The Superficial Musculoaponeurotic System of the Face: A Model Explored

Regional differences in the integument of the body are explained, at least in part, by differences in fascial arrangements. In the face, where the skin is more mobile due to the action of the underlying facial muscles, fascial organisation is important for support and separation of muscle groups. This study used bequeathed cadaver material to investigate a current model of the SMAS proposed by Macchi et al., the original boundaries of which were explored and extended using both histology and gross dissection. As a clearly identifiable structure spanning the lateral and midface, the SMAS in the specimen supported the model proposed by Macchi et al. The three main findings that support the model were the layered morphological appearance of the SMAS, its progression from fibrous to aponeurotic in a lateral to medial direction, and the enveloping of the zygomaticus musculature. Extension beyond the proposed model into the temporal region was observed, but nasal and forehead regions showed no evidence of SMAS, while its presence in the cervical platysma region remained inconclusive. Fascial and soft tissue variability was considerable within facial regions of the examined specimen, helping to explain the debate around the SMAS in the literature. 1. Introduction In 1976, a superficial musculoaponeurotic system (SMAS) was described in the parotid and cheek regions of the face, dividing superficial and deep adipose tissue [1]. Since then, the definitions and descriptions of the SMAS have been the subject of much debate in the literature. Comprehensive knowledge of regional variation within the face is important for the application of surgical facelift techniques [2, 3]. However, terminology, definitions, and descriptions of SMAS morphology are inconsistent [4–7], with some studies even questioning its existence [8, 9]. Histological studies have failed to reach consensus regarding investiture of the zygomatic musculature by the SMAS [2, 4]. Macchi et al. [2] argued that the SMAS invested the zygomaticus muscle group, while Gassner et al. [4] disagreed. The existence of the SMAS separate from the parotid fascia was more readily agreed upon [7, 10, 11], although earlier studies remained inconclusive [9, 12]. Fascial relationships of the platysma muscle are also inconclusive. Earlier studies which identified both superficial and deep fascial layers of the muscle [6] have been supported [8]; although investigative methods varied, the superficial fascial layer has not always been identified as a separate layer [13]. The concept of an SMAS is generally accepted in