Comparative significance of right colon, left colon, and rectal polyps

Abstract

Several important differences in the physical character and histology of polyps are revealed when comparing polyps of the right colon, left colon, and rectum. First, consider the concept of stalk or pedicle formation. The mechanical events in various regions of the colon account for a presence or absence of a stalk and the thickness and length of a stalk in the various regions of the colon and rectum. In the descending and sigmoid colon, peristalsis is forceful and well organized. Along with the formed fecal content characteristic of this area, a polypoid lesion is propelled intermittently, causing pulsion of the mucosa at its point of attachment; hence, the tendency for stalk formation. The longer (2 to 3 cm), thicker (1 to 2 cm) stalks are almost always seen in the sigmoid colon for these reasons. In contrast to this, peristalsis in the cecum and ascending colon is less forceful and less well organized. These factors, along with the fact that the fecal stream is liquid in this location, create less force propelling the polypoid lesion in a distal direction. Hence, the majority of right colon polyps remain sessile. In my experience (Table I), and that recou nted in the literature, the majority of right colon polyps are the stalk of the lesion is totally uninvolved with tumor. Hence, malignant pedunculated polyps are generally cured by colonoscopic polypectomy. In contrast, malignancy in a sessile polypoid lesion may be associated with metastasis. Malignant sessile polypoid lesions are best managed by colon resection. Although the reasons for these differences in outlook between malignant pedunculated and malignant sessile lesions are not fully understood, perhaps there is a partial interruption in the submucosal lymphatics during stalk formation that accounts for the less ominous nature of the malignant pedunculated polyp. It is interesting that the vast majority of cecal and rectal polyps (Table I) are sessile in nature. Although they may sometimes be teardrop in character (narrow base, but no stalk) or pseudostalked (narrow base with separation of base mucosa to suggest a stalk), polyps of the cecum and rectum almost never have long, thick stalks. Upon reviewing the histology of colon polyps, the majority (Table I) were found to be tubular adenomas. There is an increased incidence of the villous component (i.e., villous adenoma) in sessile polypoid lesions, and, therefore, an increased incidence of the villous component in right colon polyps. In examining the size of polypoid lesions, smaller polyps (less than 5 mm in size) are generally sessile in nature (Table II). In the moderate size range of polyps (1 to 2 em), the tubular adenoma predominates. The