(Radiographics. 2001;21:S237-S254.)
© RSNA, 2001
Current Concepts in the Diagnosis and Management of Renal Cell Carcinoma: Role of Multidetector CT and Three-dimensional CT1
Sheila Sheth, MD,
John C. Scatarige, MD,
Karen M. Horton, MD,
Frank M. Corl, MS and
Elliot K. Fishman, MD
1 From the Department of Radiology, Johns Hopkins Hospital, 600 N Wolfe St, HAL B176D, Baltimore, MD 21287. Presented as an education exhibit at the 2000 RSNA scientific assembly. Received January 30, 2001; revision requested April 5 and received May 8; accepted May 16. Address correspondence to S.S. (e-mail: ssheth@jhmi.edu).
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Abstract
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Renal cell carcinoma is the most common primary tumor of the kidney, with more than 30,000 new cases diagnosed in the United States each year. With the widespread use of cross-sectional imaging, many tumors are detected incidentally. Single- and multidetector computed tomography (CT) have helped refine the diagnostic work-up of renal masses by allowing image acquisition in various phases of renal enhancement after intravenous administration of a single bolus of contrast material. The scanning protocol should include unenhanced CT followed by imaging during the corticomedullary and nephrographic phases of enhancement. The nephrographic phase is the most sensitive for tumoral detection, while the corticomedullary phase is essential for imaging the renal veins for possible tumoral extension and the parenchymal organs for potential metastases. Knowledge of the tumoral stage at the time of diagnosis is essential for prognosis and surgical planning. The accuracy of CT for staging has been reported to reach 91%, with most staging errors related to the diagnosis of perinephric extension of tumor. Three-dimensional CT provides the urologist with an interactive road map of the relationships among the tumor, the major vessels, and the collecting system. This information is particularly critical if the tumor extends into the inferior vena cava and if nephron-sparing surgery is being planned.
Index Terms: Kidney neoplasms, CT, 81.12114, 81.12117 • Kidney neoplasms, staging, 81.324 • Renal veins, neoplasms, 966.336 • Venae cavae, neoplasms, 982.336
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LEARNING OBJECTIVES FOR TEST 6
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After reading this article and taking the test, the reader will be able to:
- Determine the optimal CT protocol for the diagnosis and staging of renal cell carcinoma.
- Recognize appropriate CT findings for staging the tumor in patients with renal cell carcinoma.
- Describe the role of three-dimensional CT in the surgical management of renal cell carcinoma.
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Introduction
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Renal cell carcinoma is the most common malignancy of the kidney and accounts for 2% of all cancers. It is estimated that 31,200 new cases were diagnosed during 2000 in the United States, and 11,900 of them will lead to death from the disease (1). To this day, complete surgical resection remains the only curative treatment for renal cell carcinoma.
The past 2 decades have witnessed significant changes in the manifestation, diagnosis, and management of renal cell carcinoma. With the widespread use of cross-sectional imaging, as many as one-half of such carcinomas are discovered incidentally and many are early-stage lesions. Paralleling this clinical stage migration is a growing trend for more limited surgical resection, such as adrenal-sparing radical nephrectomy, laparoscopic nephrectomy, or nephron-sparing partial nephrectomy (2).
The challenges of renal tumoral imaging include not only reliable differentiation between benign and malignant lesions but also accurate delineation of the extent of the disease to ensure optimal treatment planning. Spiral computed tomography (CT) has significantly improved imaging of renal masses by decreasing volume averaging artifacts and respiratory misregistration artifacts and allowing image acquisition during optimal contrast enhancement. Further advances, particularly optimization of volume data sets, are anticipated with multidetector spiral CT, which provides better resolution than and data acquisition speeds at least four times greater than those of single-detector spiral CT.
The objectives of this article are (a) to review and understand the protocols of single-detector and multidetector spiral CT for imaging renal cell carcinoma, (b) to present CT findings for staging of renal cell carcinoma, and (c) to discuss the value of three-dimensional CT in surgical planning and problem solving for patients with renal cell carcinoma.
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CT Techniques
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Single-detector and multidetector spiral CT have dramatically refined the diagnostic evaluation of renal pathologic conditions by allowing rapid image acquisition through the entire kidney during various phases of contrast enhancement after the administration of a single bolus of intravenous contrast material (3–6). To take full advantage of the flexibility and new opportunities offered by recent advances in technology, it is important to understand the value and limitations of each of the phases of enhancement.
Unenhanced CT
An initial series of unenhanced scans through the kidneys should be part of every protocol for evaluation of a suspected renal mass; it provides a baseline from which to measure the enhancement within the lesion after the administration of intravenous contrast material. This enhancement characteristic is important in distinguishing hyperdense cysts from solid tumors. Because most renal cell carcinomas have a rich vascular supply, they enhance significantly after administration of contrast material. Enhancement values of more than 12 HU are considered suspicious for malignancy (7).
Most renal cell carcinomas are solid lesions with attenuation values of 20 HU or greater at unenhanced CT (7). Small (
3-cm-diameter) tumors usually have a homogeneous appearance (Fig 1a), while larger lesions tend to be more heterogeneous owing to hemorrhage or necrosis. Calcifications are detected in up to 30% of cases of renal cell carcinoma.
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Figure 1a. Incidental renal cell carcinoma at unenhanced CT and at the corticomedullary and nephrographic phases of enhanced CT. (a) Unenhanced CT scan shows a 2.5-cm-diameter soft-tissue mass deforming the contour of the right kidney (arrow). (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows that the mass is hypoattenuating compared with the renal cortex and has peripheral enhancement (arrow). The cortex is brightly enhanced, whereas the medulla is relatively unenhanced. (c) Contrast-enhanced CT scan obtained during the nephrographic phase shows the hypervascular mass is well demarcated from the homogeneously enhancing renal parenchyma (arrow). The patient underwent nephron-sparing nephrectomy. The pathologic stage was T1 NX.
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Figure 1b. Incidental renal cell carcinoma at unenhanced CT and at the corticomedullary and nephrographic phases of enhanced CT. (a) Unenhanced CT scan shows a 2.5-cm-diameter soft-tissue mass deforming the contour of the right kidney (arrow). (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows that the mass is hypoattenuating compared with the renal cortex and has peripheral enhancement (arrow). The cortex is brightly enhanced, whereas the medulla is relatively unenhanced. (c) Contrast-enhanced CT scan obtained during the nephrographic phase shows the hypervascular mass is well demarcated from the homogeneously enhancing renal parenchyma (arrow). The patient underwent nephron-sparing nephrectomy. The pathologic stage was T1 NX.
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Figure 1c. Incidental renal cell carcinoma at unenhanced CT and at the corticomedullary and nephrographic phases of enhanced CT. (a) Unenhanced CT scan shows a 2.5-cm-diameter soft-tissue mass deforming the contour of the right kidney (arrow). (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows that the mass is hypoattenuating compared with the renal cortex and has peripheral enhancement (arrow). The cortex is brightly enhanced, whereas the medulla is relatively unenhanced. (c) Contrast-enhanced CT scan obtained during the nephrographic phase shows the hypervascular mass is well demarcated from the homogeneously enhancing renal parenchyma (arrow). The patient underwent nephron-sparing nephrectomy. The pathologic stage was T1 NX.
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Corticomedullary Phase
The corticomedullary phase is the first phase of contrast enhancement. It occurs between 25 and 70 seconds after the start of injection. In this phase, the contrast material is primarily within the cortical capillaries, peritubular spaces, and cortical tubular lamina and has not yet filtered through the more distal renal tubules. The renal cortex enhances brightly and is easily differentiated from the minimally enhancing renal medulla (Fig 1b) (8).
Several studies have emphasized the limitations of the corticomedullary phase in the detection of small renal lesions (3–5). Occasionally, a small, hypervascular renal cell carcinoma may enhance to the same degree as the renal cortex and may be mistaken for normal parenchyma at the corticomedullary phase. A more common source of error (false-negative) occurs when a centrally located tumor is mistaken for the normal, hypoattenuating medulla (6). On the other hand, mistaking a heterogeneously enhancing medulla for a solid tumor is a potential cause of a false-positive diagnosis (3,5,6).
Despite these pitfalls, the corticomedullary phase is essential for accurate staging of renal cell carcinoma. Maximal opacification of the renal arteries and veins occurs, allowing confident diagnosis of venous extension of tumoral tissue (9). Accurate delineation of the arterial anatomy is helpful in selected cases to plan nephron-sparing surgery. Metastases from renal cell carcinoma often show rapid enhancement during this phase. Hypervascular metastases to the liver, spleen, and pancreas are most conspicuous on the corticomedullary-phase scans, when these organs are imaged during the arterial phase of enhancement.
Nephrographic Phase
As contrast material filters through the glomeruli into the loops of Henle and the collecting tubules, the nephrographic phase of contrast enhancement begins (8). This phase is best imaged after a scanning delay of at least 80 seconds and lasts up to 180 seconds after the start of injection. The renal parenchyma enhances homogeneously, allowing the best opportunity for discrimination between the normal renal medulla and masses (6). Enhancement of solid renal tumors is time-dependent, being greater during the nephrographic phase than during the corticomedullary phase (Fig 1b, 1c) (10). The nephrographic phase is the most valuable for detecting renal masses and characterizing indeterminate lesions (3,5,10). In one study, 84 more renal masses smaller than 3 cm in diameter were seen on the nephrographic-phase scans than were seen on the corticomedullary-phase scans (5). While many of these lesions were clinically insignificant renal cysts, the authors also concluded that small renal cell carcinomas were also more conspicuous on the nephrographic-phase scans.
Excretory Phase
The excretory phase begins approximately 180 seconds after the initiation of injection of iodinated contrast material. The contrast material is excreted into the collecting system, and as a result, the attenuation of the nephrogram progressively decreases.
This phase is occasionally helpful to better delineate the relationship of a centrally located mass with the collecting system and define potential involvement of the calices and renal pelvis. Delayed scanning can also be used in lieu of unenhanced scanning to characterize an incidental renal lesion detected on a routine contrast-enhanced CT scan. Macari and Bosniak (11) have suggested that measurement of the washout of contrast material from a lesion at 15 minutes allows differentiation between hyperdense cysts and renal neoplasms. In their study, there was no change in the attenuation of high-density cysts between the initial contrast-enhanced CT scan and the 15-minute-delayed images. In comparison, all lesions that proved to be neoplasms at surgery or follow-up studies showed a decrease in attenuation or "de-enhancement" of at least 15 HU at delayed CT, which was attributed to the washout of contrast material from the vascular bed of the tumor (11).
Dedicated renal CT performed for the diagnosis and staging of renal cell carcinoma must include a combination of image data acquisitions, despite the added radiation exposure and cost. Better detection and characterization of renal masses, as well as more accurate staging, are possible when the scanning protocol includes a combination of unenhanced CT and imaging in the corticomedullary and nephrographic phases (4).
Our standard single-detector and multidetector spiral CT protocols are outlined in Table 1. When a patient is specifically referred for staging of and preoperative planning for a previously diagnosed or suspected renal cell carcinoma, our protocol includes multidetector CT scans obtained with four 1-mm section thicknesses (effective section thickness, 
1.25 mm) and reconstructed every millimeter. Because traditional oral contrast material may obscure intravascular contrast and require extensive editing at the time of three-dimensional reconstruction, we routinely use water as an oral contrast agent. This technique provides exquisite visualization of the renal vascular anatomy at CT angiography. The relationship of the tumor to the main and segmental renal arteries and veins and to the collecting system can be displayed in multiple projections. Multidetector CT offers shorter image acquisition times, reduction in tube heating, and improved spatial resolution compared with single-detector spiral CT. However, radiation doses can be higher in multidetector CT than in the single-detector spiral mode if higher milliampere seconds or lower beam pitch (table increment divided by total beam width) is used. With some multidetector CT scanners, the dosage increases in high-resolution modes, since the beam pitch is less than 1 (12).
Role of Three-dimensional CT for Surgical Planning
In staging renal cell carcinoma, the goal of any imaging study is to identify patients who have a resectable tumor and can be cured by means of surgical intervention (13). The extent of disease must be accurately delineated to allow optimal surgical planning.
Three-dimensional CT combined with CT angiography has the potential to provide all the critical information needed to plan the surgical procedure. The three-dimensional CT images can be viewed in multiple planes and orientations to define the tumor and its relationship to the renal surface, the collecting system, and adjacent organs. A three-dimensional CT angiogram can be created to delineate the renal arterial and venous anatomy (14). Our urology colleagues find this interactive display of a three-dimensional model of the affected kidney and its vascular supply particularly helpful before venous thrombectomy, extensive abdominal resection to remove a locally invasive tumor, and partial (nephron-sparing) nephrectomy.
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Staging of Renal Cell Carcinoma
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Accurate staging at the time of diagnosis is essential to determine prognosis and formulate a therapeutic plan. With a reported accuracy of 91% (4,15), CT remains the most widely available and single most effective modality for staging renal cell carcinoma (15,16).
Numerous studies have shown that the anatomic extent of the tumor at the time of diagnosis is the single most important factor in determining prognosis. The 5-year survival rate of 60%–90% among patients with organ-confined disease falls to 5%–10% among those with distant metastases (17).
In addition to stage, the type of tumor cell appears to affect survival. Spindle cell and anaplastic tumors carry a worse prognosis than clear or granular cell cancers (16).
Treatment decisions hinge on the extent and stage of the tumor. Since the only curative treatment for renal cell carcinoma remains complete surgical excision, the goals of preoperative CT are to delineate the primary tumor, detect and map the extent of venous spread, and diagnose local or distant metastases.
The two commonly used staging systems along with their CT findings are outlined in Table 2.The major disadvantage of the older and simpler Robson classification is that it groups together (in stage III) a heterogeneous patient population; patients with venous extension alone are generally surgical candidates, whereas those with lymph node metastases have a poorer prognosis and undergo palliative therapy. Thus, despite its complexity, the TNM classification, which defines the anatomic extent of the tumor more precisely, has gained wide acceptance (2).
Tumors Confined within the Renal Capsule
Patients with renal cell carcinoma confined to the kidney (Fig 2) have the best prognosis, with 5-year survival rates of 60%–90% after nephrectomy (17). Many such tumors are detected incidentally at cross-sectional imaging performed for unrelated indications. The recent modification of the TNM classification that separates tumors 7 cm or less in diameter (stage T1) from those equal to or greater than 7 cm in diameter (stage T2) reflects the impact of tumor size on survival (2).
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Figure 2a. Renal cell carcinoma confined to the kidney (TNM stages T1 and T2). (a) Contrast-enhanced CT scan obtained during the corticomedullary phase shows a 3-cm-diameter heterogeneously enhancing mass in the left kidney (arrows). Peak contrast enhancement of the left renal vein (arrowheads) is seen, and there is streaming of unopacified blood from the lower extremities into the inferior vena cava. (b) Contrast-enhanced CT scan obtained during the nephrographic phase shows more clearly the relationship between the mass (arrows) and the renal hilum. The mass does not abut the collecting system, and the inferior vena cava is shown to be patent. The renal vein is not as well opacified as on the corticomedullary-phase image. The patient underwent nephron-sparing nephrectomy; the pathologic stage was T1 NX.
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Figure 2b. Renal cell carcinoma confined to the kidney (TNM stages T1 and T2). (a) Contrast-enhanced CT scan obtained during the corticomedullary phase shows a 3-cm-diameter heterogeneously enhancing mass in the left kidney (arrows). Peak contrast enhancement of the left renal vein (arrowheads) is seen, and there is streaming of unopacified blood from the lower extremities into the inferior vena cava. (b) Contrast-enhanced CT scan obtained during the nephrographic phase shows more clearly the relationship between the mass (arrows) and the renal hilum. The mass does not abut the collecting system, and the inferior vena cava is shown to be patent. The renal vein is not as well opacified as on the corticomedullary-phase image. The patient underwent nephron-sparing nephrectomy; the pathologic stage was T1 NX.
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Perinephric Spread of Tumor
Under- and overstaging of perinephric invasion are the most common staging errors at CT (4,18). The most specific finding of stage T3a disease, the presence of an enhancing nodule in the perinephric space, is highly specific but only 46% sensitive (Fig 3) (18). Spread of tumoral tissue within the perinephric fat cannot always be reliably diagnosed, and differentiation between stage T2 and T3a tumors is problematic (Fig 4). Perinephric stranding does not reliably indicate tumoral spread and is found in about half of patients with localized T1 and T2 tumors (Fig 5). In these patients, perinephric stranding may be caused by edema, vascular engorgement, or previous inflammation. This limitation of CT does have prognostic implications but does not affect case management, since patients with stage T3a disease are candidates for radical nephrectomy or nephron-sparing nephrectomy.
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Figure 3a. Perinephric spread of renal cell carcinoma (TNM stage T3a). (a) Artist rendering of a stage T3a renal cell carcinoma shows a tumor in the middle portion of the left kidney. The tumor extends beyond the renal capsule into the perinephric fat. (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows a large hypervascular mass (solid arrows) in the upper pole of the left kidney. Several tumor nodules are in the perinephric space (open arrows). Large collateral vessels (arrowheads) are seen. (c) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal oblique plane shows that the large heterogeneous mass involves most of the kidney. A separate enhancing nodule is seen superiorly (solid arrows), which indicates perinephric spread of the tumor. The large collateral vessels (arrowheads) extending up to the level of the left hemidiaphragm are better seen. The left renal vein (open arrow) is patent. These findings were confirmed at radical nephrectomy. The pathologic stage was T3a NX.
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Figure 3b. Perinephric spread of renal cell carcinoma (TNM stage T3a). (a) Artist rendering of a stage T3a renal cell carcinoma shows a tumor in the middle portion of the left kidney. The tumor extends beyond the renal capsule into the perinephric fat. (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows a large hypervascular mass (solid arrows) in the upper pole of the left kidney. Several tumor nodules are in the perinephric space (open arrows). Large collateral vessels (arrowheads) are seen. (c) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal oblique plane shows that the large heterogeneous mass involves most of the kidney. A separate enhancing nodule is seen superiorly (solid arrows), which indicates perinephric spread of the tumor. The large collateral vessels (arrowheads) extending up to the level of the left hemidiaphragm are better seen. The left renal vein (open arrow) is patent. These findings were confirmed at radical nephrectomy. The pathologic stage was T3a NX.
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Figure 3c. Perinephric spread of renal cell carcinoma (TNM stage T3a). (a) Artist rendering of a stage T3a renal cell carcinoma shows a tumor in the middle portion of the left kidney. The tumor extends beyond the renal capsule into the perinephric fat. (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows a large hypervascular mass (solid arrows) in the upper pole of the left kidney. Several tumor nodules are in the perinephric space (open arrows). Large collateral vessels (arrowheads) are seen. (c) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal oblique plane shows that the large heterogeneous mass involves most of the kidney. A separate enhancing nodule is seen superiorly (solid arrows), which indicates perinephric spread of the tumor. The large collateral vessels (arrowheads) extending up to the level of the left hemidiaphragm are better seen. The left renal vein (open arrow) is patent. These findings were confirmed at radical nephrectomy. The pathologic stage was T3a NX.
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Figure 4. False-negative finding of perinephric spread of renal cell carcinoma at CT. Contrast-enhanced CT scan obtained during the corticomedullary phase shows a 2-cm-diameter enhancing exophytic mass with smooth borders arising from the right kidney (solid arrow) and no CT findings to suggest perinephric extension. Bilateral renal cysts are present (open arrows). The patient underwent a right nephron-sparing nephrectomy. The pathologic stage was T3a NX.
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Figure 5a. False-positive finding of perinephric spread of renal cell carcinoma at CT. (a) Contrast-enhanced CT scan obtained during the corticomedullary phase shows a heterogeneously enhancing 5-cm-diameter hypervascular right renal mass (arrow). The small filling defect in the inferior vena cava (arrowhead) is related to streaming of unopacified blood from the lower extremities and should not be mistaken for a thrombus. (b) CT scan obtained during the corticomedullary phase shows perinephric stranding (arrow) near the lower pole of the right kidney, which raises the possibility of extracapsular spread of the tumor. At radical nephrectomy, the tumor did not extend into the perinephric space. The pathologic stage was T1 N0.
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Figure 5b. False-positive finding of perinephric spread of renal cell carcinoma at CT. (a) Contrast-enhanced CT scan obtained during the corticomedullary phase shows a heterogeneously enhancing 5-cm-diameter hypervascular right renal mass (arrow). The small filling defect in the inferior vena cava (arrowhead) is related to streaming of unopacified blood from the lower extremities and should not be mistaken for a thrombus. (b) CT scan obtained during the corticomedullary phase shows perinephric stranding (arrow) near the lower pole of the right kidney, which raises the possibility of extracapsular spread of the tumor. At radical nephrectomy, the tumor did not extend into the perinephric space. The pathologic stage was T1 N0.
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Imaging of the Ipsilateral Adrenal Gland
The prevalence of adrenal metastases is low, reported at 4.3% in one large series (19). The risk of adrenal spread is higher among patients with large or advanced-stage renal cell carcinoma and tumors that involve the upper pole of the kidney. Evaluation of the adrenal gland is important for surgical management because the current trend is to spare the ipsilateral adrenal gland unless an abnormality is suggested at CT (2). In one study of 157 patients with renal cell carcinoma who underwent radical nephrectomy, visualization of a normal adrenal gland at CT was associated with a 100% negative predictive value for tumoral spread to the gland at histopathologic examination. By contrast, adrenal enlargement, displacement, or nonvisualization was associated with malignant spread in 24% of cases; adrenalectomy should be performed in these patients (20).
Venous Spread of Tumors
Because renal cell carcinoma has a propensity to extend into the venous system, accurate preoperative evaluation of the renal vein and inferior vena cava is crucial. Extension of renal cell carcinoma into the renal vein alone (stage T3b) occurs in approximately 23% of patients and does not adversely affect the prognosis (Fig 6) (2). Spread of the tumor into the inferior vena cava is found in 4%–10% of patients and is more common with right-sided lesions (21,22). Patients with extensive involvement of the inferior vena cava and with nodal or distant metastases have a relatively good prognosis, with 5-year survival of 32%– 64%, provided that the thrombus is intraluminal, does not invade the vessel wall, and can be entirely resected (22–24). In these patients, aggressive surgical resection with curative intent is justified.
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Figure 6a. Renal cell carcinoma with tumoral extension into the left renal vein (TNM stage T3b). (a) Artist rendering of stage T3b renal cell carcinoma shows a tumor in the middle portion of the left kidney. A thrombus in the left renal vein extends directly from the tumor. The inferior vena cava is not involved. (b) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal plane shows that the left kidney is replaced by an infiltrating tumor (arrows). The entire left renal vein is dilated and filled with thrombus up to its junction with the inferior vena cava (arrowheads). Heterogeneous enhancement within the vein indicates tumoral thrombus. The thrombus does not extend into the inferior vena cava. At left radical nephrectomy, the surgeon was able to milk the tumoral thrombus back into the distal part of the left renal vein.
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Figure 6b. Renal cell carcinoma with tumoral extension into the left renal vein (TNM stage T3b). (a) Artist rendering of stage T3b renal cell carcinoma shows a tumor in the middle portion of the left kidney. A thrombus in the left renal vein extends directly from the tumor. The inferior vena cava is not involved. (b) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal plane shows that the left kidney is replaced by an infiltrating tumor (arrows). The entire left renal vein is dilated and filled with thrombus up to its junction with the inferior vena cava (arrowheads). Heterogeneous enhancement within the vein indicates tumoral thrombus. The thrombus does not extend into the inferior vena cava. At left radical nephrectomy, the surgeon was able to milk the tumoral thrombus back into the distal part of the left renal vein.
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Spiral and electron-beam CT have been shown to be highly accurate in the diagnosis of spread of renal cell carcinoma into the renal vein, with a reported negative predictive value of 97% and positive predictive value of 92% (9). Venous extension is optimally shown during the corticomedullary phase of enhancement, when contrast enhancement in the renal vein is at its peak. The most specific sign of venous extension is the presence of a low-attenuation filling defect within the vein (9,13,18,25). An abrupt change in the caliber of the renal vein and the presence of a clot within collateral veins are helpful ancillary signs. Enlargement of the renal vein is not sufficient evidence by itself because it can be caused by increased blood flow within a hypervascular renal cell carcinoma or it can occur as a normal variant (25). The CT appearance of the thrombus helps distinguish malignant from bland thrombus. Heterogeneous enhancement of the thrombus with contrast material indicates neovascularity and thus tumoral thrombus (Fig 7). Direct continuity of the thrombus with the primary tumor also suggests tumoral thrombus (13).
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Figure 7a. Renal cell carcinoma with enhancing tumoral thrombus in the left renal vein. (a) Three-dimensional CT scan obtained during the corticomedullary phase in the axial plane shows a large mass arising from the anterior portion of the left kidney (arrows). Portions of the mass are necrotic, while the periphery of the lesion shows intense enhancement. The left renal vein (arrowheads) is dilated and enhances heterogeneously. (b) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal plane allows better appreciation of the ill-defined, small filling defects within the left renal vein (arrows). This tumoral thrombus enhanced to the same degree as the primary tumor and was difficult to distinguish from enhancing blood in the renal vein. The patient underwent a left radical nephrectomy with excision of a markedly enlarged left renal vein. The pathologic stage was T3b.
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Figure 7b. Renal cell carcinoma with enhancing tumoral thrombus in the left renal vein. (a) Three-dimensional CT scan obtained during the corticomedullary phase in the axial plane shows a large mass arising from the anterior portion of the left kidney (arrows). Portions of the mass are necrotic, while the periphery of the lesion shows intense enhancement. The left renal vein (arrowheads) is dilated and enhances heterogeneously. (b) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal plane allows better appreciation of the ill-defined, small filling defects within the left renal vein (arrows). This tumoral thrombus enhanced to the same degree as the primary tumor and was difficult to distinguish from enhancing blood in the renal vein. The patient underwent a left radical nephrectomy with excision of a markedly enlarged left renal vein. The pathologic stage was T3b.
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If tumoral spread within the inferior vena cava is identified, precise delineation of the superior extent of the thrombus is essential for the surgeon to plan the optimal surgical strategy for thrombectomy and minimize the risk of intraoperative tumoral embolism (21,22,26,27). The level of involvement of the inferior vena cava dictates the surgical approach. If the thrombus remains infrahepatic, it can be resected via an abdominal incision (Fig 8). If extension to the retrohepatic level of the inferior vena cava is detected, a right thoracoabdominal approach is planned for access to the suprahepatic portion of the inferior vena cava (Fig 9). Extension of the tumor into the supradiaphragmatic level of the inferior vena cava (Fig 10) or into the right atrium requires cardiopulmonary bypass to facilitate tumoral resection and is associated with higher perioperative morbidity and mortality (22–24,26). Involvement of the inferior vena cava is best shown during the late corticomedullary phase with the use of a combination of axial images and coronal and sagittal reconstruction. CT findings include a filling defect outlined by contrast material within the inferior vena cava, contiguous extension of the thrombus from the renal vein into the inferior vena cava, and enlarged paravertebral collateral veins if the inferior vena cava is completely occluded. Streaming of unopacified blood as it returns from the lower extremities can mimic a small clot and is a potential cause of false-positive diagnosis. Because of its multiplanar capability, magnetic resonance imaging is currently the preferred modality to image extension into the vena cava. However, in our experience, three-dimensional CT with sagittal and coronal reconstructions is also effective in depicting the superior extent of inferior vena caval thrombus.
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Figure 8a. Renal cell carcinoma with tumoral extension into the renal vein and inferior vena cava (TNM stage T3c). (a) Artist rendering of stage T3c renal cell carcinoma shows a tumor in the middle portion of the left kidney. The thrombus extends from the renal vein into the inferior vena cava (IVC). The inferior vena cava extension remains infrahepatic. (b) CT scan obtained during the corticomedullary phase shows a 4-cm-diameter enhancing mass arising from the posterior portion of the right kidney (solid arrow). A low-attenuation filling defect is seen within the right renal vein and extends into the inferior vena cava (arrowhead). An enhancing node is seen near the renal hilum (open arrow). (c) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal plane shows that the thrombus extends cephalad to the hepatic portion of the inferior vena cava (arrowheads). The hilar node encases the right renal artery (arrow). These findings were confirmed at surgery. The pathologic stage was T3c N1.
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Figure 8b. Renal cell carcinoma with tumoral extension into the renal vein and inferior vena cava (TNM stage T3c). (a) Artist rendering of stage T3c renal cell carcinoma shows a tumor in the middle portion of the left kidney. The thrombus extends from the renal vein into the inferior vena cava (IVC). The inferior vena cava extension remains infrahepatic. (b) CT scan obtained during the corticomedullary phase shows a 4-cm-diameter enhancing mass arising from the posterior portion of the right kidney (solid arrow). A low-attenuation filling defect is seen within the right renal vein and extends into the inferior vena cava (arrowhead). An enhancing node is seen near the renal hilum (open arrow). (c) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal plane shows that the thrombus extends cephalad to the hepatic portion of the inferior vena cava (arrowheads). The hilar node encases the right renal artery (arrow). These findings were confirmed at surgery. The pathologic stage was T3c N1.
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Figure 8c. Renal cell carcinoma with tumoral extension into the renal vein and inferior vena cava (TNM stage T3c). (a) Artist rendering of stage T3c renal cell carcinoma shows a tumor in the middle portion of the left kidney. The thrombus extends from the renal vein into the inferior vena cava (IVC). The inferior vena cava extension remains infrahepatic. (b) CT scan obtained during the corticomedullary phase shows a 4-cm-diameter enhancing mass arising from the posterior portion of the right kidney (solid arrow). A low-attenuation filling defect is seen within the right renal vein and extends into the inferior vena cava (arrowhead). An enhancing node is seen near the renal hilum (open arrow). (c) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal plane shows that the thrombus extends cephalad to the hepatic portion of the inferior vena cava (arrowheads). The hilar node encases the right renal artery (arrow). These findings were confirmed at surgery. The pathologic stage was T3c N1.
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Figure 9a. Renal cell carcinoma with tumoral extension into the left renal vein and intrahepatic portion of the inferior vena cava (TNM stage T3c). (a) Artist rendering of stage T3c renal cell carcinoma shows a tumor in the middle portion of the left kidney. The thrombus extends from the renal vein into the inferior vena cava (IVC) as far as the intrahepatic level. (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows an infiltrating tumor in the left kidney (arrows) with extension into the left renal vein and the inferior vena cava (arrowheads). (c) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal plane shows that the thrombus extends well into the hepatic portion of the inferior vena cava (arrows) but stops below the level of the hepatic veins. Numerous enhancing collateral veins are present (arrowheads).
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Figure 9b. Renal cell carcinoma with tumoral extension into the left renal vein and intrahepatic portion of the inferior vena cava (TNM stage T3c). (a) Artist rendering of stage T3c renal cell carcinoma shows a tumor in the middle portion of the left kidney. The thrombus extends from the renal vein into the inferior vena cava (IVC) as far as the intrahepatic level. (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows an infiltrating tumor in the left kidney (arrows) with extension into the left renal vein and the inferior vena cava (arrowheads). (c) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal plane shows that the thrombus extends well into the hepatic portion of the inferior vena cava (arrows) but stops below the level of the hepatic veins. Numerous enhancing collateral veins are present (arrowheads).
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Figure 9c. Renal cell carcinoma with tumoral extension into the left renal vein and intrahepatic portion of the inferior vena cava (TNM stage T3c). (a) Artist rendering of stage T3c renal cell carcinoma shows a tumor in the middle portion of the left kidney. The thrombus extends from the renal vein into the inferior vena cava (IVC) as far as the intrahepatic level. (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows an infiltrating tumor in the left kidney (arrows) with extension into the left renal vein and the inferior vena cava (arrowheads). (c) Three-dimensional CT scan obtained during the corticomedullary phase in the coronal plane shows that the thrombus extends well into the hepatic portion of the inferior vena cava (arrows) but stops below the level of the hepatic veins. Numerous enhancing collateral veins are present (arrowheads).
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Figure 10a. Renal cell carcinoma with tumoral extension into the supradiaphragmatic level of the inferior vena cava (TNM stage T4b). (a) Artist rendering of stage T4b renal cell carcinoma shows a tumor in the middle portion of the left kidney. The thrombus extends from the renal vein into the inferior vena cava and the right atrium. (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows a large, partially necrotic hypervascular tumor arising from the lower pole of the right kidney (solid arrows). Enlarged pericapsular collateral vessels are seen (arrowheads), as is thrombus within the inferior vena cava (open arrow). (c) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in b shows that the inferior vena cava is grossly expanded and filled with a vascular thrombus (arrows). The hypervascularity indicates tumoral thrombus. The right adrenal gland is normal (arrowhead). (d) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in c shows that the hypervascular tumoral thrombus extends into the intrahepatic level of the inferior vena cava. (e) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in d shows a small amount of thrombus in the supradiaphragmatic level of the inferior vena cava (arrow).
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Figure 10b. Renal cell carcinoma with tumoral extension into the supradiaphragmatic level of the inferior vena cava (TNM stage T4b). (a) Artist rendering of stage T4b renal cell carcinoma shows a tumor in the middle portion of the left kidney. The thrombus extends from the renal vein into the inferior vena cava and the right atrium. (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows a large, partially necrotic hypervascular tumor arising from the lower pole of the right kidney (solid arrows). Enlarged pericapsular collateral vessels are seen (arrowheads), as is thrombus within the inferior vena cava (open arrow). (c) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in b shows that the inferior vena cava is grossly expanded and filled with a vascular thrombus (arrows). The hypervascularity indicates tumoral thrombus. The right adrenal gland is normal (arrowhead). (d) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in c shows that the hypervascular tumoral thrombus extends into the intrahepatic level of the inferior vena cava. (e) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in d shows a small amount of thrombus in the supradiaphragmatic level of the inferior vena cava (arrow).
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Figure 10c. Renal cell carcinoma with tumoral extension into the supradiaphragmatic level of the inferior vena cava (TNM stage T4b). (a) Artist rendering of stage T4b renal cell carcinoma shows a tumor in the middle portion of the left kidney. The thrombus extends from the renal vein into the inferior vena cava and the right atrium. (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows a large, partially necrotic hypervascular tumor arising from the lower pole of the right kidney (solid arrows). Enlarged pericapsular collateral vessels are seen (arrowheads), as is thrombus within the inferior vena cava (open arrow). (c) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in b shows that the inferior vena cava is grossly expanded and filled with a vascular thrombus (arrows). The hypervascularity indicates tumoral thrombus. The right adrenal gland is normal (arrowhead). (d) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in c shows that the hypervascular tumoral thrombus extends into the intrahepatic level of the inferior vena cava. (e) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in d shows a small amount of thrombus in the supradiaphragmatic level of the inferior vena cava (arrow).
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Figure 10d. Renal cell carcinoma with tumoral extension into the supradiaphragmatic level of the inferior vena cava (TNM stage T4b). (a) Artist rendering of stage T4b renal cell carcinoma shows a tumor in the middle portion of the left kidney. The thrombus extends from the renal vein into the inferior vena cava and the right atrium. (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows a large, partially necrotic hypervascular tumor arising from the lower pole of the right kidney (solid arrows). Enlarged pericapsular collateral vessels are seen (arrowheads), as is thrombus within the inferior vena cava (open arrow). (c) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in b shows that the inferior vena cava is grossly expanded and filled with a vascular thrombus (arrows). The hypervascularity indicates tumoral thrombus. The right adrenal gland is normal (arrowhead). (d) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in c shows that the hypervascular tumoral thrombus extends into the intrahepatic level of the inferior vena cava. (e) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in d shows a small amount of thrombus in the supradiaphragmatic level of the inferior vena cava (arrow).
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Figure 10e. Renal cell carcinoma with tumoral extension into the supradiaphragmatic level of the inferior vena cava (TNM stage T4b). (a) Artist rendering of stage T4b renal cell carcinoma shows a tumor in the middle portion of the left kidney. The thrombus extends from the renal vein into the inferior vena cava and the right atrium. (b) Contrast-enhanced CT scan obtained during the corticomedullary phase shows a large, partially necrotic hypervascular tumor arising from the lower pole of the right kidney (solid arrows). Enlarged pericapsular collateral vessels are seen (arrowheads), as is thrombus within the inferior vena cava (open arrow). (c) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in b shows that the inferior vena cava is grossly expanded and filled with a vascular thrombus (arrows). The hypervascularity indicates tumoral thrombus. The right adrenal gland is normal (arrowhead). (d) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in c shows that the hypervascular tumoral thrombus extends into the intrahepatic level of the inferior vena cava. (e) Contrast-enhanced CT scan obtained during the corticomedullary phase above the level seen in d shows a small amount of thrombus in the supradiaphragmatic level of the inferior vena cava (arrow).
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Regional Lymph Node Metastases
The presence of regional lymph node metastases carries a poor prognosis, with reported 5-year survival rates of 5%–30% (17,28). The CT diagnosis of lymph node metastases is reliant on nodal enlargement of greater than 1 cm in short-axis diameter. This criterion was associated with a 4% false-negative rate in a series of 163 patients with renal cell carcinoma who underwent nephrectomy and regional lymph node dissection (24). This study also showed that in more than half of the patients, nodal enlargement was caused by benign inflammatory changes. This reactive nodal enlargement is often associated with extensive tumoral necrosis or venous thrombosis and may represent a reactive immune response (2,29). Nodal enlargement shown at CT should not disqualify patients from nephrectomy unless metastatic spread is confirmed with fine-needle aspiration. The enhancement pattern of the node may also help differentiate reactive from malignant adenopathy; metastatic nodes may enhance, particularly if the primary tumor is very vascular (Fig 11).
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Figure 11a. Renal cell carcinoma with enhancing retroperitoneal nodal metastases (TNM stage T N1-N3). (a) Artist rendering of stage T N1-N3 renal cell carcinoma shows a tumor in the middle portion of the left kidney. Multiple enlarged nodes are present in the left hilar, paraaortic, and paracaval spaces. (b) Contrast-enhanced CT scan obtained during the nephrographic phase shows a heterogeneously enhancing mass arising from the anterior aspect of the left kidney (arrow). An enlarged left paraaortic node is present (arrowhead). The node enhances to the same degree as the primary tumor.
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Figure 11b. Renal cell carcinoma with enhancing retroperitoneal nodal metastases (TNM stage T N1-N3). (a) Artist rendering of stage T N1-N3 renal cell carcinoma shows a tumor in the middle portion of the left kidney. Multiple enlarged nodes are present in the left hilar, paraaortic, and paracaval spaces. (b) Contrast-enhanced CT scan obtained during the nephrographic phase shows a heterogeneously enhancing mass arising from the anterior aspect of the left kidney (arrow). An enlarged left paraaortic node is present (arrowhead). The node enhances to the same degree as the primary tumor.
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Local Extension and Distant Metastases
Direct extension of renal cell carcinoma outside the Gerota fascia into neighboring organs (stage T4a) is difficult to diagnose with certainty unless there is a demonstrable focal change in attenuation within an organ. Loss of tissue planes and irregular margins between the tumor and surrounding structures raise the possibility of direct infiltration and can be seen in up to 15% of patients without surgically confirmed stage T4a disease (18). Three-dimensional CT displays the tumor and its relationship to the adjacent organs in multiple planes and orientations and is valuable in difficult cases for increasing diagnostic confidence and helping plan surgical resection (Fig 12) (14). Renal cell carcinoma metastasizes most frequently to the lungs and mediastinum, bones, and liver (Fig 13). Less common sites include the contralateral kidney, adrenal gland, brain, pancreas, mesentery, and abdominal wall (16,17). Like the primary tumor, metastatic lesions tend to be hypervascular. Hepatic metastases are most conspicuous on scans obtained during the hepatic arterial phase or on the unenhanced scans and may become obscured and isoattenuating to the liver parenchyma during the portal venous phase. The prognosis for these patients is dismal, with a reported 5-year survival of 5%–10%. However, patients with a solitary metastasis may benefit from aggressive management with nephrectomy and surgical removal of the metastatic lesion (2).
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Figure 12a. Large renal cell carcinoma with possible extension into the liver. (a) Three-dimensional CT scan obtained during the nephrographic phase in a sagittal reconstruction shows a large, partially necrotic tumor arising from the right kidney (arrows). The mass invaginates the inferior portion of the right hepatic lobe but does not appear to invade the liver parenchyma. (b, c) Coronal (b) and axial (c) reconstructions viewed from below help confirm the presence of a tissue plane between the mass and the right hepatic lobe (arrowheads). At surgery, the tumor did not invade the liver. The pathologic stage was T2 N0.
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Figure 12b. Large renal cell carcinoma with possible extension into the liver. (a) Three-dimensional CT scan obtained during the nephrographic phase in a sagittal reconstruction shows a large, partially necrotic tumor arising from the right kidney (arrows). The mass invaginates the inferior portion of the right hepatic lobe but does not appear to invade the liver parenchyma. (b, c) Coronal (b) and axial (c) reconstructions viewed from below help confirm the presence of a tissue plane between the mass and the right hepatic lobe (arrowheads). At surgery, the tumor did not invade the liver. The pathologic stage was T2 N0.
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Figure 12c. Large renal cell carcinoma with possible extension into the liver. (a) Three-dimensional CT scan obtained during the nephrographic phase in a sagittal reconstruction shows a large, partially necrotic tumor arising from the right kidney (arrows). The mass invaginates the inferior portion of the right hepatic lobe but does not appear to invade the liver parenchyma. (b, c) Coronal (b) and axial (c) reconstructions viewed from below help confirm the presence of a tissue plane between the mass and the right hepatic lobe (arrowheads). At surgery, the tumor did not invade the liver. The pathologic stage was T2 N0.
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Figure 13a. Renal cell carcinoma metastatic to liver and bone tissue. (a) Contrast-enhanced CT scan obtained during the corticomedullary phase shows that, in a patient with a large left renal cell carcinoma (not shown), there are several liver metastases (solid arrows). Several large left paraaortic nodes encase the left renal artery (open arrow). Tumor nodules extend into the perinephric space (arrowheads). (b) Contrast-enhanced CT scan of the pelvis shows a lytic, expansile metastasis in the right half of the sacrum (arrow).
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Figure 13b. Renal cell carcinoma metastatic to liver and bone tissue. (a) Contrast-enhanced CT scan obtained during the corticomedullary phase shows that, in a patient with a large left renal cell carcinoma (not shown), there are several liver metastases (solid arrows). Several large left paraaortic nodes encase the left renal artery (open arrow). Tumor nodules extend into the perinephric space (arrowheads). (b) Contrast-enhanced CT scan of the pelvis shows a lytic, expansile metastasis in the right half of the sacrum (arrow).
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Staging for Partial Nephrectomy
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During the past 20 years, the clinical manifestation of renal cell carcinoma has evolved. The widespread use of cross-sectional imaging techniques has led to a dramatic increase in the number of incidentally discovered tumors. These asymptomatic tumors, which now constitute 25% to almost 50% of all surgically treated renal cell carcinomas, are generally confined to the renal capsule, relatively small in size (5 cm in diameter), and associated with an excellent prognosis after surgical removal (30,31).
These changes in the manifestation of renal cell carcinoma have stimulated a growing trend toward nephron-sparing surgical techniques (32,33). Nephron-sparing surgery entails complete excision of the renal tumor with a margin of at least 0.5 cm of normal renal tissue and preservation of the largest amount of functioning renal parenchyma. It is the treatment of choice when radical nephrectomy would render the patient anephric with subsequent need for dialysis. Current accepted indications for nephron-sparing nephrectomy include a renal cell carcinoma in a solitary functioning kidney, a renal cell carcinoma in a patient with compromised renal function, and multiple bilateral tumors (2,34,35). Multiple renal cell carcinomas can be sporadic in 4%–15% cases but are much more common in patients with von Hippel–Lindau disease and hereditary renal cell carcinoma. In these
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Abstract
LEARNING OBJECTIVES FOR TEST...
