1. Microwave Ablation of a Bosniak III Renal Cyst
Marc Michael D. Lim, MD
Christopher Harnain, MD
Samuel McCabe, MD
Westchester Medical Center

2. History
88 year-old female with remote history of partial right nephrectomy for renal cell carcinoma and a left lower pole Bosniak III renal cyst presented with interval growth of the cyst’s mural nodule
The patient did not wish to undergo surgery, and minimally invasive treatment options were discussed

3. CT Abdomen/Pelvis * *
Add coronal or sag CT image
Left lower pole Bosniak III renal cyst with 2.4 x 1.4 x 2.1 cm mural nodule (↑), previously 1.7 x 0.7 x 1.5 cm. Note the proximity of the lesion to the descending colon (*). The patient declined surgical resection, and interventional radiology was consulted for further evaluation. The decision was made to perform a microwave ablation.

4. Technique
A pigtail drainage catheter was used to drain the cyst. A sample of the aspirate was sent for cytopathology, which was negative for malignancy. Despite drainage of the lower pole cyst, the descending colon was still too close to the mural nodule, so a 15 cm needle used to hydrodissect the pararenal fat between the colon and left kidney with D50-water.
Intraprocedural CT on the left with color overlay on the right demonstrates: Cyst drainage catheter Renal parynchema Target nodule Hydrodissection needle D50-water hydrodissection fluid with scattered foci of air Descending colon

5. Technique
A Certus PR 15 cm microwave probe was inserted into the renal cystic mural nodule, and a total of 3 microwave ablations were performed at 65W for 5 minutes each.

6. Technique *
Immediate post-procedural contrast enhanced CT demonstrates no residual enhancement within the renal mass (↑). Note the wide margin between renal parynchema and descending colon (*) provided by the hydrodissection fluid.

7. One Year Follow-up CT
1.4 cm non-enhancing soft tissue nodule (↑) at the ablation site. Also note the surrounding rim of scarring along the margin of the burn zone.

8. Questions
In this patient, should biopsy of the mural nodule have been performed prior to treatment?
In addition to microwave ablation, what other treatment modalities could be considered in this case?
Given the choice to use microwave ablation, what other options besides hydrodissection could be considered for displacing the colon? What degree of separation between the lesion and the colon would be considered adequate?