Facial anatomy revisited

The work presented in this thesis has significantly improved the understanding of facial anatomy for the next generation by proposing a non-contradictory explanation of the layered anatomy of the face. In this explanation, two main types of fasciae exist: deep fascia (Layer 5) and superficial fascia (Layer 2). In some areas, a layer of facial mimetic muscles or aponeuroses (superficial temporal fascia, galea, …) is situated between the superficial fascia and the deep fascia (Layer 3). However, this is not a uniform layer as was previously hypothesized with the concept of the “Superficial Musculo-Aponeurotic System” (SMAS), and where there is no Layer 3, the deep fascia (Layer 5) and superficial fascia (Layer 2) attach to each other.The deep fascia (Layer 5), the deepest layer, is a fibrofatty connective tissue layer that fills the space between the superficial fascia and deeper structures, including muscles, salivary glands, and vascular structures, which are all invested by this layer. It retains the superficial tissues of the face while providing stability in one direction and mobility in another. The facial nerve branches travel their entire extracranial trajectory within this fascia until they innervate their target muscles. The deep plane (Level 4), traditionally described as a separate layer (“Layer 4”), is a potential dissection plane within the deep fascia (Layer 5). This dissection plane can be superficial within the deep fascia such as in the lower face and neck, or deep within the deep fascia such as in the temple and forehead, which secondarily determines the nerves being visualized in the roof or the floor of the dissection. The depth of the dissection, as well as its extent, determines where the facial nerve branches are crossed and are at risk.The Superficial Musculo-Aponeurotic System (SMAS) is not an anatomical entity but a surgically created compound flap consisting of the deep part of the subcutaneous fat (Layer 2), mimetic muscle where present (Layer 3), and a thin layer of deep fascia (Layer 5).The subcutaneous fat (Layer 2) has a highly distinct architecture with connective tissue septae that are oriented largely perpendicular to the skin. This layer has specific anatomical features defining the nasolabial fold and the jowl.The platysma (Layer 3) is connected to the skin and through the deeper structures by retinacula fibers in the superficial fascia (Layer 2) and the deep fascia (Layer 5). The platysma and depressor labii inferioris are essentially continuous, being two parts of the same muscle, separated by their attachment to the mandible (“mandibular ligament”). Therefore, the cervical branches contribute significantly to the innervation of the lower lip.This unified understanding of facial anatomy provides a basis for improved surgical techniques to obtain more effective and longer-lasting surgical solutions for facial rejuvenation. This improved understanding may also help to mitigate the trend in which less experienced surgeons steer away from long-lasting surgical solutions toward non-surgical procedures which have significant limitations.