Thyroid Nodule with a Bethesda 2 FNA result

The Bethesda System category 2 is called benign, though nodules in this category prove to have cancer 4% of the time. Ongoing management recommendations depend on the clinical scenario especially the ultrasound TiRads score.

Concepts

Not all thyroid nodules that appear suspicious on ultrasound are malignant (cancerous). Not all nodules that appear benign on ultrasound are benign. A needle biopsy result may increase or decrease the likelihood of a nodule being cancerous, but still does not guarantee either the presence or absence of cancer. There is no way to absolutely guarantee that a nodule is benign, other than removing the nodule surgically.

A single benign reading on ultrasound guided fine needle aspirate is about 96% accurate. Still, 4% of nodules assigned Bethesda category 2 (benign) eventually prove to have cancer.

The decision to undergo surgery comes down to risks and benefits. In an effort to avoid unnecessary surgery, criteria for undertaking thyroid surgery are applied. Thyroid nodules suspected to have a roughly 25% or higher chance of cancer merit surgery. Nodules with less than a roughly 25% chance of cancer usually do not meet criteria for surgical removal, except when the size of the nodule causes compression of adjacent structures, an unwanted lump in the neck, or if the nodule were hyperactive (toxic thyroid nodule), or if Graves disease is present.

In order of decreasing accuracy, the indicators of possible malignancy are 1) known spread of thyroid cancer to a site outside of the thyroid gland (such as a lymph node) 2) needle biopsy results, 3) ultrasound characteristics (Ti-Rad system), and 4) growth of a nodule.

high risk Nodules with one benign usgfnab reading:

When a thyroid nodule has an ultrasound Ti-Rads score of 5 (high suspicion for malignancy) and one USGFNAB reading of benign (Bethesda system category 2) cytopathology, the available data are incongruent. In this situation, a repeat thyroid ultrasound and USGFNAB are typically performed in 12 months of the first USGFNAB, largely because of the high false negative rate of Bethesda 2 nodules with suspicious TR5 scores.

• If this second biopsy is also benign, the risk of malignancy is close to zero, and clinical judgment may be used to undertake another thyroid ultrasound in 2 years, to observe without a planned procedure, or in some cases, such as with a nodule ≥ 3 cm diameter, consider surgery.

(This is a strong recommendation with moderate-quality evidence per the 2015 ATA guidelines.)

low to intermediate risk nodules with one benign usgfnab reading:

When a thyroid nodule has a ultrasound Ti-Rads score of 3 or 4 (low to intermediate suspicion for malignancy), and one USGFNAB reading of benign (Bethesda system category 2) cytopathology, a repeat thyroid ultrasound is typically repeated at 12–24 months from the USGFNAB.

• Then, if sonographic evidence of growth (20% increase in at least two nodule dimensions with a minimal increase of 2 mm or more than a 50% change in volume) or development of new suspicious sonographic features, the FNA could be repeated or observation continued with repeat US, with repeat FNA in case of continued growth.

(This is a weak recommendation with low-quality evidence per the 2015 ATA guidelines.)

Low and Very low risk nodules with one benign USGFNAB reading:

When a thyroid nodule has a ultrasound Ti-Rads score of 1 or 2 (very low or low suspicion for malignancy), and one USGFNAB reading of benign (Bethesda system category 2) cytopathology, the utility of surveillance US and assessment of nodule growth as an indicator for repeat FNA to detect a missed malignancy is limited. If thyroid ultrasound is repeated, it would typically be done after 24 months.

(This is a weak recommendation with low-quality evidence per the 2015 ATA guidelines.)