The sacral tubercle--a cause for hot spots on bone scan.

The sacral tubercle, S1 posterior spinous process, can appear as intense as the sacroiliac joints on posterior bone scan in 4% of normal adult male patients. Due to sexual differences in anatomy, the scan appearance of the sacrum can cause false-positive readings. The converse, false-negative readings, can occur if the sacral intensity is taken as a constant when comparing ratios of sacroiliac joint intensities and sacral intensities on bone scans of patients with sacroiliac disease. This study demonstrates the normal anatomy of the sacrum and presents a sequence of tests to diagnose disease in the sacrum.