Distribution of human colonic lymphatics in normal, hyperplastic, and adenomatous tissue. Its relationship to metastasis from small carcinomas in pedunculated adenomas, with two case reports.

Prompted by 2 cases of lymphatic metastasis from focal carcinoma in the head of pedunculated adenomas, lymphatics were studied in the colonic mucosa in normal, hyperplastic, and adenomatous tissue utilizing light and electron microscopic techniques. In all three tissues there is a lymphatic plexus associated with the muscularis mucosae, but there are no lymphatics above this level. This explains why lymphatic metastases from superficial intramucosal foci of carcinoma in adenomas do not occur. In lobules of adenomatous tissue, the total distance between the free surface and the muscularis mucosae may be considerably increased, and a focus of carcinoma in adenomatous tissue must at least reach the muscularis mucosae and its lymphatics in order to metastasize. This lack of lymphatics contrasts with the profusion of blood capillaries at the mucosal surface. This may be an example of a more general biological phenomenon in that other sites also concerned with water and ion transport, such as the renal glomerulus, the gallbladder mucosa, choroid plexus, and ciliary body lack lymphatics but exhibit a rich blood capillary network at their transporting surfaces.