What causes severe pain in the rectum?
The 3 most common causes of severe rectal pain (thrombosed/strangulated hemorrhoids, fissure or abscess) can be easily diagnosed with history and visual inspection.
THROMBOSED EXTERNAL HEMORRHOIDS OR INTERNAL EXTERNAL HEMORRHOIDS
Thrombosed external hemorrhoids should be evacuated in the ER only if the pain is severe. Many patients present after 3-4 days and by this time pain is already decreasing and incision to evacuate the blood clot is not needed, Metamucil & Sitz baths should be sufficient.
If the hemorrhoidal column is extending inside the anal canal this is strangulated internal/external hemorrhoid and must not be treated by an I&D in the ER. If pain is severe and history is short then hospitalization and emergency hemorrhoidectomy is needed. If the pain is already subsiding then Sitz baths, analgesics and Metamucil along with FU with colorectal surgeon is the best option.
Usually the inspection is normal or may show the small fissure in the midline (posterior > anterior) along with the sentinel skin tag. Sitz baths, analgesics and Metamucil along with colorectal FU is needed.
A tender swelling in the anal verge is the perianal abscess which can be drained in the ER. Make incision as close to the anal verge as possible so that if a fistula develops it is close to the anus. Otherwise a long fistula tract will result! After drainage do not pack the I&D site. Packing actually retards gravity assisted drainage in this area. Advise Metamucil, Sitz baths TID.
A tender more diffuse swelling farther away from the anal verge is an ischiorectal abscess and should be drained in the operating room.
When abscess is suspected and not visualized it is most likey an intersphincteric or supra levator abscess and a rectal exam under anesthesia or CT scan is warranted.