The objective of modern anal fistula treatment is healing of the fistula without diminished fecal continence. Sphincter saving techniques have been developed for anal fistulas, for which fistulotomy is not suitable. Treatment of these anal fistulas remains challenging and to some extent disappointing.

The aim of the studies described in this thesis is to evaluate treatments for anal fistulas and to gain a better understanding of the pathogenesis of anal fistulas.

Despite our effort it seems unlikely that surgical treatment alone will ever lead to fistula healing in all patients. The outcomes of the studies in this thesis made us suggest that inflammation plays a role. Treatment of anal fistulas may need a new approach, combining surgery with treatment of inflammation.