What is the procedure and management for thyroid ablation using interventional radiology?

Thyroid Ablation in Interventional Radiology: Comprehensive Presentation

Overview and Introduction

Ultrasound-guided thermal ablation has emerged as a minimally invasive, thyroid-sparing alternative to surgery for both benign and malignant thyroid nodules, offering excellent efficacy with preservation of thyroid function and minimal complications. 1

Key Advantages Over Traditional Surgery

• No neck scarring - outpatient procedure with simple operation and short procedure time 1
• Preservation of thyroid function - most patients do not require lifelong thyroid hormone replacement 1
• Low complication rates - voice-sparing, parathyroid-sparing, and repeatable when needed 2
• Rapid recovery - patients can typically resume normal activities quickly 1

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Indications for Thermal Ablation

Benign Thyroid Nodules 1, 3

• Nodules causing clinical symptoms (compression, dysphagia, cough)
• Cosmetic concerns with visible neck swelling
• Nodules with maximal diameter ≥2 cm
• Autonomously functioning thyroid nodules (toxic adenomas) causing hyperthyroidism 4

Malignant Thyroid Nodules 1, 5

• Papillary thyroid carcinoma (PTC) <1 cm (cT1a stage)
• Confirmed by biopsy with no lymph node metastasis (cN0)
• No distant metastases (M0)
• Recurrent thyroid cancer where surgery is limited by scar tissue 2

Observation Appropriate For 3

• Asymptomatic nodules with maximal diameter <2 cm

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Contraindications

Absolute Contraindications 3

• Severe bleeding tendency or uncontrolled coagulopathy
• Severe cardiopulmonary insufficiency
• Contralateral vocal cord paralysis (risk of bilateral vocal cord injury)
• Pregnancy or lactation

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Pre-Procedure Evaluation and Preparation

Diagnostic Workup Required

All patients must undergo puncture biopsy to confirm pathological diagnosis before thermal ablation. 1

Biopsy Methods 1

• Fine-needle aspiration biopsy (FNAB) - preferred initial method, accurate, economical, safe and effective
• Core needle biopsy (CNB) - recommended for FNAB-undiagnosed nodules to improve diagnostic yield
• Cytology results should follow Bethesda System for Reporting Thyroid Cytopathology 1

Imaging Assessment 1, 6

• High-frequency ultrasound of thyroid and cervical lymph nodes - essential for detecting and characterizing nodules
• Contrast-enhanced ultrasound (CEUS) - evaluates vascularity and helps plan ablation strategy
• Assess for suspicious features: irregular borders, lymphadenopathy, extrathyroidal extension 5, 6

Laboratory Testing 1

• TSH, fT3, fT4 - baseline thyroid function (higher TSH associated with increased malignancy risk) 5
• Serum calcitonin - consider measuring to rule out medullary thyroid cancer (higher sensitivity than FNAB) 5
• Thyroid antibodies - if elevated, assess to prevent post-ablation thyroid dysfunction 1
• Coagulation studies - ensure safe bleeding parameters

Molecular Testing (When Indicated) 3

• BRAF/RAS, TERT, PIK3CA, TP53 gene testing to assist in diagnosis and prognosis determination

Patient Preparation 1, 3

Pre-Procedure Requirements

• Discontinue anticoagulant medications as per institutional protocol 3
• Fast for 4-6 hours before procedure to prevent gastric content regurgitation and aspiration 1
• Establish intravenous access for contrast-enhanced ultrasound and emergency medication administration 1
• Obtain informed consent after thorough discussion of risks, benefits, and alternatives 1, 3

Intraoperative Monitoring 1

• Multi-parameter vital sign monitoring including blood pressure, heart rate, electrocardiogram, and oxygen saturation throughout procedure

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Thermal Ablation Techniques

Available Modalities

Radiofrequency ablation (RFA) and microwave ablation (MWA) are the most widely used techniques, achieving similar clinical results in most studies. 1

Radiofrequency Ablation (RFA) 1, 7

• Sharp electrodes facilitate easy puncturing
• Preferred for standard nodules
• Uses sterile distilled water or 5% glucose for hydrodissection 1

Microwave Ablation (MWA) 1

• Strong vascular coagulation ability - clear advantages for highly vascularized tumors
• Recommended for patients with hyper-vascular nodules
• Uses 0.9% sodium chloride injection for hydrodissection 1

Laser Ablation (LA) 1

• Limited thermal field - usually used in PTC ablation
• Less commonly applied than RFA/MWA

High-Intensity Focused Ultrasound (HIFU) 1

• More painful procedure than other techniques
• Longer procedure time and highly sensitive to patient movement
• Less established efficacy - limited clinical applications

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Procedural Technique

Patient Positioning 1

• Supine position with neck extended to ensure complete neck exposure
• For obese patients or those with cervical spine conditions, use low pillow supporting upper back for comfort

Anesthesia 1, 3

• Local anesthesia with 1-2% lidocaine is routinely employed
• Systemic sedation and analgesia may be added for patients with reduced pain tolerance

Needle Insertion Approach 1

The transisthmic approach is typically preferred over lateral neck insertion. 1

• Transisthmic approach - through the thyroid isthmus (preferred route) 1
• Lateral neck approach - alternative when transisthmic not feasible

Hydrodissection Technique 1

Hydrodissection establishes safe separation between the ablation zone and vital neighboring structures. 1

Injection Method

• Use PTC needles or syringes for injecting isolation fluid 1
• For MWA: 0.9% sodium chloride injection 1
• For RFA: sterile distilled water or 5% glucose injection 1

Protected Structures 1

• Recurrent laryngeal nerve
• Trachea
• Esophagus
• Major neck vessels

Ablation Technique 1, 7

• Moving-shot technique and/or fixed electrode technique are standard approaches 1
• Ablate from deep to superficial, from central to peripheral
• Ensure complete coverage of target nodule with adequate safety margin

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Immediate Post-Ablation Assessment

Clinical Observation 1

Monitor for:

• Bleeding at puncture site
• Localized swelling in neck
• Nausea, vomiting, belching
• Hoarseness (potential vocal cord injury)

Imaging Assessment 1, 3

Routine ultrasound combined with CEUS should be used to assess ablation efficacy immediately post-procedure. 1

Complete Ablation Criteria 1

• Absence of enhancement in the ablation zone on CEUS
• Ablation zone completely covers the intended target area
• No remaining vessels within nodule

Incomplete Ablation Indicators 1

• Presence of remaining vessels on CEUS
• Enhancement within the nodule
• Inadequate coverage of designated ablation region

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Follow-Up Protocol

Follow-Up Schedule 1

Initial follow-up should begin one month after the procedure, followed by assessments at 3,6, and 12 months during the first year. 1

First Year 1

• 1 month post-procedure
• 3 months post-procedure
• 6 months post-procedure
• 12 months post-procedure

After First Year 1

• Malignant nodules: re-evaluate every 6 months 1
• Benign nodules: re-evaluate annually 1

Follow-Up Content 1

Imaging Assessment 1

• Traditional grayscale ultrasound - most frequently employed method for thyroid and cervical lymph node assessment 1
• CEUS - exhibits microvascular perfusion, facilitates precise evaluation of ablation zone extent and blood supply 1

Volume Reduction Assessment 1

Volume reduction rate (VRR) is an important objective indicator of treatment success. 1

Formula: VRR = [(Preoperative nodule volume – ablation zone volume at follow-up) × 100] / preoperative volume (%) 1

Clinical Symptom Assessment 1

• Symptom scores for compression symptoms 1
• Anxiety scales 1
• Quality of life instruments 1
• Documentation of complication recovery 1

Laboratory Testing 1

For patients with thyroid function abnormalities or suspected diffuse thyroid disease, conduct routine thyroid function tests before and after ablation. 1

Autonomously Functioning Nodules 1

• Test TSH, fT3, fT4 at each follow-up until normal function restored

Patients with Elevated Thyroid Antibodies 1

• Thorough assessment necessary to prevent post-ablation hyperthyroidism or hypothyroidism

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TSH Suppression Therapy for Malignant Nodules

Following thermal ablation of malignant thyroid nodules, TSH suppression therapy should be implemented. 1

Target TSH Levels 1

Nodules Meeting Absolute Indications 1

• Target TSH: 0.5-2.0 mU/L

Nodules Meeting Relative Indications 1

• Target TSH: <0.5 mU/L

Monitoring Schedule 1

• Follow-up at 3,6, and 12 months during first year
• After TSH control achieved: evaluate every 6 months 1

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Management of Residual or Recurrent Disease

Malignant Nodules 1

In the event of confirmed residual or recurrent disease in malignant thyroid nodules, promptly initiate supplementary treatment. 1

• Monitor ipsilateral and contralateral cervical lymph node metastasis 1
• Perform FNAB when necessary for suspicious lymph nodes 1
• Consider repeat ablation or surgical intervention 4

Metastasis Surveillance 1

• When deemed necessary, assess other organs (lungs, bones) to detect potential metastases 1

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Efficacy and Outcomes

Benign Nodules 8

• Volume reduction ratios >50% achieved in 100% of treated nodules at 6 months 8
• Mean volume reduction from 8.81 ml to 1.59 ml at 6-month follow-up 8
• Complete resolution of clinical symptoms in symptomatic patients 8

Autonomously Functioning Thyroid Nodules 4

• Hyperthyroidism resolved in 90.9% of patients following single RFA session 4
• Average volume reduction rate of 61.13% achieved within 3-6 months 4
• No serious adverse effects in treated cohort 4

Malignant Nodules 1

• Technical success rate of 100% for T1a-stage PTCs 1
• Recurrence rate <1% within 17-36 months postoperatively 1
• No major complications reported in retrospective studies 1

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Complications and Management

Common Minor Complications 4, 8

• Transient tachycardia - may require short-term beta-blocker therapy 4
• Mild hypothyroidism - requiring levothyroxine therapy in approximately 9% of patients 4
• Local pain and swelling - typically self-limited 8

Serious Complications (Rare) 7

• Vocal cord paralysis - risk minimized with hydrodissection technique
• Major bleeding - prevented by proper patient selection and technique
• Tracheal or esophageal injury - avoided with careful needle placement and hydrodissection

Prevention Strategies 1

• Hydrodissection technique to protect vital structures 1
• Careful patient selection excluding those with contraindications 3
• Experienced operator with proper training 7
• Real-time ultrasound guidance throughout procedure 1

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Key Recommendations Summary

Strong Recommendations 1

1. Pathological confirmation required before thermal ablation via FNAB or CNB 1

2. Local anesthesia, transisthmic approach, hydrodissection techniques, and moving-shot/fixed electrode technique are standard 1

3. CEUS evaluation should be performed immediately following thermal ablation to assess effectiveness 1

4. Regular follow-up required after thermal ablation of both benign and malignant nodules, including VRR assessment, symptom improvement, residual nodules, recurrence, metastasis, complications, and thyroid function 1

5. TSH suppression therapy should be implemented following thermal ablation of malignant thyroid nodules 1

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Clinical Pearls and Pitfalls

Critical Success Factors 7

• Proper patient selection - ensure appropriate indications and absence of contraindications
• Thorough pre-procedure evaluation - complete imaging and pathological confirmation
• Experienced operator - adequate training in ultrasound-guided procedures essential
• Appropriate technique selection - MWA for hypervascular nodules, RFA for standard cases 1

Common Pitfalls to Avoid 6

• False-negative FNAB results can occur - clinical suspicion should remain if concerning features present 6
• Inadequate ablation margin - ensure complete coverage of target with safety margin
• Failure to use hydrodissection when nodule near vital structures - increases complication risk 1
• Insufficient follow-up - long-term surveillance essential, especially for malignant nodules 1

Special Considerations 4, 2

• Recurrent hyperthyroidism may occur in small percentage - repeat ablation or surgery may be needed 4
• Thyroid cancer recurrence - ablation is repeatable unlike surgery, making it valuable for recurrent disease 2
• Patient preference - discuss all treatment options including surgery, radioactive iodine, and active surveillance 7