- Category II, benign, is the most common result, and its cancer risk is about 4%, according to the 2023 edition of the system.
- Categories III and IV are indeterminate: they neither confirm nor rule out cancer, so there are several options to weigh before deciding.
- Categories V and VI point to cancer with high probability, and the conversation turns to treatment.
How to read the report
In the pathology report, the category usually appears at the end, on the diagnosis line, written as a Roman numeral with its name: for example, “Bethesda II, benign”. That result, together with the The system the radiologist uses to classify a nodule by its appearance on ultrasound, from TR1 to TR5, according to how many suspicious features it has. score from the ultrasound and the size of the nodule, is what guides the next step.
The six categories
For each category, this is what it means, the average cancer risk published in the 2023 edition of the system and the step that usually follows.
- I · Nondiagnostic. The sample did not have enough cells to give a result. Cancer risk per Bethesda 2023: 13%. The usual step is to repeat the ultrasound-guided biopsy.
- II · Benign. The cells come from a benign nodule. Cancer risk per Bethesda 2023: 4%. The nodule is followed clinically and with ultrasound.
- III · Atypia of undetermined significance. Some cells show a change that is not enough for a diagnosis. Cancer risk per Bethesda 2023: 22%. The options are a repeat biopsy, a An analysis of the genetic material of the biopsy cells that helps estimate the risk in indeterminate results., a diagnostic surgery or monitoring.
- IV · Follicular neoplasm. The cells suggest a follicular tumor, which can be benign or malignant. Cancer risk per Bethesda 2023: 30%. The usual step is a molecular test or a diagnostic surgery.
- V · Suspicious for malignancy. The cells suggest cancer without fully confirming it. Cancer risk per Bethesda 2023: 74%. The usual step is a molecular test or surgery.
- VI · Malignant. The cells are cancer cells. Cancer risk per Bethesda 2023: 97%. The usual treatment is surgery.
The indeterminate categories: III and IV
These raise the most questions, because the pathologist cannot reach a decision from what is seen under the microscope. There is no single right answer in these cases, and the decision is made with the ultrasound report, the size of the nodule, the patient's history and their preferences.
- 01Repeat the biopsyA second sample, also guided by ultrasound, sometimes clarifies the category.
- 02A molecular testIt analyzes the genetic material of the cells to estimate the risk more precisely.
- 03Remove half of the thyroidThis allows the whole nodule to be examined and a diagnosis to be reached.
- 04Monitor with ultrasoundIn selected cases, the nodule is followed closely without intervening.
If the result is benign
A Bethesda II result does not call for treatment. The nodule is monitored with ultrasound, and treatment is only considered if it causes trouble swallowing, pressure in the neck or a cosmetic concern, or if it grows. In those cases, radiofrequency ablation can treat it without surgery, and the guidelines ask for two benign biopsies first, or a single one when the ultrasound shows features that are highly typical of a benign nodule.
Bethesda and TIRADS are read together
The ultrasound classifies the nodule by its appearance, with the TIRADS system, and the biopsy classifies it by its cells, with the Bethesda system. Neither decides alone: a nodule that looks low-risk with a benign biopsy can be monitored with confidence, while one that looks highly suspicious on ultrasound with a benign biopsy sometimes warrants a second biopsy.
- Ali SZ, Baloch ZW, Cochand-Priollet B, Schmitt FC, Vielh P, VanderLaan PA. The 2023 Bethesda System for Reporting Thyroid Cytopathology. Thyroid. 2023, 33(9): 1039-1044.
- Kim JH et al. 2017 Thyroid Radiofrequency Ablation Guideline: Korean Society of Thyroid Radiology. Korean J Radiol. 2018, 19(4): 632-655.
