Nasal olfactory lesions are most commonly seen in inhalation exposures, but they are also seen in feeding studies, gavage studies, and intraperitoneal injection studies. Many factors, such as the route of administration, the physical characteristics of the test agent, and the species of animal, have a significant impact on the anatomic sites affected within the nasal cavity and on the types of lesions observed. For example, the tips of the nasal and maxillary turbinates, which are lined by transitional epithelium, are frequently the initial sites of injury in inhalation studies, but they may be unaffected when nasal lesions are caused by systemic exposure to an agent administered by another route or if enzymatic activation of the agent is required for toxicity. Nasal lesions are generally site specific due to regional deposition of the chemical and regional tissue susceptibility to the chemical, so it is advantageous to subdivide the diagnoses according to site, cell type, or other anatomic designators. The diagnoses should therefore identify the specific cell type(s) or anatomic site(s) involved, and most diagnoses of nasal lesions should include an epithelial type or another relevant anatomic landmark as a site modifier. The epithelial types affected are squamous, transitional, respiratory, and olfactory epithelium.
In order to properly assess the nasal cavity for toxicity, and to allow for comparisons between studies and species, the nasal cavity must be consistently sampled at specific anatomically defined sites. For studies conducted by the National Toxicology Program, the nasal cavity is routinely sectioned at three levels, defined as follows, relative to anatomic landmarks on the maxilla ( Figure 1 ): level I, taken immediately posterior to the upper incisor teeth; level II, through the incisive papilla rostral to the first palatal ridge; and level III, at the middle of the second molar teeth.
Figure 1. The location of the three levels of the nose routinely examined by the National Toxicology Program.
Figure 2. The normal dorsal meatus of level I.
Figure 3. The normal dorsal meatus of level I (higher magnification of Figure 2).
Figure 4. The normal transitional epithelium of the lateral wall at level I.
Figure 5. The normal vomeronasal organ (asterisk) at level I.
Figure 6. The normal nasal cavity at level II. Asterisks indicate lacrimal ducts.
Figure 7. The normal olfactory epithelium and lamina propria at level II. Asterisks indicate olfactory nerves.
Figure 8. The normal appearance of the respiratory epithelium and the glands in the lamina (arrow) propria at level II.
Figure 9. The normal nasal cavity at level III, showing the nasopharyngeal duct (asterisk) and nasal associated lymphoid tissue (NALT, arrow).
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