Immune System

Thymus - Hemorrhage

Narrative
Comment:
Hemorrhage is characterized by the presence of extravasated erythrocytes within the thymic parenchyma (Figure 1, arrows). Hemorrhage can be seen in the cortex and/or medulla of the thymus of rodents and may be an agonal change. In the absence of necrosis or other lesions such as erythrophagocytosis (Figure 2, arrows) or pigment-laden macrophages, hemorrhage in the thymus may be attributed to necropsy technique (iatrogenic) and considered a dissection-induced artifact and not the result of a vascular lesion. However, thymic hemorrhage can occur with some vitamin deficiencies, so diet should be a consideration. Hemorrhage should be distinguished from congestion, where the blood is contained with well-defined vascular spaces lined by endothelial cells.
Recommendations:
Hemorrhage in the thymus that is not attributed to necropsy technique should be diagnosed and graded. Hemorrhage that is considered to be secondary to necrosis, inflammation, or neoplasia should not be diagnosed separately unless warranted by severity, but should be described in the pathology narrative.
References:

National Toxicology Program. 1990. NTP TR-371. Toxicology and Carcinogenesis Studies of Toluene (CAS No. 108-88-3) in F344/N Rats and B6C3F1 Mice (Inhalation Studies). NTP, Research Triangle Park, NC.

Abstract: https://ntp.niehs.nih.gov/go/8882

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 hemorrhage in the thymus from a male F344/N rat in a chronic study

    Thymus - Hemorrhage in a male F344/N rat from a chronic study. Multifocal to coalescing areas of hemorrhage are present within this involuted thymus (arrows). Numerous vessels are also congested (arrowheads).

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Thymus - Hemorrhage in a male F344/N rat from a chronic study. Multifocal to coalescing areas of hemorrhage are present within this involuted thymus (arrows). Numerous vessels are also congested (arrowheads).
Thymus - Hemorrhage in a male F344/N rat from a chronic study. Multifocal to coalescing areas of hemorrhage are present within this involuted thymus (arrows). Numerous vessels are also congested (arrowheads).
Thymus - Hemorrhage in a female B6C3F1/N mouse from a chronic study. Macrophages with intracytoplasmic erythrocytes (erythrophagocytosis) (arrows) are associated with the hemorrhage.
Thymus - Hemorrhage in a female B6C3F1/N mouse from a chronic study. Macrophages with intracytoplasmic erythrocytes (erythrophagocytosis) (arrows) are associated with the hemorrhage.

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