Determination of Kidney Anatomy and Renal Blood Flow



Sonography provides a good noninvasive method of obtaining an estimate of the size of the kidney, of detecting cysts and masses in or near the kidney, and of determining the presence or absence of dilatation of the ureter. It is therefore an important and safe screening test to rule out obstruction and to differentiate between acute and chronic disease. Large kidneys may indicate in­flammatory disease or infiltrative disease of the kidneys. Further delineation of the anatomy of the kidney may require radiocontrast dyes. In patients with renal insufficiency, the quality of the x-rays obtained with the use of radiocontrast agents may be suboptimal, and the radiocontrast dyes them­selves may be nephrotoxic.

Radionuclide methods are available to assess renal blood flow. These studies can easily dis­criminate between the presence or absence of renal blood flow and the symmetry of flow to the two kidneys but are less accurate in quantitating the absolute rates of flow. In a patient who pre­sents with anuria or who develops renal failure after abdominal trauma or retroperitoneal surgery, in an elderly individual in whom the etiology of the acute renal insufficiency is obscure, and in patients with abdominal, flank, or back pain, it is prudent to determine that blood is flowing to the kidney. Angiography is required if equivocal re­sults are obtained by nuclide scanning, in a pa­tient suspected of acute renal venous disease, or when time does not permit a lengthy evaluation such as in a patient with suspected dissecting aor­tic aneurysm.

Renal blood flow as assessed by nuclide scan­ning is normal or only slightly decreased in a pa­tient with established ATN. Renal blood flow is clearly decreased in patients with glomerulo­nephritis or transplant rejection. Assessment of renal blood flow may be of particular value in dif­ferentiating between renal transplant ATN and re­jection.