JPC SYSTEMIC PATHOLOGY
REPRODUCTIVE SYSTEM
January 2025
R-M07
Signalment (JPC # 2551104): A nonpregnant female rabbit.
HISTORY: This rabbit, housed singly under standard laboratory conditions, showed extensive vaginal bleeding and died.
HISTOPATHOLOGIC DESCRIPTION: Uterus: Multifocally expanding the endometrium and projecting into the uterine lumen are markedly dilated (up to 6 mm diameter) veins (venous aneurysms) lined by attenuated or mildly hypertrophied endothelial cells that are occluded by concentric lamellations of erythrocytes and fibrin with scattered enmeshed viable and necrotic heterophils and lymphocytes, and few reactive fibroblasts which is multifocally adherent to the discontinuous endothelium (organizing thrombus). The adjacent endometrium contains few macrophages with intracytoplasmic, golden brown, globular pigment (hemosiderin). The remainder of the endometrium is mildly hyperplastic, expanded by many papillary projections of hyperplastic endometrium with few mildly ectatic glands that are lined by cuboidal to low columnar, often ciliated epithelium (endometrial hyperplasia). Diffusely the lamina propria is expanded by increased clear space (edema), ectatic lymphatics, and few heterophils.
MORPHOLOGIC DIAGNOSIS: 1. Uterus, endometrial veins: Aneurysms, multiple, with organizing thrombosis, breed unspecified, lagomorph.
2. Uterus: Endometrial hyperplasia, chronic, diffuse, mild.
CONDITION: Endometrial venous aneurysm
GENERAL DISCUSSION:
- Aneurysms in general:
- Aneurysm is a localized abnormal dilation of a blood vessel
- Generally (other than in the rabbit uterus), arterial aneurysms are much more common than venous aneurysms; the venous system generally lacks the hydrostatic pressure needed to create an aneurysm
- A true aneurysm is bounded by all or most attenuated vessel wall components; in a false aneurysm the vascular wall has ruptured with formation of an extravascular hematoma that communicates with the intravascular space, forming a wall of surrounding fibrous tissue
- Endometrial venous aneurysms:
- Occurs in nonpregnant, multiparous does; natural cases not reported in other species (arterial rather than venous aneurysms more common in other species)
- Associated with persistent urogenital bleeding, hematuria, anemia, and proteinuria
PATHOGENESIS:
- In general, aneurysms arise secondary to increased intraluminal pressure or degenerative changes in the vessel wall from trauma, connective tissue disorders, inflammation, parasites (e.g. Strongylus vulgaris), or other infectious agents
- Atherosclerosis is a common cause of arterial aneurysms in people
- Endometrial venous aneurysms in rabbits are considered a congenital defect; predisposing factors (i.e. trauma or bleeding disorders) are not thought to play a role
- Endometrial venous aneurysms rupture and periodically bleed into the uterine lumen causing hematuria
TYPICAL CLINICAL FINDINGS:
- Urogenital bleeding
- Clinical pathology: Anemia, hematuria, and proteinuria
TYPICAL GROSS FINDINGS:
- Multiple dilated, blood-filled, thin walled endometrial vessels (varices)
- Clotted blood within the uterine lumen
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Endometrial stroma is expanded by one to multiple dilated, cyst-like spaces lined by attenuated vessel wall components (veins) and filled with blood or thrombi
- Ruptured aneurysms may contain neutrophilic infiltrates and necrotic debris
- +/- concurrent cystic endometrial hyperplasia (dilated endometrial glands)
DIFFERENTIAL DIAGNOSIS:
- Uterine adenocarcinoma, endometrial hyperplasia, uterine polyps, pyometra or endometritis
COMPARATIVE PATHOLOGY:
- Humans: Venous aneurysms of myometrial, vaginal and cervical veins, but not the endometrial veins, have been reported in women and are usually associated with congenital defects in the vessel wall and increased pressure in the venous system during pregnancy
REFERENCES:
- Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016:310-311.
- Bray MV, Weir EC, Brownstein DG, Delano ML. Endometrial venous aneurysms in three New Zealand white rabbits. Lab An Sci 1992;42:360-362.
- Delaney MA, Treuting PM, Rothenburger JL. Lagomorpha. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier;2018:486.
- Mitchell RN and Halushka MK. Blood vessels. In: Kumar V, Abbas AK, Aster JC, eds. Robbins and Cotran Pathologic Basis of Disease. 10th ed. Philadelphia, PA: Elsevier; 2021:504-508.
- Robinson WF and Robinson NA. Cardiovascular system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. 6th ed. vol. 3. Philadelphia, PA: Elsevier; 2016:62.
