Diagnosis | Thymoma | Lab Animal

Access through your institution Buy or subscribe In rats, the thymus is a pinkish-gray, soft organ located along the ventral aspect of the trachea, dorsal to the sternum at the thoracic

inlet. It is composed of two distinct encapsulated lobes. In contrast to most mammals, in rats, the thymus does not completely involute and atrophy with age, although thymic weight does

decrease by a factor of 7 between 3 months and 18 months of age1. The thymus is a primary lymphoid organ that serves the immune system by providing an optimal microenvironment for developing

T cells. The microenvironment of the organ is peculiar among lymphoid organs, as the supporting stroma consists of reticular epithelial cells2. Lymphocyte precursors from the bone marrow

travel to the thymus and develop into thymocytes (immature lymphocytes) and, subsequently, T lymphocytes (or T cells). Mature T lymphocytes exit the thymus and comprise the peripheral T-cell

population responsible for directing many components of the adaptive immune system. Congenital absence of a thymus (as in nude mice and rats) or surgical removal at an early age results in

severe immunodeficiency and a high susceptibility to infection3. Thymomas are composed of a mixture of lymphocytes and epithelial cells. The epithelial cells are considered the tumor cell

component in thymomas, whereas lymphocytes are the neoplastic component in thymic lymphomas. In thymomas, the relative composition ranges from almost entirely epithelial cells to almost

entirely lymphocytes with various proportions between4,5. A definitive diagnosis may be challenging in lymphocyte-rich thymomas because the histological sections may resemble a lymphoma more

than a thymoma. The presence of small groups of epithelial cells in enlarged thymuses and the absence of involvement of other organs are generally considered diagnostic features of

thymomas6,7. This is a preview of subscription content, access via your institution ACCESS OPTIONS Access through your institution ADDITIONAL ACCESS OPTIONS: * Log in * Learn about

institutional subscriptions * Read our FAQs * Contact customer support REFERENCES * Plecas-Solarovic, B. et al. Morphometrical characteristics of age-associated changes in the thymus of old

male Wistar rats. _Anat. Histol. Embryol._ 35, 380–386 (2006). Article  CAS  Google Scholar  * Henk-Jan Schuurman, C.F.K. & Kendall, M.D. Thymic microenvironment at the light microscopic

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Pharmacobiodyn._ 5, 727–733 (1982). Article  CAS  Google Scholar  Download references ACKNOWLEDGEMENTS We thank Matthew Davis (Georgia State University) for veterinary technical support and

for taking the gross photographs. RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Diagnosis | Thymoma. _Lab Anim_ 38, 116–117 (2009).

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