Ultrasound and Histologic Examination after Subcutaneous Injection of Two Volumizing Hyaluronic Acid Fillers: A Preliminary Study

BACKGROUND: This study examined the influence of hyaluronic acid (HA) crosslinking technology on the ultrasound and histologic behavior of HA fillers designed for subcutaneous injection. METHODS: One subject received subcutaneous injections of 0.25 ml Cohesive Polydensified Matrix (CPM) and Vycross volumizing HA in tissue scheduled for abdominoplasty by bolus and retrograde fanning techniques. Ultrasound analyses were performed on days 0 and 8 and histologic analyses on days 0 and 21 after injection. A series of simple rheologic tests was also performed. RESULTS: Day 0 ultrasound images after bolus injection showed CPM and Vycross as hypoechogenic papules in the hypodermis. CPM appeared little changed after gentle massage, whereas Vycross appeared more hyperechogenic and diminished in size. Ultrasound images at day 8 were similar. On day 0, both gels appeared less hypoechogenic after retrograde fanning than after bolus injection. Vycross was interspersed with hyperechogenic areas (fibrous septa from the fat network structure) and unlike CPM became almost completely invisible after gentle massage. On day 8, CPM appeared as a hypoechogenic pool and Vycross as a long, thin rod. Day 0 histologic findings confirmed ultrasound results. Day 21 CPM histologic findings showed a discrete inflammatory reaction along the injection row after retrograde fanning. Vycross had a more pronounced inflammatory reaction, particularly after retrograde fanning, with macrophages and giant cells surrounding the implant. Rheologic tests showed CPM to have greater cohesivity and resistance to traction forces than Vycross. CONCLUSIONS: CPM HA volumizer appears to maintain greater tissue integrity than Vycross after subcutaneous injection with less inflammatory activity.