What is the difference between anterior/posterior anal fissure and lateral anal fissure? what is considered abnormal in terms of anal fissure location

Posterior / anterior: Most "normally located" fissures are due to passage of hard, dry stools or explosive diarrrhea. These are almost exclusively posterior in men but can be anterior in up to 10% of women. These respond well to lateral internal sphincterotomy. Secondary anal fissures are associated with crohn disease, leukemia and certain other neutropenic blood conditions. Surgery should be avoided.

Big difference: Anterior and posterior anal fistula are almost always caused by trauma - forceful bm due to constipation. Lateral fissures are caused by crohn's disease, sexually transmitted disease and cancer, and need to be biopsied. You should see a general surgeon or proctologist.