Kidney

Renal Cell Carcinoma

With the increased availability of abdominal ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI), many renal cell carcinomas are now incidentally discovered, which has resulted in detection of such tumors at an early stage in asymptomatic patients.

CT is currently the method of choice for evaluation of suspected renal masses and for preoperative staging of renal cell carcinoma (Figure 31.1).1-3 The advent of spiral CT has had a significant impact on evaluation of renal masses. With the use of spiral CT, the sensitivity of CT in detecting renal cell carcinoma approaches 100% and specificity is 88% to 95%,4,5 or evaluation of known or suspected renal masses, both pre-and postcontrast images with intravenous contrast medium, should be obtained because small renal cell carcinomas are difficult to diagnose without intravenous contrast and diagnosis of masses requires assessment of enhancement.1,6 Spiral CT allows a high-quality scan dedicated to the kidneys during various phases of contrast enhancement after a rapid bolus of intravenous contrast material.4,7,8 In addition, reformatted and three-dimensional images created from volumetric data sets obtained by spiral CT, particularly with recently introduced multidetector CT, can help assessment of the tumor extent and accurate staging (Figure 31.2).9 For detection of renal masses, nephrographic phase images obtained with scan delay, at least 90 seconds after the start of intravenous contrast medium injection, are important because of a higher sensitivity than corticomedullary phase images to detect renal masses.6-8,10

MRI can also be used as an alternative imaging modality to CT for patients allergic to iodine or patients with an inconclusive CT study.11 Gadolinium (Gd)-containing contrast material has been shown to be remarkably safe and is well tolerated in patients with a history of iodinated contrast allergy. Recent studies showed MRI is considered equivalent to CT in accuracy for the detection and characterization of renal masses.12-14 A high-quality MR examination can be performed with torso phased-array coils and a variety of breath-hold sequences. Imaging protocols generally include T1-weighted images obtained with spin-echo and/or breath-hold spoiled gradient echo images and T2-weighted images obtained with fat-suppressed fast spin-echo images or breath-hold half Fourier single-shot fast spin-echo images. Gadolinium-containing intravenous contrast material is necessary to detect and characterize small lesions (Figure

31.3).15,16 An advantage of MRI gadolinium contrast (as opposed to CT contrast) is lack of nephrotoxicity.

Staging of the tumor by radiologic examination is relevant because prognosis and surgical planning largely depends on preoperative imaging delineation of disease extent. Reported accuracy of CT and MRI for staging of renal cell carcinoma is similar, ranging from 67% to 95% for CT and from 67% to 96% for MRI.9,11-13 It may be difficult to distinguish stage I (confined within the renal capsule) from stage II (extending into the perinephric fat) disease. Thickening of the renal fascia and dilated tortuous vessels in the perinephric space are not reliable signs of tumor extension into the perinephric fat and may be caused by edema, inflammation, or engorgement of vessels due to increased blood flow through a vascular tumor. Perinephric fat stranding has been detected in up to 50% of stage I tumors on CT (see Figure 31.1). The presence of an enhancing nodule of 1 cm or greater in the peri-nephric space has been reported to be highly specific (98%) but only 46% sensitive on CT. MRI has been reported to be slightly more accurate compared to CT to predict invasion of perirenal fat.11,12

Tumor thrombus within the renal vein, inferior vena cava (IVC), or right atrium can be directly visualized by CT or MRI. Using spiral CT and electron beam CT, sensitivity and specificity of tumor thrombus in the renal vein were 85% and 98%.17 In a recent study using multidetector CT with dedicated protocol and thin collimation, 100% accuracy of tumor thrombus in the renal vein and IVC has been reported.9 MRI and MR angiography also achieved high sensitivity of 89% to 100%, with specificity of 96% to 100%, in assessment of tumor thrombus in the renal vein and IVC.16,18,19 A recent study showed tumor invasion of the IVC wall was imaged by MRI with three-dimensional (3-D) gadolinium-enhanced MR angiography and venography with sensitivity and specificity of 100% and 89%, respectively.20

Distinction between metastatic and hyperplastic lymph nodes is limited for both CT and MRI because size remains the only criterion for diagnosis of lymph node metastasis. Studer et al. reported that CT is sensitive for the detection of enlarged lymph nodes in patients with renal cell carcinoma (95%), but more than 50% of enlarged nodes were caused by benign inflammatory changes, probably the result of tumoral necrosis or venous thrombosis.21 They also reported that when using a size criteria of 1 cm or greater for regional lymph node metastasis there is a 4% false-negative rate for lymph node staging.21

A variety of complex or complicated cystic masses occur in the kidney. Bosniak has described a classification system

figure 31.1. Renal cell carcinoma. Contrast-enhanced computed tomography (CT) scan shows heterogeneous mass in the left kidney (arrow). There is stranding around the mass, which is caused by peri-tumoral inflammation found by pathologic specimen. There was no capsular invasion. The pathologic stage was T2 Nx Mx.

figure 31.1. Renal cell carcinoma. Contrast-enhanced computed tomography (CT) scan shows heterogeneous mass in the left kidney (arrow). There is stranding around the mass, which is caused by peri-tumoral inflammation found by pathologic specimen. There was no capsular invasion. The pathologic stage was T2 Nx Mx.

in which CT features are used to classify cystic masses into four types to determine the likelihood of malignancy and aid in the management of complicated cystic lesions.22 CT and MRI with intravenous contrast material are equivalent for distinguishing cysts from neoplasms.1 Image subtraction is commonly used for MRI and aids in complex cases. Images without gadolinium are subtracted from those obtained after gadolinium contrast agent. Complex cystic lesions that may otherwise appear to enhance are subtracted from the resulting image. The method is particularly important for patients with polycystic kidneys.

With increased detection of renal tumors at an earlier stage, more limited or less invasive surgical procedures, such as nephron-sparing and laparoscopic surgery, have evolved as effective alternatives to radical nephrectomy.23 Nephron-sparing surgery is increasing in frequency because excellent preliminary results have been reported with small, low-stage renal cell carcinoma. More recently, less invasive nephron-sparing procedures have been applied to the treatment of renal cell carcinoma including laparoscopic surgery, radiofrequency ablation, and cryoablation. CT and MRI can play an important role to assess the precise location of the tumor in relation to the major vessels and the renal collecting system and to determine whether nephron-sparing surgery can be performed (see Figure 31.2).24-27

Other solid renal masses include oncocytoma, lymphoma, angiomyolipoma, pseudotumor, and metastatic tumor to the kidney (Figure 31.4). Oncocytoma requires surgical resection because it is not radiographically distinguished from renal cell carcinoma, but other tumors are generally not treated by surgery. Percutaneous renal biopsy may be useful in several clinical situations: (a) lesions that do not have the typical radiologic features of renal cell carcinoma, (b) lesions that are unresectable, (c) lesions that are of uncertain histology, (d) possibly metastatic lesions, (e) lesions for which lymphoma is a diagnostic consideration, and (f) lesions for which treatment may be altered by histologic diagnosis.28 In these populations, the accuracy of biopsy of 87% to 89% without significant complications has been reported.28,29

figure 31.2. Renal cell carcinoma. (A) Contrast-enhanced CT scan obtained during nephrographic phase shows a 3-cm mass in the left kidney. (B) Coronal reformatted CT image shows the mass is located in the periphery and is partially exophytic. There is no evidence of vascular or collecting system involvement. The patient underwent nephron-sparing nephrectomy. The pathologic stage was T1 Nx Mx.

figure 31.2. Renal cell carcinoma. (A) Contrast-enhanced CT scan obtained during nephrographic phase shows a 3-cm mass in the left kidney. (B) Coronal reformatted CT image shows the mass is located in the periphery and is partially exophytic. There is no evidence of vascular or collecting system involvement. The patient underwent nephron-sparing nephrectomy. The pathologic stage was T1 Nx Mx.

figure 31.3. Renal cell carcinoma. (A) Axial T1-weighted image shows right renal mass isointense to the kidney, which is difficult to appreciate without contrast enhancement. (B) Postcontrast T1-weighted image with fat suppression shows the minimal enhancement of the mass, which is much less than the adjacent renal cortex. The mass abuts the pancreatic head (arrow). The patient underwent right nephrectomy. Pathologically, it was papillary renal cell carcinoma with the pathologic stage of T1 Nx Mx.

figure 31.3. Renal cell carcinoma. (A) Axial T1-weighted image shows right renal mass isointense to the kidney, which is difficult to appreciate without contrast enhancement. (B) Postcontrast T1-weighted image with fat suppression shows the minimal enhancement of the mass, which is much less than the adjacent renal cortex. The mass abuts the pancreatic head (arrow). The patient underwent right nephrectomy. Pathologically, it was papillary renal cell carcinoma with the pathologic stage of T1 Nx Mx.

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