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Anatomic Considerations in Aesthetic Rhinoplasty

Rhinoplasty; Editors in Chief, Fred Fedok, M.D., Gilbert J. Nolst Trenit ,M.D., Ph.D., Daniel G. Becker,M.D., Roberta Gausas, M.D.; Guest
Editors, Edwin F.Williams, III, M.D., Samuel M. Lam, M.D. Facial Plastic Surgery, Volume 18, Number 4, 2002. Address for correspondence
and reprint requests: Edwin F. Williams, III, M.D., Williams Center for Facial Plastic Surgery, 1072 Troy-Schenectady Road, Latham, NY
12110. 1Facial Plastic Surgery Center, Dallas, TX; 2New England Laser and Cosmetic Surgery Center, Latham, NY; 3Section of Facial Plastic
Surgery, Albany Medical College, Albany, NY. Copyright   2002 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY
10001, USA.Tel: +1(212) 584-4662. 0736-6825,p;2002,18,04,209,214,ftx,en;fps00437x.
Anatomic Considerations in
Aesthetic Rhinoplasty
Samuel M. Lam, M.D.,1 and Edwin F. Williams, III, M.D.2,3
ABSTRACT
A thorough understanding of nasal anatomy and physiology remains critical when approaching the nose to correct any contour or functional deficiencies. This article reviews the salient, anatomic features of the nose that are relevant to the rhinoplasty surgeon and further highlights basic surgical techniques that illustrate the anatomy germane to aesthetic surgery. The external anatomy of the nose is discussed in regard to the skin/soft-tissue envelope, the superficial musculoaponeurtic system/muscular layer, the bony/cartilaginous framework, and the dynamic tip-support mechanisms. The discussion of internal nasal anatomy concerns functional aspects of the nose, particularly the valvular components and the septum-turbinate complex.

KEYWORDS: Nasal anatomy, rhinoplasty

Fundamental aspects of nasal anatomy have been well known for centuries but have been further refined over the past few decades owing to the advances made in functional and cosmetic surgery of the nose. Above all else, the nose remains a key regulator of respiratory exchange, and all surgical manipulations on this vital organ should respect the integrity of that function. During the incipient phases of modern rhinoplasty, the surgeon often forgot the basic tenets of nasal support and structure and whittled away the nasal tissues until the patient was left crippled both aesthetically and functionally. Today, advocates of rhinoplasty endeavor to maintain a more natural result with less aggressive reductive techniques that preserve as many structural underpinnings of the nose as possible or attempt to restore as many support mechanisms violated during surgery. Volumes have been written about nasal anatomy and physiology, and the breadth of subject matter is extensive. This brief article is not intended to provide an exhaustive review of every facet of nasal anatomy but to highlight relevant anatomic features of the nose that would serve as a practical guide to the rhinoplasty surgeon. In accordance with this objective, the effects of surgical alteration of anatomic structures, whether favorable or unfavorable, will be discussed to reinforce and to illustrate the anatomic points more lucidly.

EXTERNAL ANATOMY
Skin and Soft-Tissue Envelope

The nature of the overlying skin/soft-tissue envelope significantly influences the ultimate rhinoplasty result and must be carefully evaluated prior to any surgical endeavor. The thickness of the skin (thin, medium, thick) must be estimated by palpation during the preoperative assessment to determine how this tent-like structure will re-drape over the underlying framework as time progresses. Any irregularities due to imprecise grafting or trimming of cartilage or bone may become apparent over time if the patient exhibits very thin skin. Tardy's admonition that the attenuated skin envelope may eventually shrink wrap around the cartilage turning early successes into later failures should be well heeded. Likewise, Tardy has hailed the favorable attributes of medium-thick Skin, which reveals the subtle changes of surgery but also camouflages any minor imperfections.1 Thick, oily skin may prove equally problematic as it may resist re-draping and thereby lead to fibrosis and subsequent supratip deformity (i.e., polly beak) if a dead space develops between over-resected cartilage and the overlying skin. The non-Caucasian nose is exemplified by this unfavorable combination of thick skin and fragile cartilage. Further, the most meticulous surgical changes may go undetected under a thick-skin envelope. As a patient matures, a loss of subcutaneous tissue makes the skin envelope more attenuated so that a thick-skinned individual may exhibit thinner-skin qualities as he becomes older. The thickness of the skin also varies according to its relative position on the dorsum to tip. On the upper third of the nose, the skin is fairly thick but tapers into a thinner mid-dorsal region. The inferior third of the nose, however, regains much of the thickness of the upper third of the nose due to the sebaceous quality of the nasal-tip area. The skin/soft-tissue envelope also serves as a minor tip-support mechanism, and undermining of this tissue away from the nasal framework will cause some loss of support. However, as discussed in the following section, the plane of dissection in the nose remains below the level of the superficial musculoaponeurotic system (SMAS) and not in the subcutaneous plane. An external-rhinoplasty technique potentially disturbs the skin/soft-tissue support mechanism more than the endonasal approach as the entire envelope is freed from the underlying framework. However, the endonasal, or closed, approach also violates key tip-support mechanisms in different ways, for example, dividing the upper lateral-lower lateral junction (or scroll) in the delivery technique of the lower lateral cartilages (LLCs).Whatever surgical method is elected, the surgeon should remain cognizant of the role that the soft-tissue envelope plays in maintaining nasal support and in determining final cosmetic outcome.

SMAS and Muscular Sling

The SMAS was first defined by Mitz and Peyronie in 1976.2 This enveloping musculoaponeurotic plane extends over the entire face and is in continuity with the cervical equivalent, the superficial layer of the superficial investing fascia of the neck. The subtleties of the facial SMAS layer, for example, whether it constitutes part of the parotid-masseteric fascia or lies apart or whether it is continuous with the temporo-parietal fascia or is separate, have often been debated in academic circles and prove to be more of an arcane than practical issue. Therefore, the anatomic review of the SMAS herein concerns only the surgical ramifications that this distinct musculoaponeurotic layer holds for the practitioner. The nasal SMAS, which is continuous with the facial SMAS, invests and connects the nasal musculature. The SMAS functions as a layer that distributes the tensile forces of the nasal musculature and provides a sling against which the mimetic muscles may counteract. The nasal musculature, ensheathed in the SMAS layer, may be divided into four principal groups: the elevators, the depressors, the compressor, and the dilators. The elevators include the procerus and the levator labii superioris alaeque nasi, whereas the depressors are composed of the alar nasalis and depressor septi nasi. The compressor of the nose is the transverse nasalis, and the dilators consist of the dilator naris anterior and posterior (Fig. 1). These nasal muscles animate the nose during facial expression and also regulate nasal airflow, especially during times of aerobic activity. Seventh nerve paralysis may cause nasal obstruction due to muscular hypofunction. The depressor septi muscle may exces-

sively contract the nasal tip downward when the patient smiles and may need to be severed to minimize this unattractive feature. The vascular anatomy of the nose is intimately related to the SMAS and must be appreciated for proper dissection during rhinoplasty. In a cadaveric study, Toriumi et al. determined that the major arterial, venous, and lymphatic vasculature coursed in or above the nasal SMAS. They concluded that the most desirable plane of dissection was under the nasal SMAS so as to preserve the vascularity to the overlying flap, minimize bleeding and edema, and achieve a more favorable cosmetic result. 3 The plane of dissection in an external or endonasal rhinoplasty should therefore be under the nasal SMAS and above the perichondrium of the upper lateral cartilage (ULC) and LLC. At the level of the nasal bones, it may be debated whether to dissect below the periosteum or remain between the periosteum and the SMAS. Some advocate that undermining the periosteum will preserve the periosteum and thereby stabilize the nasal bones after an osteotomy, whereas others contend that stripping the periosteum off the nasal bones prior to an osteotomy will diminish the nourishment that the intimate contact of bone to periosteum provides.

Bony and Cartilaginous Vault

The nose may be divided into vertical thirds according to its underlying bony and cartilaginous framework. The upper third of the nose consists of the nasal bones, the middle vault is composed of the ULCs, and the lower lateral (or alar) cartilages span the lower third of the nose (Fig. 2). On palpation, the superior nasal bones are rigidly fixed in position, the ULCs are semimobile, and the LLCs are more freely mobile. When grafting the nose with pliable or rigid materials, the natural mobility of the constituent nasal regions must be kept in mind and appropriately recreated in like fashion. However, a completely collapsed nasal tip may demand more rigid support, for instance, with costal cartilage to restore airway integrity of the nose at the expense of a more natural-feeling tip. The paired nasal bones that lie at the apex of the nose articulate with the frontal bones superiorly and with the ascending maxillary processes laterally. The nasal bones are much thicker at the nasion, or junction with the frontal bones at the nasofrontal suture line, and taper as they reach the caudal union with the ULCs. This caudal border between nasal bone and ULC should not be disturbed during rhinoplasty for fear of disrupting the internal nasal valve or causing an inverted-V deformity. Short nasal bones, which offer little support to the remaining two-thirds of the nose, are prone to yield an inverted-V deformity after osteotomies are performed as the nasal bone-ULC junction becomes accentuated from ULC collapse. Therefore, nasal-bone length should be attentively palpated prior to any rhinoplasty procedure. The middle third of the nose, composed of the
ULCs and underlying septum, constitutes the internal nasal valve (vide infra) and thereby principally determines nasal airflow. A main regulator of nasal respiration, the ULC-septal complex may detract from the beauty of the nose if a large cartilaginous hump is present or if either or both components are not perfectly straight. 

Figure 2 Bony/cartilaginous vault.

Figure 3 Various configurations of the scroll.

The ULCs articulate with the nasal bones above at the rhinion, or keystone area; laterally join with the pyriform aperture via loose ligaments; medially fuse with the septum; and inferiorly interdigitate with the LLCs at the scroll. This ULC-LLC union, or scroll, defines a major tip-support mechanism and may assume various configurations (Fig. 3). The scroll is often violated
during rhinoplasty, for example, when an intercartilaginous incision is made or when a cephalic trim is performed. Lateral to the ULCs, sesamoid cartilages may be variably found embedded in the fibroareolar connective tissue. The lower third of the nose, or nasal tip, is composed principally of paired lower lateral, or alar, cartilages. Medially, the LLCs begin anterior to the nasal spine as widened medial crural footplates and taper anteriorly as medial crura to the anterior nostril margin (Fig. 4). The intermediate crura diverge and ascend from the anterior nostril margin to join with the lateral crura. On profile view, the junction of the medial and intermediate crura may be seen as a double break in which the intermediate crura ascend slightly, and this favorable aesthetic feature should be preserved by maintaining the divergence of the intermediate crura. The intermediate crura span the infratip lobule, which is the soft-tissue region of the nose extending from the anterior nostril margin to the nasal tip. The junction of the intermediate and lateral crura is termed the angle, or anatomic dome, and is evident as a narrowed portion, or isthmus. Anderson describes locating the angle by drawing an imaginary line between the apices of the external and internal soft tissue triangles. The external soft-tissue triangle is that portion of the infratip lobule that spans the fissure between the medial and lateral crura, and the internal soft-tissue triangle is defined by the tissue that corresponds
cephalically at the upper end of the membranous septum.4 The clinical dome (vestibular dome, or simply dome) lies lateral to the angle and is composed entirely of lateral crus and correlates with the deepest recess of the anterior nostril margin (Fig. 4). The lateral crura extend superiorly and join the pyriform aperture at the socalled hinge, which is composed of either smaller accessory cartilages or represents the lateral extent of the lateral crus and which bends inward upon upward rotation of the nose. Of note, a few millimeters of soft tissue at the alar margin are devoid of cartilage laterally given the superior positioning of the lateral crus within the soft tissue.

Tip-Support Mechanisms

Appraisal of tip recoil is an easy method of determining the resilience and strength of the nasal tip. By digitally depressing the nasal tip and observing the give of tissue under the pressure of one's fingertip as well as the elastic recoil of the tip back to its native position, the integrity of tip support may be accurately assessed. As alluded to, surgical incisions and excisions serve to undermine tip support,

Figure 4 Nasal base.

and every effort must be made to preserve or restore any violated tip-support mechanisms via suture or grafting techniques to prevent unwanted tip collapse. Nasal-tip support may be classified into major and minor divisions. Three principal major tip supports include the strength of the LLC, the LLC-to-septum attachment, and the LLC-to-ULC attachment. Seven minor tip supports exist, including the interdomal ligament of Pitanguy, the sesamoid complex, the membranous septum, the cartilaginous dorsum, the nasal spine, and the alar attachment to the skin and soft tissue.

INTERNAL ANATOMY

Although the previous section devoted to external anatomy has focused on the dynamics of form and function, the following text concentrates primarily on the functional role that the internal anatomy of the nose plays.

Septum and Turbinates

The nasal septum plays a significant role in the traffic of airflow through the nose. A deviated nasal septum combined with contralateral (or ipsilateral) hypertrophy of the inferior turbinate leads to turbulent, nonlaminar, and congested airflow. These two structures, the septum and the anterior portion of the inferior turbinate, constitute part of the internal nasal valve, which is discussed at length in the following section. In review, the septum is comprised anteriorly of the quadralateral cartilage, inferiorly of the maxillary crest, posterosuperiorly of the perpendicular plate of the ethmoid, and posteroinferiorly of the vomer. An imaginary vertical line may be drawn from the caudal tip of the nasal bones through the anterior nasal spine, anterior to which the septum provides support to the nose and behind which it may only contribute to nasal obstruction. Anterior to this line of support, the rhinoplasty surgeon must exercise extreme caution when resecting septal cartilage to avoid an unintended saddle deformity. A generous portion of septum along the caudal and dorsal borders (at least 1cm if not greater) should be left intact to provide an inverted L-shaped strut.However, the rhinoplasty surgeon may resect portions of the anterior septum to effect a favorable cosmetic change, for example, resection of the septal angle to rotate the tip or reduction of the dorsum to straighten the profile. The septum provides an excellent source of grafting material as well, whether it be cartilage for general onlay or structural grafting or ethmoid bone as a spreader graft for rigid realignment of the middle vault. Turbinates, which act to humidify and warm the inspired air, also serve to direct airflow back to the nasopharynx in laminar channels. Injudicious removal of turbinates may lead to atrophic rhinitis or frank ozena with concomitant nasal obstruction rather than intended airflow improvement.Oftentimes only the anterior head of the inferior turbinate may contribute to nasal blockage by virtue of its position in the internal nasal valve; selective submucous resection of this portion may partially alleviate nasal obstruction while preserving precious nasal mucosa.

VALVULAR ANATOMY

External and internal nasal valves are critical regulators of nasal airflow and may be compromised due to a host of factors, including prior rhinoplasty. The external nasal valve is simply the nostril rim, composed of the LLC and the nasal floor. Prior to insertion of a nasal speculum, the careful observer may notice dynamic alar wall collapse upon even gentle inspiration, a hallmark of external valvular collapse. The external valve may be stented open with a finger distracting the ala laterally (a Cottle test) or by insertion and opening of the nasal speculum at the nostril aperture. Besides being congenitally flimsy cartilages, the external valve may be weakened by prior rhinoplasty, especially when an overly aggressive cephalic trim of the LLC has been undertaken.Correction of external valve collapse classically entails an alar batten graft that buttresses the weakened cartilage from inspiratory collapse. The internal nasal valve is the main regulator of nasal airflow in the Caucasian nose and is comprised of the septum, ULC, and anterior aspect of the inferior turbinate. The angle between the septum and the ULC should be at minimum 10 to 15 degrees to maintain internal valve patency. The non-Caucasian nose tends to have a more obtuse angle; therefore, internal valve collapse is less likely in the ethnic population.5 Any deviation of the septum, especially a high deflection, or internal curvature of the ULC, may lead to internal valve collapse. As mentioned, the anterior head of the inferior turbinate may also contribute to blockage through this narrow aperture. A Cottle test may be performed to elucidate the level of obstruction by distracting the middle vault laterally with a finger placed on the cheek immediately adjacent to the ULC. Alternatively, a narrow cotton-tip applicator may be inserted into the nostril to push the ULC laterally and thereby open up the internal valve. Internal valve collapse may be treated in a number of ways but may be more directly addressed by spreader graft placement between the ULC and septum.
CONCLUSION

The delicate art of rhinoplasty is founded upon a diligent study of anatomy. Only the dedicated pupil of nasal form and function will be able to accomplish an aesthetically and functionally satisfactory rhinoplasty. Before the surgeon wields a knife in his hand, he must ensure that the preparatory stage of careful analysis involving the patient's peculiar anatomic constitution has been appropriately conducted. Only after assiduous inspection and palpation of the external and internal nose will the surgeon feel confident that the surgical manipulations he should carry out will be best suited to his subject's anatomy.

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