Sclerosis when describing bone is defined as a pathologicthickening of the bone. Usually one area of bone will show thisincreased thickening. Sclerotic lesions are often seen in longbones, but can be seen in most, if not all, bones of the body. Thesclerosis is caused by increased calcium deposits forming in asmall area of he bone. These sclerotic lesions are best seen onimaging studies that pick up calcium like x-rays and CAT scans.This one is in the pelvic region, thus the term sacral.Sclerotic lesions are often signs of underlying disease,especially neoplasms. There are certain metastatic lesions that canoften present with bone pain and sclerosis on x-rays. Further workup to find the underlying cause of a sclerotic lesion isneeded.