Extrarenal pelvis mimicking obstructive uropathy in nine years of serial bone scintigraphies

A woman who underwent mastectomy for left breast carcinoma has been followed-up yearly with bone scintigraphy using Tc-99m diphosphonate compounds for nine years. In the bone images of the initial three years (first, second, and third years postmastectomy), radiotracer accumulation in the right renal upper collecting system had been interpreted as obstructive uropathy. Then the patient underwent initial (third year postmastectomy) and repeat (fifth year postmastectomy) intravenous contrast pyelography (IVP), which revealed an extrarenal pelvis with no significant interval changes. The fourth and fifth bone scintigraphs and the subsequent four consecutive bone scintigraphs showed the same pattern radiotracer retention in the right renal collecting system. Thus, while interpretation of an accumulation of radiotracer in the upper renal collecting systems on a single bone scintigraphy may provide difficulty in making a differential diagnosis between obstructive uropathy and extrarenal pelvis, IVP is important for definitive diagnosis. Alternatively, a review of the previous consecutive bone studies, if available, may also aid in this differentiation, since obstructive uropathy may manifest as progressive renal dysfunction, while extrarenal pelvis may have the same pattern of radiotracer accumulation in the collecting system persistently.