Bethesda Category II Thyroid Nodules Are Not Malignant
Both the left and right thyroid nodules classified as Bethesda Category II are benign and do not require surgical intervention. The malignancy risk for Bethesda II nodules is extremely low at 1-3%, and surveillance rather than surgery is the standard of care 1, 2.
Understanding Bethesda Category II Classification
Bethesda Category II represents cytologically benign nodules, including colloid nodules, hyperplastic nodules, nodular goiter, and Hashimoto's thyroiditis 1.
The diagnostic accuracy of Bethesda II classification approaches 95%, making it highly reliable for ruling out malignancy 2.
Your specific findings are classic for benign disease: the left nodule shows follicular cells in macro and microfollicles (hyperplastic nodule), while the right nodule shows abundant colloid with few follicular cells (colloid nodule) 1.
Actual Malignancy Risk in Bethesda II Nodules
The false-negative rate for Bethesda II is approximately 1-3% based on large institutional series 2, 3.
Recent surgical series confirm this low risk: one study of 522 patients with Bethesda II nodules who underwent thyroidectomy found incidental malignancy in only 1.53% (8/522 cases) 4.
Another study of 1716 initially benign nodules found malignancy rates of 3.2% pre-Bethesda and 2.6% post-Bethesda, with no significant difference between periods 3.
Even when malignancy is found in Bethesda II nodules, it is typically low-risk disease: the vast majority are papillary thyroid microcarcinomas or follicular variant papillary carcinomas with favorable prognosis 5.
Recommended Management Algorithm
For your Bethesda II nodules, follow this approach 2:
Measure TSH levels to assess thyroid function and rule out autonomous nodules 6.
Perform baseline high-resolution ultrasound to document nodule characteristics and assess for any suspicious features that may have been missed 2.
Schedule repeat ultrasound at 12-24 months to monitor for interval growth or development of suspicious features 2.
Monitor for compressive symptoms including dysphagia, dyspnea, or voice changes 2.
Avoid immediate surgery unless specific indications are present (see below) 2.
When Surgery Might Be Considered Despite Benign Cytology
Surgery for Bethesda II nodules is only appropriate when 2:
Compressive symptoms are present and clearly attributable to the nodule (dysphagia, dyspnea, voice changes) 2.
Large nodules >4 cm due to increased false-negative rate and higher risk of compressive symptoms 2.
Cosmetic concerns are significant and patient-driven 2.
Worrisome clinical findings persist despite reassuring cytology, as false-negative results can occur in up to 11-33% of cases with concerning clinical features 1, 2.
Critical Pitfalls to Avoid
Do not override benign cytology based solely on nodule size: studies show no positive linear correlation between nodule size and malignancy rate in Bethesda II nodules 7.
Molecular testing is generally not indicated for Bethesda II nodules, as the pretest probability of malignancy is so low (1-3%) that molecular markers add minimal clinical value 2.
Do not proceed to immediate surgery without specific indications, as this leads to overdiagnosis and overtreatment of clinically insignificant disease 2.
A reassuring FNA should not be completely dismissed if highly suspicious ultrasound features are present (microcalcifications, irregular margins, marked hypoechogenicity, central hypervascularity), as false-negative results do occur 1, 2.
The Caveat About False Negatives
The pathology report correctly notes that false positives and negatives occur in all cytologic procedures 1.
However, the false-negative rate for Bethesda II is only 1-3%, which does not justify routine surgical confirmation 2, 3, 4.
Tissue biopsy confirmation is only recommended "if clinically indicated", meaning when specific concerning features are present (compressive symptoms, suspicious ultrasound features, rapid growth, worrisome clinical context) 1, 2.
Surveillance Strategy
For your specific case with bilateral Bethesda II nodules 2:
Initial ultrasound at 12-24 months to establish stability 2.
If stable, continue surveillance ultrasound every 12-24 months for at least 3-5 years 2.
Discontinue surveillance if nodules remain stable and no new concerning features develop 2.
Repeat FNA only if nodules show significant growth (>20% increase in two dimensions with minimum 2mm increase) or develop new suspicious ultrasound features 2.