Thymus - Pigment

Thymus - Pigment in a female F344/N rat from a chronic study. Brown pigment (likely hemosiderin) (arrow) is present at the thymus corticomedullary junction.
Figure 1 of 2
comment:
Pigment in the thymus is an uncommon finding and is primarily characterized by the presence of golden to dark brown pigment within macrophages. Pigment may be hemosiderin ( Figure 1

recommendation:
Pigment in the thymus should be diagnosed and given a severity grade. However, not all pigments have to be diagnosed, as some are ubiquitous in aging animals or related to some other disease process and not toxicologically meaningful. The pathologist should use his or her judgment in deciding whether deposits of pigment are toxicologically significant or prominent enough to warrant a separate diagnosis. Definitive pigment identification is often difficult in histologic sections, even with a battery of special stains. Therefore, it is recommended that a diagnosis of "pigment" (as opposed to diagnosing the type of pigment, e.g., hemosiderin or lipofuscin) is most appropriate. The pathology narrative should describe the morphologic features of the pigmentation.references:
Elmore SA. 2006. Enhanced histopathology of the thymus. Toxicol Pathol 34:656-665. Full Text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1800589/
National Toxicology Program. 2008. NTP TR-541. Toxicology and Carcinogenesis Studies of Formamide (CAS No. 75-12-7) in F344/N Rats and B6C3F1 Mice (Gavage Studies). NTP, Research Triangle Park, NC. Abstract: https://ntp.niehs.nih.gov/go/29290
Web page last updated on: February 03, 2015