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DOI: 10.1148/rg.272065083
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CT and MR Imaging after Imaging-guided Thermal Ablation of Renal Neoplasms1

Geoffrey E. Wile, MD, John R. Leyendecker, MD, Kyle A. Krehbiel, MD, Raymond B. Dyer, MD and Ronald J. Zagoria, MD

1 From the Department of Radiology, Wake Forest University Baptist Medical Center, Medical Center Blvd, Winston-Salem, NC 27103. Presented as an education exhibit at the 2005 RSNA Annual Meeting. Received May 1, 2006; revision requested July 10 and received August 24; accepted August 28. R.J.Z. is a consultant with and received a research grant from Tyco Healthcare (Valleylab); all remaining authors have no financial relationships to disclose.

Figure 1
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  		Figure 1.  Immediate postablation contrast-enhanced CT scan obtained in an 82-year-old man with RCC shows stranding and fascial thickening (arrows). Arrowhead indicates the ablation zone.

 

Figure 2A
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  		Figure 2a.  Residual tumor in an 83-year-old woman with RCC. (a) Preablation contrast-enhanced CT scan shows a small, enhancing exophytic tumor (arrow). (b) Immediate post-ablation contrast-enhanced CT scan shows a residual crescent of enhancing tumor (arrow), which was re-treated during the same session.

 

Figure 2B
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  		Figure 2b.  Residual tumor in an 83-year-old woman with RCC. (a) Preablation contrast-enhanced CT scan shows a small, enhancing exophytic tumor (arrow). (b) Immediate post-ablation contrast-enhanced CT scan shows a residual crescent of enhancing tumor (arrow), which was re-treated during the same session.

 

Figure 3A
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  		Figure 3a.  (a) Unenhanced CT scan obtained in a 74-year-old woman with RCC during cryoablation shows a low-attenuation ice ball (arrow) surrounding the cryoprobe (arrowhead). (b) Immediate post-cryoablation unenhanced CT scan obtained following thawing and cryoprobe removal shows residual low attenuation in the tumor ablation zone (arrow). (c) Unenhanced CT scan obtained 5 months later during retreatment of the same kidney with RF ablation for recurrent tumor shows fat stranding (arrow) but no appreciable change in attenuation of the ablation zone. Arrowhead indicates the electrode. (d) On an unenhanced CT scan obtained immediately after RF ablation, the ablation zone (arrow) is mildly hyperattenuating relative to the renal parenchyma.

 

Figure 3B
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  		Figure 3b.  (a) Unenhanced CT scan obtained in a 74-year-old woman with RCC during cryoablation shows a low-attenuation ice ball (arrow) surrounding the cryoprobe (arrowhead). (b) Immediate post-cryoablation unenhanced CT scan obtained following thawing and cryoprobe removal shows residual low attenuation in the tumor ablation zone (arrow). (c) Unenhanced CT scan obtained 5 months later during retreatment of the same kidney with RF ablation for recurrent tumor shows fat stranding (arrow) but no appreciable change in attenuation of the ablation zone. Arrowhead indicates the electrode. (d) On an unenhanced CT scan obtained immediately after RF ablation, the ablation zone (arrow) is mildly hyperattenuating relative to the renal parenchyma.

 

Figure 3C
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  		Figure 3c.  (a) Unenhanced CT scan obtained in a 74-year-old woman with RCC during cryoablation shows a low-attenuation ice ball (arrow) surrounding the cryoprobe (arrowhead). (b) Immediate post-cryoablation unenhanced CT scan obtained following thawing and cryoprobe removal shows residual low attenuation in the tumor ablation zone (arrow). (c) Unenhanced CT scan obtained 5 months later during retreatment of the same kidney with RF ablation for recurrent tumor shows fat stranding (arrow) but no appreciable change in attenuation of the ablation zone. Arrowhead indicates the electrode. (d) On an unenhanced CT scan obtained immediately after RF ablation, the ablation zone (arrow) is mildly hyperattenuating relative to the renal parenchyma.

 

Figure 3D
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  		Figure 3d.  (a) Unenhanced CT scan obtained in a 74-year-old woman with RCC during cryoablation shows a low-attenuation ice ball (arrow) surrounding the cryoprobe (arrowhead). (b) Immediate post-cryoablation unenhanced CT scan obtained following thawing and cryoprobe removal shows residual low attenuation in the tumor ablation zone (arrow). (c) Unenhanced CT scan obtained 5 months later during retreatment of the same kidney with RF ablation for recurrent tumor shows fat stranding (arrow) but no appreciable change in attenuation of the ablation zone. Arrowhead indicates the electrode. (d) On an unenhanced CT scan obtained immediately after RF ablation, the ablation zone (arrow) is mildly hyperattenuating relative to the renal parenchyma.

 

Figure 4
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  		Figure 4.  Contrast-enhanced CT scan obtained in a 71-year-old woman 5 weeks after RF ablation demonstrates an exophytic tumor with the typical bull’s-eye appearance. An area of nonenhancing soft-tissue attenuation (ablation zone) persists centrally (arrow) and is surrounded by fat and a thin rim of peritu-moral soft-tissue attenuation (arrowhead).

 

Figure 5A
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  		Figure 5a.  Typical MR imaging appearance of an RF ablation site. The patient was an 83-year-old man with RCC who had undergone RF ablation 14 months earlier. (a) Coronal single-shot fast SE T2-weighted MR image shows the ablation zone (arrow) with low signal intensity. A peritumoral rim (arrowhead) creates a bull’s-eye appearance. (b) Axial GRE T1-weighted MR image demonstrates the ablation zone (arrow) with mild heterogeneity but predominantly high signal intensity. (c) On an axial fat-suppressed fast SE T2-weighted MR image, the low-signal-intensity ablation zone (arrow) is isointense relative to the surrounding suppressed fat.

 

Figure 5B
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  		Figure 5b.  Typical MR imaging appearance of an RF ablation site. The patient was an 83-year-old man with RCC who had undergone RF ablation 14 months earlier. (a) Coronal single-shot fast SE T2-weighted MR image shows the ablation zone (arrow) with low signal intensity. A peritumoral rim (arrowhead) creates a bull’s-eye appearance. (b) Axial GRE T1-weighted MR image demonstrates the ablation zone (arrow) with mild heterogeneity but predominantly high signal intensity. (c) On an axial fat-suppressed fast SE T2-weighted MR image, the low-signal-intensity ablation zone (arrow) is isointense relative to the surrounding suppressed fat.

 

Figure 5C
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  		Figure 5c.  Typical MR imaging appearance of an RF ablation site. The patient was an 83-year-old man with RCC who had undergone RF ablation 14 months earlier. (a) Coronal single-shot fast SE T2-weighted MR image shows the ablation zone (arrow) with low signal intensity. A peritumoral rim (arrowhead) creates a bull’s-eye appearance. (b) Axial GRE T1-weighted MR image demonstrates the ablation zone (arrow) with mild heterogeneity but predominantly high signal intensity. (c) On an axial fat-suppressed fast SE T2-weighted MR image, the low-signal-intensity ablation zone (arrow) is isointense relative to the surrounding suppressed fat.

 

Figure 6A
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  		Figure 6a.  Usefulness of image subtraction. (a) Axial precontrast fat-suppressed T1-weighted MR image obtained in a 65-year-old man with RCC shows a high-signal-intensity ablation zone (arrow). (b) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image shows persistent high signal intensity that may be difficult to distinguish from subtle enhancement within the ablation zone (arrow). (c) Subtraction image created by subtracting the precontrast data set from the postcontrast data set shows no enhancement in the region of the ablation zone (arrow).

 

Figure 6B
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  		Figure 6b.  Usefulness of image subtraction. (a) Axial precontrast fat-suppressed T1-weighted MR image obtained in a 65-year-old man with RCC shows a high-signal-intensity ablation zone (arrow). (b) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image shows persistent high signal intensity that may be difficult to distinguish from subtle enhancement within the ablation zone (arrow). (c) Subtraction image created by subtracting the precontrast data set from the postcontrast data set shows no enhancement in the region of the ablation zone (arrow).

 

Figure 6C
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  		Figure 6c.  Usefulness of image subtraction. (a) Axial precontrast fat-suppressed T1-weighted MR image obtained in a 65-year-old man with RCC shows a high-signal-intensity ablation zone (arrow). (b) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image shows persistent high signal intensity that may be difficult to distinguish from subtle enhancement within the ablation zone (arrow). (c) Subtraction image created by subtracting the precontrast data set from the postcontrast data set shows no enhancement in the region of the ablation zone (arrow).

 

Figure 7A
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  		Figure 7a.  Expected changes in an RF ablation zone over time. (a) Preablation contrast-enhanced CT scan obtained in a 78-year-old-woman shows a small, intraparenchymal RCC (arrow). (b) Immediate postablation CT scan demonstrates a wedge-shaped unenhanced region (arrows) that encompasses the renal tumor as well as some of the surrounding renal parenchyma. (c) On a CT scan obtained 3 years later, the ablation zone (arrow) shows only mild involution, a finding that demonstrates that a substantial (albeit nonviable) mass may persist years after RF ablation.

 

Figure 7B
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  		Figure 7b.  Expected changes in an RF ablation zone over time. (a) Preablation contrast-enhanced CT scan obtained in a 78-year-old-woman shows a small, intraparenchymal RCC (arrow). (b) Immediate postablation CT scan demonstrates a wedge-shaped unenhanced region (arrows) that encompasses the renal tumor as well as some of the surrounding renal parenchyma. (c) On a CT scan obtained 3 years later, the ablation zone (arrow) shows only mild involution, a finding that demonstrates that a substantial (albeit nonviable) mass may persist years after RF ablation.

 

Figure 7C
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  		Figure 7c.  Expected changes in an RF ablation zone over time. (a) Preablation contrast-enhanced CT scan obtained in a 78-year-old-woman shows a small, intraparenchymal RCC (arrow). (b) Immediate postablation CT scan demonstrates a wedge-shaped unenhanced region (arrows) that encompasses the renal tumor as well as some of the surrounding renal parenchyma. (c) On a CT scan obtained 3 years later, the ablation zone (arrow) shows only mild involution, a finding that demonstrates that a substantial (albeit nonviable) mass may persist years after RF ablation.

 

Figure 8A
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  		Figure 8a.  (a) Coronal single-shot fast SE T2-weighted MR image obtained in a 65-year-old man 5 months prior to cryoablation shows a heterogeneous mass (arrow) within the left kidney. (b) On a coronal single-shot fast SE T2-weighted MR image obtained 2 months after cryoablation, the ablation zone (arrow) demonstrates markedly heterogeneous signal intensity and is significantly larger than the original tumor. (c) Coronal reformatted MR image from an axial gadolinium-enhanced data set created by subtracting the precontrast data set from the postcontrast data set shows no residual enhancement within the ablation zone. Note the presence of a relatively uniform enhancing rim (arrow), a finding that should not be confused with residual tumor.

 

Figure 8B
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  		Figure 8b.  (a) Coronal single-shot fast SE T2-weighted MR image obtained in a 65-year-old man 5 months prior to cryoablation shows a heterogeneous mass (arrow) within the left kidney. (b) On a coronal single-shot fast SE T2-weighted MR image obtained 2 months after cryoablation, the ablation zone (arrow) demonstrates markedly heterogeneous signal intensity and is significantly larger than the original tumor. (c) Coronal reformatted MR image from an axial gadolinium-enhanced data set created by subtracting the precontrast data set from the postcontrast data set shows no residual enhancement within the ablation zone. Note the presence of a relatively uniform enhancing rim (arrow), a finding that should not be confused with residual tumor.

 

Figure 8C
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  		Figure 8c.  (a) Coronal single-shot fast SE T2-weighted MR image obtained in a 65-year-old man 5 months prior to cryoablation shows a heterogeneous mass (arrow) within the left kidney. (b) On a coronal single-shot fast SE T2-weighted MR image obtained 2 months after cryoablation, the ablation zone (arrow) demonstrates markedly heterogeneous signal intensity and is significantly larger than the original tumor. (c) Coronal reformatted MR image from an axial gadolinium-enhanced data set created by subtracting the precontrast data set from the postcontrast data set shows no residual enhancement within the ablation zone. Note the presence of a relatively uniform enhancing rim (arrow), a finding that should not be confused with residual tumor.

 

Figure 9A
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  		Figure 9a.  Marked involution of a central RCC in a 78-year-old man with only one kidney who had undergone RF ablation for life-threatening hematuria. (a) Coronal preablation single-shot fast SE T2-weighted MR image shows a small central mass (arrow). (b) Coronal single-shot fast SE T2-weighted MR image obtained 11 months after ablation shows marked involution of the tumor (arrow). This degree of involution is more typical of tumors treated with cryoablation.

 

Figure 9B
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  		Figure 9b.  Marked involution of a central RCC in a 78-year-old man with only one kidney who had undergone RF ablation for life-threatening hematuria. (a) Coronal preablation single-shot fast SE T2-weighted MR image shows a small central mass (arrow). (b) Coronal single-shot fast SE T2-weighted MR image obtained 11 months after ablation shows marked involution of the tumor (arrow). This degree of involution is more typical of tumors treated with cryoablation.

 

Figure 10A
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  		Figure 10a.  Retained cystic component in a 68-year-old woman who underwent RF ablation for cystic RCC. (a) Axial preablation single-shot fast SE T2-weighted MR image shows a large, complex cystic mass (arrow). (b) Axial single-shot fast SE T2-weighted MR image obtained 3 years after ablation shows a significant decrease in lesion size but only incomplete involution (arrow).

 

Figure 10B
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  		Figure 10b.  Retained cystic component in a 68-year-old woman who underwent RF ablation for cystic RCC. (a) Axial preablation single-shot fast SE T2-weighted MR image shows a large, complex cystic mass (arrow). (b) Axial single-shot fast SE T2-weighted MR image obtained 3 years after ablation shows a significant decrease in lesion size but only incomplete involution (arrow).

 

Figure 11
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  		Figure 11.  Unenhanced CT scan obtained in an 82-year-old man who had undergone RF ablation for clear cell type RCC 19 months earlier shows fat attenuation within the ablation zone (arrow).

 

Figure 12A
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  		Figure 12a.  Residual lipid within the ablation zone in a 69-year-old man who had undergone RF ablation for intraparenchymal clear cell type RCC. (a) Axial in-phase GRE T1-weighted MR image obtained 3 months after RF ablation shows a region of high signal intensity within the ablation zone (arrow). (b) Corresponding axial opposed-phase T1-weighted MR image shows loss of signal intensity in the periphery of the ablation zone (arrow), a finding that indicates the presence of lipid. Gadolinium-enhanced subtraction images showed no evidence of enhancement within the ablation zone.

 

Figure 12B
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  		Figure 12b.  Residual lipid within the ablation zone in a 69-year-old man who had undergone RF ablation for intraparenchymal clear cell type RCC. (a) Axial in-phase GRE T1-weighted MR image obtained 3 months after RF ablation shows a region of high signal intensity within the ablation zone (arrow). (b) Corresponding axial opposed-phase T1-weighted MR image shows loss of signal intensity in the periphery of the ablation zone (arrow), a find-ing that indicates the presence of lipid. Gadolinium-enhanced subtraction images showed no evidence of enhancement within the ablation zone.

 

Figure 13A
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  		Figure 13a.  Residual RCC in a 57-year-old man who had undergone RF ablation followed by cryoablation. (a) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image obtained 1 month after RF ablation shows peripheral nodular enhancement within the ablation zone (arrows), a finding that is consistent with residual disease. (b) Unenhanced CT scan obtained 1 week after cryoablation for residual tumor shows resolving hemorrhage (arrowhead) and perinephric stranding surrounding the ablation zone (arrow). (c) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image obtained through the same region of the kidney 9 weeks after cryoablation shows that the original areas of residual disease no longer enhance. Arrow indicates the ablation zone. (d) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image through the upper pole of the kidney shows a new focus of nodular enhancement (arrow), a finding that indicates residual tumor.

 

Figure 13B
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  		Figure 13b.  Residual RCC in a 57-year-old man who had undergone RF ablation followed by cryoablation. (a) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image obtained 1 month after RF ablation shows peripheral nodular enhancement within the ablation zone (arrows), a finding that is consistent with residual disease. (b) Unenhanced CT scan obtained 1 week after cryoablation for residual tumor shows resolving hemorrhage (arrowhead) and perinephric stranding surrounding the ablation zone (arrow). (c) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image obtained through the same region of the kidney 9 weeks after cryoablation shows that the original areas of residual disease no longer enhance. Arrow indicates the ablation zone. (d) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image through the upper pole of the kidney shows a new focus of nodular enhancement (arrow), a finding that indicates residual tumor.

 

Figure 13C
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  		Figure 13c.  Residual RCC in a 57-year-old man who had undergone RF ablation followed by cryoablation. (a) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image obtained 1 month after RF ablation shows peripheral nodular enhancement within the ablation zone (arrows), a finding that is consistent with residual disease. (b) Unenhanced CT scan obtained 1 week after cryoablation for residual tumor shows resolving hemorrhage (arrowhead) and perinephric stranding surrounding the ablation zone (arrow). (c) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image obtained through the same region of the kidney 9 weeks after cryoablation shows that the original areas of residual disease no longer enhance. Arrow indicates the ablation zone. (d) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image through the upper pole of the kidney shows a new focus of nodular enhancement (arrow), a finding that indicates residual tumor.

 

Figure 13D
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  		Figure 13d.  Residual RCC in a 57-year-old man who had undergone RF ablation followed by cryoablation. (a) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image obtained 1 month after RF ablation shows peripheral nodular enhancement within the ablation zone (arrows), a finding that is consistent with residual disease. (b) Unenhanced CT scan obtained 1 week after cryoablation for residual tumor shows resolving hemorrhage (arrowhead) and perinephric stranding surrounding the ablation zone (arrow). (c) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image obtained through the same region of the kidney 9 weeks after cryoablation shows that the original areas of residual disease no longer enhance. Arrow indicates the ablation zone. (d) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image through the upper pole of the kidney shows a new focus of nodular enhancement (arrow), a finding that indicates residual tumor.

 

Figure 14A
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  		Figure 14a.  Renal vein tumor in a 73-year-old man who underwent RF ablation for RCC. (a) Axial fast SE T2-weighted MR image obtained 4 months after RF ablation shows expansion of and abnormal signal intensity within the left renal vein (arrow), findings that are indicative of tumor thrombus. Arrowhead indicates the ablation zone. (b) Axial fast SE T2-weighted MR image obtained 11 months after RF ablation shows an increase in the size of the tumor within the left renal vein (arrow). This recurrence had not been appreciated previously. Arrowhead indicates the ablation zone.

 

Figure 14B
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  		Figure 14b.  Renal vein tumor in a 73-year-old man who underwent RF ablation for RCC. (a) Axial fast SE T2-weighted MR image obtained 4 months after RF ablation shows expansion of and abnormal signal intensity within the left renal vein (arrow), findings that are indicative of tumor thrombus. Arrowhead indicates the ablation zone. (b) Axial fast SE T2-weighted MR image obtained 11 months after RF ablation shows an increase in the size of the tumor within the left renal vein (arrow). This recurrence had not been appreciated previously. Arrowhead indicates the ablation zone.

 

Figure 15A
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  		Figure 15a.  Development of a new tumor focus in a 74-year-old man who had undergone RF ablation for RCC. (a) Axial single-shot fast SE T2-weighted MR image obtained 7 months after ablation shows decreased signal intensity in the ablation zone (arrowhead). (b) Axial single-shot fast SE T2-weighted MR image obtained 14 months after ablation shows a new tumor (arrow) adjacent to the previous ablation zone (arrowhead).

 

Figure 15B
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  		Figure 15b.  Development of a new tumor focus in a 74-year-old man who had undergone RF ablation for RCC. (a) Axial single-shot fast SE T2-weighted MR image obtained 7 months after ablation shows decreased signal intensity in the ablation zone (arrowhead). (b) Axial single-shot fast SE T2-weighted MR image obtained 14 months after ablation shows a new tumor (arrow) adjacent to the previous ablation zone (arrowhead).

 

Figure 16A
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  		Figure 16a.  Typical contrast-enhanced CT appearance of postablation hemorrhage. (a) Contrast-enhanced CT scan obtained immediately after RF ablation for RCC shows a large perirenal and pararenal hemorrhage with active extravasation of contrast material (arrow). The hemorrhage was self limiting and did not require intervention. (b) Contrast-enhanced CT scan obtained immediately after RF ablation in a different patient shows a sub-capsular hematoma (arrowhead). Note the lower-attenuation sterile water (arrow) used to displace bowel during ablation. The patient required no intervention for bleeding.

 

Figure 16B
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  		Figure 16b.  Typical contrast-enhanced CT appearance of postablation hemorrhage. (a) Contrast-enhanced CT scan obtained immediately after RF ablation for RCC shows a large perirenal and pararenal hemorrhage with active extravasation of contrast material (arrow). The hemorrhage was self limiting and did not require intervention. (b) Contrast-enhanced CT scan obtained immediately after RF ablation in a different patient shows a sub-capsular hematoma (arrowhead). Note the lower-attenuation sterile water (arrow) used to displace bowel during ablation. The patient required no intervention for bleeding.

 

Figure 17A
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  		Figure 17a.  Ureteral stricture following RF ablation of an RCC in the lower right renal pole in a 49-year-old man. (a) Unenhanced CT scan shows the RF electrode (arrowhead) in place within the lower pole mass. Note the location of the proximal right ureter (arrow). (b) Immediate postablation contrast-enhanced CT scan shows ureteral thickening and periureteral stranding (arrow). (c) Coronal single-shot fast SE T2-weighted MR image obtained 15 months after RF ablation shows hydronephrosis and proximal ureteral obstruction (arrow) due to a ureteral stricture. The patient elected not to undergo intervention for the stricture.

 

Figure 17B
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  		Figure 17b.  Ureteral stricture following RF ablation of an RCC in the lower right renal pole in a 49-year-old man. (a) Unenhanced CT scan shows the RF electrode (arrowhead) in place within the lower pole mass. Note the location of the proximal right ureter (arrow). (b) Immediate postablation contrast-enhanced CT scan shows ureteral thickening and periureteral stranding (arrow). (c) Coronal single-shot fast SE T2-weighted MR image obtained 15 months after RF ablation shows hydronephrosis and proximal ureteral obstruction (arrow) due to a ureteral stricture. The patient elected not to undergo intervention for the stricture.

 

Figure 17C
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  		Figure 17c.  Ureteral stricture following RF ablation of an RCC in the lower right renal pole in a 49-year-old man. (a) Unenhanced CT scan shows the RF electrode (arrowhead) in place within the lower pole mass. Note the location of the proximal right ureter (arrow). (b) Immediate postablation contrast-enhanced CT scan shows ureteral thickening and periureteral stranding (arrow). (c) Coronal single-shot fast SE T2-weighted MR image obtained 15 months after RF ablation shows hydronephrosis and proximal ureteral obstruction (arrow) due to a ureteral stricture. The patient elected not to undergo intervention for the stricture.

 




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