External Valve Stenosis Rhinoplasty

Mink first coined the term nasal valve in 1903. Initially, he described the nasal valve as the slitlike opening between the caudal end of the upper lateral cartilage and the nasal septum. Since then, the term nasal valve has broadened to include both an internal nasal valve (Mink's description) and an external nasal valve. The external nasal valve is described as the region caudal to the internal valve, bounded laterally by the nasal alar and medially by the septum and columella.

Nasal valves (internal and external) may function as Starling resistors (collapsible tubes attached to rigid tubes). The transmural pressure increases as the airflow velocity increases, which leads to collapse and a decrease in airflow. This may be a mechanism to prevent large volumes of unheated and unhumidified air from reaching the lower respiratory tract. In individuals with either acquired or congenital external valve collapse, this mechanism functions at too low a transmural pressure, which leads to premature collapse and difficulty with nasal breathing.

The nose can be modeled as a tube. The Bernoulli principle demonstrates that the speed of a fluid through a tube is greatest where the diameter of the tube is the least. Where the velocity is the greatest, the pressure is the lowest. Because the nasal valves (internal and external) are choke points for the flow of air, the difference between intranasal and atmospheric pressure is the greatest at these points, which leads to the greatest potential for collapse. Individuals with alae collapse who report airflow deficiency with inspiration are candidates for surgical correction.

Nasal valve collapse or obstruction has many potential etiologies. Some of the more frequent causes include the following:

• Congenital malformation, weakness, or cephalad rotation of the lower lateral cartilage

• Deficiency of the lateral crus of the lower lateral cartilage secondary to previous surgery with overaggressive resection of cartilage

• Trauma that leads to loss of tissue

• Full-thickness surgical resection of the alar with insufficient reconstruction

• Aggressive narrowing of the nasal tip during rhinoplasty (see the Medscape Reference article Postrhinoplasty Nasal Obstruction Rhinoplasty)

• Caudal septal deflection that narrows the valve and causes increased velocity of airflow with a larger transalar pressure differential

• Facial nerve palsy that leads to loss of nasal dilators

• Sequelae of aging that leads to loss of nasal alar stiffness - A literature review by Khetpal et al listed internal and external valve collapse as one of the manifestations of an aging nose, along with soft tissue atrophy, bony fragility and resorption, tip ptosis, and worsening of the dorsal hump ^[1]

• Overprojection of nasal tip that leads to slitlike nares with increased velocity of airflow

A study by Chambers et al suggested that nasal valve dysfunction is underdiagnosed and should be taken into account as a possibility in patients with septal deviation, prior to the performance of septoplasty, particularly in those patients who demonstrate severe dorsal septum deflection and a narrow middle vault. The study involved 40 patients who, despite having undergone septoplasty, still suffered from nasal obstruction, requiring valve correction. These included 38 patients (95%) with moderate or severe internal nasal valve narrowing, 19 patients (48%) with internal nasal valve collapse, 18 patients (45%) with external nasal valve narrowing, and 16 patients (40%) with external nasal valve collapse. Aside from internal nasal valve narrowing, the most common anatomical causes of obstruction were dorsal septum deflection (26 patients; 65%) and a narrow middle vault (16 patients; 40%), indicating these as risk factors for valve dysfunction in patients with failed septoplasty. ^[2]

Any process, condition, or trauma that weakens the lower lateral cartilage or alar walls or that narrows the entrance to the nose can lead to collapse of the external valve. Upon inspiration, the increase in transmural pressure across the nasal ala leads to collapse of the external valve.

History

In obtaining patient history, elicit the following:

• Previous history of nasal surgery or trauma

• History of facial nerve injury

• Nasal obstruction, either with normal nasal respiration or with forced inspiration

• Seasonal variations in nasal obstruction

Physical examination

A complete nasal examination to exclude other causes of nasal obstruction is mandatory. More specific findings may include the following:

• Observed external valve obstruction

• Caudal septal deflection

• Width of columella base

• Nasal alar collapse

• Exaggerated medial movement of alar cartilage upon deep inspiration

• Encroachment of the lateral portion of the crus into the vestibule

• Presence of tip bossae

• Deep alar grooves

• Other fixed vestibular obstruction

• Apparent improvement in symptoms when cotton-tipped applicators or cerumen loops are used to support the external nasal valve (when collapse is evident), with specific improvement in airflow and relief of symptoms

Any airway compromise caused by obstruction of the external nasal valve is an indication of external valve stenosis/collapse. Before an attempt is made to stiffen or to suspend the lateral ala, a reasonable approach is to address fixed obstructions first. This approach helps to determine if the collapse is secondary to the decreased area that causes larger transmural pressures. Caudal septal deflections by themselves can contribute to valve collapse, but recognition of a deficient lateral nasal sidewall is important to fully address the decrease in airflow. The most absolute indication is the symptomatic collapse of the alar upon inspiration.

The internal nasal valve is the slitlike opening between the caudal end of the upper lateral cartilage and the nasal septum. The external nasal valve is described as the region caudal to the internal valve bounded superolaterally by the caudal edge of the upper lateral cartilage, laterally by the nasal alar and bony piriform aperture of the maxilla, and medially by the septum and columella. The ligamentous attachment of the lateral crus to the bony maxilla provides support for the lateral border area. The primary muscles responsible for maintaining the patency of the nasal valve include the nasal and dilator naris muscles. The measured area of the nasal valve ranges from 55-64 mm².

If the patient considers any cosmetic changes in the shape of the nose unacceptable, he or she is a poor candidate for any attempt at surgical correction of a collapsing external nasal valve. However, patients who have internal obstructions secondary to scarring or a narrow vestibule may be helped by procedures designed to increase the cross-sectional area of the external nasal valve.