Bone tracer uptake in a ureteric calculus.

Technetium-99m methylene diphosphonate was observed to concentrate in a mildly obstructive left ureteric calculus. The bone scan findings alerted the clinicians to this possibility, which was subsequently confirmed and the patient successfully treated. The stone was heterogeneous in texture and predominantly formed from magnesium ammonium phosphate. At extraction the major fragment contained 0.4% of the injected bone tracer dose and autoradiography demonstrated peripheral tracer distribution within the calculus.