The Diagnostic Performance of Thyroid Multimodal- imaging Comprehensive Risk Stratification Scoring (TMC-RSS) In Characterizing Thyroid Nodules.

Thyroid nodules are a common finding in the general population, and their detection is

increasing with the widespread use of ultrasound (US). The prevalence of thyroid

nodularity varies from 19% to 67%, and increases with age, affecting about 50% of the

population older than 40 years of age. The clinical significance of thyroid nodules relates to

the need to exclude thyroid cancer, which is found in 5–15% of cases, depending on sex,

age, and exposure to other risk factors. The incidence of thyroid cancer has increased about

fivefold in the last 50 years, mostly due to small papillary thyroid cancers, the most

indolent form of thyroid cancer.

Sonographic patterns such as hypoechogenicity, blurred or spiculated margins, spot

microcalcification, and intranodular vascularity are characteristics of malignant nodules,

but they yield a wide range of sensitivities (55–95%) and specificities (52–81%) for

diagnosis as malignant or benign. However, there is no information about the probability of

the US features associated with malignancy and which combination would be more

clinically useful. Diagnostic sensitivity ranges from 26.5% to 87.1% for hypoechogenicity,

54.3% to 74.3% for intranodular vascularity, and 26.1% to 59.1% for microcalcifications,

whereas specificity ranges from 43.4% to 94.3%, 78.6% to 80.8%, and 85.8% to 95%,

respectively

Fine-needle aspiration cytology (FNAC) is a standard method for triaging thyroid nodules

to surgery or clinical follow-up, and, with FNAC, the number of unnecessary surgeries has

decreased. The main limitation of FNAC, however, is nondiagnostic or unsatisfactory

results. According to the Bethesda System for Reporting Thyroid Cytopathology, a sample

is considered nondiagnostic or unsatisfactory when the specimen shows obscuring blood,

overlying thick smears, air drying of alcohol-fixed smears, or an inadequate number of

follicular cells. According to the Bethesda system, nondiagnostic results should ideally be

limited to less than 10% of all thyroid FNACs, but the rates of nondiagnostic results are

reported to be as high as 21%. Some authors have demonstrated that the best option for

reducing nondiagnostic results is on-site cytologic assessment. However, even with on-site

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assessment by cytopathologists, the prevalence of nondiagnostic results has still been

reported to be 10.7%.

Cytologic examination of thyroid nodules by FNA is diagnostic method for differentiating

benign from malignant nodules with reported sensitivity to be 60–98% and specificity,

54–90%. The risk of malignancy in a nodule reported as malignant or suspicious for

malignancy at FNAC is 97%–99% and 60%–75%, respectively. The accuracy of US-guided

FNAC (68%) is higher than that of palpation-guided FNAC (48%)

The main diagnostic method used is invasive FNA and

– 30% of FNA samples from thyroid nodules are not conclusive,

• 10–15% of FNA samples yielding non-diagnostic results

• 10–20% yielding indeterminate results.

– 5% false-negative rate

The thyroid imaging reporting and data system (TIRADS) developed by Kwak et al can help

stratify thyroid nodules according to malignancy risk by using the number of suspicious

ultrasonography (US) features such as solidity, hypoechogenicity or marked

hypoechogenicity, microlobulated or irregular margins, microcalcifications, and taller-

than-wide shape. TIRADS can help accurately predict malignancy and can be easily applied

in clinical practice owing to its simplicity. However, this reporting system has not been

applied to thyroid nodules with nondiagnostic results at cytologic examination, even when

it can be used in the continuous risk stratification of nodules in this category after FNAC.