Most common site of anorectal abscess is?

Anorectal abscess: # Usually produces a painful, throbbing swelling in the anal region. The patient often has swinging pyrexia # Subdivided according to anatomical site into perianal, ischiorectal, submucous and pelvirectal # Underlying conditions include fistula-in-ano (most common), Crohn's disesase, diabetes, immunosuppression # Treatment is drainage of pus in first instance, together with appropriate antibiotics # Always look for a potential underlying problem Ref: Bailey & Love&;s Sho Practice of Surgery,E25,Page-1262