Clinical presentation:
55 year old man. Treated for 'osteomyelitis' by resection of coccyx 7 years previously; resection of peri-anal soft tissue mass 3 years ago, now with repeat of symptoms.

There is a soft tissue mass in the lower part of the rectum, above the anal ring. The mass contains areas of amorphous calcification and extends forward along the line of the floor of the pelvic diaphragm (pubo-coccygeus) towards the bladder base.