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February 2015

Horse: Cranial mesenteric artery: Aneurysm, focal with chronic-active arteritis,
thrombus formation and dystrophic mineralization of the arterial wall

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History:
Horse, Shetland pony, adult

Diagnosis:
Cranial mesenteric artery: Aneurysm, focal with chronic-active arteritis, thrombus formation and dystrophic mineralization of the arterial wall

Description:
The mesenteric artery is balloon-like distended with a maximal diameter of 2.5 cm. Coagulated blood adheres multifocally to the endothelial lining (thrombus formation). The wall of the aneurysm is thickened up to ten times compared to the adjacent “normal” arterial wall and the cut surface is gritty with mineralization. The wire indicates the original arterial lumen.

Comments:
The pony was euthanized due to other reasons with the aneurysm being an incidental finding. Clinical signs attributable to this lesion were absent.
Histologically, the arterial wall was thickened due to chronic granulomatous and eosinophilic panarteritis with multifocal mineralization. The endothelium was covered by a variably thick fibrinous coating with captured blood cells.
An aneurysm is defined as abnormal dilation of a blood vessel. True aneurysms are bounded by attenuated vessel wall components while in a false aneurysm the vascular wall has been disrupted with formation of an extravascular hematoma that communicates with the arterial lumen. Due to the often great thickening of the wall of aneurysms, typically induced by verminous arteritis in horses, the lesion is also called inflammatory aneurysm.
Adult nematodes were undetectable in the intestinal lumen, nor were larvae present within the vascular lesions. Nonetheless, the lesion had been most likely caused by migrating larvae during a previous Strongylus vulgaris infection.

Author and picture by: Olivia Kershaw, Department of Veterinary Pathology, Freie Universität Berlin, Germany