Figure 14-75.

Choroid Plexus Tumor (Carcinoma), Brain, Sagittal Section, Dog.

The third ventricle contains an expansile mass (arrow) that has invaded the normal tissue ventral to it. The mass ventral to the medulla (right) may be a metastasis arising from tumor cells that entered the third ventricle and then spread in the cerebrospinal fluid caudally, through the mesencephalic duct, into the fourth ventricle, and out through a lateral aperture into the subarachnoid space.

(Courtesy Dr. Y. Niyo, College of Veterinary Medicine, Iowa State University; and Noah's Arkive, College of Veterinary Medicine, The University of Georgia.)