Effects of Anatomical Variations of the Nasal Cavity on Acoustic Rhinometry Measurements: A Model Study Ozcan Cakmak, M.D.,* Huseyin C ¸ elik, Ph.D.,# Mehmet Cankurtaran, Ph.D.,# and Levent Naci Ozluoglu, M.D.,* (Turkey) ABSTRACT Background: The goal of this study was to assess how ana- tomic variations of the nasal cavity affect the accuracy of acoustic rhinometry (AR) measurements. Methods: A cast model of a human nasal cavity was used to investigate the effects of the nasal valve and paranasal sinuses on AR measurements. A luminal impression of a cadaver nasal cavity was made, and a cast model was created from this impression. To simulate the nasal valve, inserts of varying inner diameter were placed in the model nasal passage. To simulate the paranasal sinuses, side branches with varying neck diameters and cavity volumes were attached to the model. Results: The AR measurements of the anterior nasal passage were reasonably precise when the passage area of the insert was within the normal range. When the passage area of the insert was reduced, AR measurements significantly underesti- mated the cross-sectional areas beyond the insert. The volume of the paranasal sinus had limited effect on AR measurements when the sinus ostium was small. However, when the ostium size was large, increasing the volume of the sinus led to significant overestimation of AR-derived areas beyond the ostium. Conclusion: The pathologies that narrow the anterior nasal passage result in the most significant AR error by causing area underestimation beyond the constriction. It also appears that increased paranasal sinus volume causes overestimation of areas posterior to the sinus ostium when the ostium size is large. If these physical effects are not considered, the results obtained during clinical examination with AR may be misin- terpreted. (American Journal of Rhinology 19, 262–268, 2005) A coustic rhinometry (AR) is a technique developed to measure the dimensions of the nasal cavity. 1 AR is a quick, painless, and noninvasive method and is potentially useful for quantifying the dimensions of nasal obstructions, evaluating the nasal cavity geometry, monitoring the nasal pathologies, and assessing the surgery results and response to medical treatment. AR has been widely accepted in a very short period of time, and it has been applied in a variety of ways in clinical trials. Clinical studies on healthy human subjects have documented significant correlations between the cross-sectional areas in the anterior part of the nasal cavity determined by AR and those determined by imaging modalities such as magnetic resonance imaging and com- puterized tomography (CT). 2–5 However, this does not hold true for the posterior part of the nasal cavity and the epipharynx, where AR significantly overestimates the cross-sectional areas compared with magnetic resonance imaging and CT. When investigating the accuracy of acoustic wave assess- ment of the nose, the effects of the complex anatomy of the From the *Faculty of Medicine, Department of Otorhinolar- yngology, Baskent University, Ankara, Turkey, and #Faculty of Engineering, Department of Physics, Hacettepe University, Beytepe, Ankara, Turkey Address correspondence and reprint requests to Ozcan Cak- mak, M.D., Baskent Universitesi Hastanesi, Kulak Burun Bo- gaz Anabilim Dali, Bahcelievler, 06490, Ankara, Turkey Copyright © 2005, OceanSide Publications, Inc., U.S.A. 262 May–June 2005, Vol. 19, No. 3