Anatomic Location of Hyaluronic Acid Filler Material Injected into Nasolabial Fold: A Histologic Study

BACKGROUND Products instilled within or beneath the skin to improve its physical features are known as fillers. The position of the filler within the skin is one determinant of the end cosmetic result. OBJECTIVE The objective was to histologically determine the anatomic location of injected hyaluronic acid (HA) filler within nasolabial fold (NLF) skin. METHODS AND MATERIALS Sixteen patients (12 females, 4 males; median age, 59 years) undergoing Mohs micrographic surgery for basal cell carcinoma of the NLF area consented to injection of Burow's triangle or dog‐ear redundant skin with HA gel (Juvederm), ex vivo, in vivo, or in vivo with delayed (1–4 weeks) removal. Sections of alcohol‐fixed, paraffin‐embedded tissue specimens were stained with hematoxylin and eosin and with Hale's colloidal iron for detection of acid mucins. Dermal thickness was measured and HA distribution assessed. RESULTS NLF dermal thickness was 1.37±0.27 mm (mean±SD), with a range of 1.04 to 1.86 mm. All 16 patients showed HA filler localized to the subcutis. In 9/16 tissue samples, some HA was present in the deep dermis, but filler was only observed in more superficial dermis in 1 patient. The thickness of injected filler was 2.11±0.63 mm, but filler was often transected at the specimen base. CONCLUSION The predominant localization of injected HA filler is within the subcutis. A relatively thin NLF dermal thickness, typically