Musculoskeletal ImagingSacrum
1. Anatomythe triangular bone usually formed by fusion of five sacral vertebrae. The sacrum lies beneath the lowermost lumbar vertebra and between the two hip bones. Also, see sacrum.
2. Pathology
Agenesis of the sacrum may occur separately or as part of the VATER syndrome.
Insufficiency fractures, a type of stress fracture, may occur in the sacrum in persons with osteoporosis or rheumatoid arthritis or in patients receiving corticosteroids or radiation therapy (Fig.1). These fractures may be subtle on radiographs but have a characteristic appearance on scintigraphy, with horizontal and vertical regions of increased uptake of bone-seeking radiopharmaceutical agent, leading to a configuration termed the H pattern. CT scanning and MR imaging provide helpful information relating to bone alterations.
Fatigue fractures of the sacrum have also been described.
Chordoma, a tumour of notochord origin that is locally aggressive but grows slowly, often involves the sacrum or sacrococcygeal region.
Skeletal metastasis to the sacrum from primary tumours are relatively common. Radiographs may be less than optimal, and CT scanning or MR imaging may be required for diagnosis.
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a. AP radiograph of the pelvis demonstrates subtle patchy sclerosis along the lateral aspects of the sacrum.
b. Axial CT scan demonstrates an insufficiency fracture of the right sacral ala.
(Courtesy of Tere Trout, MD, San Diego, CA)
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Sacrum, Fig.1 (a) | | Sacrum, Fig.1 (b) | |