_Fistula in ano is a disease of such very fre quent occurrence, and so well understood and described by every surgical writer, that it is scarcely necessary to do more than allude to it in this place : strictly speaking it is not a disease of the anus, as that opening is in general totally unaffected, except as regards its functions : it should rather be regarded as a disease of the anal region. There is one form of fistula in ano, however, which is seated on the very confines of this opening; it is trou blesome and distressing, attended with heat, itching, and excoriation, pain during defeeca tion, and constant purulent or sero-purulent discharge : without due attention it may be overlooked by the surgeon, as the orifice is so close to the anus as to be concealed by the natural rugT, and so small as only to admit a lachrymal probe ; the sinus is not more than an inch or half an inch long; its internal opening is on the very edge of the anus, the whole is immediately under the skin, and does not involve any other structure; it is not pre ceded by regular abscess, neither does it or the treatment necessary for its cure involve the sphincter or any other structure, except the fine integuments ; it most probably originates in irritation of some of the anal ,sebaceous follicles, and sometimes two or three of such fistulae may exist at the same time.
The true or deep fistula in ano has its origin in deep-seated abscess commencing close to the rectum, or in the centre of the ischio-rectal space of either side : when in the former, some mechanical irritant or some disease of the intestine may have been the cause or origin of the abscess ; when in the latter, it often arises without any obvious reason, hut frequently appears to have been connected with some peculiar delicate or morbid con dition of the constitution. All abscesses in this situation do not necessarily end in fistula ; if they have been small, superficial, opened early, and treated judiciously, they may be healed as perfectly as abscesses in any other situation ; but when deap-seated, of slow growth, and long continuance, and when de pending on some deep-seated mechanical irri tant or on constitutional causes, then the ab scess usually attains considerable size, and having opened either into the rectum or through the integuments, or in both these directions, it continues to secrete and to discharge a con siderable quantity, and spews no disposition to alter its action or to heal. We have already detailed all the local peculiarities of the ischio rectal region (the seat of this abscess) which can satisfactorily explain the difficulty or the impossibility of keeping at rest or retaining in apposition the sides of the cavity, a condition almost essential to the healing of an abscess in any situation, and hence the necessity of sur gical interference. Abscess in this region frequently originates close to the rectum in consequence of irritation and ulceration in this intestine; this irritation may be caused by disease, such as cancer or stricture of the rectum, or by some foreign body becoming impacted in one of the lacunae. Above the sphincter is the rectal pouch, and an irre gularly shaped or sharp substance, such as a pin, a fish-bone, or one of the small bones of a fowl, &c. brought into this in the faecal mass, may catch in its villous or rugous surface, the muscular powers of the intestine are excited by this irritation to increased and repeated efforts of expulsion ; these only serve to im pact more closely the foreign body in the parietes of the intestine ; the submucous tissue, which may now contain the whole or part of this substance, becomes inflamed, suppuration follows, an abscess is formed close to the intes tine ; in some time the matter is discharged either through the rectum and anus, or coming to the surface of the nates it receives exit by puncture. In this case of abscess, which we
suppose to have been caused by a foreign body impacted in the intestine, the matter is usu ally discharged by the rectum, at least at first, although this exit will not always prevent it still tending towards the cutaneous surface : in cases of fistula, however, arising from such a cause, we are most likely to meet with the blind internal fistula, at least in the early period; whereas, when abscess forms spon taneously in this region, and opens on the surface, the intestine is often at first and for some time wholly disengaged from the disease, even after the abscess has opened, notwith standing which it is productive of great in convenience and more or less, of pain during defwcation ; in this state, when the fistula or abscess remains discharging through the skin only, it constitutes what is termed a blind external fistula; by degrees the rectum comes denuded, and ultimately ulceration opens it by one, and sometimes, but rarely, by more orifices; this opening is usually about half an inch above the edge of the anus, and between the two sphincters. I have observed it to hold this situation in a great number of cases, which I have examined both in the living and the dead; in a few instances, how ever, I have found it opening at a higher point.
When the abscess arises from irritation in the rectum, then I have observed the internal opening to be higher, that is, in the dilated pouch of the rectum, which during life will appear to be from an inch and a half to two inches from the anus ; but when the abscess has commenced spontaneously in the anal adeps, and opened on the surface first, I have then in general found the rectal opening less than an inch distant from the anal orifice, and in a groove or recess between the two sphinc ters. When the abscess discharges by two openings, that is, through the skin and through the rectum, a perfect or complete fistula is then said to exist.
Fistulae occasionally appear in the anal region which have their source at a much greater dis tance; thus, any diseases of the uterus or vagina in the female, of the prostate or urethra in the male, which end in suppuration, may cause collections of pus which will burrow under the fasciae and skin to the vicinity of the anus, and open near it or even into the rectum. Psoas and lumbar abscesses also may descend into the pelvis and approach the sur face, either in front or at one side of the anus. In morbus cox also chronic abscesses which form about the nates not unfrequently open in the same situation.
Polypus is seldom a disease of the anus ; it most usually grows from the rectum, and pro trudes occasionally only at the anus.
(Robert Harrison.)