Non‐invasive Reduction of Accessory Breast Fat Using Multilayer High‐Intensity Focused Ultrasound: A Quantitative Ultrasound‐Based Study

OBJECTIVES: Accessory breast tissue often presents as localized axillary subcutaneous fullness, presenting as a palpable soft-tissue bulge composed of adipose or glandular elements, causing mechanical discomfort and esthetic concern. While surgical excision remains effective, it ma result in scarring, postoperative pain, and risks of seroma/hematoma or contour irregularity, leading to growing interest in noninvasive approaches. The objective of the study is to investigate the effect of noninvasive high-intensity focused ultrasound (HIFU) on subcutaneous fat thickness in axillary accessory breast tissue. METHODS: and accessory breast fat. All participants underwent a single HIFU session using multiple focal depths of 4.5, 6.0, and 9.0 mm at operating frequencies of 4 and 2 MHz, with energy settings of 1.5-2.0 J per shot. Fat thickness was measured by ultrasound at baseline and 8 weeks. Secondary outcomes included investigator-rated Global Aesthetic Improvement Scale (GAIS) and patient satisfaction scores. RESULTS: Among the 28 participants who completed the 8-week follow-up, mean subcutaneous fat thickness decreased from 19.2 ± 3.4 mm at baseline to 15.8 ± 3.1 mm at 8 weeks. The mean paired reduction was 3.4 ± 1.6 mm (17.7%), which was statistically significant (95% CI, 2.8-4.0 mm; p = 1.1 × 10⁻¹¹). All participants showed GAIS improvement with high satisfaction. No serious adverse events were observed; mild and transient effects included transient thermal discomfort and localized erythema resolving within several hours to 2 days, and no cases of skin burn were identified. CONCLUSION: Non-invasive HIFU produced a measurable reduction of accessory breast fat with favorable esthetic outcomes and an acceptable safety profile.