1) Thrombosed external hemorrhoid is a painful swelling at the anal opening caused by a blood clot forming in an external hemorrhoid. 2) It is usually caused by factors that increase pressure in the abdomen like pregnancy, constipation from poor diet or lack of exercise, or prolonged sitting or standing. 3) Symptoms include a bluish swollen lump near the anus that is painful. Seeking treatment is important to address pain and rule out other potential issues. Maintaining a high fiber diet and drinking plenty of water can help prevent hemorrhoids.