Fig. 9.
Extension of perianal inflammation (cryptoglandular hypothesis).
If an abscess develops in a superficial gland, the rupture of the abscess extends into the intersphincteric space forming a fistular tract that reaches the skin. Alternatively, a pelvic infection may pass through the external sphincter and enter the ischioanal fossa. The infection sometimes extends to the low perianal space and the supralevator space.