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Papillary renal cell carcinoma and clear cell renal cell carcinoma: Differentiation of distinct histological types with contrast – enhanced ultrasonography Li-Yun Xue a , Qing Lu a , Bei-Jian Huang a,∗ , Zheng Li b , Cui-Xian Li a , Jie-Xian Wen a , Wen-Ping Wang a a Department of Ultrasound Zhongshan Hospital, Fudan University, Shanghai institute of medical imaging, Bldg. 1#, 180 Fenglin Rd., Xuhui District, Shanghai 200032, China b Department of Echocardiography, Zhongshan Hospital, Fudan University, Shanghai 200032, China
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Article history: Received 16 March 2015 Received in revised form 10 June 2015 Accepted 16 June 2015 Keywords: Contrast-enhanced ultrasound (CEUS) Contrast-enhanced computed tomography (CECT) Papillary renal cell carcinoma (pRCC) Clear cell renal cell carcinoma (ccRCC) Renal lesions
a b s t r a c t Purpose: Papillary renal cell carcinoma (pRCC) and clear cell renal cell carcinoma (ccRCC) have different biological behaviours and imaging features. The role of contrast-enhanced ultrasound (CEUS) in differentiating these two carcinoma subtypes has not been comprehensively studied. Materials and methods: Forty-eight patients with 49 pRCC lesions and 153 patients with 156 ccRCC lesions underwent preoperative conventional ultrasound (US) and CEUS. Among them, 91 patients (25 pRCCs and 66 ccRCCs) also underwent preoperative contrast-enhanced computed tomography (CECT) in our hospital. The characteristics of CEUS and CECT images for each patient imaged were analysed by each of two blinded observers. Results: Images for five (5/25, 20%) pRCC patients demonstrated equivocal or no enhancement using CECT, while all lesions were enhanced using CEUS. From CEUS, images of pRCCs, when compared with ccRCC images, demonstrated significantly higher frequencies of slow wash-in (59.2% vs. 5.8%), fast wash-out (87.7% vs. 46.1%), and hypo-enhancement (57.1% vs. 7.1%) patterns, p < 0.001, as well as the presence of pseudocapsule (42.9% vs. 23.1%), p = 0.007. For lesions with large diameters (>3 cm), a higher percentage of pRCC images demonstrated homogeneous enhancement compared with ccRCC images. Using the combination of slow wash-in, fast wash-out, and hypoenhancement patterns at peak as criteria to differentiate pRCC from ccRCC, positive and negative predictive value, and sensitivity and specificity were found to be 86.7%, 86.9%, 53.1%, and 97.4%, respectively. Conclusions: CEUS imaging features of slow-in, fast-out, and hypo-enhancement patterns may be useful for differentiating pRCC and ccRCC. In addition, CEUS may be helpful for diagnosing hypovascular renal lesions that demonstrate equivocal or no enhancement by CECT and, thus, for improving diagnostic confidence. © 2015 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Renal cell carcinoma (RCC) is the most common primary malignancy of the kidney, with clear cell RCC (ccRCC) and papillary RCC
Abbreviations: pRCC, papillary renal cell carcinoma; ccRCC, clear cell renal cell carcinoma; CEUS, contrast-enhanced ultrasound; CECT, contrast-enhanced computed tomography; US, conventional ultrasound; CDFI, colour Doppler flow imaging; CKD, chronic kidney disease; MRI, magnetic resonance imaging; RCC, renal cell carcinoma; ICC, interclass correlation coefficient; NPV, negative predictive value; PPV, positive predictive value. ∗ Corresponding author. E-mail address: [email protected] (B.-J. Huang).
(pRCC) as the most and second-most prevalent subtypes, accounting for 70% and 10–15% of all RCCs, respectively [1,2,3]. Features of pRCCs are less aggressive and prognoses are better in comparison with ccRCCs [3,4]. ccRCC has an overall five-year survival rate of 55–60%, while pRCC is associated with a higher five-year survival rate (80–90%) [5]. Accordingly, precise classification has become an important theme due to the differences in tumour behaviour and prognoses for the two subtypes [6]. Diagnosis of ccRCC is relatively easy because of its typical hypervascular appearance in colour Doppler flow imaging (CDFI). Conversely, pRCC, as a hypovascular RCC subtype, tends to be difficult to diagnose because of a weak or absent blood flow signal [7]. Thus, it is essential to use a contrast medium for differential
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diagnosis of RCC. Dynamic contrast-enhanced computed tomography (CECT) and magnetic resonance imaging (MRI) technology have played important roles in identification of the subtypes. CcRCC shows a significantly higher degree of enhancement in corticomedullary phase compared with pRCC [8,9,10], and the degree of enhancement in the corticomedullary phase correlates with microvessel density observed via staining of CD34 [9]. However, it is insufficient to diagnose a renal lesion as benign (e.g., a hyperdense cyst) if no enhancement is detected using CECT [3]. Contrast-enhanced ultrasound (CEUS) imaging technology is capable of detecting microvascularization of tumours and is superior to CECT with respect to revealing intralesional vascularity [7,11]. Currently, research involving CEUS for differentiating subtypes of RCC is still in the early stages. To date and to our knowledge, few studies have reported imaging characterization of RCC by CEUS [7,11,12]. These reports included a few cases of pRCC, but the studies did not completely evaluate enhancement patterns and morphological features of pRCC, nor the value of CEUS in differential diagnosis of pRCC and ccRCC. Ignee A. et al. [12] investigated the value of CEUS in differentiating between 20 benign and 117 malignant renal lesions, including 20 pRCCs. Gerst S. et al.[11] reported the value of CEUS in differentiating clear cell carcinoma and non–clear cell renal tumours, in which one pRCC was included. Tamai H. et al. [7] reported that four of six pRCCs showed no enhancement by CECT, while all six pRCCs were enhanced by CEUS. In our study, we retrospectively analysed the CEUS image characteristics of ccRCC and pRCC lesions with the largest amount of pathologically-proven positive lesions reported, and we investigated the diagnostic criteria for preoperative differentiation between these two histological subtypes of RCC.
ethics committee approval was obtained to retrospectively review images and patient medical records. 2.2. Examination technique CEUS examinations were performed using one of two US systems: IU22 (Philips Medical Systems, Netherlands; C5-1, 1-5 MHz) or E9 (GE Healthcare, England; C1-5, 1-5 MHz). Gray-scale US was conducted to observe tumour size, shape, echogenicity, and demarcation from adjacent tissues, while colour Doppler flow imaging (CDFI) was used to examine blood flow within and outside of the tumours. For each patient, CEUS was performed after conventional US examination using the same scanning system. During contrastenhanced imaging, low-acoustic power modes were used with a mechanical index (MI) of 0.05–0.11. Every patient received an intravenous 1.2-mL bolus injection of the second-generation contrast agent SonoVue® (Bracco, Italy), followed by a flush of 5 mL of 0.9% (w/v) sodium chloride. A timer was activated at initiation of contrast agent administration. At the same time, patients were asked to hold their breath as long as possible. Slow shallow breathing was allowed for patients unable to hold their breath. During each CEUS imaging session, the scan beam was swept through the entire anatomical area of the lesion to acquire enhancement information from the whole lesion and imaging duration, from administration of SonoVue to completion of the entire lesion scan, was greater than 4 min. Repeated injections of SonoVue were performed at intervals of greater than 15 min if necessary; a total of 16 patients with 16 lesions received a second injection. Real-time CEUS image videos were acquired for image analysis and interpretation. 2.3. Computed tomography (CT) protocols
2. Materials and methods 2.1. Patient enrolment Between October 2004 and November 2013, 49 consecutive patients with 50 renal lesions underwent preoperative CEUS and their lesions were pathologically proven to be positive for pRCC after surgery in our hospital. From January 2012 to November 2013, 155 consecutive patients with 158 renal lesions also underwent CEUS and their lesions were proven positive for ccRCC by pathological examination. One patient having a pRCC lesion was excluded from this study because of insufficient video quality and two patients with two ccRCC lesions were excluded due to inadequate contrast-enhanced video length (3 cm. Using the above CEUS patterns and feature definitions, the pRCC and ccRCC lesions were characterized. To evaluate the degree of enhancement of tumours by CT, two reviewers measured the attenuation of regions of interest (ROI) independently. The mean of these values was then calculated. An ROI was chosen to cover as much of the solid enhancing area as possible and exclude any area of calcification. The reviewers were instructed to keep the ROI size and location the same among all three scanning phases: unenhanced, corticomedullary, and nephrographic phase. The degree of enhancement was calculated by subtracting the mean attenuation values for unenhanced images from mean attenuation values for the corresponding corticomedullary or the nephrographic phase [3,5]. An increase in attenuation of ≥20HU when unenhanced values were compared to values for any series of contrast-enhanced images indicated definite enhancement. An increase of 10–19HU was considered suspicious and an increase of 0.75). Pearson’s chi-squared (2 ) tests were used to compare pRCC and ccRCC lesions in terms of enhancement pattern, as well as homogeneity of enhance-
Twenty (20/25, 80%) pRCC lesions showed definite enhancement of the corticomedullary or nephrographic phase with an increase in attenuation >20HU. Three (3/25, 12%) pRCCs demonstrated equivocal enhancement with the change of attenuation between 10 and 19HU, and two (2/25, 8%) pRCC lesions showed no enhancement (changing 20HU. Attenuation and degree of enhancement of pRCC lesions were much lower than values for ccRCC in both corticomedullary and nephrographic phases (Table 1).
Please cite this article in press as: L.-Y. Xue, et al., Papillary renal cell carcinoma and clear cell renal cell carcinoma: Differentiation of distinct histological types with contrast – enhanced ultrasonography, Eur J Radiol (2015), http://dx.doi.org/10.1016/j.ejrad.2015.06.017
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Fig. 2. The same patient with that in Fig 1. A – C, unenhanced (A), corticomedullary phase (B), and nephrographic phase (C) CT scans show that the degree of enhancement is less than 10HU in the lesion (big arrows). The mean attenuation values were 20.3HU, 25.3HU and 29.2HU, respectively. The adjacent small lesions were simple cysts (small arrows).
Fig. 3. A papillary renal cell carcinoma of the right kidney in a 33-year-old man (arrow). (A) A isoechoic lesion located in upper pole of the kidney is visualized by ultrasonography. (B) At the time point of 19 s after the injection of SonoVue, the mass enhances later than the renal cortex tissue. (C) The lesion gets peak enhancement at 26 s and the degree is less than adjacent cortex. (D) In the process of de-enhancement the degree of lesion is continuously low.
Please cite this article in press as: L.-Y. Xue, et al., Papillary renal cell carcinoma and clear cell renal cell carcinoma: Differentiation of distinct histological types with contrast – enhanced ultrasonography, Eur J Radiol (2015), http://dx.doi.org/10.1016/j.ejrad.2015.06.017
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Fig. 4. A clear cell renal cell carcinoma of the left kidney in a 56-year-old man (big arrow). (A) The conventional US scan shows a slightly hyperechoic mass in the mid-portion of the left kidney. (B) In the initial enhancement, the tumour enhances simultaneous with the cortex. (C) The peak enhancement of the lesion, at 30 s postinjection, is higher than that of renal parenchyma. It is heterogeneous enhancement with nonenhancing area in the middle (small arrow). (D) The enhancement wash-out of the lesion is slower than parenchyma.
Fig. 5. A papillary renal cell carcinoma of the right kidney in a 57-year-old woman (big arrow). (A) The conventional US scan demonstrates a slightly hyperechoic mass in the lower pole of the kidney. (B) In the initial enhancement, the tumor enhances latter than the cortex. (C) The peak enhancement of the lesion is lower than that of renal parenchyma. (D) The enhancement wash-out of the lesion is faster than parenchyma and the perilesional pseudocapsule is detected clearly (small arrow).
Please cite this article in press as: L.-Y. Xue, et al., Papillary renal cell carcinoma and clear cell renal cell carcinoma: Differentiation of distinct histological types with contrast – enhanced ultrasonography, Eur J Radiol (2015), http://dx.doi.org/10.1016/j.ejrad.2015.06.017
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Table 1 Attenuation and degree of contrast enhancement in pRCC and ccRCC by CECT. Features Unenhanced (HU)
pRCC 35.6 ± 13.0
Corticomedullary phase (HU) Attenuation Enhancement Parenchymal phase (HU) Attenuation Enhancement No. of tumors with definite enhancement (>20HU) No. of tumors with equivocal enhancement (10–19HU) No. of tumors with no enhancement (
ARTICLE IN PRESS European Journal of Radiology xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
Papillary renal cell carcinoma and clear cell renal cell carcinoma: Differentiation of distinct histological types with contrast – enhanced ultrasonography Li-Yun Xue a , Qing Lu a , Bei-Jian Huang a,∗ , Zheng Li b , Cui-Xian Li a , Jie-Xian Wen a , Wen-Ping Wang a a Department of Ultrasound Zhongshan Hospital, Fudan University, Shanghai institute of medical imaging, Bldg. 1#, 180 Fenglin Rd., Xuhui District, Shanghai 200032, China b Department of Echocardiography, Zhongshan Hospital, Fudan University, Shanghai 200032, China
a r t i c l e
i n f o
Article history: Received 16 March 2015 Received in revised form 10 June 2015 Accepted 16 June 2015 Keywords: Contrast-enhanced ultrasound (CEUS) Contrast-enhanced computed tomography (CECT) Papillary renal cell carcinoma (pRCC) Clear cell renal cell carcinoma (ccRCC) Renal lesions
a b s t r a c t Purpose: Papillary renal cell carcinoma (pRCC) and clear cell renal cell carcinoma (ccRCC) have different biological behaviours and imaging features. The role of contrast-enhanced ultrasound (CEUS) in differentiating these two carcinoma subtypes has not been comprehensively studied. Materials and methods: Forty-eight patients with 49 pRCC lesions and 153 patients with 156 ccRCC lesions underwent preoperative conventional ultrasound (US) and CEUS. Among them, 91 patients (25 pRCCs and 66 ccRCCs) also underwent preoperative contrast-enhanced computed tomography (CECT) in our hospital. The characteristics of CEUS and CECT images for each patient imaged were analysed by each of two blinded observers. Results: Images for five (5/25, 20%) pRCC patients demonstrated equivocal or no enhancement using CECT, while all lesions were enhanced using CEUS. From CEUS, images of pRCCs, when compared with ccRCC images, demonstrated significantly higher frequencies of slow wash-in (59.2% vs. 5.8%), fast wash-out (87.7% vs. 46.1%), and hypo-enhancement (57.1% vs. 7.1%) patterns, p < 0.001, as well as the presence of pseudocapsule (42.9% vs. 23.1%), p = 0.007. For lesions with large diameters (>3 cm), a higher percentage of pRCC images demonstrated homogeneous enhancement compared with ccRCC images. Using the combination of slow wash-in, fast wash-out, and hypoenhancement patterns at peak as criteria to differentiate pRCC from ccRCC, positive and negative predictive value, and sensitivity and specificity were found to be 86.7%, 86.9%, 53.1%, and 97.4%, respectively. Conclusions: CEUS imaging features of slow-in, fast-out, and hypo-enhancement patterns may be useful for differentiating pRCC and ccRCC. In addition, CEUS may be helpful for diagnosing hypovascular renal lesions that demonstrate equivocal or no enhancement by CECT and, thus, for improving diagnostic confidence. © 2015 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Renal cell carcinoma (RCC) is the most common primary malignancy of the kidney, with clear cell RCC (ccRCC) and papillary RCC
Abbreviations: pRCC, papillary renal cell carcinoma; ccRCC, clear cell renal cell carcinoma; CEUS, contrast-enhanced ultrasound; CECT, contrast-enhanced computed tomography; US, conventional ultrasound; CDFI, colour Doppler flow imaging; CKD, chronic kidney disease; MRI, magnetic resonance imaging; RCC, renal cell carcinoma; ICC, interclass correlation coefficient; NPV, negative predictive value; PPV, positive predictive value. ∗ Corresponding author. E-mail address: [email protected] (B.-J. Huang).
(pRCC) as the most and second-most prevalent subtypes, accounting for 70% and 10–15% of all RCCs, respectively [1,2,3]. Features of pRCCs are less aggressive and prognoses are better in comparison with ccRCCs [3,4]. ccRCC has an overall five-year survival rate of 55–60%, while pRCC is associated with a higher five-year survival rate (80–90%) [5]. Accordingly, precise classification has become an important theme due to the differences in tumour behaviour and prognoses for the two subtypes [6]. Diagnosis of ccRCC is relatively easy because of its typical hypervascular appearance in colour Doppler flow imaging (CDFI). Conversely, pRCC, as a hypovascular RCC subtype, tends to be difficult to diagnose because of a weak or absent blood flow signal [7]. Thus, it is essential to use a contrast medium for differential
http://dx.doi.org/10.1016/j.ejrad.2015.06.017 0720-048X/© 2015 Elsevier Ireland Ltd. All rights reserved.
Please cite this article in press as: L.-Y. Xue, et al., Papillary renal cell carcinoma and clear cell renal cell carcinoma: Differentiation of distinct histological types with contrast – enhanced ultrasonography, Eur J Radiol (2015), http://dx.doi.org/10.1016/j.ejrad.2015.06.017
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diagnosis of RCC. Dynamic contrast-enhanced computed tomography (CECT) and magnetic resonance imaging (MRI) technology have played important roles in identification of the subtypes. CcRCC shows a significantly higher degree of enhancement in corticomedullary phase compared with pRCC [8,9,10], and the degree of enhancement in the corticomedullary phase correlates with microvessel density observed via staining of CD34 [9]. However, it is insufficient to diagnose a renal lesion as benign (e.g., a hyperdense cyst) if no enhancement is detected using CECT [3]. Contrast-enhanced ultrasound (CEUS) imaging technology is capable of detecting microvascularization of tumours and is superior to CECT with respect to revealing intralesional vascularity [7,11]. Currently, research involving CEUS for differentiating subtypes of RCC is still in the early stages. To date and to our knowledge, few studies have reported imaging characterization of RCC by CEUS [7,11,12]. These reports included a few cases of pRCC, but the studies did not completely evaluate enhancement patterns and morphological features of pRCC, nor the value of CEUS in differential diagnosis of pRCC and ccRCC. Ignee A. et al. [12] investigated the value of CEUS in differentiating between 20 benign and 117 malignant renal lesions, including 20 pRCCs. Gerst S. et al.[11] reported the value of CEUS in differentiating clear cell carcinoma and non–clear cell renal tumours, in which one pRCC was included. Tamai H. et al. [7] reported that four of six pRCCs showed no enhancement by CECT, while all six pRCCs were enhanced by CEUS. In our study, we retrospectively analysed the CEUS image characteristics of ccRCC and pRCC lesions with the largest amount of pathologically-proven positive lesions reported, and we investigated the diagnostic criteria for preoperative differentiation between these two histological subtypes of RCC.
ethics committee approval was obtained to retrospectively review images and patient medical records. 2.2. Examination technique CEUS examinations were performed using one of two US systems: IU22 (Philips Medical Systems, Netherlands; C5-1, 1-5 MHz) or E9 (GE Healthcare, England; C1-5, 1-5 MHz). Gray-scale US was conducted to observe tumour size, shape, echogenicity, and demarcation from adjacent tissues, while colour Doppler flow imaging (CDFI) was used to examine blood flow within and outside of the tumours. For each patient, CEUS was performed after conventional US examination using the same scanning system. During contrastenhanced imaging, low-acoustic power modes were used with a mechanical index (MI) of 0.05–0.11. Every patient received an intravenous 1.2-mL bolus injection of the second-generation contrast agent SonoVue® (Bracco, Italy), followed by a flush of 5 mL of 0.9% (w/v) sodium chloride. A timer was activated at initiation of contrast agent administration. At the same time, patients were asked to hold their breath as long as possible. Slow shallow breathing was allowed for patients unable to hold their breath. During each CEUS imaging session, the scan beam was swept through the entire anatomical area of the lesion to acquire enhancement information from the whole lesion and imaging duration, from administration of SonoVue to completion of the entire lesion scan, was greater than 4 min. Repeated injections of SonoVue were performed at intervals of greater than 15 min if necessary; a total of 16 patients with 16 lesions received a second injection. Real-time CEUS image videos were acquired for image analysis and interpretation. 2.3. Computed tomography (CT) protocols
2. Materials and methods 2.1. Patient enrolment Between October 2004 and November 2013, 49 consecutive patients with 50 renal lesions underwent preoperative CEUS and their lesions were pathologically proven to be positive for pRCC after surgery in our hospital. From January 2012 to November 2013, 155 consecutive patients with 158 renal lesions also underwent CEUS and their lesions were proven positive for ccRCC by pathological examination. One patient having a pRCC lesion was excluded from this study because of insufficient video quality and two patients with two ccRCC lesions were excluded due to inadequate contrast-enhanced video length (3 cm. Using the above CEUS patterns and feature definitions, the pRCC and ccRCC lesions were characterized. To evaluate the degree of enhancement of tumours by CT, two reviewers measured the attenuation of regions of interest (ROI) independently. The mean of these values was then calculated. An ROI was chosen to cover as much of the solid enhancing area as possible and exclude any area of calcification. The reviewers were instructed to keep the ROI size and location the same among all three scanning phases: unenhanced, corticomedullary, and nephrographic phase. The degree of enhancement was calculated by subtracting the mean attenuation values for unenhanced images from mean attenuation values for the corresponding corticomedullary or the nephrographic phase [3,5]. An increase in attenuation of ≥20HU when unenhanced values were compared to values for any series of contrast-enhanced images indicated definite enhancement. An increase of 10–19HU was considered suspicious and an increase of 0.75). Pearson’s chi-squared (2 ) tests were used to compare pRCC and ccRCC lesions in terms of enhancement pattern, as well as homogeneity of enhance-
Twenty (20/25, 80%) pRCC lesions showed definite enhancement of the corticomedullary or nephrographic phase with an increase in attenuation >20HU. Three (3/25, 12%) pRCCs demonstrated equivocal enhancement with the change of attenuation between 10 and 19HU, and two (2/25, 8%) pRCC lesions showed no enhancement (changing 20HU. Attenuation and degree of enhancement of pRCC lesions were much lower than values for ccRCC in both corticomedullary and nephrographic phases (Table 1).
Please cite this article in press as: L.-Y. Xue, et al., Papillary renal cell carcinoma and clear cell renal cell carcinoma: Differentiation of distinct histological types with contrast – enhanced ultrasonography, Eur J Radiol (2015), http://dx.doi.org/10.1016/j.ejrad.2015.06.017
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Fig. 2. The same patient with that in Fig 1. A – C, unenhanced (A), corticomedullary phase (B), and nephrographic phase (C) CT scans show that the degree of enhancement is less than 10HU in the lesion (big arrows). The mean attenuation values were 20.3HU, 25.3HU and 29.2HU, respectively. The adjacent small lesions were simple cysts (small arrows).
Fig. 3. A papillary renal cell carcinoma of the right kidney in a 33-year-old man (arrow). (A) A isoechoic lesion located in upper pole of the kidney is visualized by ultrasonography. (B) At the time point of 19 s after the injection of SonoVue, the mass enhances later than the renal cortex tissue. (C) The lesion gets peak enhancement at 26 s and the degree is less than adjacent cortex. (D) In the process of de-enhancement the degree of lesion is continuously low.
Please cite this article in press as: L.-Y. Xue, et al., Papillary renal cell carcinoma and clear cell renal cell carcinoma: Differentiation of distinct histological types with contrast – enhanced ultrasonography, Eur J Radiol (2015), http://dx.doi.org/10.1016/j.ejrad.2015.06.017
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Fig. 4. A clear cell renal cell carcinoma of the left kidney in a 56-year-old man (big arrow). (A) The conventional US scan shows a slightly hyperechoic mass in the mid-portion of the left kidney. (B) In the initial enhancement, the tumour enhances simultaneous with the cortex. (C) The peak enhancement of the lesion, at 30 s postinjection, is higher than that of renal parenchyma. It is heterogeneous enhancement with nonenhancing area in the middle (small arrow). (D) The enhancement wash-out of the lesion is slower than parenchyma.
Fig. 5. A papillary renal cell carcinoma of the right kidney in a 57-year-old woman (big arrow). (A) The conventional US scan demonstrates a slightly hyperechoic mass in the lower pole of the kidney. (B) In the initial enhancement, the tumor enhances latter than the cortex. (C) The peak enhancement of the lesion is lower than that of renal parenchyma. (D) The enhancement wash-out of the lesion is faster than parenchyma and the perilesional pseudocapsule is detected clearly (small arrow).
Please cite this article in press as: L.-Y. Xue, et al., Papillary renal cell carcinoma and clear cell renal cell carcinoma: Differentiation of distinct histological types with contrast – enhanced ultrasonography, Eur J Radiol (2015), http://dx.doi.org/10.1016/j.ejrad.2015.06.017
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Table 1 Attenuation and degree of contrast enhancement in pRCC and ccRCC by CECT. Features Unenhanced (HU)
pRCC 35.6 ± 13.0
Corticomedullary phase (HU) Attenuation Enhancement Parenchymal phase (HU) Attenuation Enhancement No. of tumors with definite enhancement (>20HU) No. of tumors with equivocal enhancement (10–19HU) No. of tumors with no enhancement (
