Bladder diverticulum simulating a pelvic metastasis on a Tc-99m HDP bone scan

Carcinoma of the prostate was diagnosed in a 74-year-old man. A Tc-99m HDP bone scan was performed as part of the initial staging process. The findings on the bone scan were normal except for an area of increased tracer uptake projected over the left sacroiliac joint, which was seen best on the anterior view. When this was investigated further, the findings of a plain radiograph were inconclusive. Computed tomography showed a large diverticulum projecting from the left side of the bladder; the tracer retained within this diverticulum had produced the findings on the bone scan.