Understand Asian Rhinoplasty: Nasal Envelope & Base
An essential component of all surgical operations is surgical anatomy. Anatomy gives a surgeon the fundamental and in-depth information needed and necessary when carrying out an operation. Although it might seem boring and routine, this topic is necessary and shouldn't be ignored or disregarded in order to prevent any potential postoperative complications. Despite the fact that the surgical anatomy of the nose is quite straightforward, a quick and aggressive procedure without anatomical considerations may result in negative effects that are permanent.
Nasal Envelope: Skin and Soft Tissue Envelope
The nasal envelope, also known as skin and soft tissue envelope (SSTE), is the skin that covers the exterior of nose. The nasal envelope is made up of soft tissues and includes all intranasal soft tissue except the osteocartilaginous framework. Because the epidermis, dermis and subcutaneous tissues are among the tissues that make up the nasal envelope, it may at times lead to confusion for surgeons. No matter how thick or thin the skin may be, it is the SSTE which guides a surgeon for understanding the elasticity of the nasal envelope. Therefore, when performing rhinoplasty on a patient with thin skin, the skin and soft tissue might be considered as a single compound.
There are five layers that make up the nasal envelope. They include skin, superficial fatty layer, fibro-muscular layer, deep fatty layer, and perichondrium or periosteum (See table below).
Asian nasal envelope is described as the skin with a thick subcutaneous fat layer which is oilier and denser in fibro-fatty layer. Thus, the elasticity of a patient’s SSTE is an important aspect that must be considered during a surgical procedure. The thickness, texture and elasticity are significant characteristics of the nasal envelope and must be observed before any rhinoplasty procedure (See table below).
Skin
A nasal skin is very specialized organ keeping its own shape and characteristics with differing from other parts of body. In short, it especially at thick nasal tip keeps its own shape and pattern if cadaveric nasal skin is harvested and observed. It is an evidence of difficulty for change at nasal tip with surgical manipulation. Therefore, it is important to evaluate individual characteristics of patient’s skin before the operation to make surgical plan and predict prognosis because manipulation on cartilage framework is not visible due to thick skin during tip plasty.
The characteristics of the nasal envelope varies significantly in different portion of the nose. The nasal skin is thicker when the elasticity and stretch capacity are lower, and the proportions of the fibrous tissue and sebaceous glands are higher. The nasal skin of dorsum is the thinnest, less sebaceous, and more mobile, hence can be shortened and wrinkled by a facial expression. However, it gets thicker caudally and is the thickest at supra-tip area. The dermal component of the skin is thinnest over the rhinion and thickest in the supratip area. The subcutaneous layer at the alar groove is very dense, hard and tightly attached to underlying tissue. An alar skin is considerably firm with tightly wrapping fibrous tissue. On the other hand, the columellar skin gets thinner and less sebaceous. The external part of columellar skin is tightly attached to medial crura and connected with vestibular skin internally.
Below shows the subunits of the nose and the difference in skin thickness by subunits. Zone II is the thickest portion.
Superficial Fatty Layer
The superficial fatty layer consists of adipose tissue. In histology, the superficial fatty layer has interlacing vertical fibrous septae that is evenly distributed around the nose, typically at the glabella and the supratip area. The superficial layer is tightly attached to the overlying skin with vertically oriented fibrous septae and supplied by horizontally running subdermal vascular network. It is thickest at the nasal radix and thinnest at the rhinion. The fat pad of the nasal radix is located over the procerus and extends to laterally medial brow and depressor supercilii. Fat pad of the supratip and sidewall is densely attached to dermis. The interdomal fat pad is located caudally from supratip fat and between both medial and middle crus. Dermocartilaginous ligament and interdomal ligament exist inferiorly.
Fibromuscular Layer
The fibromuscular layer is the core part of nose; consisting of nasal superficial musculo-aponeurotic system (SMAS) along with a superficial fatty layer. The main function of the fibromuscular layer is to allow movement of the nasal envelope, to offer blood supply and to maintain the thickness of the skin. They also integrate and transmit the contractile force of nasal muscles. The fibromuscular layer mainly consists of the procerus, anomalous nasi and transverse nasalis. It is also connected to the dermis layer tightly as a facial network, making facial animation possible. Details about each muscle will be discussed later. Since nasal muscles originate from glabella and cheek, these muscles covering the underlying structure as a single unit, are fused in the middle
Below shows as a single layer, nasal superficial musculo-aponeurotic system (SMAS) contains the various muscular system:
Although a nasal SMAS is considered as a continued structure from the facial SMAS, there is a slight compositional difference between the nasal dorsum and the tip. The proximal nasal SMAS is a collection of collagen supporting the dynamic property, whereas the distal nasal SMAS is a structure that is firmly attached between the skin and muscle. According to a study, SMAS can be divided into two types. Type I is the common architecture and can be found in the forehead, zygomatic and infraorbital regions. Characteristic of proximal portion of the nose composed of type I. Supratip and tip area consist of type II SMAS. The characteristics of SMAS differ from each side above and below the scroll area. While dissecting through open approach, the transitional zone where incorporation from the alar cartilage to upper lateral cartilage can be observed. The dissection plane should be kept under deep fatty layer while monitoring the SMAS layer not to injure major vessels of the nose. A severe injury on it may lead to a secondary contracture because the nasal SMAS is a core structure in blood supply. A damage to the nasal SMAS or deep dermis, accompanied by an uncontrolled postoperative inflammation might result in irreversible complication related to formation of a severe and irregular scar at the nasal envelope.
Deep Fatty Layer
The open approach is preferred to dissect the deep fatty layer while separating the nasal envelope. Lack of major vessels and fibrous septa along with the movement of muscular aponeurosis makes it less challenging. The advantage of dissection on this plane is possible to maintain the integrity of nasal envelope and to reduce the chance of damaging the neurovascular bundles.
Periosteum or Perichondrium (Longitudinal Fibrous Sheath)
The fifth layer consists of fused perichondrium or periosteum with fibrous tissue. It is located under the deep fatty layer. It can be divided as a periosteal component and a perichondral component. Histologically, a periosteum consists of superficial and deep layers. These layers cover nasal bone, frontal process of maxilla and nasal portion of frontal bone. A perichondral component covers nasal cartilage and contains nutrient vessels. It wraps above and beneath the nasal cartilages, and fuses to form a hard, fibrous tissue at accessory cartilage.
Below shows the periosteal component and perichondral component are fused and form a hard-longitudinal fibrous sheath (red arrow)
A periosteum is a special tissue consisting of fibro-vascular membrane. In Asian rhinoplasty, a dorsal implant material is usually located under the periosteum. It might cause migration, descent or deviation of the implant if pocket dissection is located within superficial plane, too wide or out of place. The periosteum becomes thicker as it ascends above the nasofrontal suture line. The collagen fibers called Sharpey’s fiber, extending from the periosteum intervene with the suture line. Sharpey’s fiber may hinder more subperiosteal cephalic dissection in cases with acute nasofrontal angle and flat nasal dorsum.
Nasal Base
The nasal base is the least understood and thus most complex area of the nose. Therefore, analysis is also complex, and surgical results and outcome is difficult to predict before the operation because every tip plasty affects the nasal base on the final result afterwards.
The topographic anatomy of the nasal base is illustrated as below, including columellar base, central columellar pillar, infralobule (infralobular triangle), soft triangle (facet), lateral wall of ala, alar base, and nostril sill.
Alar rim breakpoint (nostril break point) is caused by central sweeping of lateral crura away from alar rim. This point is a junction of tip lobule (lateral wall of ala in subunit) and alar base in lateral view. Alar base is composed of subcutaneous tissue and muscles. The soft triangle (facet) is the surface expression of domal notch in the nose. This area reflects the entire middle crus, beginning at the columellar breakpoint and continuing into the medial half of the lateral crus. The boundary and shape in this area are obscure due to thick skin in Asian and no cartilage within the facet. A scar contracture on this area by surgical manipulation might cause alar notching or retraction. The nostril sill serves as a transverse bridge from the columellar base to the alar lobule and as a longitudinal bridge from the nasal vestibule to the upper lip.
The pyriform ligament had various different names such as the lateral sesamoid complex ligament, lateral crural complex, nasal hinge and etc. Pyriform ligament can be understood as a wide fascial network system from nasal bone to anterior nasal spine. A condensation of pyriform ligament attached along the pyriform aperture is similar with the one in the orbit. In short, a pattern of pyriform ligament supporting alar cartilage is similar to the pattern of orbicularis oculi retaining ligament attaching to the orbital rim. It is connected to periosteum of maxilla in a fascial network.
Below shows the Pyriform ligament (red line area):
There is a distinct fibrous structure, “tela subcutanea cutis” laterally, without any muscular or cartilaginous component that forms alar side wall and nostril sill in the lower nasal base. It is obvious that structural integrity of the alar side wall and nostril sill is well maintained without any support of underlying cartilages or bones. This structure is distinct soft tissue independent from cartilages and bones. They are connected with muscles in basal area.
Conclusions
The anatomy of Asian nose is quite different from Caucasian one in characteristics of skin, bone, and cartilage. In addition, the surgical purpose and direction of Asian rhinoplasty are different from Caucasian rhinoplasty. Therefore, it is important to review surgical anatomy from the viewpoint of an Asian rhinoplasty surgeon to get the best result in practice.
Reference
Surgical anatomy for Asian rhinoplasty (2019)
Rebuilding nose: rhinoplasty for Asians (2018)
Managing the difficult soft tissue envelope in facial and rhinoplasty surgery (2017)
Management of the thickskinned nose: a more effective approach (2006)
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