[Etiology, pathogenesis and classification of anal fissure].

Anal fissure is one of the most common causes of anal pain but its etiology and pathophysiology remain obscure. Many theories have been advanced to explain the origin of anal fissures but trauma of faecal mass and hypertonicity of the internal sphincter seem to be the most important factors. The initial lesion in anal fissure is a tear in the anoderm mostly in its posterior midline caused by overstretching of the anal canal. Secondary fissures may occur on a commonly lateral position as a result of inflammatory bowel disease, previous anal surgery, venereal, dermatologic, infectious or neoplastic disease. As the fissure becomes deeper and more chronic the sclerotic fibres of the internal anal sphincter are seen as well as a sentinel pile and a hypertrophied anal papilla. The disease enters in a vicious circle of anal pain, constipation, faecal trauma and sphincter spasm.