Microwave Thermal Ablation for Thyroid Nodules: 2025 Update

Direct Recommendation

Microwave ablation (MWA) is now an established treatment option for benign thyroid nodules ≥2 cm causing symptoms, cosmetic concerns, or progressive growth, and represents an alternative to surgery for select patients with recurrent papillary thyroid carcinoma or metastatic lymph nodes when surgery is not feasible. 1

Patient Selection Criteria

Benign Thyroid Nodules - Primary Indications

All patients must undergo fine-needle aspiration biopsy (FNAB) twice, or FNAB combined with core needle biopsy (CNB), to confirm benign pathology before thermal ablation. 1 This is a mandatory prerequisite—thermal ablation should never be performed without cytological or histological confirmation. 1

MWA is indicated for benign nodules meeting any of the following criteria: 1

Nodules ≥2 cm with progressive growth documented on serial ultrasound
Symptomatic nodules causing compression (dysphagia, dyspnea, globus sensation)
Cosmetic concerns causing patient distress
Autonomously functioning thyroid nodules (toxic adenomas)
Recurrent nodules after chemical (ethanol) ablation

Critical technical specification: MWA is appropriate for solid nodules or cystic nodules with ≥10% solid composition. 1 For predominantly cystic nodules (<10% solid component), chemical ablation with ethanol remains the preferred approach. 1

Malignant Disease - Limited Indications

MWA is an optional treatment for: 1

Recurrent papillary thyroid carcinoma (PTC) in patients who refuse or cannot tolerate repeat surgery
Metastatic cervical lymph nodes with limited number of lesions
Patients with contraindications to surgery who have biopsy-proven low-risk PTC

Absolute contraindications for malignant disease: 1

Diffuse sclerosing papillary carcinoma
Any pathologic type other than PTC (follicular, medullary, anaplastic, poorly differentiated)

Absolute Contraindications

The following are absolute contraindications to MWA regardless of nodule characteristics: 1

Severe bleeding tendency (uncorrected coagulopathy)
Severe cardiopulmonary insufficiency or inability to tolerate the procedure
Contralateral vocal cord paralysis (ablation-related nerve injury would result in bilateral paralysis)
Pregnancy and lactation (relative contraindication—proceed with extreme caution only if absolutely necessary)

Technical Approach and Equipment

Microwave Technology Advantages

MWA operates at 902-928 MHz wavelength and offers several advantages over radiofrequency ablation (RFA): 2

Higher intratumoral temperatures achieved more rapidly
Less susceptibility to heat sink effect from adjacent blood vessels
Larger ablation zones per application
Better penetration through cystic or calcified tissue

Internally cooled microwave systems are now standard, reducing collateral thermal injury while maintaining ablation efficacy. 3

Energy Requirements by Nodule Type

Energy transmission must be adjusted based on nodule composition: 4

Solid nodules: 2.30 ± 1.5 kJ/ml (range: 0.9-4.6 kJ/ml)
Complex (mixed solid-cystic) nodules: 1.5 ± 0.9 kJ/ml (range: 0.4-3.6 kJ/ml)
Predominantly cystic nodules: 0.75 ± 0.25 kJ/ml (range: 0.4-1.2 kJ/ml)

Solid nodules require significantly more energy than cystic nodules (p<0.03). 4 Underestimating energy requirements leads to incomplete ablation and early recurrence, while overtreatment increases complication risk. 4

Procedural Technique

Anesthesia: Local anesthesia with 1-2% lidocaine via isthmus or lateral neck approach. 5 General anesthesia is rarely required. 6

Needle insertion approach: 5, 6

Trans-isthmic approach (preferred for anterior nodules)
Lateral neck approach (for laterally positioned nodules)
Real-time ultrasound guidance throughout the procedure

Protective maneuvers: 6

Hydrodissection with saline or 5% dextrose to displace critical structures (recurrent laryngeal nerve, esophagus, trachea, carotid artery)
"Moving-shot technique" for large nodules to ensure complete ablation
Continuous visualization of the ablation zone margin

Expected Outcomes and Efficacy

Volume Reduction

MWA achieves significant volume reduction at 3 months: 4

Mean volume reduction: 12.4 ± 13.0 ml (range: 1.5-63.2 ml)
Mean relative reduction: 52 ± 16% (range: 22-77%)
Strong correlation between transmitted energy and volume reduction (r=0.82, p<0.05)

Volume reduction rate (VRR) is the primary efficacy endpoint and should be monitored at 1,3,6, and 12 months post-ablation. 5

Biochemical Response

Periablative efficacy can be assessed within 24 hours: 3

Serum thyroglobulin (Tg) increases significantly post-ablation (mean increase: 4495 ng/ml, p<0.05) 3
This acute Tg elevation reflects successful tissue destruction
Ultrasound changes at 24 hours: decreased blood flow, decreased echogenicity, increased elasticity (all p<0.05) 3

Functional Imaging Verification

99mTc-pertechnetate and 99mTc-MIBI scintigraphy can verify ablation effectiveness: 2

Center-specific functional imaging score (CSFIS) decreased by 1.4 points on average
66.7% of nodules showed 1-point decrease, 27.8% showed 2-point decrease, 5.6% showed 3-point decrease
Functional imaging provides early verification of treatment success 2

Post-Procedure Monitoring

Immediate Post-Ablation Assessment

Contrast-enhanced ultrasound (CEUS) is the gold standard for confirming complete ablation immediately after the procedure. 5 Non-enhancing areas indicate successful ablation, while residual enhancement indicates viable tissue requiring additional treatment.

Follow-Up Protocol

Structured follow-up schedule: 5

24 hours: Ultrasound to assess for hematoma, measure serum Tg
1 month: Ultrasound to assess early volume reduction
3 months: Ultrasound with VRR calculation, CEUS if available
6 months: Ultrasound with VRR calculation
12 months and annually thereafter: Ultrasound surveillance

For malignant disease (recurrent PTC or lymph node metastases): More intensive surveillance with serial thyroglobulin measurements and neck ultrasound every 3-6 months. 5

Safety Profile and Complications

Observed Safety Data

MWA is well-tolerated with minimal complications: 2, 3

Mean pain intensity: 2.1 ± 0.8 on 10-point scale (range: 1-3) 3
Post-ablative hematoma: Observed in all cases but self-limited 3
No cases of: Hoarseness, vocal cord paralysis, superficial burns, nodule rupture, vagal reactions, or dysphagia 3

Common minor complications: 6, 7

Transient pain (managed with local anesthesia and oral analgesics)
Small hematomas (resolve spontaneously)
Transient thyrotoxicosis (from acute thyroid hormone release)

Rare major complications: 6, 7

Recurrent laryngeal nerve injury (<1% with proper technique)
Skin burns (avoided with adequate hydrodissection)
Tracheal or esophageal injury (extremely rare with real-time ultrasound guidance)

Comparison to Other Modalities

MWA vs. Radiofrequency Ablation (RFA): 2, 7

MWA achieves higher temperatures and larger ablation zones
MWA is less affected by tissue impedance and heat sink effect
Both have similar safety profiles and volume reduction rates

MWA vs. Laser Ablation (LA): 1

Both are effective for benign nodules
MWA may achieve faster ablation times
Choice depends on operator experience and equipment availability

MWA vs. Surgery: 1, 7

MWA preserves thyroid function (no need for lifelong levothyroxine in most cases)
MWA avoids surgical scar and general anesthesia
Surgery remains gold standard for malignant disease and provides definitive histology
MWA is appropriate for patients refusing surgery or with surgical contraindications

Key Clinical Pearls

Pre-procedure checklist: 1, 5

Confirm benign pathology with at least two biopsies (FNAB + FNAB or FNAB + CNB)
Assess coagulation function, complete blood count, thyroid function tests
Perform comprehensive neck ultrasound including lymph node evaluation
Document baseline nodule volume and symptoms

Intra-procedure optimization: 6, 4

Calculate required energy based on nodule composition (solid vs. cystic)
Use hydrodissection liberally to protect critical structures
Monitor ablation zone in real-time to avoid over- or under-treatment
Confirm complete ablation with CEUS before concluding procedure

Post-procedure management: 5, 3

Expect transient Tg elevation (confirms successful ablation)
Monitor for hematoma (usually self-limited)
Reassure patients about expected ultrasound changes (decreased echogenicity, increased stiffness)
Schedule structured follow-up to document VRR

Future Directions

Emerging applications: 1, 7

Expanding use for select low-risk papillary thyroid microcarcinomas
Combination with molecular testing to refine patient selection
Development of standardized energy protocols based on nodule characteristics
Integration of artificial intelligence for real-time ablation monitoring

Current limitations: 1, 6

Cannot distinguish follicular adenoma from carcinoma (requires surgical excision)
Limited long-term data beyond 5 years for malignant disease
Operator-dependent technique requiring specialized training
Not suitable for diffuse thyroid disease or multifocal malignancy

What is the latest update on the use of microwave thermal ablation (MTA) in the treatment of thyroid nodules or cancer, particularly for patients who are not suitable for surgery or have failed other treatments?

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