Image-Guided Thyroid Ablation: Proposal for Standardization of Terminology and Reporting Criteria

Indications

In all studies, indication(s) for treatment should be reported (e.g., compression symptoms, cosmetic reasons, abnormal thyroid function, other) (21).

Nodule description

Currently, no classification of thyroid nodules according to solid component percentage has been adopted and recognized as standard, and nodule classification might vary among different studies. To provide better uniformity in future studies, it is suggested that a detailed description of the internal structure of each treated nodule should be stated. The following classification is proposed: solid (≤10% of fluid component), predominantly solid (11–50% of fluid component), predominantly cystic (51–90% of fluid component), or cystic (>90% of fluid component). If the cystic portion is aspirated prior the procedure, it should be stated as such. As “spongiform” appearance of nodules has been reported to be correlated with benign nodules, it is proposed that “spongiform nodules” be reported differently from other nodules. Spongiform nodules are defined as those nodules containing multiple small cysts <5 mm interspersed within solid tissue for nearly all the volume (21,31,32).

Nodule size

Nodule volume should be reported in mL using the ellipsoid volume formula: \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*} length \; \times \;width \; \times \;depth \; \times \;0.524 \end{align*} \end{document}

with measures expressed in centimeters, and nodules should also be classified according to their size. In the literature, several different cutoffs have been proposed (13,15,21). To increase uniformity, identifying nodules as small (≤10 mL), medium (11–30 mL), or large (>30 mL) as appropriate is proposed.

Blood tests

Blood tests including at least thyrotropin (TSH) and free thyroxine (fT4) should be performed prior to the procedure. Free triiodothyronine (fT3) should also be performed in case of TSH and fT4 abnormalities. If fT4 and fT3 are not available in a specific setting, total T4 and total T3 can be performed (21).

Finality of treatment

In defining “technical success” for each procedure, it is suggested that authors should define a priori the goal of their treatment, for example to achieve a nodular volume ablation of 50% at a specific time point etcetera, 50% volumetric reduction at one year is proposed as a reasonable threshold for defining technical success. For atonomously functioning thyroid nodules, the technical purpose of treatment should be achieving the largest amount possible of nodule ablation to destroy the largest amount of atonomously functioning thyroid tissue, with a proposed threshold of at least 80% nodule volume destruction to define technical success. In association with such a threshold, it should be pointed out that the ultimate goal of treatment is to achieve satisfactory normalization of thyroid function.

Type of ablation

Image-guided thyroid ablation procedures can be performed using either thermal energy or chemical agents such as ethanol instillation.

Technical success

This term indicates whether the nodule was treated according to the planned protocol. This parameter is important to differentiate nodules that were treated according to a predefined protocol from those where protocol could not be completed due to a specific reason (which should be stated).

Technique efficacy

Distinction between technical success and technique efficacy is essential. Technique efficacy indicates the ability of the treatment to achieve a predetermined clinical result and should be assessed using specific clinical or instrumental parameters.

In the setting of ablation of benign nodules, technique efficacy should be defined as a volumetric reduction ≥50% of the initial nodule volume, that is: \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*} { \frac { { \rm { final \;nodule \;volume } } } { { \rm { initial \;nodule \;volume } } } } \; \times \;100 \end{align*} \end{document}

Technique efficacy should be always related to specific follow-up time points, generally a minimum follow-up of one year is considered optimal. Ideally, long-term follow-up should be reported, with a proposed time interval of one year after the first year.

Primary efficacy rate is defined as the percentage of nodules successfully treated following the initial procedure or at the end of the planned course of treatment. Secondary or assisted efficacy rate includes nodules that have undergone successful retreatment after continued nodule regrowth. Nodule regrowth should be defined as nodule volume increase of ≥50% compared to the minimum recorded volume measured at a given follow-up time point (12,37,38). Although some authors have proposed considering the regrowth of nodule periphery as a marker of recurrence, this parameter may not be easy to assess and standardize with conventional US techniques (37,39,40).

For atonomously functioning nodules, a volumetric reduction of at least 80% of the initial nodule volume is proposed as the preferred target for technique efficacy. In association with volumetric reduction, the ultimate goal of treatment is to achieve satisfactory normalization of thyroid function (24,41 –43).

In general, US is the method of choice for evaluation of nodule volume, while contrast-enhanced US may provide a more precise evaluation of the ablated area immediately after the procedure.

Clinical success

As thyroid ablation is aimed in these cases to treat a benign condition (mainly resulting in compression symptoms or cosmetic concerns), the concept of clinical success is introduced, which should be defined as the ability of treatment to resolve the condition itself. It is recommended classifying clinical success as complete (i.e., complete resolution of presenting symptoms), partial (i.e., symptom improvement but still present), or absent (i.e., no symptom improvement). In addition, a validated visual analogue scale (grade 0–10) may be used to have a semi-quantitative assessment of treatment (21). Cosmetic assessment should be ideally performed on the basis of a four-point scale: 1 = no palpable mass; 2 = palpable mass without cosmetic problems; 3 = cosmetic problems on swallowing only; and 4 = visible mass (21). For atonomously functioning thyroid nodules, clinical success is defined as the normalization of serum thyroid hormones and TSH, and the suspension of oral therapy.

Adverse events related to the procedure

To assess adverse events related to the procedure, a combination of the SIR standardized grading system (44) and Image-Guided Tumor Ablation: Standardization of Terminology and Reporting Criteria—A 10-Year Update (11) is proposed.

Adverse events should be reported on a per session and per patient basis, and their severity should be reported. They should be classified as major complications, minor complications, and side effects. A major complication is regarded as an unexpected event that leads to substantial morbidity and disability, which also increases the level of care. All other unexpected adverse events should be regarded as minor. It is noted that complications may be classified as either major or minor according to their severity. Side effects are those adverse events that are potentially anticipated during or after a procedure and do not result in long-term clinical sequelae. Peri- or post-procedural discomfort and/or pain that is or is not treated with local ice and/or oral NSAIDs and/or painkillers and that does not increase the expected level of care should be considered as a side effect and not as a minor complication. A proposed grading scale for adverse events associated with thyroid thermal ablations is reported in Table 1.

Events should be also differentiated as immediate (0–24 hours), peri-procedural (1–30 days), and delayed (>30 days) (1,11).