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Abstract
Early detection and surgical excision of renal cell carcinomas are critical to improve the patient’s survival.
The characteristic highly echogenic appearance of angiomyolipomas on sonography is well known, however it is not pathognomonic. Other tumors, including renal cell carcinoma, can be hyperechoic. Therefore, echogenic tumors depicted on ultrasonograms should be further characterized with CT and MR imaging. CT permits confident non-invasive diagnosis of renal angiomyolipoma. Attenuations of less than –20 Hounsfield units are widely accepted to confirm the presence of fat, and this finding virtually confirms the diagnosis in more than 90% of angiomyolipoma.
Helical CT offers excellent topographic display and demonstrates the size and location of renal carcinomas greater than 2 cm in diameter with a high degree of accuracy. Papillary renal cell carcinomas are often hypovascular with low heterogeneity ratios. The corticomedullary phase is useful for staging information, while the nephrographic phase is the most valuable for detecting renal masses and characterizing indeterminate lesions. The excretory phase is occasionally helpful to better delineate the relationship of a centrally located mass with the collecting system.
Involvement of peri-renal fat tissue represents a key point in modifying the surgical approach. The identification of a pseudocapsule has been proposed as a sign for a localized intra-renal lesion which is clearly depicted in MRI examination. The sensitivity of CT in detecting pseudocapsule is very low.
Sonography is clearly superior to excretory urography for both detection and characterization of renal masses, and CT is superior to sonography for these tasks. CT and MR imaging are nearly ideal techniques for the detection, diagnosis, staging, and preoperative evaluation of small renal masses. Helical CT scanning is essential in the differentiation of angiomyolipoma with minimal fat from renal cell carcinoma. However, MRI is superior to CT in detecting microscopic fat in AMLs and for staging of RCCs.