Histological examination is important to detect and differentiate among different types of tissue changes at the microscopic level. An enlarged organ can be hyperplastic, hypertrophied, or neoplastic. It can also be merely inflamed or infected. Only a histological examination can differentiate among the various growth disturbances and pathological changes at the microscopic level. Histopathology is indispensable when neoplasia induced by transgenes is the subject of study (1 –4 ).