The sacrum and bones of the pelvis are involved in about 12% of skeletal metastases and may show either lytic or blastic lesions. Seeding from the viscera via Batson’s venous plexus explains this high incidence in the pelvis, as well as in the lumbar spine. Blowout lesions of renal and thyroid origin often affect the bony pelvis. Lesions located in the sacral ala or the posterior ilium are often difficult to perceive on standard radiographs. With the advent of CT scans, a wide variety of lesions involving the osseous pelvis can be more readily seen. The ability of CT to provide accurate measurements of tissue attenuation coefficients and to provide a cross-sectional scan for three dimensional viewing has made it a powerful tool in musculoskeletal diagnosis, with a profound influence on patient management. It provides information about the extent of the bony lesion, localization (for biopsy and radiation therapy), and relationships with other structures. As equipment improves, it seems probable that CT will assume a more primary role in diagnostic evaluation, particularly of the pelvis, where the complexity of bones and the overlying bowel content prevent ideal evaluation with conventional radiographs.

Occasionally, blastic lesions affecting the pelvic rim, especially from carcinoma of the prostate, exhibit an expansion of bone. This occurs as a result of cortical thickening from endosteal or periosteal apposition of bone. The bony enlargement may mimic the appearance of Paget’s disease. Usually, other skeletal lesions are present to assist in radiologic differentiation. Biopsy of the lesion may be necessary as a final step in diagnosis.