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Management strategies for patients with kidney cancer are progressing significantly, based on advances in basic research and the growing number of clinical trials. Numerous classifications have been proposed, with varying degrees of acceptance, based on morphological and molecular futures; therefore, to arrive at the correct differential diagnosis, it is essential for the pathologist and radiologist to provide effective histological and imaging information to the urologist.

Ultrasound plays a key role in screening renal cancer in asymptomatic patients. With the exception of large solid RCC with venous invasion, most renal tumors remain indeterminate on US and require CT for accurate characterization; however, US may help characterize cystic RCC that remain equivocal on CT. Recent technical improvements in gray-scale imaging have increased the accuracy of US in the diagnosis and staging of kidney cancer. Intraoperative evaluation of radio-frequency tumor ablation also can benefit from recent advances in the use of US contrast agents.

With the advent of MDCT, the role of CT in the diagnosis and pre-surgical planning of RCC has been greatly expanded. Along with these technical improvements, new challenges facing the radiologist have emerged. These challenges include the adoption of scanning protocols designed to maximize diagnostic accuracy while at the same time minimizing radiation to the patient and image overload for the radiologist. Renal CT with multiple-phase image acquisitions as well as 3D reconstructions provides the clinician with all the information necessary for surgical planning.

Magnetic resonance imaging is a powerful and versatile tool for single-modality evaluation of potential renal malignancies. A well-planned and executed high-field MR imaging examination can simultaneously detect and characterize a renal neoplasm. Multiphasic post-contrast imaging can generate MRA/MRV/MRU data sets with which, after post-processing, the radiologist can characterize the renal vasculature and stage the tumor. Magnetic resonance imaging also has an important role to play in helping clinicians to select the proper therapy for a renal tumor and in evaluating the patient following therapy. Ongoing advances in MR imaging, including the development of new pulse sequences, the increased availability of whole-body 3-T scanners, and the growing practicality of parallel imaging techniques will likely expand the role of MR imaging in imaging patients with known or suspected renal malignancies.

From occupying a central role in the evaluation of kidney cancer, renal arteriography has been relegated to a problem-solving secondary role in the modern era. This is partly due to the changing presentation of renal tumors; most are now identified at an early stage, and renal arteriography is insensitive when compared with the cross-sectional modalities for evaluation of small renal masses. Arteriography is now seldom used for diagnosis. For staging it may help in the occasional case with indeterminate findings regarding venous involvement on CT and MR imaging. It may have some utility for pre-operative surgical planning, but mostly it is now used for planning of therapeutic or palliative tumor embolization.

Renal cell carcinoma comprises about 3% of all malignancies. FDG has a modest affinity for RCC related to a lower expression of GLUT-1 than other cancers. Metabolic imaging using FDG and PET has a modest accuracy for primary lesions and local recurrence. The data for staging and restaging of RCC is similar: low sensitivity and high specificity. Possible interpretation problems related to the excreted FDG can be overcome by fusion of anatomic and metabolic images (PET/CT). Newer-generation scanners have improved spatial resolution, which will reduce false negatives. To date, there are no series available about the utility of this emerging dual-modality imaging technique in RCC. The modality is also suitable for therapy monitoring, but again there is insufficient data to assess the contribution of PET or PET/CT.

Because a significant percentage of RCCs are discovered incidentally on an imaging study ordered for another purpose, the radiologist must remain vigilant. Once a suspected mass is identified, US is a cost-effective means to further characterize those lesions that are statistically most likely to be simple cysts. Solid or complex cystic lesions are best characterized by CT or MR imaging. These crosssectional modalities are also indispensable in the staging and restaging of suspected RCC lesions, although other modalities, such as PET, may play a complementary role.

Transitional cell carcinoma is a common urological malignancy and in up to 5% of cases occurs in the kidney. The multicentric nature of TCC makes assessment of the entire urothelium essential prior to treatment. Vigilant urological and radiological follow-up is also warranted post-treatment to assess for metachronous lesions and recurrence. Conventional imaging modalities, such as IVU, RP, and US, still play a pivotal role in the assessment of hematuria in conjunction with endourological techniques. The recent advent of minimally invasive surgery that allows renal preservation makes accurate staging, usually with CT or MR imaging, mandatory to determine appropriate therapy. The technique of CTU has recently developed and offers superior detection of urinary tract tumors and calculi, as well as the ability to assess perirenal tissues and stage lesions, as a single comprehensive study. In the future, it is probable that CTU will become the standard investigation in the initial assessment and follow-up of patients with suspected TCC. Similar MR imaging protocols can also be used in patients not suitable for CTU, although detection of calculi may be suboptimal.

Magnetic resonance imaging is a powerful and versatile tool for single-modality evaluation of potential renal malignancies. A well-planned and executed high-field MR imaging examination can simultaneously detect and characterize a renal neoplasm. Multiphasic post-contrast imaging can generate MRA/MRV/MRU data sets with which, after post-processing, the radiologist can characterize the renal vasculature and stage the tumor. Magnetic resonance imaging also has an important role to play in helping clinicians to select the proper therapy for a renal tumor and in evaluating the patient following therapy. Ongoing advances in MR imaging, including the development of new pulse sequences, the increased availability of whole-body 3-T scanners, and the growing practicality of parallel imaging techniques will likely expand the role of MR imaging in imaging patients with known or suspected renal malignancies.

Even though the accurate diagnosis of a cystic renal mass is multifactorial, the quality of the examination (CT or MR imaging) is often not emphasized, and yet it is a significant factor in making a correct diagnosis. The techniques for high-quality CT and MR imaging have been reviewed and their role in the characterization of cystic renal masses has been summarized. The Bosniak renal cyst classification has proven helpful in classifying renal cysts into surgical and nonsurgical lesions and its application to MR imaging appears promising. In the future, with further experience using state-of-the-art CT and MR imaging, our ability to diagnose and manage complex cystic renal masses will further advance, leading to improved patient care.