The anatomic basis for the jowl has not been fully described. A formal analysis was performed of the sub-superficial musculoaponeurotic system (SMAS) areolar tissue layer, which overlies the lower part of the masseter. For this research, facial dissections were performed on 16 fresh cadavers ages 12 to 89 years, and detailed anatomic observations were made during the course of several hundred rhytidectomy procedures. Tissue samples from varying age groups were examined histologically. The areolar cleavage plane overlying the lower masseter has specific boundaries and is a true space named the "premasseter space." This space is rhomboidal in shape, lined by membrane, and reinforced by retaining ligaments. The masseter fascia lines the floor, and branches of the facial nerve pass under its deep surface. Histologically, the floor is formed by a thin layer of dense connective tissue, which undergoes minor deterioration in architectural arrangement with age. The roof, lined by a thin transparent and adherent membrane on the underside of the platysma, has a less dense collagen network and contains more elastin. With age, there is a significant reduction in the collagen density of the roof. Expansion of the space with aging, secondary to weakness of the anterior and inferior boundaries, results in formation of the jowl. Medial to the premasseter space is the buccal fat in the masticator space, which descends with aging and contributes to the labiomandibular fold and jowl. Application of the premasseter space in surgery provides significant benefits. The SMAS incision should be forward of the traditional preauricular location to be over the space, not behind. Because the space is a naturally occurring cleavage plane, dissection is bloodless and safe, as all facial nerve branches are outside. The premasseter space should be considered as the preferred dissection plane for lower (cervicofacial) facelifts.
