Carotid Body Tumor: An Incidental Finding in Older Ranch Mink

Carotid body tumors were found incidentally at necropsy in 15 ranch mink (Mustela vison), mostly royal pastels, kept for studies on slow viral diseases. The mink, five males and ten females, were 77 to 135 months old (mean age 107 months). Loosely or firmly attached at the bifurcation of the common carotid artery, and 1 I larger tumors were smooth-surfaced, discrete, pale brown, globoid masses that varied from 2.5 to 16 mm in diameter. Four tumors of microscopic size occurred in otherwise normal-looking carotid bodies. All were composed of densely packed polygonal cells disposed in sheets and cords or arranged in clusters by a reticulin meshwork rich in blood vessels. Always unilateral, the tumors had not invaded locally or metastasized. As seen in the smallest tumors, the neoplastic cells usually arose centrally in the carotid body and formed an expansive growth that replaced much of the normal parenchyma without necessarily enlarging the organ beyond normal limits. The cause of the tumors was not apparent. All tumor-bearing mink had lived at an elevation of 1,100 meters, and none had suffered from any obvious chronic cardiopulmonary disease. First described 253 years ago by the Danish anato- mist Jacques-Bhigne Win~low,~~ the carotid body is a chemoreceptor responsive to changes in the PO2, PC02, and pH of systemic arterial blood.22 In a way still poorly understood, this chemosensitivity gener- ates neural impulses that act through reflex pathways in the brain stem to help maintain normal respiration and blood cir~ulation.'~ The carotid body also takes part in certain pathologic processes.6 For example, un- der conditions of chronic hypoxia, it enlarges as a result of capillary dilatation and parenchymal cell hyperpla- sia.4J5,28,29 To the general pathologist, however, this tiny organ is of concern mainly as the site of an un- common neoplasm-the carotid body tumor, one of the chemodectomas or extra-adrenal paraganglio- mas. 19,50 Although the tumor may invade locally and even metastasize, it usually is benign clinically and histo- 10gically.l~~~~ In man (about 950 cases reported), it gen- erally occurs during middle age and occasionally is familia1.23,50 In animals, the tumor is best known for its occurrence in older dogs, notably those of the boxer and Boston terrier breeds.13,27,42 About 50 cases have been reported-far fewer than the number of compa- rable tumors derived from the aortic bodies, where, by contrast, chemodectomas in man seldom arise.5o Nine or so cases of carotid body tumor have been reported in ~attle.~,~~ It has been seen in two but not in the common laboratory animals or in non- human primate^.^^,^^,^^,^^ It has not occurred in any other mammal. Birds, too, have carotid bodies situated in the tho- racic inlet with the ultimobranchial and parathyroid glands instead of at the angles of the jaw.L,2,34 Tumors have not arisen from them.7J8,21,38 Among reptiles, only lizards have small groups of cells, in the adventitia of the carotid arch, that seem homologous with chief cells of the mammalian carotid In amphibians, a cavernous swelling at the cranial end of the common carotid artery, the carotid labyrinth, likewise may be homologous with the mammalian carotid b~dy.~,~~ Neither homologue, however, has been the site of tu- mor~.~,~~,~~,~~ Fishes do not have identifiable carotid b~dies,~,~~ but in the Atlantic cod (Gadus morhua), and in a few other species of Gadidae, a tumor likened to that of the carotid body has been described in the pseudobranch (parabranchial body), a chemoreceptive structure derived from the rudimentary first gill.16,35 Reported here is the occurrence of the carotid body tumor in older ranch mink (Mustela vison).