Cutaneous mast cell tumours with pulmonary metastasis in a hen

Multiple, firm, white, 0.5- to 2-cm dermal nodules and three discrete 0.5- to 1-cm pulmonary masses were discovered in a hen carcass at slaughter. Microscopic examination of both dermal and pulmonary tumours revealed solid sheets of individual cells with central round nuclei and granular to vacuolated cytoplasm. Both toluidine blue and Giemsa stains revealed numerous cells with metachromatic cytoplasmic granules. Dermal tumours contained both collagen degeneration and infiltrates of eosinophils. Ultrastructural examination of tumour cells confirmed the presence of typical avian mast cell granules.