A thrombus in the hemorrhoidal plexus distal to the dentate line is a thrombosed external hemorrhoid (pile). It presents with acute severe pain and a tender, dark red to purplish nodule at the anal verge. "Thrombosed hemorrhoid" (B) is less precise because it does not say external. A fissure is a tear, not a purple lump, and an ischiorectal abscess is a larger, deeper fluctuant swelling.