Diagnostics: Bethesda classification system for assessing cancer risk of a thyroid nodule by fine needle biopsy

What is The Bethesda system?

The Bethesda classification system is a standardized system used to categorize the results of fine needle aspiration (FNA) biopsies of the thyroid gland. Developed initially in 2007 during a conference at the National Cancer Institute in Bethesda, Maryland, it estimates risk of a thyroid nodule being malignant and is used to make treatment recommendations.

The most recently updated Bethesda system (2023) categorizes thyroid FNA results into six diagnostic categories:

1. Non-diagnostic/Unsatisfactory: Samples in this category are inadequate for evaluation and may require repeat FNA or different diagnostic approaches. A Bethesda category 1, Non-diagnostic score does not indicate the likelihood of cancer—it only indicates that no information is available from the fine needle biopsy.

2. Benign: Specimens meeting criteria for this category demonstrate normal thyroid cells. Routine monitoring is often undertaken for these nodules.

3. Atypia of Undetermined Significance (AUS): Samples in this category show some abnormal cells, but it is unclear whether these indicate a benign or malignant process. Further evaluation or repeat FNA may be recommended.

4. Follicular Neoplasm / Suspicious for Follicular Neoplasm: This category indicates the presence of follicular cells that may suggest a neoplasm, which could either be benign or malignant. Surgical evaluation is usually warranted for a definitive diagnosis, but molecular testing or observation before deciding on surgical management may be used carefully in some cases.

5. Suspicious for Malignancy: This classification suggests a significant concern for thyroid cancer, though it is not definitive. Patients typically undergo surgical intervention for further assessment.

6. Malignant: This category is reserved for samples that clearly exhibit cancerous cells. Immediate management typically includes surgical treatment.

The Bethesda classification system enhances the management of thyroid nodules by providing a framework for assessing the likelihood of cancer and guiding clinical decision-making. It aids in stratifying the risk, which facilitates appropriate surveillance or treatment strategies for patients. Note that the Bethesda categories 3, 5, and 6 do not indicate which type of thyroid cancer is suspected or diagnosed, but the pathologist may comment on a specific type of thyroid cancer suspected in their report.