Invasive well-differentiated mucin producing adenocarcinoma (6.0 cm) arising in a small bowel villous adenoma that extends through the bowel wall and into the adjacent liver capsule without invasion of the underlying hepatic parenchyma. There is no angiolymphatic invasion identified. The surgical margins of resection showed no evidence of malignancy.
AJCC Pathologic staging: T4, NX, MX
Primary adenocarcinoma of the small intestine has been estimated to occur 40 to 60 times less than adenocarcinoma of the large intestine. Several explanations have been put forth to explain the low frequency. One is that since the contents of the small bowel lumen are liquid, any potential carcinogen within the lumen would be diluted, leading to very little contact between the carcinogen and the mucosa. The transit time through the small bowel, in comparison to the large bowel, is much more rapid. This results in less carcinogen-mucosa contact. This is in contrast to the large intestine where in the distal colon the contents are solid, more concentrated and transit time is the slowest. This presumably allows for greater contact between carcinogens and the mucosa. It has been found that certain conditions can predispose an individual to the development of small intestinal carcinoma. These conditions include: Chron's disease, adenomas, dysplasia, long-standing ileostomies, Celiac disease (gluten sensitive enteropathy), familial polyposis, and Peutz-Jegher's syndrome. The average age of presentation is between 50 and 60 years of age (median age 55) with the most common clinical presentation being that of obstruction. Other presentations include bleeding, intussusception, and/or perforation. Males are effected more than females and Afro-Americans more than the Caucasian population. Approximately 50 to 70% of small intestinal adenocarcinomas arise in the duodenum, which constitutes only 4% of the entire small intestine. The prognosis for patients with a primary small intestinal adenocarcinoma remains uniformly poor due to the fact that these individuals often become symptomatic late in the course of the disease. Metastatic disease is commonly present at the time of diagnosis. Moderate to poorly differentiated adenocarcinomas have a worse prognosis compared to well-differentiated adenocarcinomas.
With the overwhelming clinical history of recurrent metastatic adenocarcinoma, the diagnosis of a new primary was much lower on the differential diagnosis. The interesting aspect in this case was the overwhelming histological evidence that this was actually a primary small bowel adenocarcinoma. There is a definite sequence from small intestinal mucosa to villous adenoma and finally well differentiated adenocarcinoma.
Contributed by Maurice R. Grant, MD and Joseph Huth, MD