Figure 14-41.

Abscess, Right Cerebral Hemisphere, Horse.

A, The cerebral cortex contains an abscess (arrow) caused by Streptococcus equi subsp. equi entering the central nervous system via the blood. A fibrous capsule is present on the lateral, medial, and dorsal sides of the abscess (most obvious on the lateral side as a gray band). There is no obvious capsule present on the ventral side (i.e., toward the right lateral ventricle). Microscopically, there is a thin glial capsule (astrogliosis). Note also the increased size of the right hemisphere with blurring of the distinction between gray and white matter, an indication of edema. B, Chains of Gram-positive (blue staining) cocci in the inflammatory exudate from an abscess caused by Streptococcus equi subsp. zooepidemicus. Gram stain.

(A courtesy Dr. K. Read, College of Veterinary Medicine, Texas A&M University; and Noah's Arkive, College of Veterinary Medicine, The University of Georgia. B courtesy Dr. J.F. Zachary, College of Veterinary Medicine, University of Illinois.)