Not a Cause of acute anal pain:

Ans. (c) Fistula in anoRef: Bailey & Love 26/h ed. /1259Clinical Features* Thrombosed hemorrhoids# External hemorrhoids are located distal to the dentate line and are covered with anoderm. Because the anoderm is richly innervated, thrombosis of an external hemorrhoid may cause significant pain.# Internal hemorrhoids may prolapse or bleed, but rarely become painful unless they develop thrombosis and necrosis (usually related to severe prolapse, incarceration, and/or strangulation).* Acute anal fissure# Characteristic symptoms include tearing pain with defecation and hematochezia (usually described as blood on the toilet paper)* Fistula in ano# Patients usually complain of intermittent purulent discharge (which may be bloody) and pain (which increases until temporary relief occurs when the pus discharges).# Schwartzs 9th ed and oxford textbook of surgery do not mention pain as a feature of fistula in ano* Perianal abccess# Severe anal pain is the most common presenting complaint. Walking, coughing, or straining can aggravate the pain.