The absence of lymphatic drainage from the lamina pro-pria of the large intestine was initially discovered using stan-dard techniques of analyzing tissue samples obtained from biopsies with the light and electron microscopy. Recently, specific monoclonal antibodies D2-40 that react with a 40-kilodalton O-linked sialoglycoprotein expressed on the lym-phatic endothelium became available to study distribution of lymphatic vessels. This examination becomes important to monitor the morphologic integrity of the lamina propria in the large intestine that is associated with the absence of lymphatic vessels. For instance in a chronic superficial in-flammation of the colon and rectum known as ulcerative colitis, the formation of granulation tissue is associated with proliferation of blood and lymphatic vessels within the lamina propria. The lymphangiogenesis (the growth of lym-phatic vessels) in this disease is linked to the expression of vascular endothelial growth factors (VEGFs). The progress of treatment in ulcerative colitis can be monitored by biop-sies, which show the disappearance of lymphatic vessels from the lamina propria. On the other hand, the increased number of lymphatic vessels in the lamina propria signals the presence of active inflammation. Discovery of the distribution of lymphatic vessels in the large intestine established the basis for the current man-agement of adenomas (adenomatous polyps of the large intestine). These are intraepithelial neoplasms located on the mass of tissue that protrudes into the lumen of the large intestine (Fig F17.6.1). The absence of lymphatic vessels from the lamina propria was important in under-standing the slow rate of metastasis from certain colon cancers. Cancers that develop in large adenomatous colonic polyps may grow extensively within the epithelium and lamina propria before they even have access to the lymphatic vessels at the level of the muscularis mucosae. Because almost 50% of all adenomatous polyps of the large intestine are located in the rectum and sigmoid colon, they can be detected with rectosigmoidoscopy. As long as the lesion is confined to the mucosa, the endo-scopic removal of such polyps is regarded as an adequate clinical treatment. However, the final therapeutic decision must be confirmed after careful microscopic examination of the resected specimen. aa b FIGURE F17.6.1 • Adenomatous polyp of the large intestine. a. This image shows a macroscopic view of the polyp (about 2 cm in diameter) that was surgically removed from the large intestine during endoscopic colonoscopy. It has characteristic bosselated surface (with rounded swellings) and a stalk by which attaches to the wall of the colon. b. This photomicrograph was obtained from the center of the polyp. At the tip of the polyp, note a repetitive pattern of tubules covered with the neoplastic epithelial cells that have migrated and accumulated on the intestinal surface. Stalk in the center is continuous with the submucosa of the colon. Note also the presence of a normal simple columnar epithelium of the large intestine at the base of the stalk. (Reproduced from Mitros FA, Rubin E. The Gastrointestinal Tract. In: Rubin R, Strayer DS (eds): Rubin’s Pathology: Clinicopathologic Foundations of Medicine, 5th ed. Baltimore: Lippincott Williams & Wilkins, 2008.) skin internal anal sphincter lymphatic nodules anal columns external anal sphincter transverse rectal folds ampulla of rectum mucosal folds rectum anal canal perianal skin colorectal zone anal transitional zone squamous zone anal sinuses