GANGLIOCYTOMA WITH IMMATURE NEURONAL CELL ELEMENTS IN THE PITUITARY OF A RAT

A spontaneous pituitary gangliocytoma with abundant, immature neuronal cell elements was found incidentally in a 109-week-old female Fischer 344 rat. The pituitary parenchyma was largely occupied by a tumor nod ule with necrotic and hemorrhagic foci and cyst. The tumor was compose d of mature ganglion-like (M) cells, small immature ganglion (I) cells and transitional (T) cells, with a fibrillar matrix. The I and T cell s were intermingled with the M cells or were arranged in compact clust ers, in which the I cells formed perivascular rosette-like structures, sometimes with mitotic figures. Immunohistochemically, all types of t umor cells were positive for neuron-specific enolase, and only the M c ells was positive for chromogranin A. This result may be correlated wi th the degree of cytodifferentiation.