Regarding classifications of polyps of the colon, earlier investigations suggested that there may be several kinds of colonic polyps that are dissimilar morphologically. Hauser, in 1894, suggested that polyps could be grouped according to the amount of what he named "degenerated epithelium." [51] Quinu attempted to classify epithelial polyps histopathologically as adenomata, papillomata, and carcinomata. [24] Tuttle in his textbook in 1905 adopted Quinu's classification of adenomata, papillomata, and carcinomata. [27] What today is termed "hyperplastic polyp" was considered by them as a type of adenomatous polyp, and has not been recognized as a separate entity. Fitzgibbon, in 1931, classified polyps into three groups named I, II, and III based on the degree of differentiation of epithelial cells. [2] Group I consisted of polyps that today are called hyperplastic polyps. Helwig, in 1947, criticized the work of Fitzgibbon and claimed serial sections taken from same polyp did not always show a uniform cytologic and histologic picture. [5] He viewed all adenomatous polyps as a group of lesions that could not be subclassified consistently based on morphologic characteristics. For him as later for Sanderland and Binkley, adenomatous polyps appeared basically similar and no significance practically could be attributed to minor variations of structure and cells. In 1956, Bargen categorized polyps based on their origin, inception, and development and put them in five groups named single polyps, multiple polyps, disseminated polyposis, diffuse polyposis, and polyposis secondary to inflammatory disease. [52] He believed with this classification one can get a broader view of the subject and will be able to do right decision in any given case of polyposis or intestinal polyps. Morson, in 1961, presented a unique classification of colorectal polyps that was solely based on histopathological features [53] and presented with some modifications by WHO again in 1976. In this classification, adenoma, papillary adenoma and villous papilloma were put in the same group as benign epithelial neoplasms of colon and rectum. For him, hyperplastic polyp was not well understandable lesion and he considered it as a metaplastic mucosal polyp deemed to be unclassifiable.

In 1976, the World Health Organization proposed another histologic classification of polyps of the colon that is widely accepted to date. [54] According to this classification, polyps of the colon are put in two broad categories as nonneoplastic and neoplastic types (Table 2). Adenoma as a general category put under neoplastic, and hyperplastic polyp under non-neoplastic group. Although most pathologists and clinicians use the WHO classification, Giltman suggested classifying epithelial polyps of the colon based on their biologic behavior. According to this classification, polyps are divided into three major categories of low, intermediate and high malignant potential. [55] Giltman placed villous adenoma in the category of high malignant potential and hyperplastic polyp in the group with low malignant potential.