Figure 1.

A 70 year-old man with history of colon cancer underwent CT imaging for staging purposes. Axial CT image of the abdomen after intravenous administration of contrast (a) shows a 2.5 cm incidental mass (arrowheads) in the right kidney. He was referred for percutaneous biopsy. Non-contrast, axial CT image of the right kidney in prone position (b) shows intervening lung in the base of the right pleural cavity (arrow). The tumor (arrowhead) is isodense with normal kidney and is difficult to identify. Patient was placed in the right lateral decubitus position to decrease the right lung volume and was given iodinated contrast to better delineate the tumor margins for the biopsy (c). Pathology showed renal cell carcinoma, clear cell type, Fuhrman nuclear grade 2. Subsequently, he was referred for image guided ablation. Considering that the tumor was isodense to the kidney on CT images and the fact that intervening lung precluded placement of cryoprobes in an axial plane, a decision was made to perform the ablation under MRI guidance rather than CT. Sagittal T2-weighted image of the kidney (d) clearly demonstrates a hyperintense tumor (arrowhead) in the upper pole of the right kidney. Intervening lung parenchyma is identified posterior to the tumor (arrow). Using a sagittal plane of imaging, three cryoprobes were inserted into the tumor from an inferior approach to avoid puncturing the lung. Probes were placed under real-time MRI guidance in the medial (e), center (f), and lateral (g) border of the tumor. Axial (h), sagittal (i), and coronal (j) T2-weighted images of the kidney performed using a HASTE sequence show a hypointense ice ball (arrowheads) covering the entire tumor with adequate margins. Post-treatment dynamic contrast-enhanced MRI (k) demonstrates perfusion deficit (arrowheads) within the expected area of damage based on the MRI monitoring feedback.