We also find in the nervous mechanism of the part an explanation of the predisposing causes, important symptoms, and pathology of this peculiar affection.
As to the immediate origin of this lesion, it may be said to arise from a variety of causes, such as atony of the rectum, or other conditions leading to constipated habits. In these cases the bowel becomes impacted with hardened feces, which when discharged overstretch the delicate mucous membrane, and thus, either by irritation or by direct abrasion, the ulcer is formed.[[8]]
In consequence of spasmodic or organic contraction of the external sphincter ani, fecal matter or some other foreign body lodges in the fossa between the two anal sphincters, and by its long-continued presence in this pent-up situation becomes highly irritating and gives rise to an obstinate fissure.[[9]]
Anal fissure sometimes results from the excoriations produced by vitiated and acrid discharges, such as occur in dysentery, chronic diarrhœa, cholera, leucorrhœa, etc. Hemorrhoids are frequently a predisposing cause and a complication of this affection.[[10]] They narrow the outlet of the bowel, and through the successive inflammatory attacks to which they are subject the neighboring tissue loses its elasticity, is rendered brittle, and is easily lacerated.
Polypi are not uncommon causes of this lesion.[[11]] The polypus is usually situated at the upper or internal end of the fissure, but it may be on the opposite side of the rectum, as in several cases coming under the author's observation.
Allingham[[12]] states that ulcer of the rectum may result from a congenital narrowness of the anal orifice, being then usually seen in children; or it may be caused by an hypertrophied condition of the sphincters, which has arisen from severe constipation or some rectal affection.
Anal fissure is sometimes produced by a superficial excoriation or ulceration of the outlet of the bowel, analogous to that so frequently observed upon the inside of the lips, the tongue, and other parts of the mouth. Bodenhamer[[13]] mentions having seen several severe cases of this disease produced by a kind of aphthous ulceration in nursing mothers, and one in a child. They were attended with extreme burning pain and more or less anal spasm. He also states that in these cases the ulcerations of the anus were contemporaneous with similar ulcerations of the mouth; their coexistence and the exact similarity of their appearance left little doubt as to their identity.
Harrison Cripps[[14]] states that a source from which these ulcers sometimes take their origin is a little marginal abscess which has led to the destruction of the portion of the muco-cutaneous surface lying over it.
The anus is liable to a species of chapping resembling that of the lips in winter, which sometimes results in extremely painful fissures. Such a condition is supposed to be induced by the influence of a dry atmosphere or by some slight disturbance in the general health, rendering the parts friable and liable to crack from the slightest violence.
Fissure is sometimes of syphilitic origin. Finally, it may be due to mechanical injuries, such as uterine displacement, the severe straining efforts made in parturition, the careless use of the enema syringe, the awkward employment of instruments by the surgeon in the diagnosis and treatment of rectal diseases, etc.