CARCINOID TUMORS of the rectum are uncommon, slow-growing, malignant submucosal lesions having full potentialities for local invasion and widespread metastatic dissemination. They were first described by Lubarsch in 1888 and named by Oberndorfer in 1907. Since that time they have been reported occurring in almost any tissue derived from primitive ectoderm as well as in teratomas. They are, however, most frequently encountered in the appendix. Occurrence within the rectum was first recorded by Saltykow in 1912. With the acceptance of proctosigmoidoscopy as an established procedure in the routine physical examination, the occurrence of this lesion in the rectum has been mentioned with increasing frequency.
These tumors are derived from the Kulschitzky (or argentaffin) cells located deep in the crypts of Lieberkühn. Initially these lesions, like simple adenomata, have no characteristic signs or symptoms. But upon examination, they are found to be small, rubbery, firm, discrete, freely movable, nonencapsulated, nodular thickenings
McGregor JK, Eisenberg SW, Bacon HE. Carcinoid Tumors of the Rectum. JAMA. 1962;181(6):552-554. doi:10.1001/jama.1962.03050320090010