Rationale and Objectives
To investigate whether imaging features on multiphasic multidetector computed tomography (MDCT) can help discriminate sarcomatoid renal cell carcinoma (RCC) and collecting duct carcinoma (CDC) from other solid renal masses.
Materials and Methods
With institutional review board approval for this HIPAA-compliant study, we derived a cohort of 7 sarcomatoid RCCs, 4 CDCs, 165 clear cell RCCs, 56 papillary RCCs, 22 chromophobe RCCs, 49 oncocytomas, and 16 lipid-poor angiomyolipomas with preoperative multiphasic MDCT with up to four phases (unenhanced, corticomedullary, nephrographic, and excretory). Each lesion was reviewed for contour, spread pattern, pattern of enhancement, neovascularity, and calcification.
Results
Sarcomatoid RCCs and CDCs were more likely than other solid renal masses to have an irregular contour (64% vs 2%, P < 0.001) and an infiltrative spread pattern, defined as infiltration into adjacent renal parenchyma, collecting system, or neighboring structures (82% vs 7%, P < 0.001). When used to discriminate sarcomatoid RCC and CDC from other solid renal masses, an infiltrative spread pattern had a specificity of 93% (287/308) and sensitivity of 82% (9/11), and an irregular contour had a specificity of 98% (303/308) and sensitivity of 64% (7/11).
Conclusions
Solid renal lesions with an irregular contour or an infiltrative spread pattern are suspicious for sarcomatoid RCC or CDC.
Introduction
Within the Heidelberg classification system, the most common subtype of renal cell carcinoma (RCC) is clear cell, which accounts for 70%–80% of cases of RCC, followed by papillary and chromophobe RCC, which account for 14%–17% and 4%–8% of RCCs, respectively . Of these common RCC subtypes, clear cell RCC has the worst prognosis with a 5-year survival rate of 44%–69%, accounting for 94% of metastatic RCC . On the other hand, papillary RCC has a 5-year survival rate of 82%–92% and accounts for 4% of metastatic RCC, and chromophobe RCC has a 5-year survival of 78%–87% and accounts for 2% of metastatic RCC . In contrast to these common subtypes of RCC, sarcomatoid RCC and collecting duct carcinoma are rare, aggressive variants of RCC with even more dismal prognoses with median survivals of 4–9 months and 11 months, respectively . Up to 83% of patients with collecting duct carcinoma have distant metastases at the time of diagnosis; 45%–84% of patients with sarcomatoid RCC have distant metastases at the time of diagnosis . In contrast to collecting duct carcinomas, sarcomatoid RCCs are not a distinct RCC subtype. They represent a group of RCCs with high-grade features and extensive chromosomal rearrangements that result in dedifferentiation and a spindle-like histologic morphology and can arise from any of the RCC subtypes .
Recent studies have demonstrated that enhancement on multiphasic multidetector computed tomography (MDCT) can help differentiate between clear cell RCC, papillary RCC, and chromophobe RCC, as well as oncocytoma and lipid-poor angiomyolipoma (benign mimics of RCC) . However, while there are several published case series concerning sarcomatoid RCC and collecting duct carcinoma , there are currently no robust means of differentiating sarcomatoid RCC and collecting duct carcinoma from common RCC subtypes without sarcomatoid elements or from benign RCC mimics on imaging. Schieda et al. found that quantitative texture feature analysis on unenhanced images can help discriminate sarcomatoid RCCs from clear cell RCCs . However, texture feature analyses require sophisticated postprocessing, and the support vector machine classifier used by Schieda et al. had limited accuracy, ranging from 55% to 68%. A simple, robust noninvasive means of differentiating sarcomatoid RCC and collecting duct carcinoma from other solid renal masses can be of great clinical value because sarcomatoid RCC and collecting duct carcinoma should be managed differently than common RCC subtypes and benign RCC mimics . Common RCC subtypes are typically surgically resected. Even in the setting of metastasis, surgical resection can be beneficial in common RCC subtypes, as upfront cytoreductive nephrectomy has been shown to provide survival benefit. However, for sarcomatoid RCC and collecting duct carcinoma, surgical resection prior to systemic targeted therapies may actually worsen outcomes because it delays the administration of systemic therapy . The goal of this study was to investigate whether simple imaging features reproducible in routine clinical imaging with multiphasic MDCT could help discriminate sarcomatoid RCC and collecting duct carcinoma from common RCC subtypes and benign RCC mimics.
Materials and Methods
Patients
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TABLE 1
Characteristics of Solid Renal Lesions
Characteristic All (n = 319 Lesions, 294 Patients) Aggressive RCC Variants Common RCC Subtypes Benign RCC Mimics Sarcomatoid RCC (n = 7 Lesions, 7 Patients) Collecting Duct Carcinoma (n = 4 Lesions, 4 Patients) Clear Cell RCC (n = 165 Lesions, 155 Patients) Papillary RCC (n = 56 Lesions, 52 Patients) Chromophobe RCC (n = 22 Lesions, 22 Patients) Oncocytoma (n = 49 Lesions, 45 Patients) Lipid-Poor AML (n = 16 Lesions, 16 Patients) Gender \* Male 192 (65) 7 (100) 3 (75) 96 (62) 43 (83) 15 (68) 31 (69) 3 (19) Female 102 (34) 0 (0) 1 (25) 59 (38) 9 (17) 7 (32) 14 (31) 13 (81) Mean age (y) † 60 (21–87) 50 (33–66) 61 (53–72) 61 (27–87) 62 (39–84) 60 (23–85) 65 (38–86) 47 (21–78) Method of specimen acquisition Partial nephrectomy 143 (45) 2 (29) 1 (25) 65 (39) 34 (61) 5 (23) 24 (49) 12 (75) Radical nephrectomy 120 (38) 4 (57) 2 (50) 72 (44) 17 (30) 13 (59) 10 (20) 2 (13) Biopsy 54 (17) 1 (14) 1 (25) 28 (17) 3 (5) 4 (18) 15 (31) 2 (13) Autopsy 2 (1) 0 (0) 0 (0) 0 (0) 2 (4) 0 (0) 0 (0) 0 (0) Pathologic T stage T1a 134 (42) 2 (29) 1 (25) 88 (53) 33 (59) 10 (46) — — T1b 55 (17) 1 (14) 0 (0) 37 (22) 11 (20) 6 (27) — — T2 20 (6) 1 (14) 0 (0) 10 (6) 6 (11) 3 (14) — — T3 42 (13) 2 (29) 3 (75) 28 (17) 6 (11) 3 (14) — — T4 3 (1) 1 (14) 0 (0) 2 (1) 0 (0) 0 (0) — — Side Left 161 (50.5) 3 (43) 1 (25) 83 (50) 24 (43) 16 (73) 23 (47) 11 (69) Right 158 (40.5) 4 (57) 3 (75) 82 (50) 32 (57) 6 (27) 26 (53) 5 (31) Lesion size (cm) † 4.3 (0.7–22.0) 9.4 (2.9–22.0) 7.2 (2.5–9.6) 4.6 (0.7–18.7) 3.7 (1.3–12.0) 4.7 (1.6–12.0) 3.3 (0.9–12.7) 3.8 (1.2–15.0) MDCT study type Two-phase 100 (31) 0 (0) 2 (50) 47 (29) 15 (27) 8 (36) 19 (39) 9 (56) Three-phase 55 (17) 4 (57) 0 (0) 34 (21) 8 (14) 2 (9) 5 (10) 2 (13) Four-phase 164 (51) 3 (43) 2 (50) 84 (51) 33 (59) 12 (55) 25 (51) 5 (31)
AML, angiomyolipoma; MDCT, multidetector computed tomography; RCC, renal cell carcinoma.
Unless otherwise indicated, data are numbers of lesions, with percentages in parentheses.
Oncocytomas and lipid-poor AMLs were not staged, as the staging criteria apply only to renal cell carcinomas.
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Computed Tomography Examination
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CT Image Analyses
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Statistical Analyses
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Results
Lesions
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Qualitative Features
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TABLE 2
Qualitative Features of Solid Renal Lesions
Aggressive RCC Variants Common RCC Subtypes Benign RCC Mimics Sarcomatoid RCC (n = 7) Collecting Duct Carcinoma (n = 4) Clear Cell RCC (n = 165) Papillary RCC (n = 56) Chromophobe RCC (n = 22) Oncocytoma (n = 49) Lipid-Poor Angiomyolipoma (n = 16) Pattern of enhancement Heterogeneous 7 (100) 4 (100) 146 (89) 17 (30) 12 (55) 34 (69) 6 (37.5) Homogeneous 0 (0) 0 (0) 19 (12) 39 (70) 10 (45) 15 (31) 10 (62.5)P value 0.040 0.012 Contour Irregular 4 (57) 3 (75) 4 (2) 1 (2) 0 (0) 0 (0) 0 (0) Lobular 3 (43) 1 (25) 96 (58) 23 (41) 17 (77) 21 (43) 6 (37.5) Smooth 0 (0) 0 (0) 65 (39) 32 (57) 5 (23) 28 (57) 10 (62.5)P value <0.001 <0.001 Spread pattern Infiltrative 5 (71) 4 (100) 17 (10) 1 (2) 2 (9) 1 (2) 0 (0) Noninfiltrative 2 (29) 0 (0) 148 (90) 55 (98) 20 (91) 48 (98) 16 (100)P value <0.001 <0.001 Neovascularity Present 5 (71) 3 (75) 106 (64) 2 (4) 7 (32) 21 (43) 5 (31) Not present 2 (29) 1 (25) 59 (36) 54 (96) 15 (68) 28 (57) 11 (69)P value 0.099 0.044 Calcification Present 2 (29) 2 (50) 40 (24) 11 (20) 5 (23) 5 (10) 0 (0) Not present 5 (71) 2 (50) 125 (76) 45 (80) 17 (77) 44 (90) 16 (100)P value 0.31 0.006
RCC, renal cell carcinoma.
Data are numbers of lesions, with percentages in parentheses.
P values for common RCC subtypes (clear cell RCC, papillary RCC, and chromophobe RCC) and benign RCC mimics (oncocytoma and lipid-poor angiomyolipoma) were calculated in comparison to aggressive RCC variants (sarcomatoid RCC and collecting duct carcinoma).
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TABLE 3
Performance Parameters of Using Spread Pattern or Lesion Contour to Discriminate Aggressive RCC Variants (Sarcomatoid RCC and Collecting Duct Carcinoma) From Other Solid Renal Masses (Common RCC Subtypes and Benign RCC Mimics)
Infiltrative Spread Pattern Irregular Contour Sensitivity (%) 82 (9/11) 64 (7/11) Specificity (%) 93 (287/308) 98 (303/308) Positive Predictive Value (%) 30 (9/30) 58 (7/12) Negative Predictive Value (%) 99 (287/289) 99 (303/307)
RCC, renal cell carcinoma.
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Discussion
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