The External Nasal Valve




The external nasal valve is a complex entity comprised of multiple structures and tissue types. As such, there is no single operation that can address all problems of the external valve. This article reviews the relevant anatomy, pathologic conditions, and treatments for external nasal valve dysfunction, including a detailed review of the nasal muscles and their contribution to external nasal valve patency. Surgical and nonsurgical options for treatment and the evidence supporting the importance of proper external nasal valve function on quality-of-life measures are discussed.


Key points








  • Nasal obstruction has a negative effect on quality of life. The external nasal valve plays an important role in nasal breathing and, consequently, nasal obstruction.



  • Multiple anatomic structures make up the external nasal valve. Surgery to correct external nasal valve pathologic conditions must be tailored to the specific needs of the patient.



  • A detailed understanding of the anatomy of the lower third of the nose is critical to proper treatment. Knowing how the anatomy contributes to pathologic conditions is as important as where it is.



  • There are effective surgical and nonsurgical treatments for external nasal valve dysfunction.



  • The muscles of the nose may play a bigger role in external nasal valve problems than is typically recognized.




Because the internal nasal valve has been identified as the narrowest segment in the nasal cavity, more has been written about the internal nasal valve than the external. A PubMed search at the time of this writing shows 202 articles when searching for “internal nasal valve” and 156 for “external nasal valve.” However, the external nasal valve is the gateway to the nose. Pathologic conditions in the external valve are a complex interplay between the cartilage, skin, nasal muscles, vibrissae, and even the force of inspiration. This article aims to consolidate much of the current knowledge of external nasal valve problems and their treatment.




Anatomy


Mink was the first to identify the nasal valve as a single entity in 1903. To this day, in some articles, there is no differentiation between the internal nasal valve and the external nasal valve. Constantian and Martin rightfully assert that this lack of consensus probably hinders rhinoplasty education. Distinguishing the internal from the external valve is important because they are distinct anatomic areas, though they do share a common border at the scroll. Many investigators describe the external nasal valve as the nostril opening; however, it is more clinically helpful to consider the nostril opening as a component of the external nasal valve. In other words, the nostril opening is an area, whereas the external nasal valve is a volume. The borders of this space are the nostril opening caudally, the septum and medial crura medially, the alar cartilage and fibrofatty tissue anterolaterally, and the internal nasal valve opening posteriorly. With this many structures playing an important role in the integrity of the external nasal valve, it should be no surprise that there are multiple ways that external nasal valve insufficiency can manifest. Further complicating matters is that external nasal valve problems may be static, dynamic, or both.


The alar lobule is the convexity that abuts the cheek at the alar-facial junction, bordered superiorly by the alar groove. This curves medially, ending in a concavity posterior to the nasal tip lobule ( Fig. 1 ). Ali-Salaam and colleagues sectioned 15 cadavers and found that the alar lobule was devoid of cartilage in all specimens. The alar lobule is composed of skin, fibrofatty fascia, and muscle. The lateral crus travels superior to the alar groove and the investigators found that the lateral crura had 4 distinct anatomic variants. In some specimens, the lateral crus ended near the alar groove. In others, it continued along the alar groove and was either smooth or corrugated. Several had smaller, discontiguous sesamoid cartilages laterally.




Fig. 1


The lower lateral cartilages are shown in white. The alar lobule is blue. The alar groove is the dotted line. Note that the lateral crura are not located in the alar lobule and that the point of maximal concavity of the alar groove is typically located at the lateral end of the lateral crus.


The paired lower lateral cartilages are the primary structural component of the external nasal valve. Despite this, the alar cartilages are not usually as stiff as the septum. They begin medially at the feet of the medial crura. These are typically splayed somewhat from the midline. The medial crura sweep anterocephalically to the intermediate crura, where they twist laterally, creating a divergence in the area of the infratip lobule. The intermediate crura transition to the domes, a tighter bend that creates the definition of the tip. The domes should have an angle between them that is very obtuse. When the interdomal angle is too acute, the caudal margins of the lateral crura lie closer to the septum. This has important implications for both form and function. When the caudal edge of the lateral crus is close to the septum, the volume of the nasal vestibule is decreased. Aesthetically, this results in an alar rim that is poorly supported and will have a characteristic parenthesis deformity on the frontal view.


When describing the position of the lateral crus, it is helpful to think of it as having both a long and a short axis. The long axis is a line that bisects the dome and roughly bisects the lateral crus along its length. The long axis should be oriented toward the lateral canthus. When the long axis is positioned closer to the medial canthus, the lateral crura are said to be cephalically malpositioned. Cephalically malpositioned lateral crura are a significant contributor to external nasal valve incompetence. In a study by Constantian, all secondary rhinoplasty patients in the sample who had cephalically malpositioned lateral crura had external nasal valve incompetence.


The short axis is perpendicular to the long axis and extends from the cephalic border of the lateral crus to the caudal border. Ideally, the short axis makes nearly a 90° angle with the septum. When the angle between the septum and the short axis becomes more acute, the lateral crura are sagittally malpositioned and the vestibular volume is decreased. Fig. 2 shows the relationships between the septum, dome angles, and the short and long axes of the lateral crura. Sagittally malpositioned lateral crura are also prone to acting like a hinge, predisposing to collapse of the valve.




Fig. 2


The dome angles are represented by the black dotted lines. The short axes of the lateral crura are the yellow dotted lines. Note that they are parallel to the dome angles. Modifying the dome angles is an important component of repositioning the short axis of the lateral crus. The long axes of the lateral crura are represented by the green dashed lines.


Ideally, the shape of the lateral crus should be gently convex or flat. Markedly convex lateral crura will create a bulbous tip and will often be internally recurvate. Internally recurvate lateral crura create a mass effect in the nasal vestibule because the tail of the lateral crus is positioned too far medially toward the septum ( Fig. 3 ). Concave lateral crura also decrease the volume of the external nasal valve and can lead to nasal obstruction.




Fig. 3


When the lateral end of the lateral crus is internally recurvate, it obstructs the airway by impinging on the external nasal valve.


The caudal septum should lie in a midsagittal plane between the medial crura. Therefore, the medial crura typically affect the nostril opening more than the caudal septum. Short or flared medial crura will widen the columella and subsequently narrow the nostril ( Fig. 4 ). However, in patients with a severe caudal septal deflection, it may lie laterally to the medial crura and become the medial border of the nostril ( Fig. 5 ).




Fig. 4


Short medial crura create a widened columella, which narrows the nostrils and can lead to nasal obstruction.



Fig. 5


A significant caudal septal deviation can also obstruct the external nasal valve.


The circumference of the external nasal valve, with the exception of the thin skin under the lateral crus and the mucosa of the septum, is lined with hair-bearing skin. Though the vibrissae have an important job filtering out larger airborne particles, they have recently been shown to make a significant contribution to resistance in the external nasal valve.


Externally, the region of the external nasal valve is covered with skin. Under the skin are several important muscles of facial expression that affect the rigidity of the external nasal valve. Though Henry Gray first described the nasal muscles in 1858, they are often overlooked in typical texts and lectures about rhinoplasty. One reason that these muscles may be less frequently discussed is that there is little agreement on concepts as basic as their names. In an effort to clarify descriptions of the muscles in this article, alternate, typically older, names will be placed in parentheses.


The nasalis muscle (compressor nasi, musculus transversus) originates from the maxilla near the canine fossa and divides into a transverse and an alar part (dilator naris posterior, pars alaris). The transverse nasalis spans the dorsum and contracts the nostrils and compresses the nose. Its contraction narrows the external nasal valve. The alar part inserts onto the surface of the lateral crus and assists in dilating and stiffening the alar lobule.


The musculus myrtiformis (musculus depressor septi nasi) also has 2 parts and originates near the nasalis on the maxilla near the canine fossa. The medial part inserts onto the caudal septum and medial crura. It is often referred to as the musculus depressor septi nasi and is responsible for depressing the nasal tip. The lateral part (depressor alae nasi) surrounds the nostril opening and opposes the lifting forces of the levator labii superioris alequae nasi and depresses and dilates the nostril.


Similarly, the musculus procerus (musculus pyramidalis nasi) has 2 parts. It is located at the root of the nose between the eyebrows. The glabellar part joins with the transverse part of the nasalis and is primarily responsible for moving the medial eyebrow inferiorly. The alar part originates from the nasal bones and upper lateral cartilages, and inserts into the cephalic edge of the lateral crus and continues into the alar lobule. Its function is to elevate and dilate the alar rim.


The levator labii superioris alequae nasi (caput angulare musculi quadrati labii superioris) inserts superiorly at the medial canthus, frontal process of the maxilla, and the nasal bones. It also divides into 2 parts. The alar part inserts on the cephalic border of the lateral crus and interdigitates with the alar part of the nasalis muscle. It elevates and dilates the nostril. The labial fascicle joins the musculus myrtiformis and orbicularis oris, and contributes to the nasal tip depressors.


Though originally described by Gray in the first edition of his text, there has been disagreement from subsequent investigators about the exact location of the musculus anomalous nasi (musculus rhomboideus). Figallo and Acosta describe it as a transverse muscle between the alar part of the procerus and the alar fascicle of the levator labii superioris alequae nasi. As it intermingles with the fibers of these muscles, it assists with elevation of the alar margin.


The musculus dilator naris anterior (apices nasi) and the musculus compressor narium minor are in close apposition to the lower lateral cartilages, and play an important role in compressing the alae Table 1 summarizes the locations and functions of the previously described clinically relevant muscles.



Table 1

Nasal muscles
















































Muscle Function
Musculus procerus (musculus pyramidalis nasi)
Glabellar part Moves the medial eyebrow inferiorly
Alar part Elevates the alar rim and dilates the nostril
Levator labii superioris alequae nasi (caput angulare musculi quadrati labii superioris)
Alar part Elevates the alar rim and dilates the nostril
Labial part With musculus myrtiformis depresses the nasal tip
Musculus anomalous nasi (musculus rhomboideus) Elevates alar rim with levator labii superioris alequae nasi and procerus
Nasalis muscle (compressor nasi, musculus transversus)
Transverse part Narrows the external nasal valve
Alar part (dilator naris posterior, pars alaris) Dilates and stiffens the alar lobule
Musculus myrtiformis
Medial part (musculus depressor septi nasi) Depresses the nasal tip
Lateral part (depressor alae nasi) Depresses and dilates the nostril
Musculus dilator naris anterior (apices nasi) Compresses the ala
Musculus compressor narium minor Compresses the ala


Fig. 6 shows the effects of the muscles that insert into the external nasal valve. This patient had significant alar retraction and compression of the alar groove before surgery, in part due to excessive tone of his alar nasal musculature. Fig. 6 A shows his nose before any intervention. Before his operation, he was treated with 10 units of onabotulinumtoxinA into each alar margin. His lateral nasal wall was reinforced with lateral crural strut grafts extending into the area of the alar groove during surgery. He declined any further chemodenervation treatment and is shown 2 weeks, 3 months, and 1 year after surgery. Despite the reinforcement of his lateral nasal wall with the lateral crural strut grafts, his alae returned to nearly their preoperative state.




Fig. 6


This patient had nasal obstruction in part due to external nasal valve insufficiency. He had hypertonic nasal valve compressors before surgery. ( A ) Nose before any intervention. ( B ) Nose after treatment with 10 units of onabotulinumtoxinA. Note that his alar retraction and nasal sidewall pinching is already improved. ( C ) The combined effects of onabotulinumtoxinA and lateral crural strut grafts 2 weeks after surgery. There is further improvement in the shape of his nasal alae and lateral nasal walls. ( D ) Three months after surgery. At this point, the effects of the onabotulinumtoxinA are gone. His alae are retracting and his sidewall becoming more pinched. ( E ) One year after surgery without any further onabotulinumtoxinA treatments. Though his breathing has improved, his nasal muscles have returned the shape of his nose to approximately its preoperative state.


Though some investigators have described the nasal muscles as rudimentary, as muscles of facial expression controlled by the facial nerve, the nasal musculature may be more voluntary and more integral to nasal breathing than typically thought. Vaiman and colleagues performed several studies demonstrating the efficacy of treating nasal valve weakness with biofeedback via surface electromyography (EMG) with and without transcutaneous electrical stimulation of the nasal muscles. Aksoy and colleagues specifically examined the role that the nasal muscles play in nasal valve dysfunction. When patients with dynamic nasal valve collapse were compared with healthy volunteers, those with collapse had statistically significant abnormalities in their use of musculus dilator naris anterior and the transverse part of the nasalis muscle during inspiration. Researchers at the Mayo Clinic measured both patency of the airway with rhinomanometry and alar stiffness in healthy volunteers. Measurements were taken before and after induced muscular paresis with lidocaine. There was a statistically significant change after the injection, supporting their hypothesis that the nasal muscles make an important contribution to the patency of the airway.




Anatomy


Mink was the first to identify the nasal valve as a single entity in 1903. To this day, in some articles, there is no differentiation between the internal nasal valve and the external nasal valve. Constantian and Martin rightfully assert that this lack of consensus probably hinders rhinoplasty education. Distinguishing the internal from the external valve is important because they are distinct anatomic areas, though they do share a common border at the scroll. Many investigators describe the external nasal valve as the nostril opening; however, it is more clinically helpful to consider the nostril opening as a component of the external nasal valve. In other words, the nostril opening is an area, whereas the external nasal valve is a volume. The borders of this space are the nostril opening caudally, the septum and medial crura medially, the alar cartilage and fibrofatty tissue anterolaterally, and the internal nasal valve opening posteriorly. With this many structures playing an important role in the integrity of the external nasal valve, it should be no surprise that there are multiple ways that external nasal valve insufficiency can manifest. Further complicating matters is that external nasal valve problems may be static, dynamic, or both.


The alar lobule is the convexity that abuts the cheek at the alar-facial junction, bordered superiorly by the alar groove. This curves medially, ending in a concavity posterior to the nasal tip lobule ( Fig. 1 ). Ali-Salaam and colleagues sectioned 15 cadavers and found that the alar lobule was devoid of cartilage in all specimens. The alar lobule is composed of skin, fibrofatty fascia, and muscle. The lateral crus travels superior to the alar groove and the investigators found that the lateral crura had 4 distinct anatomic variants. In some specimens, the lateral crus ended near the alar groove. In others, it continued along the alar groove and was either smooth or corrugated. Several had smaller, discontiguous sesamoid cartilages laterally.




Fig. 1


The lower lateral cartilages are shown in white. The alar lobule is blue. The alar groove is the dotted line. Note that the lateral crura are not located in the alar lobule and that the point of maximal concavity of the alar groove is typically located at the lateral end of the lateral crus.


The paired lower lateral cartilages are the primary structural component of the external nasal valve. Despite this, the alar cartilages are not usually as stiff as the septum. They begin medially at the feet of the medial crura. These are typically splayed somewhat from the midline. The medial crura sweep anterocephalically to the intermediate crura, where they twist laterally, creating a divergence in the area of the infratip lobule. The intermediate crura transition to the domes, a tighter bend that creates the definition of the tip. The domes should have an angle between them that is very obtuse. When the interdomal angle is too acute, the caudal margins of the lateral crura lie closer to the septum. This has important implications for both form and function. When the caudal edge of the lateral crus is close to the septum, the volume of the nasal vestibule is decreased. Aesthetically, this results in an alar rim that is poorly supported and will have a characteristic parenthesis deformity on the frontal view.


When describing the position of the lateral crus, it is helpful to think of it as having both a long and a short axis. The long axis is a line that bisects the dome and roughly bisects the lateral crus along its length. The long axis should be oriented toward the lateral canthus. When the long axis is positioned closer to the medial canthus, the lateral crura are said to be cephalically malpositioned. Cephalically malpositioned lateral crura are a significant contributor to external nasal valve incompetence. In a study by Constantian, all secondary rhinoplasty patients in the sample who had cephalically malpositioned lateral crura had external nasal valve incompetence.


The short axis is perpendicular to the long axis and extends from the cephalic border of the lateral crus to the caudal border. Ideally, the short axis makes nearly a 90° angle with the septum. When the angle between the septum and the short axis becomes more acute, the lateral crura are sagittally malpositioned and the vestibular volume is decreased. Fig. 2 shows the relationships between the septum, dome angles, and the short and long axes of the lateral crura. Sagittally malpositioned lateral crura are also prone to acting like a hinge, predisposing to collapse of the valve.




Fig. 2


The dome angles are represented by the black dotted lines. The short axes of the lateral crura are the yellow dotted lines. Note that they are parallel to the dome angles. Modifying the dome angles is an important component of repositioning the short axis of the lateral crus. The long axes of the lateral crura are represented by the green dashed lines.


Ideally, the shape of the lateral crus should be gently convex or flat. Markedly convex lateral crura will create a bulbous tip and will often be internally recurvate. Internally recurvate lateral crura create a mass effect in the nasal vestibule because the tail of the lateral crus is positioned too far medially toward the septum ( Fig. 3 ). Concave lateral crura also decrease the volume of the external nasal valve and can lead to nasal obstruction.




Fig. 3


When the lateral end of the lateral crus is internally recurvate, it obstructs the airway by impinging on the external nasal valve.


The caudal septum should lie in a midsagittal plane between the medial crura. Therefore, the medial crura typically affect the nostril opening more than the caudal septum. Short or flared medial crura will widen the columella and subsequently narrow the nostril ( Fig. 4 ). However, in patients with a severe caudal septal deflection, it may lie laterally to the medial crura and become the medial border of the nostril ( Fig. 5 ).




Fig. 4


Short medial crura create a widened columella, which narrows the nostrils and can lead to nasal obstruction.



Fig. 5


A significant caudal septal deviation can also obstruct the external nasal valve.


The circumference of the external nasal valve, with the exception of the thin skin under the lateral crus and the mucosa of the septum, is lined with hair-bearing skin. Though the vibrissae have an important job filtering out larger airborne particles, they have recently been shown to make a significant contribution to resistance in the external nasal valve.


Externally, the region of the external nasal valve is covered with skin. Under the skin are several important muscles of facial expression that affect the rigidity of the external nasal valve. Though Henry Gray first described the nasal muscles in 1858, they are often overlooked in typical texts and lectures about rhinoplasty. One reason that these muscles may be less frequently discussed is that there is little agreement on concepts as basic as their names. In an effort to clarify descriptions of the muscles in this article, alternate, typically older, names will be placed in parentheses.


The nasalis muscle (compressor nasi, musculus transversus) originates from the maxilla near the canine fossa and divides into a transverse and an alar part (dilator naris posterior, pars alaris). The transverse nasalis spans the dorsum and contracts the nostrils and compresses the nose. Its contraction narrows the external nasal valve. The alar part inserts onto the surface of the lateral crus and assists in dilating and stiffening the alar lobule.


The musculus myrtiformis (musculus depressor septi nasi) also has 2 parts and originates near the nasalis on the maxilla near the canine fossa. The medial part inserts onto the caudal septum and medial crura. It is often referred to as the musculus depressor septi nasi and is responsible for depressing the nasal tip. The lateral part (depressor alae nasi) surrounds the nostril opening and opposes the lifting forces of the levator labii superioris alequae nasi and depresses and dilates the nostril.


Similarly, the musculus procerus (musculus pyramidalis nasi) has 2 parts. It is located at the root of the nose between the eyebrows. The glabellar part joins with the transverse part of the nasalis and is primarily responsible for moving the medial eyebrow inferiorly. The alar part originates from the nasal bones and upper lateral cartilages, and inserts into the cephalic edge of the lateral crus and continues into the alar lobule. Its function is to elevate and dilate the alar rim.


The levator labii superioris alequae nasi (caput angulare musculi quadrati labii superioris) inserts superiorly at the medial canthus, frontal process of the maxilla, and the nasal bones. It also divides into 2 parts. The alar part inserts on the cephalic border of the lateral crus and interdigitates with the alar part of the nasalis muscle. It elevates and dilates the nostril. The labial fascicle joins the musculus myrtiformis and orbicularis oris, and contributes to the nasal tip depressors.


Though originally described by Gray in the first edition of his text, there has been disagreement from subsequent investigators about the exact location of the musculus anomalous nasi (musculus rhomboideus). Figallo and Acosta describe it as a transverse muscle between the alar part of the procerus and the alar fascicle of the levator labii superioris alequae nasi. As it intermingles with the fibers of these muscles, it assists with elevation of the alar margin.


The musculus dilator naris anterior (apices nasi) and the musculus compressor narium minor are in close apposition to the lower lateral cartilages, and play an important role in compressing the alae Table 1 summarizes the locations and functions of the previously described clinically relevant muscles.



Table 1

Nasal muscles
















































Muscle Function
Musculus procerus (musculus pyramidalis nasi)
Glabellar part Moves the medial eyebrow inferiorly
Alar part Elevates the alar rim and dilates the nostril
Levator labii superioris alequae nasi (caput angulare musculi quadrati labii superioris)
Alar part Elevates the alar rim and dilates the nostril
Labial part With musculus myrtiformis depresses the nasal tip
Musculus anomalous nasi (musculus rhomboideus) Elevates alar rim with levator labii superioris alequae nasi and procerus
Nasalis muscle (compressor nasi, musculus transversus)
Transverse part Narrows the external nasal valve
Alar part (dilator naris posterior, pars alaris) Dilates and stiffens the alar lobule
Musculus myrtiformis
Medial part (musculus depressor septi nasi) Depresses the nasal tip
Lateral part (depressor alae nasi) Depresses and dilates the nostril
Musculus dilator naris anterior (apices nasi) Compresses the ala
Musculus compressor narium minor Compresses the ala

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Aug 26, 2017 | Posted by in General Surgery | Comments Off on The External Nasal Valve
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