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Kidney - Ectopic Tissue

Image of ectopic liver tissue in the kidney from a female F344/N rat in a chronic study
Kidney - Ectopic tissue, Liver in a female F344/N rat from a chronic study. Ectopic liver (arrow) involves the capsule of the kidney.
Figure 1 of 2
Image of ectopic adrenal tissue in the kidney from a  Harlan Sprague-Dawley rat in a  study
Kidney - Ectopic tissue, Adrenal gland in a young Sprague-Dawley rat. A well-demarcated subcapsular lesion (arrow) is diagnosed as an ectopic adrenal gland. (Image provided courtesy of Dr. Johnson Thomas, Dow Chemical USA.)
Figure 2 of 2
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comment:

In rare cases, various foci of extrarenal tissue can be noted in the kidney, particularly near the capsule. Liver tissue and adrenal tissue have been reported ( Figure 1image opens in a pop-up window and Figure 2image opens in a pop-up window ). These ectopic tissues occur spontaneously with no pathologic or toxicologic significance. They must be differentiated from the presence of either primary or metastatic neoplasia.

recommendation:

Ectopic tissues should be diagnosed when present but should not be graded. The diagnosis should be modified with the tissue of origin (e.g., Kidney - Ectopic tissue, Liver).

references:

Frazier KS, Seely JC, Hard GC, Betton G, Burnett R, Nakatsuji S, Nishikawa A, Durchfeld-Meyer B, Bube A. 2012. Proliferative and non-proliferative lesions in the rat and mouse urinary system. Toxicol Pathol 40:14S-86S.
Abstract: http://www.ncbi.nlm.nih.gov/pubmed/22637735

Prentice DE, Jorgenson W. 1979. Ectopic adrenal tissue in the kidney of rhesus monkeys (Macaca mulatta). Lab Anim 13:221-223.
Full Text: http://lan.sagepub.com/content/13/3/221.full.pdf