Spreading Pattern and Tissue Response to Hyaluronic Acid Gel Injections in the Subcutis: Ultrasound Videos, Ultrasound Measurements, and Histology.

Background: Despite the popularity of hyaluronic acid (HA) filler treatments, few publications focus on their effects on adipose tissue.

Objectives: The authors assessed the deposition pattern in the subcutis of injected HA, the tissue response at short and intermediate term, and the effects of remodeling the filler by strong finger pressure immediately after the treatment.

Methods: Two brands, specifically developed by the industry for deep injection, were compared. The gels were injected subcutaneously in 5 candidates for abdominoplasty or breast reduction, in the area of excision, 6 to 98 days before surgery. Ultrasound measurements and films were compared with postoperative histological findings. Tissue response was scored semi-quantitatively.

Results: Real-time ultrasound showed a slightly different deposition pattern of the 2 brands. Histologically, both were present in large pools of the same magnitude and looked the same. Linear retrograde injection sometimes resulted in a globular deposit due to elastic recoil of septae. After remodeling and over time, HA deposits became difficult to detect by ultrasound. Firm remodeling of the tissue immediately after injection or time had no significant effect on filler spread or tissue response. Except for 1 zone of granuloma formation, tolerance for both fillers was good.

Conclusions: HA deposition in adipose tissue occurs in much larger pools than in the dermis. Ultrasound examination is useful during and immediately after the injection but less reliable after filler remodeling or over time. Filler deposition can be less precise, and reshaping by finger pressure can have less effect than expected.