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Spleen - Accessory Spleen

Image of accessory spleen in the spleen from a male B6C3F1/N mouse in a chronic study
Spleen - Accessory in a male B6C3F1/N mouse from a chronic study. A nodule of splenic tissue (accessory spleen) (arrow) is connected to the spleen via a mesenteric attachment (arrowhead).
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Image of accessory spleen in the spleen from a male B6C3F1/N mouse in a chronic study
Spleen - Accessory in a male B6C3F1 mouse from a chronic study (higher magnification of Figure 1). The accessory spleen (arrow) contains red pulp and white pulp components.
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Accessory spleens ( Figure 1image opens in a pop-up window , arrow) are rare findings in rodents and may be congenital, acquired following splenectomy, or a consequence of traumatic injury. When observed grossly in the peritoneal cavity, an accessory spleen may appear as one or more dark red to black nodules that have a smooth surface and range from less than a millimeter to several millimeters in diameter. These small nodules of splenic tissue have been observed in the mesenteric attachment of the spleen ( Figure 1image opens in a pop-up window , arrowhead), pancreas, and elsewhere in the abdominal cavity. Histologically, accessory spleens may have all or some splenic components, such as the capsule, trabeculae, red pulp, and/or white pulp ( Figure 2image opens in a pop-up window ).


Accessory spleen should be diagnosed but not graded.


National Toxicology Program. 2011. NTP TR-570. Toxicology and Carcinogenesis Studies of α,β-Thujone (CAS No. 76231-76-0) in F344/N Rats and B6C3F1 Mice (Gavage Studies). NTP, Research Triangle Park, NC.

Stefanski SA, Elwell MR, Stromberg PC. 1990. Spleen, lymph nodes, and thymus. In: Pathology of the Fischer Rat: Reference and Atlas (Boorman GA, Eustis SL, Elwell MR, Montgomery CA, MacKenzie WF, eds). Academic Press, San Diego, 369-394.

Ward JM, Mann PC, Morishima H, Frith CH. 1999. Thymus, spleen, and lymph nodes. In: Pathology of the Mouse (Maronpot RR, ed). Cache River Press, Vienna, IL, 333-360.

NTP is located at the National Institute of Environmental Health Sciences, part of the National Institutes of Health.