Type:
Educational Exhibit
Keywords:
Cancer, Ablation procedures, CT, Oncology, Kidney, Interventional non-vascular
Authors:
M. F. S. Shaukat, S. Sultana , M. Djearaman, S. Hussain; BIRMINGHAM/UK
DOI:
10.26044/ecr2019/C-1859
Findings and procedure details
After RFA of renal tumours,
follow up CT scan at our institution is performed at 1,4,7 and 11 months and then yearly for 5 years.
Appearances post RFA can be variable.
Disease surveillance must be undertaken using a dedicated CT renal mass protocol with unenhanced and contrast-enhanced CT scan as the bare minimum [6],
because abnormal enhancement is key indicator of residual or recurrent local disease.
After successful effective ablation,
tumor is seen as area of hyper-density (> 40 HU) [7] on unenhanced CT scan with a surrounding rim of fat (called “bull’s-eye” appearance),
particularly with exophytic masses.
Hyperdense central zone represents successfully ablated tumor with a penumbra of devitalized renal parenchyma surrounding the tumor included as a treatment margin.
With time,
successfully ablated tumor will decrease in size,
but complete disappearance is seen in only a minority of cases (8,
9).
However,
change in size is not a reliable indicator of treatment adequacy.
There must be no enhancement after contrast administration on CT scan because it is a sign of active tumor.
Unfortunately,
rim enhancement is not rare after percutaneous ablation [10].
This can cause problems,
because residual tumor is more likely at the periphery of ablation area.
However,
benign rim enhancement has smooth margins,
whereas residual tumor has heterogeneous enhancement / enhancing nodules.
Most reliable sign of tumour relapse is enlarging nodular area showing unequivocal enhancement (11).
Increase of 20 HU or more on post contrast follow up scans is highly suspicious for residual tumour.
An increase of 10 HU or less is indicative of successful tumour ablation.
An intermediate increase of 10-20 HU is equivocal.
(12) In such cases,
close surveillance must be adopted. Biopsy may be performed to confirm a suspected residual tumor in equivocal cases.