Utility of pelvic bone SPET in imaging urinary bladder filling defects in urinary bladder carcinoma

Urinary bladder carcinoma sometimes can be recognized on bone scans as a filling defect in the bladder. This paper illustrates in three patients that the filling defects of urinary bladder on pelvic bone single photon emission tomography (SPET) scans in cases of bladder carcinoma correspond to those on computerized tomography (CT). In one patient, the void sign could only be discerned on the SPET images, but not on the planar images. In the same patient, the filling defect was almost entirely surrounded by urinary activity, suggesting an intrinsic bladder lesion. The differential diagnosis of filling defects is presented. The above findings are compared to other related studies, although we have found no similar cases in the literature. When compared with CT, pelvic SPET is more sensitive than planar imaging in recognizing bladder filling defects on bone scans and may allow distinguish between intrinsic and extrinsic bladder lesions.