An adequate ablation zone covers the tumour with a 5–10 mm margin; on the first follow-up it is a non-enhancing zone larger than the tumour, and nodular enhancement at its edge is residual or recurrent disease.
Orient first
- Radiofrequency and microwave ablation for small HCC, colorectal metastases and small renal masses.
- A thin, smooth peripheral rim of enhancement early after ablation is benign hyperaemia; nodular or growing enhancement is tumour.
- Heat sink from large vessels and adjacency to bowel or bile ducts limit ablation.
Acquire the study
- Multiphase CT: non-contrast, arterial and portal venous phases.
The manoeuvre
- Planning: tumour size in mm, distance to vessels over 3 mm diameter, bowel, gallbladder, diaphragm, collecting system.
- Follow-up: ablation zone size in mm compared with the tumour — margin all round.
- Arterial and portal venous phases: nodular or crescentic enhancement at the edge (residual).
- Complications: haematoma, biloma, abscess, bowel injury, urinoma.
What confirms it
- A non-enhancing ablation zone with a circumferential margin on the first follow-up.
What licenses you to exclude it
- No nodular enhancement at the ablation margin on multiphase follow-up excludes visible residual disease.
The classic misread
- Calling benign peri-ablational hyperaemia residual tumour.
- On MRI, reading T1-bright necrosis as enhancement — confirm with subtraction images.