(518) Two-Dimensional Geometric Morphometric Analysis of Nasopharyngeal Shape

Introduction: The nasopharynx is an important structure that functions in respiration, vocalization, and deglutition. Understanding variations in nasopharyngeal anatomy is essential for otorhinolaryngologists, as alterations in its shape have severe clinical implications. For instance, a reduction in nasopharyngeal transverse diameter can affect airway patency increasing the risk of developing sleep disorders. Limited research exists on variation in nasopharyngeal structure and its influence on physiological processes. This study aims to assess shape variation of the nasopharynx and its relationship to nasopharyngeal size to better understand adaptive changes in this region.

Methods: We used ImageJ to collect two-dimensional coordinate data on 10 to 15 transverse CT slices from 69 Rhesus macaques. Homologous landmarks were placed on clearly identifiable hard tissues demarcating the maximum anteroposterior and transverse margins of the nasopharynx from its most cranial to most inferior boundary. Trajectory of shape change along the nasopharyngeal tract was analyzed using MorphoJ and shape variation was assessed using Principal Components Analysis.

Results: The nasopharynx of Rhesus macaques tends to increase in size caudally, changing from a narrow diamond shape to a more triangular shape with the area of greatest transverse breadth located more dorsally. Individuals vary in the location of the shape change of the nasopharynx, and this variation may translate to altered respiratory functions. Shape is significantly associated with size in the nasopharynx but only in the upper regions of the tract (p < 0.001 upper, R2 = 0.215 versus p = 0.198-0.579 lower, R2 = 0.112).

Conclusions: By recognizing the relationship of size and shape in the upper respiratory region, clinicians can be on the look-out for potential pathologies arising from morphological variations in the cranial aspects of the nasopharynx. In humans, individuals with obstructive sleep apnea have smaller pharyngeal size than those without. Early recognition can lead to better prognosis and therapeutic options in these patient populations.