Adrenal tumour (pheochromocytoma) in a harbour porpoise
An adult male harbour porpoise found stranded last summer in Cloridorme, Gaspésie, Quebec was submitted for necropsy at the Quebec Regional Center of the Canadian Wildlife Health Cooperative (CQSAS). Macroscopic examination of the animal revealed that the carcass was thin and presented various parasitic infections affecting the lungs, liver and stomach. This type of parasitism is common in adult porpoises and is often well tolerated by the animal. This individual’s left adrenal gland was increased in size (see photo 1). In fact, the weight of the left adrenal gland was 4 times greater than that of the right adrenal gland. Upon sectioning the gland, we observed that the medulla (central portion) of the gland occupied most of the organ; on the other hand, the cortex (external portion) of this gland was essentially absent.
Microscopic examination of the affected gland confirmed that this animal was affected by a pheochromocytoma, a tumour of the medulla of the adrenal gland. This tumour is often functional and secretes catecholamines (epinephrine, norepinephrine). These hormones that are normally produced during stressful events, can be overproduced by the tumour and can have negative systemic effects, such as hypertension, weakness, arrhythmia and even collapse of the individual.
In the case of this porpoise, the microscopic examination of different tissues revealed a thickening of the wall of certain arterioles, which suggests a state of hypertension. It is therefore hypothesized that this glandular tumour was potentially responsible for the stranding of this porpoise.
Pheochromocytomas are rare tumours among wildlife. They have already been described in a white-beaked dolphin as well as in a spotted dolphin. Tumours and proliferative lesions have also been diagnosed in the adrenal medulla of 11 belugas from the St. Lawrence River. However, to our knowledge, this tumour has not yet been reported in harbour porpoises.
As of today, the risk factors for this tumour are not known. Continued efforts to document the causes of mortality in harbour porpoises as well as the incidence of adrenal tumours in cetaceans in general could eventually give us more information on the cause of pheochromocytomas.