Approaches to the Identification and Recording of Nasal Lesions in Toxicology Studies *

The identification, recording, and interpretation of nasal lesions can be a difficult task in toxicology studies. The objective of this article is to provide some guidelines for approaches to nasal toxicologic pathology, based on the author's experience and information available in the published literature. Identification of treatment-induced nasal lesions requires adequate in-life and post-mortem observation, and thorough histopathology. Histopathologic assessment is dependent upon high quality and consistent histologic preparations, adequate knowledge of nasal anatomy and histology, and experience with the range of aging, background, and treatment-induced lesions that may be encountered. In recent years there has been a marked increase in the number of articles reporting nasal pathology in studies for which materials were delivered by inhalation and by non-inhalation routes. Because of the increasing size of this database, it is recommended that standardized and systematic nomenclature be developed for these changes. The following points are considered to be particularly important: 1) alert animal care staff to clinical changes that may indicate nasal lesions; 2) screen animals for nasal disease, such as nasal nematodes in non-human primates; 3) record gross lesions during trimming of decalcified nasal tissues; 4) save spare tissue in fixative; 5) remember that the normal bilateral symmetry of the nose can be a valuable diagnostic aid; 6) avoid excessive lumping or splitting of diagnoses; 7) develop a logical order for recording of lesions (the approach preferred by the author is degenerative, inflammatory, regenerative, proliferative, for each of the epithelial types in a logical anatomical order, such as squamous, transitional, respiratory, and olfactory); 8) accurately determine the site of toxic responses; 9) keep a notebook of interesting or important observations and ideas if you are using a computerized data acquisition system; 10) consider the role of factors that may account for lesion distribution (regional dose and tissue susceptibility) during interpretation of tissue responses; and 11) during preparation of the descriptive narrative, clearly define what occurred, where and when it occurred, and consider the use of simple anatomical diagrams as an adjunct to the text. Adequate lesion detection and characterization by the toxicologic pathologist is often a critical feature of toxicology studies, and can play an important role in determination of human risks associated with exposure to xenobiotics. A systematic but flexible approach is recommended.