Causes.
A. Congenital.
—There are numerous points about the body where, as the result of arrest of development or failure to grow, fistulous passages which are comprised within the normal fetal arrangements, but which should close later, either before or at birth, fail to do so. Thus we have congenital fistulas of the neck, persistent urachus, persistent omphalomesenteric duct, etc. These are in no sense primarily connected with diseased conditions, but may become so secondarily.
B. Pre-existing Abscess with Unhealed Channel of Escape
—e. g., rectal, fecal, and other fistulas and sinuses which connect with tuberculous foci in any part of the body.
C. Previous Traumatic or other Destruction of Normal Tissues
—e. g., vesicovaginal fistulas due to tissue death from pressure, buccal fistulas from gangrene of the cheek, as in noma.
D. Foreign Bodies
—bullets, ligatures, etc.—which prove irritating or infectious enough to prevent absolute healing. More or less tortuous sinuses will generally be found leading down to the irritating material.