CT and MRI are both excellent modalities for preoperative imaging of renal tumors, and either can be used for surgical planning (1,2,28-32). CT is the study used most frequently because it is readily available, has superior spatial resolution, and unlike MRI, is able to detect calcifications. Success with 3-D real-time rendering using CT datasets has also contributed to preferential use of CT. CT examinations are performed before and after administering intravenous contrast agents but without oral contrast material because any positive enteric contrast media interferes with 3-D renderings. In our institution, patients with normal or mildly elevated serum creatinine levels (below 2.0mg/dL) are given a full dose of a low-osmolar nonionic contrast agent. Patients with elevated serum creatinine levels between 2.0 and 2.5mg/dL are hydrated intravenously with normal saline solution before the examination and are also instructed to drink fluids after the scan; however, at the present time, the use of iso-osmolar contrast agents is also recommended in these patients because of the reported reduction in nephrotoxicity during coronary angiography (33). Patients with creatinine levels of 2.5mg/dL or higher are referred for MRI, which avoids the increased risk for nephrotoxicity in already compromised kidneys. Also, when renal function is poor, the optimal enhancement of normal parenchyma that is needed to best detect small tumors does not occur.
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