PATHOGENESIS — The development of symptomatic hemorrhoids has been associated with advancing age, diarrhea, pregnancy, pelvic tumors, prolonged sitting, straining, and chronic constipation. The association with chronic constipation, however, was not supported in a large epidemiologic study.
The cause of symptomatic internal hemorrhoids is not completely understood, but three predominant theories have been advanced. The first theory posits that, with advancing age or aggravating conditions, the connective tissue which anchors hemorrhoids to the underlying sphincter mechanism deteriorates. Eventually, the weakly anchored hemorrhoids begin to bulge, and "slide" into the anal canal leading to progressive symptoms.
The second theory suggests that symptomatic hemorrhoids arise from hypertrophy or increased tone of the internal anal sphincter. During defecation, the fecal bolus forces the hemorrhoidal plexus against the internal sphincter, which causes them to enlarge and become symptomatic.
The third theory attributes the development of symptoms to swelling of the hemorrhoidal cushions. This theory assumes that the anatomic properties of the hemorrhoidal plexus are similar to those of erectile tissue. In support of this hypothesis is the observation that hemorrhoids regress following ligation of the hemorrhoidal arteries.
Several lines of evidence support or contradict each theory. However, the cause may be different in individual patients or multiple factors may coexist.