Facial fold and crease development: A new morphological approach and classification.

Facial folds and creases are established descriptive anatomical terms for structures of which the morphological characteristics and origins are not clearly defined. The aim of this study was to perform a morphological investigation of the nasolabial fold (NLF), mandibular fold (MF), deep transverse forehead (DTFC), infraorbital fold (IOF) and upper eyelid fold (UEF), correlating their phenotypes to differences in the superficial musculoaponeurotic system (SMAS), noting morphological differences and similarities. Full-graft tissue blocks of skin, subcutaneous tissue, and mimic muscles collected postmortem were studied histologically. Serial histological sections were stained with Azan. Location- and composition-specific morphological differences were determined. Histological serial section digitalization and three-dimensional reconstruction of the tissue blocks were performed. Three different types of SMAS architecture were identified. Type I SMAS consisted of parallel-aligned fibrous septa connecting the mimic muscles to the skin that covered the cheek, infraorbital and supraorbital, and forehead areas. Type II SMAS morphology appeared as a condensed Type I SMAS architecture with stronger fibrous septa and smaller fatty tissue compartments covering the lower and upper lip areas. Type III SMAS consisted of loose connective tissue covering the lower and upper eyelid regions. NLF, MF, IOF, and UEF are habitual primary folds induced by morphological changes in the underlying SMAS architecture. The secondary, accidental creases (DTFC) are cutaneous depressions derived from interacting dermal-skeletal-muscular changes without SMAS structure changes. The upper and lower eyelid wrinkles were tertiary, age-related undulating skin redundancy formations. Clin. Anat. 32:573-584, 2019. © 2019 The Authors. Clinical Anatomy published by Wiley Periodicals, Inc. on behalf of American Association of Clinical Anatomists.