Anatomical Boundaries of the Nasal Valve
The internal nasal valve is bounded medially by the nasal septum, superiorly and laterally by the caudal margin of the upper lateral cartilage, and inferiorly by the floor of the pyriform aperture and the head of the inferior turbinate. 1, 2
Internal Nasal Valve (Primary Valve)
The internal nasal valve represents the narrowest portion of the nasal airway and is responsible for more than two-thirds of total nasal airflow resistance. 1 Its specific boundaries include:
- Medial boundary: The nasal septum (specifically the anterior cartilaginous septum) 1, 2, 3
- Superior and lateral boundary: The caudal margin of the upper lateral cartilage and its fibro-adipose attachment to the pyriform aperture (sometimes called the "empty triangle") 2, 3
- Inferior boundary: The floor of the pyriform aperture and the head of the inferior turbinate 1, 2, 4
The valve itself is the specific slit-like segment between the caudal margin of the upper lateral cartilage and the septum, typically forming an angle of approximately 10-15 degrees. 2, 5
Nasal Valve Area vs. Nasal Valve
It is critical to distinguish between the "nasal valve" and the "nasal valve area"—these are not interchangeable terms. 2 The nasal valve area is a broader three-dimensional construct that encompasses the entire narrowest region of the anterior nose, while the nasal valve specifically refers to the slit-like opening between the upper lateral cartilage and septum. 2, 5
Clinical Significance of Valve Anatomy
Small deformities in the nasal valve area produce disproportionately severe impairment of nasal airflow because this region accounts for the majority of nasal resistance. 1, 2 According to Poiseuille's law, even minor constrictions at this "flow limiting segment" result in clinically significant breathing difficulties. 5
The anterior location of the valve explains why anterior septal deviations are far more clinically significant than posterior deviations—a small anterior deviation affects the valve area directly, while larger posterior deviations may be asymptomatic. 1
External Nasal Valve
The external nasal valve, though less commonly discussed in the provided guidelines, consists of the nasal vestibule and nostril aperture, bounded by the columella medially, the nasal sill inferiorly, and the alar rim laterally. 3 This region is stabilized by cartilaginous structures and alar dilator muscles during inspiration. 3
Common Clinical Pitfall
Approximately 80% of the general population have off-center nasal septums, but only 26% have clinically significant deviation causing symptoms. 1, 6 The key determinant is whether the deviation affects the valve area specifically—deviations that spare the valve region may be anatomically present but functionally insignificant. 1, 7