Immune System

Spleen - Accessory Spleen

Narrative
Comment:
Accessory spleens (Figure 1, 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 1, 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 2).
Recommendations:
Accessory spleen should be diagnosed but not graded.
References:

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.

Abstract: https://ntp.niehs.nih.gov/go/36137

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.

  • 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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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).
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).
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.
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.

Authors

Kristen Hobbie, DVM, PhD
Principal Pathologist
Huntingdon Life Sciences
Peterborough, UK

Susan A. Elmore, MS, DVM, DACVP, DABT, FIATP
Staff Scientist, NTP Pathologist
NTP Pathology Group
National Toxicology Program
National Institute of Environmental Health Sciences
Research Triangle Park, NC

Holly M. Kolenda-Roberts, DVM, PhD, DACVP
Veterinary Pathologist
SNBL USA
Everett, WA

Reviewers

Jerrold M. Ward, DVM, PhD, DACVP, FIATP
Veterinary Pathologist
Global VetPathology
Montgomery Village, MD

Robert R. Maronpot, DVM, MS, MPH, DACVP, DABT, FIATP
Senior Pathologist
Experimental Pathology Laboratories, Inc.
Research Triangle Park, NC