Four aged retired Chinese native pigs, three females and one male, estimated as over
10-year-old, were subjected to autopsy because of infertility due to aging. Grossly,
nodular lesions were found bilaterally in the adrenal medulla of all four pigs. Based on
the gross and the histopathological findings, they were diagnosed as either medullary
nodular hyperplasia or pheochromocytoma. Immunohistochemically, proliferating cells of all
these lesions were immuno-positive for chromogranin-A, indicating adrenal medulla-derived.
Ultrastructurally, cytoplasmic neurosecretory granules suggestive of secretion were
observed in these proliferating cells. There have been only limited numbers of reports on
adrenal medullar proliferative changes including pheochromocytoma in pigs. The present
cases will provide a valuable information for the characterization of similar changes in
animals and human.