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Parathyroid Gland - Ectopic Tissue

Image of ectopic tissue in the parathyroid gland from a female B6C3F1 mouse in a subchronic study
Parathyroid Gland - Ectopic Tissue, Thymus in a female B6C3F1 mouse from a subchronic study. A large piece of ectopic thymus with pronounced basophilic staining is adjacent to the parathyroid and thyroid, and a small focus of ectopic thymus is present within the parathyroid parenchyma (arrow).
Figure 1 of 2
Image of ectopic tissue in the parathyroid gland from a female B6C3F1 mouse in a subchronic study
Parathyroid Gland - Ectopic Tissue, Thymus in a female B6C3F1 mouse from a subchronic study. This higher magnification of Figure 1 shows the focus of ectopic thymus in the parathyroid (arrow) along with an adjacent collection of lymphocytes (arrowhead).
Figure 2 of 2
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comment:

Ectopic thymic tissue can be found in or adjacent to the parathyroid, as well as in or adjacent to the thyroid. It is considered a congenital anomaly. Both thymic cortical and medullary features may be evident in the ectopic tissue. This change is generally not believed to be a consequence of treatment. In some cases the ectopic thymus can largely replace the parathyroid.

recommendation:

When studies include in utero exposure, developmental alterations potentially related to treatment could influence the occurrence of tissue ectopia. Therefore, ectopic thymus in or adjacent to the parathyroid gland should be diagnosed. A severity grade is not necessary. If both parathyroids are involved, the diagnosis should be qualified as bilateral. The diagnosis should be modified with the tissue of origin (e.g., parathyroid gland - ectopic tissue, thymus).

references:

Hardisty JF, Boorman GA. 1990. Thyroid gland. In: Pathology of the Fischer Rat: Reference and Atlas (Boorman GA, Eustis SL, Elwell MR, Montgomery CA, MacKenzie WF, eds). Academic Press, San Diego, 519-536.
Abstract: http://www.ncbi.nlm.nih.gov/nlmcatalog/9002563

Seely JC, Hildebrandt PK.. 1990. Parathyroid gland. In: Pathology of the Fischer Rat: Reference and Atlas (Boorman GA, Eustis SL, Elwell MR, Montgomery CA, MacKenzie WF, eds). Academic Press, San Diego, 537-543.
Abstract: http://www.ncbi.nlm.nih.gov/nlmcatalog/9002563