A Hidden Threat: A Case Report on Pheochromocytoma in a Horse (Equus ferus caballus)

Pheochromocytomas are rare neuroendocrine tumors in horses, originating from chromaffin cells within the adrenal medulla. This case report describes a 15-year-old Friesian horse that presented with progressive ataxia, muscular weakness, and lateral recumbency, leading to euthanasia. During necropsy, a 2x3 cm dark-red mass with focal necrosis was diagnosed in the left adrenal gland, along with perirenal hematoma and haemoperitoneum, indicating hemorrhagic complications. Histopathological analysis confirmed an adrenal pheochromocytoma, characterized by nests of polygonal to spindle-shaped cells with small amount of cytoplasm and low mitotic activity. Areas of necrosis and hemorrhage suggested potential malignancy. The clinical signs were likely due to catecholamine hypersecretion and the acute haemoperitoneum was caused by the tumor rupture and hemorrhage. Pheochromocytomas, though often diagnosed post-mortem, can cause life-threatening cardiovascular and systemic effects, underscoring the importance of histopathological evaluation and the need for improved antemortem diagnostic techniques in equine practice.