Single-Session High-Intensity Focused Ultrasound Treatment in Large-Sized Benign Thyroid Nodules.

BACKGROUND: High-intensity focused ultrasound (HIFU) is a new promising thermal ablation technique for treating benign thyroid nodules, but its effectiveness in larger-sized nodules has been less well described. The present study aimed to evaluate the treatment efficacy (i.e., extent of shrinkage at six months) of large-sized benign thyroid nodules by ultrasound (USG)-guided HIFU ablation.

MATERIALS AND METHODS: After ethics approval, all consecutive patients who underwent HIFU ablation of a symptomatic benign thyroid nodule with six or more months of follow-up were analyzed. Treated nodules were categorized according to their pre-ablation volume (group I: <10 mL; groups II: 10-30 mL; group III: >30 mL). After treatment, the nodule volume was measured by USG at one week, one month, three months, and six months. Total energy delivered to each nodule (in kJ) and the time taken (in minutes) for that delivery were automatically recorded. The primary outcome was a change in nodule volume after six months, where percentage nodule volume change was calculated as (baseline volume - volume at six months)/(baseline volume) × 100. Ablation success was defined as >50% volume reduction.

RESULTS: Seventy-three nodules were treated successfully and followed for ≥6 months. The overall median six-month volume reduction was 68.3% (range 22.77-96.50%). At six months, group III had a significantly less volume shrinkage than group I (48.1% vs. 77.6%; p < 0.001) and group II (48.1% vs. 67.9%; p = 0.002). Also, the proportion of ablation success at six months in group III was significantly less than in the other two groups (p < 0.001). Pre-ablation nodule volume >30 mL (odds ratio = 7.813 [confidence interval 1.908-32.258]; p = 0.004) and lower total energy per nodule volume (odds ratio = 3.313 [confidence interval 1.113-9.688]; p = 0.029) were significant factors for less ablation success.

CONCLUSIONS: Single-session HIFU ablation was highly effective in causing shrinkage of benign thyroid nodules at six months, but the extent of shrinkage for larger-sized nodules (>30 mL) was noticeably less than that of smaller-sized nodules. Both pre-ablation nodule volume and total energy per nodule volume were significant determinants of ablation success. For larger-sized nodules, additional HIFU treatment three to six months after initial treatment might be preferred over sequential treatment within the same session.