Tumors of the Gastrointestinal Tract: Endoscopic Diagnosis
Patrick Lecoindre, DVM, Dip ECVIM(CA)
TUMORS OF THE OESOPHAGUS
Primary oesophageal tumors are rare. Squamous cell carcinoma is the most common primary oesophageal neoplasm in old cats. In dogs, we observe fibrosarcomas and osteosarcomas developed from spirocercal granulomas. Endoscopy and biopsy are indicated for the definitive diagnosis of oesophageal neoplasia. Endoscopically these tumors appear commonly as proliferative and obstructive mass often very ulcerated.
TUMORS OF THE STOMACH
Malignant gastric tumors in dogs
In the canine species, malignant tumors of the stomach are classically considered infrequent and account for less than 1% of all neoplastic diseases. Recently, numerous authors have reported that an increasing number of neoplastic diseases of the stomach have been observed in the dog. It is however difficult to determine whether this finding is related to a change in environmental factors (diet, etc.) or the increasing sophistication of diagnostic resources, particularly endoscopic and ultrasonic resources . Histologically, epithelial tumors (carcinoma, adenocarcinoma) predominate and account for 70 to 90% of the malignant gastric neoplasms in the dog. Leiomyosarcoma and lymphoma are the other 2 types of gastric cancer most frequently described in the dog.
All the studies to date show that the mean age of age of dogs presenting with cancer is 8 to 10 years. The predisposing influence of sex is not clear and the observations are contradictory. One study suggested that 7-fold more males than females (as a function of histological subtype) may present with gastric neoplastic disease.
Certain breeds seem to be more predisposed (Welsh collie, collie, chow chow). In the Welsh collie, a genetic mechanism may contribute to the pathogenesis of the disease.
The gastrointestinal symptoms of gastric cancer are little specific. Vomiting predominates. The frequency, time to onset following food intake and appearance of the vomitus depend on the case and the stage of disease progression. Weight loss, dysorexia and anorexia, regurgitation, hematemesis and melena, and ptyalism are frequently observed clinical signs during progression of the disease, which is generally slow, over several months (2 weeks to 18 months). A gastric retention syndrome has sometimes been described when severe parietal invasion has occurred and is responsible for gastric hypomotility. The syndrome has also been reported when the tumor induces pyloric obstruction. The advanced stage of gastric adenocarcinoma at the time of diagnosis, the frequently diffuse and deep spread of the neoplasm to the serous membrane, and the high metastasis rate, in particular in the perigastric lymph nodes and viscera, explain the short post-chirurgical survival. The results of chemotherapy for that type of cancer have not been reported in the dog.
The endoscopic diagnosis of gastric cancer in the dog has become banal in recent years. The technique enables description of the location, size, spread and gross characteristics of the tumor.
The zones which constitute the most frequent sites of malignant epithelial tumors in the dog are the lesser curvature and the junction between the corpus of the stomach and the antrum, less frequently the pylorus and cardia.
Borrmann's classification used in man to define the various grades of gastric cancer may be applied to gastric carcinoma in the dog. By analogy, 4 grades may be distinguished (table 1).
Grade I is a non-ulcerated, very exophytic, polypoid mass. The mass is clearly delimited and may be distinguished from benign tumors by the granular, irregular and sometimes friable mucosa which bleeds easily on contact with the endo scope. Biopsies of that mass are frequently positive since the neoplastic cells are present at the surface of the lesion. This grade in, however, rarely observed in the dog since the tumor has frequently progressed to other grades at the time of diagnosis.
Table 1. Endoscopic grading of carcinoma in the dog
Grade I Nodular or polypoid form
Sessile, exophytic, irregular, polypoid mass rarely ulcerated
Grade II Ulcerative form "ulcerocancer"
Well delimited mass centered on a large and deep ulcer clearly delimited by a lipped margin around of the ulcer
Grade III Ulcerative and infiltrating form
Less clearly delimited infiltrating lesion with marked superficial ulceration and poorly visible margins of the ulcer
Grade IV Infiltrative form
Localized infiltrating lesion or diffuse lesion affecting all the stomach (linitis plastica)
In some cases, the margins of the ulcer are poorly delimited and irregular. In that case, multiple biopsies of the peripheral mucosa should be conducted.
Grade III is the most frequent form observed in endoscopy. It is an infiltrating
tumor associated with a large central ulcer. The infiltration generally
deforms the rugae of the mucosa which appear hypertrophied. The ulcer
is more shallow and less clearly delimited than in grade II, but frequently
very extensive. The margins of the ulcer are difficult to define since
the peripheral mucosa is friable and bleeds or exudes readily on contact
with the endoscope.
The various endoscopic pictures are highly suggestive of a carcinomatous process and the diagnosis of gastric carcinoma is most frequently endoscopic. Endoscopic biopsy specimen histology and/or cytology enable histological confirmation and a determination of histological type. However, in the case of a submucosal infiltrating tumor, the histology findings may not confirm the endoscopic diagnosis.
Malignant gastric tumors in cats
Lymphoma is the most common malignant gastric tumor in the cat. Endoscopically, we can observe polypoid lesions projecting from the lumen, infiltrative mass invading the stomach wall, large and deep ulcer clearly delimited. Certain evolutive forms are difficult to differentiate from severe inflammatory lesions and biopsies are required.
Gastric polyps are rare in the dog and very rare in cat but more frequently diagnosed during endoscopic examination of the upper gastrointestinal tract, particularly in elderly animals. Gastric polyps are most frequently isolated but occasionally, numerous polyps may be observed. The polyps may measure from a few millimeters to 1 or 2 centimeters. The presence of a bulky polyp or several polyps in pyloric canal may be responsible for a gastric retention syndrome. The histological study is important since some polyps may prove malignant.
Adenomatous polyps are most frequently isolated, pediculate and sometimes multilobar. The surface of the polyp is generally smooth, but superficial ulceration of the apex of the polyp may be observed.
Certain polyps, termed pseudopolyps, or regenerative or hyperplastic polyps, are totally benign. Those polyps are the most frequent. However, the endoscopic appearance of such polyps is not specific. Regenerative or hyperplastic polyps lesions accompanying certain cases of gastritis (variolate gastritis) may resemble hyperplastic polyps. Since the endoscopic appearance of polyps is not specific, histological confirmation of the benign nature of the polyp is required.
Leiomyoma is a tumor observed most frequently in elderly animals and more frequently in the canine species. The most frequent site is the esophagogastric junction. The tumor is generally asymptomatic but the presence of ulceration may induce chronic bleeding responsible for an anemia that is little regenerative. These tumors of the smooth muscle fibers may sometimes give rise to hypoglycemia, gastric retention syndrome and gastrointestinal perforation. The treatment of such tumors is surgical. Attempts at excision using a diathermal loop may be hazardous.
Leiomyoma generally has the form of a rounded mass, sometimes considerably ulcerated and most frequently located in the cardia. Retroversion of the zone is frequently necessary to image the tumor. The histology of biopsy specimens is disappointing and does not provide confirmation of the histological type of the tumor since biopsy is too superficial. It should be noted that these tumors frequently mainly spread outside the stomach with only their superficial part protruding into the gastric lumen.
SMALL BOWEL NEOPLASIA
Lymphoma and adenocarcinoma are the tumor types most frequently found in the small bowel. Mast cell tumors, leiomyoma, sarcoma and carcinoid tumors are rare.
The diagnosis of intestinal neoplasia on endoscopic examination is directly related to the area of involvement and the presence of mucosal involvement. If the duodenum or the ileo-cecocolic region are involved, endoscopic examination allow frequently diagnosis.
In cats differentiating benign lymphocytic enteritis from lymphoma can be difficult and repeat endoscopic biopsies or full-thickness intestinal biopsies during laparotomy may be required.
Endoscopically, erosions with hemorrhage, mucosal irregularity with marked patchy erythema, proliferative tissue, exophytic and ulcerative mass, stenosis are the most frequent signs observed.
Benign and malignant colorectal neoplasms are rare in cats and more frequent in dogs. We can observe lymphoma or mastocytoma in cat and benign or malignant epithelial tumors in dogs. It is particularly important in dog to differentiate benign polyps from cancer.
Benign colorectal tumors are much more frequent than colorectal cancer in the dog and are very rarely intramural and bulge into the intestinal mucosa. They are thus frequently termed 'polyps'. While the tumors may sometimes lie directly on the mucosa, they are most frequently pediculate. THE foot or pedicle of the polyp forms part of the wall of the colon. This form of the tumor is induced mechanically as a consequence of the traction exerted by the fecal bolus in transit on the mucosa an muscularis mucosae. In the dog, such tumors are frequently isolated or present in small numbers. The location is most frequently rectal and at the colorectal and rectoanal junctions. However, this type of tumor may also be observed in other segments of the colon. Precise and complete endoscopic investigation is thus required.
The polyp may be sessile or pediculate. When the villous contribution is greater, the tumor loses the pediculate aspect and my spread superficially over the periphery of the colonic lumen. Villous tumors are very sessile and bleed readily on contact with the fiberscope.
Colonic cancer, which is difficult to separate from rectal, is the leading neoplastic disease in man. The incidence of that disease in the dog has yet to be fully elucidated. Colorectal cancer would appear less frequent than in man but is very probably under-diagnosed. The development of endoscopic semiology will doubtless enable, in the near future, not only definition of the frequency of the tumor but, above all, clear definition and analysis of the risk factors and main clinical signs reflecting the early phase of tumor development. Colorectal cancer has a poor prognosis when diagnosed at its terminal symptomatic phase, while early surgery may enable long-term survival.
The aim of endoscopy is to image the tumor and above all, obtain biopsy specimens. Endoscopy enables detection of more distal lesions not accessible to rectal touch. The endoscopic presentation sometimes only confirm a patent tumor: a friable, irregular growth, a broad and hard ulceration with thickened, indurated and hemorrhagic margins, rigid stenosis. Endoscopic examination is of the greatest value in the diagnosis of more minimal lesions: limited ulceration, polypoid or villous tumors that are suspect since the neighboring mucosa is abnormal, edematous and hyperemic. In addition to enabling biopsy specimens to be obtained, endoscopy enables measurement of the distance between the anal margin and lower extremity of the tumor. This is important information for the surgeon.
An infiltrating form: the tumor deforms the colonic wall and induces circular stenosis.
An ulcerative form: this is the typical carcinomatous ulceration which may excavate within a zone of proliferation
A proliferative form: this consists in partially necrotic and infected polypoid proliferation.
ENDOSCOPIC ULTRASONOGRAPHY (EUS) or ECHOENDOSCOPY
EUS consists in exploring the gastrointestinal wall and its environment using an ultrasonic transducer inserted into the gastrointestinal lumen. High-frequency (>7MHz) ultrasound is used to generate high-definition images. The main field of application in man is oncology, particularly to stage neoplastic diseases. The depth of tumor invasion of the gut wall in the rectum, esophagus or stomach can be predicted in over 80% of cases. The determination of adjacent organ invasion has yet to be fully studied. The lymph node analysis is superior to that obtained with CT-scanning (precision of the order of 70 to 75%), but requires improvement through enhanced description of the criteria for malignancy. The method is currently little documented with respect to the gastroenterology of domestic carnivores since the equipment used remains very expensive and little compatible with our everyday practice. However, progress and improvement in the equipment used in human medicine have rendered the initial systems obsolete and it is thus possible to more realistically envisage the use of first-generation echoendoscopic in veterinary medicine.
This lecture aims to show a few echoendoscopic images obtained in the course of gastric and colorectal tumor staging.
Patrick Lecoindre, DVM, Dip ECVIM(CA)