Kidney - Karyomegaly

Image of karyomegaly in the kidney from a male B6C3F1 mouse in a chronic study
Kidney - Karyomegaly in a male B6C3F1 mouse from a chronic study. Numerous enlarged nuclei (karyomegaly) are present in the renal tubular epithelium.
Figure 1 of 2
Image of karyomegaly in the kidney from a male F344/N rat in a subchronic study
Kidney - Karyomegaly in a male F344/N rat from a subchronic study. Karyomegaly is present in several tubular epithelial cells.
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comment:

Karyomegaly is presumed to result from nucleic acid replication without nuclear division. It is characterized by marked enlargement of nuclei observed predominantly in the proximal convoluted tubule cells ( Figure 1image opens in a pop-up window ). Affected nuclei are often hyperchromatic with multiple nucleoli ( Figure 2image opens in a pop-up window ). Karyomegaly has been associated with chemical administration. It is generally considered preneoplastic, leading to tubule neoplasia in chronic studies.

recommendation:

Karyomegaly should be diagnosed and given a severity grade whenever present. Details of the karyomegaly should be discussed in the pathology narrative (e.g., the tubular segment affected).

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

Hard GC, Alden CL, Bruner RH, Frith CH, Lewis RM, Owen RA, Krieg K, Durchfeld-Meyer B. 1999. Non-proliferative lesions of the kidney and lower urinary tract in rats. In: Guides for Toxicologic Pathology. STP/ARP/AFIP, Washington, DC, 1-32.