17 Nasal analysis and anatomy
A thorough understanding of nasal anatomy enables the practitioner to accurately perform reconstructive and aesthetic rhinoplasty.1 Nasal surgery is recognized as one of the most difficult procedures in plastic surgery, and accomplishing predicable results is a challenging task for the surgeon. Rhinoplastic surgery can be approached with these points in mind.
Surgery begins with a careful preoperative analysis utilizing standardized measurements. One must accurately describe the deformity in order to establish an operative goal. Less than hoped for results often occur as a direct result of failure to recognize one or more features prior to surgery.2
All tissues including bone, cartilage and soft tissue may contribute to any one measurement, e.g., nasal length. This is the main reason that understanding nasal anatomy is so critical to the performance of successful rhinoplasty surgery. Any rhinoplastic problem can be analyzed by individual components and their relationship to one another.3
Nasal anatomy is considered within the context of facial shape, facial proportions, and the size and shape of adjacent structures.4 The size and position of the chin, facial width, and facial height, are examples of factors that may influence the operative goal.
A basic knowledge of blood supply increases the safety of the open approach to rhinoplasty. This information is also important to avoid injury to the angular artery during external percutaneous osteotomy, and to avoid inadvertent intravascular injections.5
The nose is described employing a standardized terminology (Fig. 17.1). These terms allow standardized measurements to be defined (Fig. 17.2).
Fig. 17.1 Standardized terminology of external nasal landmarks exists that facilitates a discussion of proportionate and disproportionate nasal aesthetics. These landmarks, essentially reference points of nasal topography, often relate directly to the shape and relationship of underlying structures.
The nasolabial angle gives an approximation of tip rotation relative to the Frankfort Horizontal plane, drawn through the external auditory canal to the orbital rim. The nasofrontal angle is defined from the glabella to radix to nasal tip. Normative values exist for these measurements and vary according to gender (Fig. 17.3).
The normative values for tip projection, the distance from the alar crease to the nasal tip, is calculated in three ways, and described later in the text. The tip defining points seen on anterior view are located where the lateral crurae begin to diverge.
The crurae themselves consist of three sections or parts, each with its own curvature. The pyriform aperture, best visualized on basal view, corresponds with the bony aperture of the maxilla along the inferior nasal passage (Fig. 17.4).
Fig. 17.4 The lower lateral cartilages, comprising the lower third nasal vault, have three defined segments. These segments are determined by where the lower lateral cartilages display marked changes in curvature.
The algorithm for preoperative assessment follows that previously described.1 The relationship of the nose to the face is first analyzed. The nose is thus considered in the context of overall facial proportions for precise analysis. A simple technique for understanding facial proportions is using the fractal technique of thirds: the upper, middle, and lower face vertical heights are considered to be equal thirds. The lower face is the distance from the alar base to the chin (menton). This is further divided into thirds with the distance from the alar base to lip crease (stomion) being one-third of this height.
Frontal view allows nasal length to be analyzed relative to lower facial proportions. One measurement suggests that the distance from radix to tip defining points is equal to the distance from stomion to menton. (Fig. 17.5)
Fig. 17.5 General guidelines exist to assess nasal aesthetics in relation to the rest of the face. One guideline suggests that nasal length is equal to lower facial height. M, menton; R, radix; S, stomium; T, tip.
The nose is viewed from the frontal view (Fig. 17.6). A line drawn from the glabella, radix through the middle lip and chin helps to assess nasal deviation. The vertical line drawn from the radix to the midline lip and chin analyzes several structures. It helps to determine septal deviation, the position of the nasal bones and upper vault, and points out asymmetries of the lower lateral cartilages.6
Fig. 17.6 A line drawn from midline glabella to menton helps to assess nasal symmetry. This simple method is one of the best means to analyze septal deviation and the position of the nasal bones. It also emphasizes asymmetries of the maxilla or mandible.
The dorsal aesthetic lines are determined by a line drawn from the medial brow to the tip defining points, and should be two gently diverging curves. These can be judged relative to vertical lines drawn from the medial brows through the lateral nostril (Fig. 17.7).
The distance between the alar bases is approximately equal to intercanthal width. Alar shape is analyzed on frontal view and has a gull wing shaped curve, defined by the curvature of the lateral and middle crurae (Figs 17.8, 17.9).
Fig. 17.8 For measurements, especially angular values to be reproducible, head position is standardized. Here the Frankfort horizontal is shown: the line from the external auditory canal to the orbital rim is parallel to the horizon.
Fig. 17.9 The width of the bony base relative to the alar base is then assessed. (A) The bony base width should be 80% of the normal alar base width. (B) A normal alar base width is equal to the intercanthal distance or the width of one eye.
On lateral view, the alar base should lie slightly anterior to the medial canthus. The upper lip is slightly anterior to the lower lip; the lower lip slightly anterior to the chin. This analysis can reveal micro or macrogenia, as well as skeletal disharmonies including maxillary retrusion with a retro displaced alar base.
The nose itself is analyzed in lateral view beginning with the position and depth of the nasal root at the nasofrontal angle (radix). The radix lies at a point between the lash line and supratarsal crease with the eyes in horizontal gaze. The depth of the radix, or the nasion-medial canthal distance is approximately 15 mm.
Radix is an important point that helps to define the nasofrontal angle defined as the angle formed by the frontal bone, and a line drawn parallel to the nasal bone. If the nasofrontal angle is positioned more anteriorly or superiorly than normal, the nose appears elongated, and the tip projection will appear less, while if the nasofrontal angle is more posterior and inferior than normal, the nose will look shorter, and the tip will appear to project more. The radix forms the cephalic end for the measurement of nasal length, which is the distance from the radix to the nasal tip. Normally, nasal length is equal to the distance from stomion to menton (Fig. 17.11).
Fig. 17.11 A line drawn from radix to nasal tip helps to analyze dorsal aesthetics. The dorsum is located behind this line, and the steepest curve occurs just cephalad to the nasal tip. This supratip break is determined by the relationship between tip projection and septal and upper lateral (middle vault) height.
The nasal dorsum is then analyzed. The nasal dorsum lies slightly behind a line drawn from the radix to the nasal tip, more so in females than in males. The supratip break occurs cephalad to the tip defining points, and 2–3 mm behind the line from radix to nasal tip in women (Fig. 17.12). A slightly lower value is more desirable in males.
Fig. 17.12 The nasolabial angle is shown on the left and the columellar lobular angle is shown on the right. While less discussed, it is important to remember that the nasolabial angle is determined by alar base position as well as tip projection and nasal length. Maxillary deficiency has a tremendous effect in determining the nasolabial angle. The columellar lobular angle is determined by fewer variables: it simply represents the transition from medial to middle crura.
The nasolabial is then assessed. It is formed by a line drawn through the anterior and posterior ends of the nostril and the vertical facial plane. The nasolabial angle is usually 95–100° in females, and 90–95° in males (Fig. 17.13). This is slightly different than the columellar-labial angle which is formed by the columella and the upper lip, an angle which is often influenced by a prominent caudal septum which gives the impression of increased tip rotation despite a normal nasolabial angle.
Another determinant of tip rotation is the columellar-lobular angle, formed at the junction of the columella and the infratip lobule and represents the junction between the middle and medial crura. The ideal columellar lobular angle is 30–45° in females.