What is the clinical significance of the thyroid ultrasound findings, which include a homogeneous isthmus, heterogeneous right and left lobes with multiple complex nodules, and varying echogenicity and vascularity?

From the Guidelines

The patient should undergo a fine needle aspiration (FNA) biopsy of the largest nodule (0.84 cm in the right lower pole) to rule out malignancy, given the moderately suspicious ultrasound findings and the presence of complex features in the nodules. The ultrasound findings show multiple nodules in both thyroid lobes, all classified as TR 3 (moderately suspicious). The right lobe is extremely heterogeneous with three complex nodules: a lower pole nodule (0.84 x 0.52 x 0.29 cm), a midpole vascular nodule (0.4 x 0.4 x 0.3 cm), and another midpole hypoechoic nodule (0.49 x 0.41 x 0.18 cm). The left lobe is heterogeneous with one solid hyperechoic vascular nodule (0.39 x 0.31 x 0.25 cm) in the upper pole. According to the most recent guidelines, as stated in 1, the management of "small" thyroid nodules is challenging due to the lack of uniformity and standardization among recommendations. However, given the complex features of the nodules, an FNA biopsy is warranted to assess the risk of malignancy.

Some key points to consider in the management of these nodules include:

• The size of the nodule alone is not a reliable indicator of malignancy, as stated in 1
• The ultrasound pattern of a thyroid nodule is crucial for assessing the risk of malignancy, as stated in 1
• Fine needle aspiration cytology (FNAC) is an important technique used along with US for the diagnosis of thyroid nodules, as stated in 1
• The results of FNAC are very sensitive for the differential diagnosis of benign and malignant nodules, although there are limitations, such as inadequate samples and follicular neoplasia, as stated in 1

Following the biopsy, regular monitoring with repeat ultrasounds every 6-12 months would be appropriate to assess for any changes in size or characteristics of the remaining nodules, as stated in the example answer. Thyroid function tests should also be performed to determine if the nodules are affecting thyroid hormone production. The overall rate of thyroid cancer in patients with thyroid nodules is less than 3%–5%, as stated in 1, but given the complex features of the nodules in this patient, further evaluation is necessary to rule out malignancy.

From the Research

Thyroid Nodule Findings

• The isthmus measures 0.21 cm with no nodules seen.
• The right lobe is extremely heterogeneous, measuring 2.74 x 1.32 x 0.60 cm with a volume of 1.03 ml.
• The right lobe contains three nodules:
  • A lower pole complex heterogeneous nodule measuring 0.84 x 0.52 x 0.29 cm, TR 3.
  • A midpole complex heterogeneous vascular nodule measuring 0.4 x 0.4 x 0.3 cm, TR 3.
  • A third nodule measuring 0.49 x 0.41 x 0.18 cm, noted as a complex hypoechoic nodule, TR 3.
• The left lobe is heterogeneous and nodular, measuring 2.61 x 0.57 x 1.27 cm.
• The left lobe contains an upper pole solid hyperechoic vascular nodule measuring 0.39 x 0.31 x 0.25 cm, TR 3.

Diagnostic Considerations

• According to 2, thyroid nodules with initial benign US and cytologic results may still develop suspiciously malignant US features after fine needle aspiration biopsy (FNAB).
• The study by 3 suggests that thyroid nodules ≥4 cm require a diagnostic lobectomy regardless of their benign fine needle aspiration results, due to the high false-negative rate of FNAB in large nodules.
• 4 emphasizes the importance of a standardized technique for US-guided FNAB to increase diagnostic results and lower the yield of nondiagnostic specimens and false-negative results.
• The diagnostic performance of US-based FNAB criteria varies according to individual international society guidelines, as shown in 5.
• 6 found that US-FNAB has similar diagnostic efficacy for thyroid nodules of different sizes, with no significant differences in accuracy, sensitivity, specificity, false positive accuracy, and false negative rate.