xRead - Facial Reconstruction Following Mohs Micrographic Surgery

Joseph et al

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nose. The structural support of the upper third of the nose is provided by the paired nasal bones, which articulate with the nasal (ascending) pro cess of the maxilla. The nasal bones are thinner at their caudal aspects and become progressively thicker in the cephalic portions. The middle third and lower third of the nose derive structural sup port primarily from cartilaginous structures and their fibrous attachments. The structure of the middle third of the nose results from paired upper lateral cartilages, which join the cartilaginous nasal septum at the midline. The lower third of the nose, namely the tip and portions of the nasal alae, receives its support from the lower lateral nasal cartilages and the caudal cartilaginous nasal septum. The lining of the inner surface of the nose changes in its composition depending on the proximity to the nasal vestibule. Within the nasal vestibule, the inner surface of the nose is lined by keratinized stratified squamous epithelium. As one proceeds deeper into the nose, this epithelium transitions into pseudostratified columnar ciliated epithelium (nasal mucosa), which often takes a glistening appearance. Early twentieth century approaches to facial reconstruction focused on obliteration of soft tis sue defects without attention to whether donor tis sue possessed similar qualities. Since then, surgeons have begun to discuss and implement notions of the facial aesthetic subunits. 14 Recon structions that respect facial aesthetic subunits allow resultant scars to be situated along natural boundaries and to mimic natural shadows or lighted ridges. The nose was originally considered a single aesthetic subunit of the face, despite an apprecia tion that there was differing thickness of nasal skin. 14 However, the pioneering work by Burget and Menick 15 recognized the topographic nature of the nose and described the following nasal sub units: nasal tip, dorsum, sidewalls, alar lobules, and soft tissue triangles. Most reconstructive sur geons now also consider the nasal columella to be a separate subunit. There have been several pro posed additions or modifications to the original nasal aesthetic subunits, including consideration of the nasal dorsum and nasal tip as one subunit. Others have proposed consideration of the nasal tip as 2 independent hemitip subunits. 16 Fig. 2 de tails the currently recognized nasal aesthetic subunits. Nasal Lining Aesthetic Subunits of the Nose

in later discussion). On average, skin is thickest at the radix and supratip area, and thinnest at the rhin ion and columella 10,11 ( Fig. 1 ). The cephalic half of the nose is composed of smaller and less densely populated sebaceous glands compared with the caudal half. 12 Skin with higher density of sebaceous glands, such as that on the caudal aspect of the nose, tends to be less pliable and more likely to develop trapdoor deformities following surgical procedures. Surgeons should be mindful of these differences when planning local flap reconstruc tions, because skin recruited from an area of skin with different thickness or density of sebaceous glands may result in a more conspicuous scar. The superficial subcutaneous layer located just deep to the skin has fibrous connective tissue lig aments that transit the layer and anchor the under lying SMAS to the overlying dermis. The SMAS layer contains the encapsulated facial mimetic muscles of the nose, including the transverse nasalis, anomalous nasi, levator labii superioris alaeque nasi, dilator naris, compressor narium mi nor, and the depressor septi, and alar nasalis. These muscles were well described more than 70 years ago and serve a role in both facial expres sion as well as a functional role in preventing collapse of the nasal airway with respiration. 13 Subcutaneous Tissues and Superficial Musculoaponeurotic Layer

Bony and Cartilaginous Framework

The underlying skeletal support of the nose differs among the upper, middle, and lower thirds of the

Fig. 1. Average changes in nasal skin thickness by anatomic subunit. In general, nasal skin thickness in creases as one proceeds caudally along the nasal side walls and dorsum. ( Courtesy of Carl Truesdale, MD, Ann Arbor, MI.)