Usefulness of magnetic resonance imaging in diagnosis and monitoring of treatment of perianal fistulas.

A fistula-in-ano (also referred to as anal fistula, rectal fistula, perianal fistula or anorectal fistula) is an abnormal tract or cavity communicating with the rectum or the anal canal by an identifiable internal opening (1). The problem is still up-to-date and remains a difficultone to handle, with an overall incidence of 8.6:100,000 annually, affecting patients with a mean age of 38.3 years. The problem is much more common in men, with a female to male ratio of 2:15. There is a wide spectrum of potential causes of fistulas, but it appears that the majority of fistulas result from infection (abscess) in the anal glands extending from the intersphincteric plane to various anorectal spaces (2). The fistula-in-ano significantly decreases the quality of life, most patients experience recurrent perianal drainage, fever, perianal pain, itching and/or recurrent abscesses (3). Although anal fistulas were known to Hippocrates and have been described throughout the centuries, they began to receive special attention in the 19th century. In 1835, Frederick Salmon founded the Benevolent Dispensary for the Relief of the Poor Afflicted with Fistula, Piles, and Other Diseases of the Rectum and Lower Intestines, he now world famous St Mark’s Hospital in London. Much of our understanding of perianal fistulas comes from the work of surgeons at St Mark’s Hospital: Salmon, who operated on Charles Dickens; Goodsall, who described the course of fistulous tracks from the skin to the anus (4); and Parks, whose classification of fistulas in relation to anal anatomy is widely used in surgical practice (5). In this article we will discuss the anatomy of the perirectal area, the causes of anal fistulas and MRI protocols useful to assess the position of the fistula duct. Also, we will present classification types (gradation) of fistulas in surgery based on MR imaging.