Background & aims: Little is known about the histogenesis of human colorectal hyperplastic polyp, although this polyp is clinically very common. Therefore, the structural features of the polyp and their implications regarding histogenesis were studied.
Methods: A total of 261 foci were examined using scanning electronmicroscopic observation of the isolated crypt and surface structure, NaOH cell maceration and scanning electron microscopy, dissecting microscopy, and standard histological analysis.
Results: In surface view, each polyp crypt was discretely demarcated as in the normal crypt, suggesting that the crypt epithelium had not replaced the adjoining crypt. Notches at the base and various stages of branching, observed in 21.8% of the isolated crypts, were considered to reflect crypt fission. Several polyps with a single crypt mouth consisting of fissioned multiple crypts suggested polyp origin from a single crypt and growth by fission. Juxtaposition of small polyps and their fusion suggested polycentric origin. Almost all polyps showed increased stromal inflammatory cell infiltration and/or a lymphoid follicle at the base.
Conclusions: Hyperplastic polyps originate by the apparent fusion of single abnormal crypts within a small region of mucosa. The polyps grow by fission of the crypt and fusion of the polycentrically originated polyps. Chronic inflammation has some relation to this process.