History

A 48-year-old 4.57-kg female American flamingo (Phoenicopterus ruber) with a 4-year history of decreased mobility in its left wing was found dead. The flamingo had received annual West Nile virus vaccines.

Clinical and Gross Findings

At necropsy, the flamingo was overconditioned with large deposits of subcutaneous and coelomic adipose. Large amounts of clotted blood were present within the coelom. Along the aorta, there were multifocal to coalescing thickened and hardened areas with yellow-orange plaques and gritty mineralization. The aorta was focally dilated and ruptured with an adhered luminal blood clot (Figure 1). Hemorrhage was present within the lungs; sections partially floated in formalin. The ovarian follicles were darkened and enlarged. No other significant findings were identified.

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Necropsy photographs of isolated aorta and congested lung of a 48-year-old female American flamingo. A—The aorta has a focal area of dissection (asterisk) that is surrounded by marked hemorrhage. The aortic wall in this area is focally thinned and dilated. Along the aortic intima, there are multifocal to coalescing, orange, irregular, raised plaques. B—A focal thrombus (arrow) is adhered to the aortic intima and occludes the lumen just distal to the area of dissection.

Citation: Journal of the American Veterinary Medical Association 261, 10; 10.2460/javma.23.02.0092

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Formulate differential diagnoses, then continue reading.

Histopathologic Findings

Sections of the aorta, cardiac great vessels, lung, heart, kidney, liver, proventriculus, ventriculus, intestine, pancreas, ovary, and soft tissues of the left wing were evaluated microscopically. In sections of the grossly affected aorta, on the luminal aspect, there was marked, loosely organized fibrin and cellular debris adhered to the tunica intima with loss of the endothelium (Figure 2). The tunica intima was expanded by edema, hemosiderophages, and fibrosis with foci of mineralization. The tunica media was multifocally markedly expanded by deposits of mineralized debris that disrupted and effaced smooth muscle and connective tissue. There was multifocal osseous and chondroid metaplasia with variable amounts of fibrosis. Often associated with these mineralized areas within the tunica media were clear, well-defined, elongate, spicular spaces (cholesterol clefts) with mild infiltrates of heterophils and foamy macrophages (Figure 3). Gomori trichrome stain highlighted the disruption of aortic mural architecture and marked deposition of fibrosis. There was variable hemorrhage in the surrounding adventitia.

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Photomicrograph of the aorta of the flamingo in Figure 1. The tunica media (†) is focally expanded by deposits of mineralized debris with chondroid and osseous metaplasia (*), disrupting smooth muscle and connective tissue fibers. The tunica intima (‡) is effaced with loss of the endothelium by adhered, disorganized fibrin with associated edema and fibrosis. H&E stain; bar = 200 µm.

Citation: Journal of the American Veterinary Medical Association 261, 10; 10.2460/javma.23.02.0092

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Photomicrograph of the aorta of the flamingo in Figure 1. The tunica media is expanded by edema with cholesterol clefts (*), infiltrates of heterophils and foamy macrophages, and mineralized debris. H&E stain; bar = 20 µm. Inset: Disruption of collagen and smooth muscle fibers of the tunica media is evident. Gomori trichrome stain; bar = 20 µm.

Citation: Journal of the American Veterinary Medical Association 261, 10; 10.2460/javma.23.02.0092

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Other significant histologic findings include similar cholesterol cleft deposits and disruption of the tunica media in coronary vessels and pulmonary hemorrhage.

Morphologic Diagnosis and Case Summary

Morphologic diagnosis: aortic atherosclerosis with aneurysm and rupture.

Case summary: ruptured aortic aneurysm caused by atherosclerosis in a flamingo.

Comments

Atherosclerosis is a common disease process found in avian species. Factors that contribute to its development include advanced age and high-energy/high-fat diets.¹ Female psittacines have been shown to be more susceptible as well, especially reproductively active individuals, presumably due to the effects of estrogen on protein metabolism. Higher levels of estrogen in reproductively active, egg-laying females induce increased plasma calcium, protein, cholesterol, and triglycerides, which may promote atherogenesis.^2,3 The flamingo in this report may have been additionally predisposed to atherosclerosis due to reproductive activity and her chronically injured wing, which may have led to a decreased activity level and increased risk for obesity.

The history of sudden death observed in this case is a frequent clinical presentation for birds affected by atherosclerosis. Cases of acute death are frequently attributed to weakened and ruptured vessel walls, such as the aortic aneurysm described in this case. The cholesterol buildup in the walls of the aorta induces reactive remodeling with buildup of collagen, evidenced by the cholesterol clefts and collagen buildup in the tunica media described. The collagen is deposited in an attempt to strengthen the vessel walls, but in doing so decreases aortic elasticity and increases vessel wall fragility. The aorta eventually erupts at the location of this aneurysm from the shearing forces of the heart pumping blood against the plaque formed there. Other causes of aneurysms described in other species include hypertension, aberrant parasite migration, and spontaneous dissecting aneurysm, which are suspected to have a genetic component in some species. Other differential diagnoses for hemocoelom include trauma, anticoagulant rodenticide poisoning, or other clotting deficiencies.⁴

Other clinical presentations associated with atherosclerosis can include a chronic wasting syndrome, including both physical and mental insufficiencies.¹ Symptoms depend on which vessels are most affected. If the carotid arteries are involved, narrowing of the vessels can lead to death due to decreased perfusion of the brain. General arterial involvement can increase systemic blood pressure, eventually leading to heart failure.

In a living avian patient affected by atherosclerosis, serum chemistry results would potentially indicate increased cholesterol levels²; however, in a reproductively active female, cholesterol levels would also be increased. Identifying chronic hypertension has also been shown to be useful in diagnosing atherosclerosis in psittacines, and this clinical finding could be extrapolated for diagnostic use in other species in which blood pressure can practically be measured.² More commonly, however, chronic atherosclerosis is not diagnosed until there are more advanced clinical signs, at which point imaging, especially CT, is the most useful diagnostic tool in visualizing the lesions in the great vessels.²

While little definitive evidence exists for prevention of atherosclerosis, managing the lifestyle of those with increased risks, such as older females, may be feasible. Maintaining adequate activity levels and preventing obesity where possible could lower the risk of developing this disease and help manage the results of the disease.² Inclusion of omega-3 fatty acids and fish oil in the diet has reduced atherosclerosis and mediated associated clinical signs.⁵ In 1 unconfirmed case of atherosclerosis of a 35-year-old female Amazon parrot, 3 years of peripheral vasodilator treatment with isoxsuprine successfully resolved signs of hind limb weakness and loss of prehensive abilities.⁶

Although atherosclerosis has been diagnosed in several avian species, it is rarer in domestic mammals. Swine are the most well-characterized domestic species to present with this pathology.⁴ Dogs with hypothyroidism or diabetes mellitus may develop atherosclerosis in severe cases.⁴ Miniature Schnauzers with idiopathic hyperlipidemia are also considered predisposed to developing atherosclerosis.⁴ Much more common is arteriosclerosis, which is vascular hardening that excludes the degenerative changes associated with cholesterol deposition that are the hallmark of atherosclerosis.⁴ Arteriosclerosis generally is less severe and less clinically relevant than atherosclerosis in domestic veterinary species.