Canine pheochromocytoma: diagnosis and surgical management

Pheochromocytomas are tumours of the adrenal medulla which develop from the chromaffin cells within the inner medulla, with a high rate of metastasis and local invasion (Gilson et al, 1994b; Barthez et al, 1997). This is an uncommon tumour type, most often diagnosed in older dogs, but without any sex or breed predisposition.

Clinical signs associated with pheochromocytomas are secondary to the release of catecholamines, local infiltration and metastatic disease (Gilson et al, 1994b; Barthez et al, 1997). Catecholamine release results in hyperstimulation of alpha- and beta-adrenergic receptors, leading to hypertension, tachyarrhythmias and, in some cases, sudden death. Catecholamine release is often paroxysmal in nature, thus clinical signs can be intermittent. Hypertension is reported in approximately 50% of cases (Barthez et al, 1997) and can cause associated clinical signs including signs of renal dysfunction such as polyuria and polydipsia, epistaxis and acute onset blindness after retinal detachment. Tachyarrhythmias can cause weakness and episodic collapse. Local tumour invasion into the vena cava, predominantly via the phrenicoabdominal vein, can give rise to tumour thrombi and obstructed venous return, leading to pelvic limb oedema or ascites. Distant metastasis occurs in up to 40% of cases in sites such as the regional lymph nodes, liver, spleen, lung and vertebral column (Gilson et al, 1994b; Barthez et al, 1997; Spall et al, 2011). Therefore, clinical signs attributable to metastasis may be many and varied. On occasion, a pheochromocytoma is found incidentally on abdominal imagining during investigation for other disease processes and has no associated clinical signs.