Hyaluronic Acid Filler Incidentally Found During Mohs Micrographic Surgery: Observations in 36 Patients Regarding Skin Depth, Degradation Size, and Estimated Persistence Time

BACKGROUND Although its clinical effect is reported to last up to 2 years, how long hyaluronic acid filler (HAF) histologically persists in the skin is unknown. OBJECTIVE To determine the approximate persistence time of HAF in the skin and to correlate persistence time with HAF histological appearance, size, depth, and location. METHODS Retrospective review of patient data and available frozen sections from 2003 to 2021 in which HAF was identified in 36 Mohs micrographic surgery patients. RESULTS Incidental HAF histologically persisted in the skin for as long as 10.75 years in 1 patient and 3 years or more in 36.8% (7/19) of the patients who remembered the time of implantation. HAF is more apparent in frozen sections stained with toluidine blue than those stained with hematoxylin and eosin. Although HAF volume tended to be less with time, fragmentation was present both early at 3 months and at 3 years or more. There was no correlation of persistence time with anatomic location or depth. In 90.3% of the cases (28/31), HAF was located in the subcutaneous fat. There was no granulomatous or giant cell response at any time period. CONCLUSION Hyaluronic acid filler may be seen histopathologically in the skin, usually in the subcutaneous fat, up to 10.75 years after implantation.