**5. Incidence and etiology**

Anal fissures presents mostly in children aged 6-24 months. The overall incidence in children is not well described. Anal fissures are located in the posterior midline in 90% of the cases, although 10-20% in women and 1-10% in men are located in the anterior midline (Notaras, 1988). The posterior commissure of the anoderm is less well perfused than other anodermal regions (Schouten et al., 1994). Pressure over the branches of the inferior rectal artery (increased tone at the internal sphincter and high canal pressures) causes relative ischemia (Klosterhalfen et al., 1989). First described as a disease entity in 1934, the cause of anal fissures is still unknown. Constipation and passage of hard stool were traditionally blamed and believed to be the causative factor of anal fissure, but a history of constipation is elicited in only approximately 20% of the patients (McCallion & Gardiner, 2001). Trauma, usually because of passage of a large or hard stool, is believed to be a common initiating factor. Ball suggested that passage of hard stool tore down the anal valve, leaving the coiledup skin at the anal verge as the "sentinel pile" (Lund & Scholefield, 1996). The remaining fissures are associated with chronic diarrhea, food allergy, Crohn's disease, syphilis, human immunodeficiency virus (HIV), or tuberculosis.
