- Guidelines ask for two matching benign biopsies before an ablation, and a single one is enough in very few specific cases.
- In a Korean series, 7 of 148 nodules treated as benign turned out to be cancer, and six of them had two previous biopsies.
- Malignant nodules shrink much less with ablation, so a cancer that had gone unnoticed does show up in follow-up, later than anyone would want.
Radiofrequency ablation does not remove the nodule: it heats it from the inside and lets the body reabsorb it. That is why no tissue is obtained for the pathologist afterwards, as it is in surgery. Whatever is known about the nodule has to be known before treatment, and that is where the rule comes from.
What the guidelines say
And the result has to be Category II of the Bethesda system: a benign result. It is the most frequent and the one that allows treatment without surgery., that is, benign. Indeterminate results, categories III and IV, are not treated this way as first line: no society endorses it outside a research study.
The study that justifies it
A group at Samsung hospital in Seoul reviewed 148 nodules that had been ablated with confirmed benignity. Seven turned out to be cancer, 4.7 %. The unsettling part is not the figure: it is that six of those seven had two previous benign punctures. Fine-needle biopsy, when the nodule is large, takes a small sample of a large nodule, and it can fail to reach the malignant area.
- 4.7 %of 148 nodules ablated as benign turned out to be malignant. Six of the seven had two fine-needle biopsies.Kim MK, Shin JH, Hahn SY, Kim H. Korean J Radiol. 2023, 24(9): 903-911.
- 51 %is how much the malignant ones shrank at 12 months, versus 84 % for the benign ones. Cancer responds less, and that weaker response is what reveals it.Same series. Median volume reduction at one year.
Fine needle or core needle
Fine-needle aspiration: cells are aspirated from the nodule with a very thin needle, guided by ultrasound. aspirates cells with a very fine needle, and core needle biopsy obtains a small cylinder of tissue, which the pathologist can study with its full architecture. The authors of that series recommend core needle, instead of fine needle, in large, symptomatic nodules, which are precisely the ones most often ablated. At the evaluation you are advised which one is needed in your case and whether the one you already have can count as one of the two.
What to do with the biopsy you already have
- 01It is reviewed together with its full reportThe Bethesda category, the type of needle and the date matter. A benign biopsy from another center is reviewed, not discarded.
- 02Whether a second one is needed is decidedAnd of which type. In a large nodule, the second is usually a core needle biopsy, guided by ultrasound.
- 03With both in hand, the plan is madeOnly then are dates discussed.
- Kim JH et al. 2017 Thyroid Radiofrequency Ablation Guideline: Korean Society of Thyroid Radiology. Korean J Radiol. 2018, 19(4): 632-655.
- Kim MK, Shin JH, Hahn SY, Kim H. Korean J Radiol. 2023, 24(9): 903-911.
- Noel JE et al. Ann Thyroid. 2022, 7: 7.
