Experimental brain abscess development in the chronically immunosuppressed host

Abstract

The neuropathological progression of brain abscess formation was studied experimentally in paired immunosuppressed and control dogs. The immunosuppressed animals received azathioprine and prednisone beginning 7 days prior to intracerebral inoculation with alpha streptococcus. Histological findings were correlated with computerized tomography (CT) brain scans. The evolution of brain abscess in the immunosuppressed animals could be divided into three stages based on histological evaluation: cerebritis stage (1 to 11 days), early-capsule stage (12 to 17 days), and late-capsule stage (18 days and later). There was a significant delay in the evolution of alpha streptococcus brain abscess compared to the authors' previous studies. Histologically, abscesses in immunosuppressed dogs were characterized by a decrease and delay in collagen formation, a reduction in polymorphonuclear leukocytes and macrophages, longer persistence of bacterial organisms, and an increase in gliosis. During the cerebritis stage, abscesses in control animals were consistently larger and more edematous than those in immunosuppressed animals and reached their maximum size by Day 8, whereas abscesses in immunocompromised animals reached their maximum size around Day 12. In the late-capsule stage, abscesses in immunosuppressed animals remained larger than those of control animals and continued to show signs of delayed development. This was evidenced by diffusion of contrast medium into the lucent center of ring-enhancing lesions on delayed CT scans. The results suggest that the decreased inflammatory response and edema formation in the immunosuppressed host resulted in less initial mass effect from brain abscess, but that the eventual size and area of the abscess may have become larger due to the less effective host response.

HIV-Related Cerebral Toxoplasmosis Revisited: Current Concepts and Controversies of an Old Disease

“…23 In addition, a significant delay in the evolution of the stages of brain abscess can occur in an immunocompromised host. 24 Thus, early cerebritis that correlates better with the necrotizing encephalitis is characteristically observed in toxoplasmosis. 23 For this reason, the terms ”toxoplasmic encephalitis,” 7,25-27 “toxoplasma encephalitis,” 28,29 or “cerebral toxoplasmosis” 30-33 seem to be more appropriate than “toxoplasma abscess.”…”

Thickening of the walls of deep brain abscesses is associated with macrophage infiltration

“…Comparing the CT appearances and the neuropathologic findings in dogs, Britt et al ( 13 ) and Enzmann et al ( 34 ) determined that ring-shaped contrast enhancement appeared on CT imaging in the early cerebritis stage and well-encapsulated brain abscesses occurred at the age of 14 days and beyond through the accumulation of fibroblasts and neovascularization, with the thickness and diameter of ring-like abscesses decreasing as cerebritis later receded. Pathological abscess formation processes may slow down in the chronically immunosuppressed host ( 35 ). However, the results of the present study indicated that time was not significantly correlated with the thickness of a brain abscess.…”

Neuroimmunopathology in Toxoplasmic Encephalitis

“…Pus may be seen in the latter three stages [92]. Additionally, an immunocompromised host may have a considerable delay in the progression of the phases of a brain abscess [93]. Thus, early cerebritis that more closely resembles necrotizing encephalitis is often seen in toxoplasmosis patients [92].…”