Upper Respiratory Tract Lesions in Inhalation Toxicology

This paper describes some important differences in normal histology of the upper respiratory tract of laboratory animals. It also provides examples of lesions observed or reported in the upper respiratory tract of laboratory animals, predominantly rodents, exposed via inhalation. The anatomy and physiology of upper respiratory tract tissues play a major role in the response to an insult, given that different epithelial types vary in susceptibility to injury and toxicant exposure concentrations throughout the airway vary due to airflow dynamics. Although dogs and nonhuman primates are utilized for inhalation toxicology studies, less information is available regarding sites of upper respiratory injury and types of responses in these species. Awareness of interspecies differences in normal histology and zones of transition from squamous to respiratory to olfactory epithelium in different areas of the upper respiratory tract is critical to detection and description of lesions. Repeated inhalation of chemicals, drugs, or environmental contaminants induces a wide range of responses, depending on the physical properties of the toxicant and concentration and duration of exposure. Accurate and consistent fixation, trimming, and microtomy of tissue sections using anatomic landmarks are critical steps in providing the pathologist the tools needed to compare the morphology of upper respiratory tract tissues from exposed and control animals and detect and interpret subtle differences.