Revised morphology and hemodynamics of the anorectal vascular plexus: impact on the course of hemorrhoidal disease.

Purpose: The pathogenesis of hemorrhoidal disease is based mainly on the vascular hyperplasia theory. The aim of this study was to reassess the morphology and the functional mechanisms of the anorectal vascular plexus with regard to hemorrhoidal disease.
Materials and Methods: The anorectal vascular plexus was investigated in 17 anorectal and five hemorrhoidectomy specimens by means of conventional histology and immunohistochemistry. Vascular corrosion casts from two fresh rectal specimens were used for scanning electron microscopy. Transperineal color Doppler ultrasound (CDUS) with spectral wave analysis (SWA) was performed in 38 patients with hemorrhoidal disease and 20 healthy volunteers.
Results: The anorectal vascular plexus was characterized by a network of submucosal vessels exhibiting multiple thickened venous vessels separated by distinct sphincter-like constrictions. CDUS and SWA showed significant flow differences in peak velocities (6.8 +/- 1.3 cm/s vs. 10.7 +/- 1.5 cm/s; P = 0.026) and acceleration velocities (51 +/- 4 ms vs. 94 +/- 11 ms; P = 0.001) of afferent vessels between the control group and patients with hemorrhoidal disease.
Conclusions: Coordinated filling and drainage of the anorectal vascular plexus is regulated by intrinsic vascular sphincter mechanisms. Both morphological and functional failure of this vascular system may contribute to the development of hemorrhoidal disease.