References
Abstract
Phaeochromocytomas are neuroendocrine tumours arising from chromaffin cells of the adrenal medulla. Clinical signs are primarily associated with excessive catecholamine secretion and, to a lesser extent, with the space-occupying or invasive nature of the tumour. The diagnosis of phaeochromocytoma relies on clinical suspicion, biochemical testing, diagnostic imaging and histopathology. Biochemical testing mainly depends on the measurement of levels of plasma or urinary metanephrines, with normetanephrine demonstrating superior diagnostic performance compared to metanephrine. Adrenalectomy is the treatment of choice, but may not be possible in cases with extensive local invasion, concurrent disorders or distant metastasis. Contrast-enhanced computed tomography is recommended for surgical planning and metastasis screening. Vascular invasion is frequently observed, yet surgery remains a viable option in many cases. Recent studies question the necessity of alpha-blockade before surgery, and randomised controlled clinical trials are necessary to evaluate this. Long-term survival is often seen in dogs that survive the perioperative period. For patients in which surgery is not deemed feasible, medical treatment with tyrosine-kinase inhibitors may be considered. Given the current scarcity of effective medical treatment, there is an urgent need to identify novel therapeutic options. This review provides recommendations on the diagnosis and management of canine phaeochromocytoma.
A phaeochromocytoma is a catecholamine-producing neuroendocrine tumour of chromaffin cells of the adrenal medulla. It occurs most often in older dogs, with an average age between 10.5 and 12 years, and there is no apparent breed or sex predilection (Reusch, 2015; Galac, 2017). Catecholamines (dopamine, adrenaline and noradrenaline) are synthesised from phenylalanine through a series of enzymatic conversions. Noradrenaline is converted to adrenaline by the cytoplasmic enzyme phenylethanolamine-N-methyl-transferase. The expression of phenylethanolamine-N-methyl-transferase is dependent on glucocorticoids so its expression is mainly localised to chromaffin cells of the adrenal medulla, which have a high exposure to cortisol because of centripetal (ie, from outside to inside) blood flow from the adrenal cortex (Eisenhofer et al, 2001). Upon sympathetic stimulation, catecholamines are secreted into the circulation from their secretory vesicles by exocytosis and exert their physiological effects by activation of adrenergic α- and β-receptors. The most important physiological effects include an increase in blood pressure, increase in heart rate and contractility, decrease in gastrointestinal motility and increase in levels of blood glucose and fatty acids (Reusch, 2015; Galac, 2017).
Register now to continue reading
Thank you for visiting UK-VET Companion Animal and reading some of our peer-reviewed content for veterinary professionals. To continue reading this article, please register today.