What are the indications for hemithyroidectomy (partial removal of the thyroid gland) in patients with micro papillary thyroid carcinoma (micro PTC)?

Hemithyroidectomy Indications for Papillary Thyroid Microcarcinoma

Hemithyroidectomy (lobectomy) is appropriate for unifocal papillary microcarcinomas (≤10 mm) with no evidence of extracapsular extension or lymph node metastases, and can be extended to selected low-risk tumors up to 2 cm (T1a-T1b) that are N0 with no extrathyroidal extension. 1

Primary Indications for Hemithyroidectomy in Micro PTC

Absolute Requirements (All Must Be Present)

• Tumor size ≤10 mm for papillary microcarcinoma, though this can extend to tumors ≤4 cm for selected low-risk cases 1, 2, 3
• Unifocal disease (single tumor focus) 1
• No extracapsular/extrathyroidal extension 1, 4
• No lymph node metastases (N0) confirmed by preoperative ultrasound and clinical examination 1, 2
• No distant metastases 2, 3
• No prior radiation exposure to the head and neck 2, 3

Additional Favorable Criteria

• Classical papillary or follicular variant histology (not poorly differentiated) 1, 2
• Intrathyroidal location without invasion of surrounding structures 1
• Low-risk classification by staging systems (T1a-T1b-T2, N0) 1

Alternative to Surgery: Active Surveillance

Active surveillance with ultrasound monitoring every 6-12 months can be proposed as an alternative to immediate surgery for unifocal papillary microcarcinomas ≤10 mm meeting the above criteria. 1, 3

• Progression rates are low: 4.9% enlargement at 5 years, 8.0% at 10 years; novel lymph node metastasis 1.7% at 5 years, 3.8% at 10 years 3
• Critical caveat: Patients younger than 40 years have higher risk of progression and may not be ideal candidates for surveillance 3

When Total Thyroidectomy Is Required Instead

The National Comprehensive Cancer Network mandates total thyroidectomy when any of these factors are present 2:

• Tumor >4 cm in diameter
• Known distant metastases
• Cervical lymph node metastases (even if microPTC)
• Extrathyroidal extension (even minimal extension remains controversial—see below)
• Poorly differentiated histology
• Multifocal disease, particularly if bilateral 5

The Minimal Extrathyroidal Extension Controversy

Recent evidence suggests hemithyroidectomy may be acceptable even with minimal extrathyroidal extension in highly selected cases 4:

• A 2019 study of 255 patients with cN0 PTC ≤2 cm with minimal ETE showed no difference in recurrence rates (3.0% vs 1.5%, p=1.0) or recurrence-free survival between total thyroidectomy and hemithyroidectomy 4
• However, this contradicts the more conservative ESMO guidelines that list extrathyroidal extension as a contraindication to lobectomy 1
• Recommendation: For minimal ETE in tumors ≤1 cm, hemithyroidectomy can be considered; for tumors 11-20 mm with minimal ETE, proceed cautiously and consider patient-specific factors 4

Critical Pitfalls to Avoid

Multifocality Detection

• 22% of patients undergoing total thyroidectomy for presumed unifocal microPTC had multifocal disease, with 14 showing bilobar involvement 5
• Preoperative ultrasound has limited sensitivity for detecting multifocality
• If multifocality is discovered on final pathology after hemithyroidectomy, completion thyroidectomy should be strongly considered 5

Occult Lymph Node Metastases

• MicroPTC presenting with palpable lateral lymphadenopathy (cN1b) occurs in 1.7% of cases and represents aggressive disease requiring total thyroidectomy plus RAI 6
• These patients have 19% biochemical/structural persistence or recurrence rates despite small primary tumor size 6
• Careful preoperative neck ultrasound is mandatory to exclude occult nodal disease 2, 7

Age Considerations

• Younger patients (<40 years) with microPTC paradoxically have higher risk of progression during active surveillance, contrasting with larger PTC where older age predicts worse outcomes 3
• This should influence the decision between surveillance, hemithyroidectomy, or total thyroidectomy in young patients

Post-Hemithyroidectomy Management

No Radioactive Iodine

• RAI is not indicated after hemithyroidectomy for low-risk microPTC 1
• RAI administration is specifically not recommended for small (≤1 cm) intrathyroidal DTC with no locoregional metastases 1

Thyroid Hormone Replacement

• Levothyroxine replacement to maintain TSH in the normal range (not suppressed) 1
• TSH suppression (<0.1 μIU/ml) is reserved for high-risk patients who undergo total thyroidectomy 2, 7

Surveillance Protocol

• Serial thyroglobulin measurements have limited utility after hemithyroidectomy due to remaining thyroid tissue 1
• Neck ultrasound annually is the primary surveillance tool 1
• Monitor for contralateral lobe development: 5.3% risk of developing PTMC in remaining lobe over time 5

Completion Thyroidectomy Indications

If final pathology reveals any of these unexpected findings after hemithyroidectomy 5, 8:

• Multifocal disease, especially bilateral
• Extrathyroidal extension
• Lymph node metastases
• Vascular invasion
• Tumor size actually >4 cm
• Elevated postoperative thyroglobulin levels