally a feature. Therefore, it is rarely possible to make a diagnosis from visual examination of the colon, and biopsy samples should be collected in order to reach a definitive diagnosis.

Adenocarcinoma is normally a more focal disease of the colon and may appear very similar to granulomatous colitis (described above). The majority of the colon will appear macroscopically normal, but an area of proliferative change and bleeding, which may occlude the lumen of the colon, will be found (Figure 5.20). The mass may be very friable and irregular in outline, and secondary infection is common. Conse quently, superficial biopsy samples often only reveal inflammation and infection. In order to confirm neoplasia deeper biopsy samples are essential. This is achieved by carefully collecting several biopsy samples from the same site within the mass. The superficial samples may reveal only evidence of inflammation, whilst deeper samples may be more typical of neoplasia. Great care is required when carrying out this ‘mining’ for tissue, to ensure that only the proliferative mass is sampled and the bowel is not perforated.

IBS is difficult to diagnose as there are no visual or pathological changes present. However, at endoscopy the bowel may be difficult to dilate and an excessive amount of mucus may be observed.

5.19

Adenocarcinoma is an aggressive tumour, which invades the lumen of the colon. The tumour will appear irregular and proliferative in

appearance, may bleed easily and may even appear very friable to touch. The remainder of the colon usually remains unaffected.

5.20

Neoplasia

Colonic neoplasia is most often associated with lymphoma or adenocarcinoma in the dog and cat, although leiomyosarcoma may rarely be diagnosed,

Colonic vascular ectasia

This is a very rare condition of the canine colon, which has been observed sporadically throughout the world; it has not been described in the cat. Patients present with a history of acute episodes of passing large amounts of fresh blood in their faeces. There is often an associated anaemia but no other evidence of systemic disease or coagulopathy. Endoscopy will reveal a focal area where there are enlarged, dilated mucosal blood vessels, whilst the remaining colon appears completely normal. Biopsy is not recommended in these cases due to the risk of inducing a major haemorrhage. Patients should be referred for surgical exploration and resection of the affected bowel. It is therefore very important to measure the exact location of the lesion, using the insertion tube ruler, in order to assist the surgeon in locating the lesion at laparotomy. In humans, laser cautery using diode or argon lasers may be used to treat these cases, although this has not been reported in the dog. See Chapter 14 for more information on endoscopic laser surgery.

A similar condition has been observed in both humans and animals, and no obvious underlying cause has been identified. This lack of agreement as to what type of change is being observed in these patients has resulted in considerable variations in terminology used to describe the lesions, which includes angiodysplasia, arteriovenous malformation and vascular ectasia.

Caecal disorders

Typhlitis, although rare, may be diagnosed on its own, associated with whipworm, or in conjunction with severe colitis. Whipworms (Trichuris vulpis) will be observed at endoscopy and biopsy samples will reveal evidence of inflammation with similar cellular infiltrations to those found in the colon.

When a mass is found within the caecum this may be due to neoplasia or abscessation. Great care is therefore required in collecting biopsy samples in this situation, and surgery may be considered the safer option for obtaining a definitive diagnosis and correcting the problem.

Intussusception

Both ileocolic and ileocaecal intussusception occur in the dog and cat, although the former is more common than the latter. In both cases, patients may present with chronic diarrhoea with or without blood. Therefore, it is not unreasonable for endoscopy to be used in the investigation of these cases. Intussusception is readily recognized at endoscopy (Figure 5.21) and, when found, the endoscopic examination should be immediately halted and the patient referred for surgery.

Constipation

Endoscopy in constipated animals is rarely carried out for the obvious reason that it is impossible in the presence of large volumes of faecal material. However, constipation carries a large list of differential diagnoses, which includes partial obstruction of the distal colon and rectum. In such cases, once the

faecal mass has been cleared, endoscopy may be a useful method of examining the distal large bowel for evidence of disease.

Rectal adenomatous polyps

Rectal polyps are a common cause of rectal tenesmus, haematochezia and malformed faeces in the dog. They most often occur in the older dog and in the smaller breeds, especially the West Highland White Terrier. A rectal examination may detect a mass but because polyps are friable and soft in consistency, they can sometimes be difficult to palpate. Where a polyp is suspected, endoscopic examination to assess the extent of the lesion and to collect biopsy samples is essential. Some of these rectal masses are benign adenomatous polyps, whilst other may be malignant carcinomas.

Enemas administered prior to proctoscopy must be carried out with great care, and in some cases should be avoided due to the risk of tissue damage and induction of bleeding. Each case must be individually assessed for risk and in some patients endoscopy may have to be carried out with little preparation.

In order to examine the rectum thoroughly, the dis-tal end of the endoscope should be lubricated (as pre-viously described) and gently inserted into the rectum to about 10 cm. If resistance is felt the procedure should be halted, and in some cases a gloved finger may assist in directing the endoscope into the rectum. Once at the 10 cm mark, the colon should be inflated with air until the descending colon can be clearly seen; the endoscope should then be gently withdrawn under positive air insufflation whilst viewing the entire circumference of the rectum. The polyp will come into view during this procedure and its size and its exact position can be determined (Figure 5.22). The mass is usually markedly proliferative, partially obstructs the lumen of the rectum, bleeds readily and appears very friable. Biopsy samples can be taken from the proliferative mass but additional samples must be taken from the base of the mass where it attaches to

Observation of an intusussception when carrying out large bowel endoscopy is rare. However, when present the ileum will appear as a normal pink colour filling the lumen of the colon, with no bleeding or ulceration in the majority of cases.

References and further reading

Fan TM, Simpson KW, Polack E, Dykes N and Harvery J (1999) Intestinal haemorrhage associated with colonic vascular ectasia (angiodysplasia) in a dog. Journal of Small Animal Practice40, 25–30

German AJ, Hall EJ, Kelly DF, Watson AD and Day MJ (2000) An immunohistochemical study of histiocytic ulcerative colitis in Boxer dogs. Journal of Comparative Pathology122, 163–175

Hall EJ, Rutgers HC, Scholes SFE, et al. (1994) Histiocytic ulcerative colitis in Boxer dogs in the UK. Journal of Small Animal Practice35,

509–515

Jamieson PM, Simpson JW, Kirby BM and Else RW (2002) Association between anal furunculosis and colitis in the dog: preliminary observations. Journal of Small Animal Practice43, 109–114

Knottenbelt CM, Simpson JW, Tasker S, et al. (2000) Preliminary clinical observations on the use of piroxicam in the management of rectal tubulopapillary polyps. Journal of Small Animal Practice41, 393–

397

Ridyard AE, Nuttall TJ, Else RW, Simpson JW and Miller HR (2002) Evaluation of Th1, Th2 and immunosuppressive cytokine mRNA expression within the colonic mucosa of dogs with idiopathic lymphocytic–plasmacytic colitis. Veterinary Immunology and Immunopathology86, 205–214

the mucosa. The reason for this second biopsy site is to help determine its malignancy. Samples from the main mass are often difficult to interpret due to the amount of secondary infection present. This differen-tiation is not possible from visual assessment of the mass alone as both malignant and benign tumours can look very similar. Clearly, making such a differen-tiation has major prognostic implications.

Rectal stricture

Strictures of the rectum occur reasonably commonly in dogs but less so in cats. Although the aetiology in the majority of cases is rarely determined, it is assumed that the majority are the result of trauma or inflammation, which heal by fibrosis. However, there is a significant minority which may be due to neoplasia. So, where a rectal stricture has been detected by rectal examination, it is wise to carry out an endoscopic examination of the tissues to assess the mucosal changes present (Figure 5.23) and to collect biopsy samples to rule out neoplasia, prior to treatment.

Rectal adenomatous polyps can be diagnosed easily with the aid of endoscopy. They appear very similar to adenocarcinoma and must be differentiated from the latter.

5.22 Rectal strictures often appear as an obvious

narrowing of the lumen and a circumferential lip may prevent forward movement of the endoscope past the stricture.