What is the recommended management for a 1.9x1.1x1.4 cm TIRADS (Thyroid Imaging Reporting and Data System) 4 thyroid lesion, wider than tall on Ultrasound (USG), with a diagnosis of Hurtle Cell Adenoma on Fine Needle Aspiration Cytology (FNAC)?

Management of Hürthle Cell Adenoma on FNAC

For this 1.9 cm TIRADS 4 thyroid nodule with Hürthle cell adenoma on FNAC, diagnostic thyroid lobectomy is the recommended approach, as cytology cannot reliably distinguish benign Hürthle cell adenoma from carcinoma, and molecular testing performs poorly for Hürthle cell neoplasms. 1

Why Surgery is Necessary

Hürthle cell lesions require histopathologic examination to definitively distinguish adenoma from carcinoma, as the diagnosis of malignancy requires evidence of capsular or vascular invasion that cannot be determined by FNA alone. 1, 2, 3

• Fine needle aspiration cytology has poor specificity (19.3%) for detecting malignancy in Hürthle cell tumors, with a positive predictive value of only 18.6%. 3
• The presence of Hürthle cells on cytology does not reliably predict malignancy in most Bethesda categories. 4
• Molecular diagnostics are specifically not recommended for Hürthle cell neoplasms, as they do not perform well in this context. 1

Surgical Approach

Thyroid lobectomy (hemithyroidectomy) is the appropriate initial surgical procedure for a unilateral Hürthle cell neoplasm diagnosed on FNA. 1, 2, 3

• Clinical risk factors, sonographic patterns, and patient preference should guide the decision between active surveillance and lobectomy. 1
• Given your nodule size of 1.9 cm and TIRADS 4 classification, lobectomy is more appropriate than surveillance. 1
• If final histopathology demonstrates capsular or vascular invasion confirming Hürthle cell carcinoma, completion thyroidectomy should be performed. 2, 3, 5

Key Clinical Factors

Several features help assess risk, though they cannot definitively predict malignancy preoperatively:

• Tumor size >4 cm is associated with higher malignancy risk (57% vs 20% for tumors <4 cm). 2
• Your nodule at 1.9 cm falls well below this threshold, suggesting lower malignancy probability.
• Male gender is associated with higher rates of Hürthle cell carcinoma (75% vs 29% in females). 2
• The "wider than tall" ultrasound feature is generally reassuring and associated with benign lesions in most thyroid nodules. 6

Why Not Active Surveillance?

Active surveillance is not appropriate for Hürthle cell neoplasms because:

• The nodule size (1.9 cm) exceeds the typical threshold for surveillance of thyroid nodules (<1 cm). 1
• TIRADS 4 classification indicates moderate-to-high suspicion requiring tissue diagnosis. 1
• Molecular testing cannot reliably reclassify Hürthle cell lesions as low-risk, unlike other follicular lesions. 1

Expected Outcomes

Unilateral lobectomy for Hürthle cell adenoma has excellent outcomes with minimal morbidity:

• No recurrence of Hürthle cell adenomas has been reported after appropriate lobectomy. 2, 3
• Operative morbidity is low (3.8%), including transient recurrent laryngeal nerve palsy (rare), and transient hypocalcemia (rare with lobectomy). 3
• If histology confirms adenoma without capsular or vascular invasion, no further surgery is needed. 2, 3

Common Pitfalls to Avoid

• Do not rely on FNA cytology alone to rule out malignancy in Hürthle cell neoplasms—histologic confirmation is mandatory. 1, 3
• Do not order molecular testing (e.g., Afirma, ThyroSeq) for Hürthle cell lesions, as these tests are unreliable in this context. 1
• Do not perform total thyroidectomy initially unless bilateral disease or confirmed carcinoma is present, as lobectomy is adequate for unilateral adenoma. 2, 3
• Be aware that frozen section has limited sensitivity (40%) for detecting malignancy in Hürthle cell tumors, so definitive histopathology is required. 3