The sacrum: Pathologic spectrum, multi-modality imaging, and subspecialty approach

The sacrum is a structure that is imaged by both general and subspecialty r adiologists. A wide variety of disease processes can involve the sacrum eit her focally or as part of a systemic process. Plain radiographs, although l imited in evaluation of the sacrum, should be carefully examined when abnor malities of the sacrum are suspected. Cross-sectional imaging, particularly computed tomography and magnetic resonance (MR) imaging, plays a crucial r ole in identification, localization, and characterization of sacral lesions . Congenital lesions of the sacrum, including sacral agenesis and meningoce le, are optimally imaged with MR. The most common sacral neoplasm is metast atic disease. Primary neoplasms of the sacrum, which include giant cell tum or, chordoma, and teratoma, are infrequent. Infection of the sacrum or sacr oiliac joint is most often due to contiguous spread from a suppurative focu s. A wide variety of arthritic disorders such as ankylosing spondylitis and osteoarthritis can involve tree sacroiliac joints as part of a localized o r systemic process. Sacral fractures related to acute trauma or repetitive stress are difficult to diagnose and treat. Knowledge of these abnormalitie s and familiarity with the imaging of these processes will allow radiologis ts of all subspecialties to contribute to the diagnosis and management of s acral disorders.