Intestinal Tumors

Intestinal Tumors

Description– According to reports, intestinal tumors are found in less than 10% of dogs. Among all the intestinal lesions, lymphoma has been estimated at 29%, adenocarcinoma at 17% , leimyosarcoma at 23% and small intestinal tumors at a little over 1%. 

Other types of intestinal tumors include extramedullary plasmacytoma, extraskeletal osteosarcoma, mast cell tumors and hemangiosarcoma. However a report from the United Kingdom estimated intestinal tumors at 22%. The difference in the rates of occurrence between US and other countries normally stems from cultural and environmental factors especially neutering practices. 


Although intestinal tumors are generally malignant in nature, there are some exceptions. In a majority of the cases, lesions that originate in the rectum are found to be benign polyps (abnormal growth of tissue projecting from a mucous membrane) or adenomas, although carcinomas also occur quite frequently. 


Older dogs especially males are over represented in intestinal tumors. Breeds between 6-9 years of age are said to be predisposed. The over represented breeds, however, include Collies and German Shepherds. In dogs the most common sites for instestinal tumors are the colon and the rectum. This is also known as ‘colorectal adenocarcinoma’. In this type of cancer, the rectum is affected more than the colon. On the other hand, leimyosarcomas and gastrointestinal stromal tumors normally originate in the cecum (first part of the
small intestine). 


Adenomatous (benign) polyps that originate in the colon and rectum are solitary and diffuse. Although they start off as benign tumors, over the years they can aggravate into malignant structures. In that case they would be called ‘adenocarcinomas’. However, in the non-malignant form also, they can cause potential damage. On the other hand, lymphoma mostly affects the stomach and the small intestine. They are diffuse and highly neoplastic in nature. 


The metastatic sites for intestinal tumors include mesenteric lymph nodes, liver, mesentry omentum (repositories for fat in the body), spleen, kidney, bone, peritoneum/carcinomatosis (it is used to describe a cancer that has metastasized widely to other parts of the body), lung, testes and skin. 


Symptoms – The clinical signs for intestinal tumors include weight loss, diarrhea, vomiting, anorexia, less frequently melena (tarry feces), anorexia (loss of appetite) and hypoglycemia (state characterized by lower than normal level of blood glucose). However, the symptoms vary depending upon the location of the tumor. If the lesions grow very big in size, the clinical signs would include vomiting. In case of large bowel lesions, the symptoms are tenesmus (feeling of difficulty during defecation) and hematochezia (maroon stool). Sometimes due to intestinal obstruction caused by tumors, the clinical signs may include perforation and peritonitis (inflammation of the peritoneum). The presence of smooth muscle tumors within the muscular layer of the intestine have been associated with melena and anemia. 


There have been cases where hematologic abnormalities like neutrophilic leukocytosis (an elevated number of white blood cells in the blood), monocytosis (increase in the number of circulating monocytes) and eosonophilia (having a high concentration of white blood cells) can be resolved following extirpation of adenomatous rectal polyp. 


Diagnostic work-ups– They may include physical examination, complete blood count, chemistry profile, imaging, thoracic radiographs, endoscopy, laparoscopy and exploratory laparotomy. 


Physical examination– A mass may be detected upon palpation in approximately 20-40% of dogs with lymphoma and approximately 20-50% dogs with non-lymphomatous solid intestinal lesions. 


Other clinical signs include pain and fever. If palpation doesn’t yield good results, then doctors go for digital rectal examination. This may reveal masses or annular strictures (ring like structure surrounding the wall of a canal) as a result of rectal lesions or polyps in approximately 63% of dogs.

Clinical Pathology– Symptoms like anemia, melena and elevated blood urea nitrogen (BUN) are quite common in dogs suffering from intestinal tumors. Therefore, leukogram is important as it helps in determining changes including leukocytosis in majority of the cases.

Chemistry profile– Dogs with intestinal lesions may experience hypoproteinemia (abnormally low level of protein in the body) and elevated liver enzymes (extremely low levels of protein in the blood). An elevated blood urea nitrogen may indicate renal insufficiency, absorption following intestinal bleeding or dehydration. Patients suffering from lymphoma may experience hypercalcemia (elevated calcium levels in the blood). 


Imaging
Plain and contrast abdominal radiographs 


If it is a case of intestinal lymphoma, the liver, mesenteric lymph nodes (lymph nodes that lie between the layers of the mesentry [double layer of peritoneum that suspends the jejunum and the ileum]) and spleen would be enlarged. Plain radiographs may reveal a large abdominal mass in approximately 40% of cases. It is generally difficult to identify an abdominal mass on plain radiography as it involves other organs. Moreover, there might be peritoneal (fluid in the peritoneum that may be benign or malignant) effusion or diffuse intestinal lesions. Other abnormalities may include poor serosal detail (less fat deposits) and thickening of the stomach wall. 

Contrast radiographs may be useful at times when ultrasonography fails to take clear images because of the accumulation of gas in the abdomen.

Thoracic radiographs
They are important for the proper evaluation of a person suffering from cancer. But if there is no pulmonary metastasis, the yield is generally low.

Abdominal ultrasound
This is important for identifying the location of the tumor, evaluating other metastatic sites, improving staging, guiding needle aspiration, biopsy and assisting in charting the proper course of treatment. However, ultrasounds are much more effective than radiographs in identifying an abdominal mass. Another advantage is that it also takes lesser time. 


For dogs with intestinal neoplasia, the ultrasound findings include bowel wall thickening and loss of normal wall layering. One study showed 2/3 dogs with adenocarcinoma having hypoechoic tumors with decreased motility (ability to move smoothly and actively) rates. The lesions averaged 4cm in diameter with a wall thickening of 1.2 cm. Normally, smooth muscle lesions average 4.8 cm in diameter and are normally anechoic (echo free) or hypoechoic (giving off new echoes). 

Ultrasonography helps in differentiating neoplastic lesions from non-hypoechoic neoplastic intestinal disease because dogs with neoplasms normally have a thickened wall with a significant loss of wall layering. 

However, leiomyomas are tumors with very smooth contours. 

Endoscopy and laparoscopy
The endoscopic images in dogs with intestinal lymphoma reveal