Practical pathology of aging mice

Pettan-Brewer, Christina; Treuting, Piper M.

Numbers of specific neoplastic and non-neoplastic diagnoses in aging B6 mice were determined by review of individual histopathology reports and databases. Nonneoplastic lesions were counted and tabulated by disease processes regardless of lesion severity. Prevalence was calculated as the number of mice affected. Table 1 has the numbers of mice with the histologic neoplastic diagnosis. Table 2 lists the non-neoplastic disease diagnosed either at cage level, necropsy, and/or histologically. Results were tabulated with sexes combined except where noted. A Clinical and histological presentations of common skin lesions. A. A 28Ámonth-old female B6 mouse in relatively good health deemed clinically normal. Note mild alopecia on the head, normal eyes, and well-groomed pelage. B. A 28-month-old female B6 mouse with ill-kept fur due to lack of adequate grooming. Note the hunched posture, opaque cornea, the elongated shape of the nose, and relatively boney appearance of this mouse in contrast to the mouse pictured in 2A. Internally, this mouse had a large pituitary adenocarcinoma (see Fig. 5C ,D). C. Moderate patch alopecia in a B6 mouse (age unknown). This clinical presentation may be a result of dermatitis or alopecia due to other causes such as primary follicular dysplasia. Histology would aid in determining a definitive cause. D. Ulcerative and likely pruritic dermatitis in an agouti mouse (background and age unknown). This historical clinical presentation was often seen associated with fur mites, although numerous causes have been implicated in a similar clinical spectrum in C57BL/6 mice. See text for details. E. Hematoxylin and eosin-stained section of mild alopecia with minimal chronic inflammation within the dermis (arrow). Note thickness of the subcutis (SC). Follicles are sparse and devoid of hair shafts. F. Hematoxylin and eosin-stained section of severe proliferative dermatitis (pseudoepitheliomatous). The epidermis is markedly thickened with irregular rete peg formation in this somewhat tangentially oriented section. Dyskeratosis and mild orthokeratotic hyperkeratosis are also present with moderate chronic dermatitis that extends into the SC. Pseudoepitheliomatous hyperplasia is frequently seen histologically at the thickened edges of chronic ulcerative foci (see 2D). comprehensive review of gender-specific lesion spectrums in a number of inbred strains, including UW aged C57BL6, will be published elsewhere. Compete blood counts with differentials and clinical chemistry panels for two of the mice are presented in Table 3 .