From the Guidelines
Bethesda IV classification for fine needle aspiration biopsy (FNAB) of a thyroid mass indicates a "Follicular Neoplasm or Suspicious for Follicular Neoplasm" result, which carries an estimated risk of malignancy of 15%–40% and generally requires surgical intervention, typically a diagnostic hemithyroidectomy or lobectomy, for definitive diagnosis. The management approach for Bethesda IV thyroid nodules, as suggested by the NCCN guidelines insights: thyroid carcinoma, version 2.2018 1, involves considering lobectomy for definitive diagnosis/treatment, especially when molecular diagnostics indicate a suggestive of malignancy. Some key points to consider in the management of Bethesda IV thyroid nodules include:
- The diagnosis of follicular carcinoma or Hürthle cell carcinoma requires evidence of either vascular or capsular invasion, which cannot be determined by FNA, hence the need for surgical intervention 1.
- Molecular diagnostics may be useful to allow reclassification of follicular lesions as either more or less likely to be benign or malignant based on the genetic profile, but should be interpreted with caution and in the context of clinical, radiographic, and cytologic features of each individual patient 1.
- Clinical factors such as nodule size, patient age, imaging features, and molecular testing results may influence the urgency and extent of surgical management.
- Regular follow-up is essential regardless of the management approach chosen, and patients should be counseled that approximately 70-85% of Bethesda IV nodules ultimately prove benign after surgical pathology, but the significant malignancy risk necessitates tissue diagnosis. It's also important to note that molecular diagnostics are not recommended for Hürthle cell neoplasm, as they may not perform well for these types of neoplasms, and clinical risk factors, sonographic patterns, and patient preference can help determine whether active surveillance or lobectomy is appropriate 1.
From the Research
Bethesda IV Classification
- The Bethesda IV classification is part of the Bethesda System for Reporting Thyroid Cytopathology, which provides standardized reporting and cytomorphological criteria for thyroid fine needle aspiration biopsy (FNAB) results 2.
- This classification is used to guide the management of thyroid nodules and to predict the risk of malignancy 3.
- The Bethesda IV category is specifically defined as "follicular neoplasm/suspicious for follicular neoplasm" (FN/SFN) 2, 4.
Malignancy Rates
- The malignancy rates for Bethesda IV category have been reported to vary in different studies, ranging from 15.3% to 33.3% 2, 4.
- A study found that the malignancy rate for Bethesda IV category was 20.7% 2.
- Another study reported a malignancy rate of 15.3% for the same category 4.
Clinical Implications
- The Bethesda IV classification has important clinical implications, as it can help guide the management of thyroid nodules and predict the risk of malignancy 3, 5.
- The use of the Bethesda System, including the Bethesda IV category, has been shown to result in a lower rate of surgery for nonmalignant nodules 5.
- However, the system is not perfect, and discrepancies between cytological and histological data can occur, highlighting the need for further evaluation and study 5, 6.