Hemorrhoids can occur inside of the anal canal, called internal hemorrhoids, or in the area just outside of the anus, known as external hemorrhoids. Either type of hemorrhoid may develop a blood clot, but it is seen more commonly in external hemorrhoids. Internal hemorrhoids may push out of the anal opening, or prolapse, and may retract themselves following a bowel movement. External hemorrhoids are generally more painful, especially while sitting or during activities that place more pressure on the hemorrhoid.
An external thrombosed hemorrhoid will likely cause extreme pain in the anal region. The sufferer should be able to feel the lump of swollen tissue, which may look a bluish color due to the back up of blood from the veins. Other symptoms might include burning or itching in the anal area. Because an anal abscess, which can be serious, may mimic the symptoms of an external thrombosed hemorrhoid, it is important to see a specialist as soon as possible to diagnose and treat the problem.