Why the most potent toxin may heal anal fissure.

An anal fissure is a painful linear ulcer in the lower part of the anal canal. It is very often referred to as an ischemic ulcer. Anodermal blood flow is negatively correlated with resting pressure of the anus. Increased activity of the internal anal sphincter may decrease the anodermal blood supply by compressing arterioles. Surgical procedures and botulinum treatment for patients with chronic anal fissure produce a temporary reduction in anal pressure, reverse sphincter spasm, and promote fissure healing. However, recent studies have shown that fissure healing does not appear to be dependent on reduction in mean resting anal pressure. On the basis of the published literature, this article attempts to explain this phenomenon in detail. The mechanism of action of botulinum toxin on the internal anal sphincter is not yet fully understood. This review focuses on problems associated with anal fissure treatment and presents them from the wider angle of science about botulinum toxin. In our opinion, anodermal blood flow depends not only on the "mechanical" force of sphincters but also on biochemical processes that occur in the fissure region.