Olfaction and its alteration by nasal obstruction, rhinitis, and rhinosinusitis

Abstract

The sense of smell has been largely ignored by otorhinolaryngologists, even though 1) its medical stewardship falls within their specialty's purview, 2) olfactory dysfunction is not uncommon in the general population, and 3) disorders of olfaction have significant quality of life, nutritional, and safety consequences. This report provides a succinct overview of the major intranasal neural systems present in humans (namely, cranial nerves O, I, and V, and the nonfunctional accessory [vomeronasal] organ system), along with a summary of notable findings resulting from the application of modern olfactory tests to patient populations, emphasizing diseases of the nose. Such tests have led to the discovery of significant influences of age, gender, smoking, toxic exposure, and genetics on the ability to smell. Within the field of otorhinolaryngology, they have revealed that 1) surgical and medical interventions in patients with rhinosinusitis do not, on average, lead to complete recovery of olfactory function, despite common beliefs to the contrary, and 2) associations are generally lacking between measures of airway patency and olfactory function in such cases. These findings have thrown into question the dogma that olfactory loss in rhinosinusitis is attributable primarily to blockage of airflow to the receptors and have led to histopathological studies demonstrating significant olfactory epithelial compromise in sinonasal syndromes.

Figure Fig. 1.

Low‐power electron photomicrograph of cross section of the human neuroepithelium depicting the four major types of cells: bipolar receptor cells (arrows point to cilia at dendritic knob; c = cell body), microvillar cells (M), sustentacular cells (S), and basal cells (B). BG = Bowman's gland; LP = lamina propria; N = collection of axons within an ensheathing glial cell; D = degenerating cells; BS = basal cell undergoing mitosis. From Moran et al., with permission.

Figure Fig. 2.

The Smell Threshold Test™, a commercially available test for assessing odor detection thresholds. Concentrations of phenyl ethyl alcohol, ranging from 10⁻² to 10⁻¹⁰ log vol/vol in half‐log concentration steps, are provided, along with blanks for forced‐choice testing. (Photograph courtesy of Sensonics, Inc., Haddon Heights, NJ. Copyright 2000, Sensonics, Inc.)

Figure Fig. 3.

The four booklets of the 40‐odorant University of Pennsylvania Smell Identification Test (UPSIT). Each page contains a microencapsulated odorant that is released by means of a pencil tip. This test, which has been administered to approximately 200,000 patients since its development, is the most widely used olfactory test in the world (commercially known as the Smell Identification Test™). The UPSIT is considered to be the “eyechart for the nose.” (Photograph courtesy of Sensonics, Inc., Haddon Heights, NJ. Copyright 2000, Sensonics, Inc.)

Figure Fig. 4.

(A) Nasal obstruction ratings, based on assessment of mouth breathing and hyponasality, in 28 children before and after adenoidectomy. (B) Phenyl ethyl alcohol odor detection thresholds before and after adenoidectomy in the same study population. Each line joins preoperative and postoperative values for an individual subject. (Reprinted with permission from Ghorbanian et al. Copyright 1983, American Academy of Pediatrics.)