3 CASES OF CARCINOID IN THE EQUINE NASAL CAVITY AND MAXILLARY SINUSES- HISTOLOGIC AND IMMUNOHISTOCHEMICAL FEATURES

Three cases of carcinoid tumor in horses are described. The tumors ori ginated from the maxillary sinuses and the retrobulbar region and caus ed exophthalmos. Histologically, they had a characteristic endocrine p attern and were argyrophilic with the Grimelius stain. All tumors cont ained reactivity for neuron-specific enolase and synaptophysin. Two of three tumors were reactive for both bovine and porcine chromogranin A . These immunohistochemical results confirm the neuroendocrine nature of these tumors. Neuroendocrine cells could not be detected in the nas al mucosa and maxillary sinuses of a normal horse; therefore, the orig in of these carcinoid tumors remains obscure.