JPC SYSTEMIC PATHOLOGY
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: Focally expanding the endometrium is a markedly dilated (up to 5 mm diameter) vein lined by attenuated or hyperplastic endothelial cells (venous aneurysm) that is occluded by concentric lamellations of erythrocytes and fibrin with scattered enmeshed heterophils and lymphocytes, and few reactive fibroblasts (organizing thrombus) which is multifocally adherent to the disrupted endothelium. The adjacent endometrium contains golden brown pigment-laden macrophages (hemosiderosis). The remainder of the endometrium is mildly expanded by many papillary projections of hyperplastic endometrium with few 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 and ectatic lymphatics (edema).
- Uterus, endometrium: Aneurysm, venous, multiple, with organizing thrombosis, breed unspecified rabbit, lagomorph.
- Uterus: Endometrial hyperplasia, diffuse, mild.
CONDITION: Endometrial venous aneurysm
- Occurs in nonpregnant, multiparous does; natural cases not reported in other species
- Associated with persistent urogenital bleeding
- 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 attenuated vessel wall components; in a false aneurysm the vascular wall has been breached with formation of an extravascular hematoma that communicates with the intravascular space
- 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
- 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 uterus
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Endometrial stroma is expanded by dilated, cyst-like spaces lined by attenuated vessel wall components and filled with blood or thrombi
- Uterine adenocarcinoma, endometrial hyperplasia or uterine polyps, pyometra or endometritis
- 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
- 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.
- Mitchell RN. Blood vessels. In: Kumar V, Abbas AK, Aster JC, eds. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Philadelphia, PA: Saunders Elsevier; 2015:501-505.