Rationale and Objectives
Thyroid nodules are common on ultrasonographic examination and are mostly benign. Ultrasound characteristics may help discriminate thyroid carcinoma (TC) from benign nodules. The aims of this study were to identify ultrasonographic characteristics associated with TC and to validate a previously proposed model based on the presence of three ultrasonographic characteristics.
Materials and Methods
From a protocolized prospective registry of 1108 fine needle aspiration biopsies performed during a 16-month period at an ambulatory center, the ultrasonographic characteristics of TC and non-TC biopsies were compared. Adjusted odds ratios (ORs) and likelihood ratios for TC were estimated for eight combinations of three previously identified characteristics (microcalcifications, hypoechogenicity, and irregular borders).
Results
Microcalcifications (OR, 6.6; 95% confidence interval [CI], 4.4–9.9), hypoechogenicity (OR, 4.7; 95% CI, 2.8–8.0), and irregular borders (OR, 4.3; 95% CI, 2.8–6.5) were independently associated with TC. When added to a logistic regression model, the three ultrasonographic characteristics remained statistically significant. In the absence of these three features, the likelihood ratio for TC was 0.1 (95% CI, 0.0–0.2), while in their simultaneous presence, the likelihood ratio was 11 (95% CI, 6.6–19.0).
Conclusions
The absence or simultaneous presence of three simple ultrasonographic characteristics generates a large change of pretest probability of TC and could avoid unnecessary fine needle aspiration biopsy.
Thyroid nodules are highly prevalent in adult population, found in up to 70% on routine ultrasound examination . After considering some clinical and ultrasonographic characteristics, their assessment includes determination of thyrotropin-stimulating hormone concentration and, in the absence of hyperthyroidism, a fine needle aspiration biopsy (FNAB), whose results are benign in 93% to 95% of patients . This procedure is considered safe and inexpensive and has proven to reduce the number of unnecessary thyroidectomies . However, it is considered a moderately invasive technique, with a rate of unsatisfactory samples hovering around 10%, a number that is high considering that its purpose is to identify an uncommon disease such as thyroid carcinoma (TC) (present in about 5%–10% of patients who undergo this procedure) . Considering the high rate of unnecessary biopsies, and to focus the cytologic study in patients with higher risk for cancer, several groups have investigated the ultrasound characteristics associated with TC and developed predictive models to guide the clinical decision-making process .
Thyroid ultrasound examination describes nodules according to their size, structure, shape, echogenicity, borders, pattern of blood flow (Doppler), presence of calcifications, halo, local invasion, and abnormal lymph nodes . Several of these characteristics have been associated with TC, with heterogeneous results. In a previous investigation, we proposed a discriminatory model for TC diagnosis on the basis of data obtained from historical records, in which microcalcifications (odds ratio [OR], 28.1), hypoechogenicity (OR, 9.4), and irregular borders (OR, 4.7) were independently and significantly associated with TC. This model had high discriminatory capacity both to rule out TC in the absence of these three ultrasonographic characteristics and to suggest TC diagnosis when they present simultaneously . Nevertheless, because data were collected retrospectively, there is considerable risk for bias, which threatens the validity of the model.
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Materials and methods
Ultrasound Evaluation
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Histopathologic Diagnosis
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Statistical Analysis
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Results
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Table 1
Univariate Association Between Ultrasonographic Characteristics and Thyroid Cancer
Ultrasound Characteristic OR (95% CI) Sensitivity (%) Specificity (%) LR (95% CI) Microcalcifications 6.6 (4.4–9.9) 52 86 3.73 (2.9–4.7) Hypoechogenicity 4.7 (2.8–8.0) 86 43 1.5 (1.4–1.7) Irregular borders 4.3 (2.8–6.5) 39 87 3.0 (2.3–4.0) Abnormal lymph node 6.1 (2.3–16.1) 7 99 5.8 (2.2–15.0) Solid predominance 3.4 (1.9–6.1) 89 30 1.3 (1.1–1.4) Absence of hypoechogenic halo 1.8 (1.2–2.8) 77 35 1.2 (1.0–1.3) Central vascularization 1.6 (1.0–2.6) 21 86 1.5 (1.0–2.2)
CI, confidence interval; LR, likelihood ratio; OR, odds ratio.
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Table 2
LR of Thyroid Cancer According to the Presence of the Included Ultrasonographic Characteristics
Microcalcifications Hypoechogenicity Irregular Borders Sample Probability of TC LR (95% CI) No No No 1.7% 0.1 (0.0–0.2) No No Yes 11.1% 0.8 (0.2–2.7) No Yes No 9.9% 0. 7 (0.6–0.9) Yes No No 20.6% 1.8 (1.0–3.1) No Yes Yes 22.9% 2.0 (0.9–4.3) Yes No Yes 6.7% 0.5 (0.0–3.6) Yes Yes No 30.1% 2.9 (1.8–4.6) Yes Yes Yes 62.7% 11.0 (6.6–19.0)
CI, confidence interval; LR, likelihood ratio; TC, thyroid cancer.
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Discussion
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Conclusions
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Acknowledgments
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