3. Microangiographical and Histological Studies of Anal Vasculature in Japanese

Abstract

In order to clarify the morphology of the anal vasculature, microangiograms were made in eight patients without anal lesion who underwent amputation of the rectum because of rectal cancer and they were histologically studied.Vascular running can be classified into six types.(1) That which is descending under the mucosa with twigs between the internal anal sphincter muscle bundles.(2) That which is divided into two branches one of which is descending the rectal longitudinal muscle and turning up under the mucosa at the upper end of the internal sphincter muscle and the other which is descending the conjoined longitudinal muscle.(3) That which branches, entering the conjoined longitudinal muscle along the levator ani muscle, into two, one of which turns up under the mucosa passing through the internal sphincter muscle and the other which shoots twigs in the internal anal sphincter muscle descending the conjoined longitudinal muscle.(4) That which enters the conjoined longitudinal muscle at nearly a right angle through the upper part of the external anal sphincter muscle from the upper exterior side to the lower interior side of the external anal sphincter muscle at the lower end of the levator ani muscle and penetrates the middle part of the internal anal sphincter muscle with branching.(5) That which reaches the conjoined longitudinal muscle passing through the external anal sphincter muscle from the exterior end of the middle external anal sphincter muscle and turns out under the ephithelium passing through the internal anal sphincter muscle with branching.(6) That which is coming from the exterior side bifurcates at the lower exterior end of the external anal sphincter muscle, the one of which (6') runs into the conjoined longitudinal muscle passing through the lower part of the external anal sphincter muscle and flows into the rete vasculosum taking a long way around the lower end of the internal anal sphincter muscle. The other one (6") ascends going around the exterior end of the external anal sphincter muscle.All of these blood vessels run under the ephithelium (submucosally and subcutaneously) and from the reticular vasculosum which tends to gathering in the crypt.Usually barium sulfate filled the small arterioles but did not pass beyond the capillaries when injected from an artery. In our cases barium sulfate injected from superior rectal artery, but in the histological study, barium was found also in the venous system. This was the barium which had entered the sinusoid vein entered the venous system accrossing the sinusoid vein.There is sinusoid vein into which the arterial capillaries flow directly in the submucosal and under layer of the anoderm. The wall of this vein differs in thickness with a very thin part. It is generally characterized by extremely scanty tunica media smooth muscle and abundant collagenous fibers. Hemorrhoids are thought to be produced by excessive stretch of the venous wall due to repeated congestion over a long period of time.