Computed Tomography

Computed tomography is considered the gold standard for detection, diagnosis, and staging of renal cell carcinoma (7,8).

However, both computed tomography (9-14) and magnetic resonance (15,16) are highly sensitive and specific for the detection of solid renal masses and can characterize cystic renal lesions. Magnetic resonance has higher soft-tissue contrast resolution and is more sensitive to intravenous contrast enhancement than computed tomography, but spatial resolution and availability are less than that of computed tomography.

Magnetic resonance is often reserved for problem solving, or for those patients with renal insufficiency or a history of severe allergy to iodinated contrast.

Either computed tomography or magnetic resonance imaging can be used for surgical planning (7,8,15-19). Success with 3-D real-time rendering using computed tomography datasets has led to a preferential use of computed tomography by most centers.

Computed tomography examinations are performed before and after intravenous contrast, but without oral barium contrast because positive enteric contrast material interferes with three-dimensional renderings.

■ Patients with a normal or mildly elevated creatinine level (below 2.0 mg/dL) are given a full dose of low-osmolar nonionic contrast agent.

■ Patients with any degree of renal insufficiency are instructed to drink fluids after the scan.

■ Patients with elevated creatinine levels between 2.0 and 2.5 mg/dL are hydrated intravenously with 0.9 normal saline solution before the examination and also instructed to drink fluids after the scan. Iso-osmolar contrast agents are recommended in these patients because of the reduced nephrotoxicity that has been reported in studies evaluating renal function after coronary angiography (20).

■ Patients with creatinine levels of 2.5 g/dL or higher are referred for magnetic resonance imaging, which avoids the increased risk for nephrotoxicity in already compromised kidneys. Also, when renal function is poor,the enhancement of normal parenchyma that is needed in order to detect small tumors does not occur.

Developments in computed tomography technology have been dramatic in the last 15 years. Spiral or helical computed tomography was developed in the early 1990s. This revolutionary advancement allows for the constant acquisition of computed tomography data while the patient moves through the scanner gantry, with the X-ray tube rotating continuously around him. Rather than the individual slices that were obtained with prior nonspiral technology, a volume of data is acquired. To better depict anatomy or pathology, this volume can then be reformatted electronically into planes other than the axial plane in which it was obtained. Additional advantages of spiral technology include faster image acquisition, so that the dynamics of contrast enhancement can be exploited and motion artifacts reduced. By late 1998, computed tomography manufacturers developed a further advancement consisting of multirow detector arrays (multirow or multislice helical computed tomography) (21). Rather than one X-ray detector row encircling the patient as he moves through the scanner, multiple rows of detectors are used in this advanced model. In addition to further increasing the speed of scanning compared to single row scanners, multiple row scanners achieve true isotropic voxel (volume element) resolution. The elements that are summed up to make an image are cubic and, therefore, can be reformatted in any plane and be equally sharp. This development has allowed for true three-dimensional imaging.

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