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The two most common mechanisms of bilateral decreased renal uptake are either loss of renal function or increased osteoblastic activity . With end-stage renal disease the kidneys are small with faint uptake or are not visualized. In the case of increased osteoblastic activity, the renal uptake is diminished because there is increased accumulation of radiotracer in the skeleton, with diminished amount of radiotracer available for renal excretion. Superscans are bone scans with uniformly increased bone-to-soft-tissue ratio with resultant faint or absent renal visualization. These can be caused by extensive metastatic disease, usually from prostate or breast carcinoma, widespread Paget's disease, hyperparathyroidism, and a variety of hematological disorders, such as myelofibrosis, aplastic anemia, leukemia, orWaldenström macroglobulinemia. As the kidneys are the principal pathway of excretion of bone seeking radiopharmaceuticals, in the setting of renal failure the soft tissue uptake is increased because of decreased renal clearance, whereas in the case of a superscan there is decreased soft tissue activity due to relative increased uptake in the axial skeleton.
Focal areas of decreased renal uptake are generally caused by
space-occupying lesions which destroy or replace normal renal
parenchyma, such as abscesses, cysts , primary, and metastatic
neoplasms. Irregularity of the renal contour may be seen with infarcts
or scarring from chronic pyelonephritis. Iatrogenic focal decreased
uptake is seen after partial nephrectomies.
Renal Cyst
Bone scintigram (posterior view) shows a large area of decreased uptake in the upper pole of the left kidney, a finding that corresponds to a large renal cyst seen on CT scan (B).
Renal Cyst
Bone scintigram (posterior view) shows a large area of decreased
radionuclide uptake in the lower pole of the right kidney, a finding
that corresponds to a large cyst on the longitudinal view of the right
renal sonogram (B).
Renal Cell Carcinoma
(A) Bone scintigram (posterior view) in a patient with renal cell
carcinoma shows a large area of decreased uptake in the lower pole of
the left kidney, a finding that corresponds to a large mass seen on the
CT scan (B). On the bone scan there is also decreased uptake in the
lower pole of the right kidney (arrow) which corresponds to a cyst seen
on CT. The focal area of increased radiotracer uptake in the lower
thoracic spine probably represents metastatic disease.
Renal cell carcinoma.
The bone scintigram (A) shows a focal photopenic region in the lower
pole of the right kidney, which corresponds to a large mass seen on CT
scan (B).
Non-Hodgkin Lymphoma
Bone scintigram (posterior view) in a patient with non-Hodgkin's
lymphoma shows enlarge kidneys bilaterally with multiple areas of
diminished radiotracer uptake, a finding that corresponds to multiple
low-attenuation masses seen on CT scan (B).
Gallstone
Anterior view (A) of a bone scan shows a photopenic area in the
superior pole of the right kidney (arrow), the posterior view (B) is
normal, US image (C) demonstrate a large shadowing gallstone.
Attenuation from calcified gallstone causes the photopenic area in the
kidney.