CHAPTER I.
RELATIVE FREQUENCY—AGE AND SEX AFFECTED—ETIOLOGY—CLASSIFICATION.
Fistula in Ano which is not due to ulceration and perforation of the rectal wall from within is the result of a previous abscess. Such an abscess forms in the ischio-rectal fossa, and, although opened early by a free incision even before the cavity becomes distended with pus, it frequently fails to heal. It may fill up and contract to a certain extent, but it does not become entirely obliterated; a narrow track remains, which constitutes the affection designated fistula in ano.
There are several reasons why rectal abscesses so frequently degenerate into fistulæ. One is, that, owing to an internal opening within the bowel, small particles of fecal matter find their way into the sinus, and, acting as foreign bodies, prevent the healing; another, that, owing to the frequent movement of the parts by the sphincter muscles, sufficient rest is not obtained for the completion of the reparative process; and, finally, the vessels near the rectum are not well supported, and the veins have no valves, hence there is a tendency to stasis, which is unfavorable to rapid granulation.
According to the authority of Mr. Harrison Cripps,[[33]] if the fistula be divided its surface will be seen to be lined with a smooth, gelatinous membrane, which when examined under the microscope is found to consist of granulation-tissue exactly analogous to that which lines the interior of a chronic abscess. The leucocytes constituting the outer wall of this membrane are but loosely adherent, and constantly becoming free they form the chief part of the pus which drains from the fistula.
Relative Frequency of this Affection.—In point of frequency, compared with other rectal diseases, fistula is next to hemorrhoids. This statement is contrary to the showing made by the published statistics of St. Mark's Hospital, as quoted by Allingham.[[34]] This table shows that out of four thousand cases taken consecutively from the out-patient department of the hospital there were one thousand and fifty-seven persons suffering from fistula and one hundred and ninety-six from abscess, of which latter number one hundred and fifty-one subsequently became fistulæ, so that more than one-fourth of the whole number of cases treated were fistulæ. Allingham also states that a recent examination of the records of the in-patients of the same institution, covering a period of several years, shows that two-thirds of those operated upon were cases of fistula.
Mr. Allingham[[35]] justly calls attention to one source of error in drawing conclusions from statistics—namely, the fact that many patients suffer from more than one malady. He states that it constantly happens that a fistula is found in connection with hemorrhoids, either as the substantive disease or as a complication. Again, a fissure or circular ulcer often has a sinus running from it, so that it may fairly be considered as the opening of an internal fistula, and the case called a fistula; or the sinus is not detected, and the case is called ulcer or fissure.
Another fallacious element in the statistics of Mr. Allingham, which should not be overlooked, is pointed out by Mr. Chas. B. Ball.[[36]] St. Mark's has a special reputation for the cure of fistula, so that many persons suffering from this disease go there, and in this way the records show an apparent greater frequency of fistula. Mr. Ball also states[[37]] that at the Dublin General Hospital, although fistula is common, it is by no means the commonest of rectal diseases; and in his own practice this affection has not furnished more than one-sixth of rectal operative cases.
Age and Sex Affected.—This disease is commonly met with during middle age, but it is by no means restricted to that period of life. Allingham states[[38]] that he has operated upon an infant in arms, and upon a man over eighty years old. Dr. Henry R. Wharton[[39]] mentions having seen a number of cases at the Children's Hospital, Philadelphia, among which he records one of complete fistula in a child a few months old.
Causes.—Fistula in ano may originate in ulceration and perforation of the mucous membrane of the bowel—the result of the irritation produced by fecal accumulations (arising from any cause, such as atony of the intestines, irregularity of habits, rectal stricture, etc.), or by foreign bodies, such as fish- or rabbit-bones, grape- or fig-seeds, etc.; more frequently it owes its origin to an abscess caused by injuries, such as blows or kicks upon the anus, or by exposure to cold, as from sitting upon damp seats—especially after exercise, when the parts are hot and perspiring; it may also arise from excessive irritation of the rectum occasioned by the presence of any of the forms of parasites which infest the anus and its immediate neighborhood. Other predisposing causes are thrombosed veins and suppurating hemorrhoids. Abscess, and then fistula, may likewise supervene in fevers and certain depressed conditions of the blood, such as frequently give rise to boils or carbuncles.[[40]]