Diseases of the Rectum and Anus

BY THOMAS G. MORTON, M.D.,

AND

HENRY M. WETHERILL, M.D., PH.G.

Diseases of the inferior and terminal portion of the large intestine may be divided into primary and secondary—the former when the morbid cause is local and independent of disease elsewhere, the latter when it is consequent upon or incident to some other bodily affection. Among the primary lesions may be classed congenital malformations, prolapse of the rectum, hemorrhoids, and some varieties of new growths; also diseases caused by local irritations, infection, or traumatism, such as proctitis, ulceration, fissure, non-malignant stricture, chancroidal invasion and primary syphilis, including obstruction of the bowel by impacted feces and foreign bodies. Thread-worms and various cutaneous eruptions about the anus may also be included among the causes of the primary diseases of this portion of the alimentary canal.

The secondary affections are quite numerous, and may be caused by direct extension of disease from the colon, as in the dysentery following typhoid fever, and follicular enteritis, or entero-colitis of children; by contiguity, from diseases in neighboring organs—e.g. ischio-rectal abscess causing fistula—or by changes in the nervous or vascular supply, such as is seen in spasmodic contraction, paralysis, epidemic dysentery, cholera, and the action of certain remedies.

The rectum, the third or terminal portion of the large intestine, has no sharply-defined upper limits: it is usually understood to begin at the sigmoid flexure, opposite the left sacro-iliac symphysis; it is from six to eight inches in length and terminates in the anus. As the sigmoid flexure is the narrowest portion of the colon, so the calibre of the first part of the rectum is narrower than the portion below, where it gradually becomes more commodious, and near the anus presents a peculiar condition of the walls which gives it a capacity for remarkable distension. The rectum, which is somewhat cone-shaped, in its anatomical and pathological characters retains those of the large intestine with slight variation. Upon the upper or first part of the rectum the duplicature of the peritoneum is continued, forming the meso-rectum, which invests the bowel, attaching it to the sacrum. Below this the middle portion of the rectum (extending to the tip of the coccyx) is attached to the sacrum by connective tissue only, but also has a peritoneal investment on the upper portion of its anterior surface.

The third or terminal part of the rectum, which is only an inch and a half in length, and is entirely without peritoneal covering, terminates at the anus. The circular and transverse muscular fibres, mucous crypts, and appendages throughout the rectum are identical with those above, except that the general muscular tunic is thicker; but the longitudinal fibres are less distinctly aggregated into bands than in the colon, being disposed in a more uniform manner, except that, like the circular fibres, they are especially aggregated between the sacculi. The fact that the meso-rectum limits the mobility of the upper and more narrow part of the rectum has led some to locate a third sphincter at this point, but the existence of such an organ has not been generally admitted. Van Buren characterizes it as an organ which "anatomy and physiology had been equally unsuccessful in assigning either certainty of location or certainty of function."

Kelsey, Diseases of the Rectum and Anus, New York, 1882, p. 20.

The anus guards the outlet of the bowel by its double sphincter muscle, which under normal circumstances affords voluntary control, within certain limits, over defecation. The well-known peculiarity of the vascular supply, a sort of erectile tissue being formed by the inferior hemorrhoidal plexus and the passage of some of the efferent veins through the sphincter muscle, by which they are subjected to pressure, is very favorable to the development of certain forms of disease which will be considered among the local disorders. As embryology has thrown considerable light upon the pathology of morbid growths by demonstrating relationships that were previously unsuspected, so a consideration of the development of the lower portion of the intestinal canal may lead to a better understanding of some of its diseases, especially those which are symptomatic or secondary. In early foetal life the third division of the primitive intestine, the pelvic portion, terminates in a cloaca in common with the urachus; subsequently, about the eighth week, a partition (the perineum) is formed which divides the cavity into two portions, the uro-genital sinus and the anal cavity. In the mean time, at an early period a depression occurs on the cutaneous surface at the site of the anus, which deepens progressively until it encounters the primitive intestine, with which it unites at the end of the fourth week, and the continuity of the tube becomes established. It therefore is seen that the rectum in its upper and middle portions is derived from the internal and middle layers of the blastodermic membrane, while its lower third, with the anus, like the buccal cavity, is formed by the external and middle layers.

In its diseases, then, the greater part of the rectum would seem to naturally participate in those of the large intestine, to which it structurally belongs, while its inferior portion and the anus would partake more in the disorders of the general cutaneous system. This peculiarity of development also explains the difference noticed in the vascular supply. The rectal veins are usually divided, like the rectal arteries, into three sets—superior, middle, and inferior. They are arranged so as to form two distinct venous systems, the rectal returning its blood through the inferior mesenteric veins into the portal system, the anal terminating in the internal iliac. The first system is made up of the superior hemorrhoidal, the second of the remaining veins.

The superior hemorrhoidal forms a venous plexus which surrounds the internal sphincter muscle; the inferior hemorrhoidal vein also forms a plexus, but it is subcutaneous and principally below the inferior border of the external sphincter.

There are, however, a number of communicating branches passing along the walls of the rectum from one plexus to the other. The internal hemorrhoidal veins also communicate freely with the branches of the internal iliac around the trigone of the urinary bladder by means of small vessels, which pass through the prostate gland and seminal vesicles. By this method of anastomosis some relief is afforded when there is an obstruction in the portal circulation, which is such a common cause of turgescence of these veins, often resulting in permanent dilatation or hemorrhoids.

At the lower part, or at the junction of the middle and lower third of the rectum, the internal circular fibres of the muscular coat of the intestine become quite numerous, forming what is called the internal sphincter muscle; it is nearly an inch in breadth, and completely surrounds the lowest part of the rectum. It is about an inch above the margin of the anus; its muscular fibres are of the involuntary or unstriped variety; in function it assists the external sphincter in closing the anus and preventing the involuntary escape of the contents of the bowel.

The external sphincter lies directly under the skin and upon the internal sphincter and the levator ani muscle; its fibres encircle the anus: arising from the coccyx, they are inserted into the tendinous centre of the perineum, joining the transversus perinæi, the levator ani, and accelerator urinæ muscles. The sphincter ani is constantly in a state of tonic contraction, but the force of its contraction may be voluntarily increased. In the skin and superficial fascia are found minute branches of the pudic and small sciatic nerves; in the ischio-rectal space the internal pudic nerve; crossing about the centre are the inferior hemorrhoidal nerves, which are distributed to the anus and the lower portion of the rectum; the perineal nerve is especially distributed to the anterior part of the anus.

Thus it is seen that the rectum and anus have vascular and nervous supplies of considerable diversity and importance.