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As bone-seeking radiopharmaceutical are excreted by the kidneys, focal areas of increased uptake usually represent accumulation of activity in normal or obstructed collecting systems; this is particularly common in the upper pole calyces, which, due to their dependent position in the supine patient, often show accumulation of radiotracer. The pooled tracer usually drains in the upright position. Retention of activity can be seen in an extrarenal pelvis. Urinary diversion, ileal conduit , urinary extravasation, and urinoma can be recognized on skeletal scintigraphy due to the large amount of radiotracer present in the urine. Activity in an ileal loop may be mistaken with abnormal accumulation in the pelvis.
Focal areas of increased renal parenchymal uptake after radiation therapy, and rarely in renal cell carcinoma or renal metastasis may be explained by accumulation of diphosphonates in portions of the kidneys where there is tissue damage or necrosis. This is analogous to the increased uptake described in the ischemic myocardium and is related to increased intracellular calcium. In renal metastasis from osteosarcoma, radionuclide uptake is probably associated with osteoid production .
Hydronephrosis
(A) Bone scintigram shows accumulation of radiotracer in the right collecting
system. (B) CT of the right kidney confirms the presence of hydronephrosis.
Hydronephrosis.
The bone scintigram (A) shows accumulation of radiotracer in the dilated
collecting system of the right kidney. Note multiple bony metastases in this
patient with prostatic carcinoma. The sonogram (B)of the right kidney confirms
the presence of hydronephrosis.
Urinary Diversion
Bone scintigram (posterior view) in a patient with ureterosigmoidostomy shows
activity in the colon.
Ileal Conduit
(A) Bone scintigram (anterior view) shows absence of the bladder and a
collection of activity projecting over the right hemipelvis, a finding that
corresponds to an ileal conduit on retrograde pyelography (B).
Urine Extravasation
Bone scintigram (posterior view) in a patient with urinary leak after
placement of a nephrostomy tube shows large collection of activity inferior to
the right kidney.
Radiation Therapy
Bone scintigram obtained in a patient with extensive metastatic breast
carcinoma after radiation to the spine shows decreased uptake in the spine and
medial aspect of the ribs, and concomitant increased uptake of the medial aspect
of the kidneys included in the radiation port.