An anatomic study was performed on living subjects using magnetic resonance imaging (MRI) to distinguish the relative contribution of skin, subcutaneous tissue, and muscle to dynamic changes in the nasolabial fold during facial animation and aging. MRI scans with the face in repose and then holding a full smile were performed in both young and old adult subjects. Anatomic landmarks were identified, and measurements characterizing their position were made on the MRI console. MRI resulted in excellent image resolution of facial tissue planes. Comparison between young and old subjects with the face in repose demonstrated that progressive thickening of the dependent portion of the cheek fat pad and overlying skin, with no appreciable change in the muscle plane comprising the levators of the upper lip, resulted in a deeper and more acute nasolabial fold in older subjects. In both age groups there was significant shortening of the mimetic muscles with smiling, with the lateral mimetic muscles drawn closer to the underlying facial bones. This was accompanied by redistribution of the cheek fat pad, thereby maintaining projection of surface landmarks within the cheek mass in young subjects with smiling. These findings indicate that in order to diminish the nasolabial fold, surgery for facial rejuvenation should be directed to the skin and subcutaneous tissue planes superficial to the mimetic muscles to the upper lip. In order to recreate a natural nasolabial fold during surgery for facial reanimation, contraction of the levator muscles to the upper lip should result in redistribution of the cheek fat pad without change in surface projection of the cheek mass or upper lip; this can only be accomplished if the reconstructed levator muscle is positioned deep to the cheek fat pad, with its insertion toward the deep (mucosal) surface of the upper lip.
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