Pathology in Practice.

This study documents the pathology of a horse with signs of depression, lack of appetite, and weight loss. Its condition was found to be caused by an aortic sinus of Valsalva aneurysm and an aortocardiac fistula, both rare conditions in horses. The owner elected euthanasia due to the poor prognosis. Post-mortem examination revealed additional abnormalities including mucoid extracellular matrix accumulation.

Clinical History and Findings

• The study began with an analysis of the horse’s condition, which involved symptoms primarily manifesting as depression, anorexia, and severe weight loss. Cardiac examination revealed a heart murmur, tachycardia, tachypnea, and pale mucous membranes.

Echocardiographic Findings

• The clinicians utilized various examinations including echocardiographic and echo-Doppler assessments to identify abnormalities. The mare displayed severe dilation of the pulmonary artery and right atrium and an aneurysm in the right sinus of Valsalva.
• Further investigations following euthanasia revealed the aorto-cardiac fistula as the suspected cause of these abnormalities.

Gross Findings

• Postmortem examination identified severe dilation of the right atrium and pulmonary artery, a 1-cm-diameter dome-shaped swelling in the right atrium, and a fistula between the right sinuses of Valsalva and a thickened part of the aortic valve.
• Additional findings included subcutaneous and pulmonary edema and dilated venous vessels.

Histopathological Findings

• Microscopic examination of the tissues surrounding the ruptured area highlighted a host of abnormalities, such as severe fragmentation and thinning of the elastic fibers, interstitial homogeneous material, and large aneurysm in the aortic wall.
• The histological changes, primarily the accumulation of mucoid extracellular matrix, were similar to those found in humans with conditions like the Marfan syndrome.

Morphologic Diagnosis and Case Summary

• The morphology of the horse’s condition led to a diagnosis of aortic mucoid extracellular matrix accumulation with a ruptured aneurysm of the right sinuses of Valsalva and an associated aorto-cardiac fistula.

Analysis and Conclusion

• The case aligned with known diseases of equine arteries such as aortitis, arteritis, arteriovenous fistulas, and arterial aneurysms or rupture.
• The particular manifestation in this mare is considered rare in both humans and horses. However, it showed that degenerative conditions similar to those in humans, such as mucoid extracellular matrix accumulation, can be responsible for equine aortic sinus aneurysm and rupture.