Viral Infections

A great number of viruses have affinity for the neural tissue and account for a significant number of serious neurologic diseases, especially in patients who are immunosuppressed.

Viral infections of the CNS occur sporadically or in epidemics, either worldwide or in particular geographic areas. Viruses can infect individuals of all ages from infancy to old age, but some favor particular age groups. Viruses enter the host via respiratory or oral routes, sexual contact, or cutaneous inoculation. Mothers can infect fetuses transplacentally and neonates during parturition from a genital infection or from breast milk.

FIGURE 6.5

Tuberculous meningitis/encephalitis. A. Thick gelatinous exudate fills the basal cisterns B. Macrosection of the infundibulum shows massive granulomatous exudate in the subarachnoid space (Cresyl violet). C. Subarachnoid exudate shows lymphoplas-macytic infiltrations, Langhans'-type multinucleated giant cells, and epithelioid cells, and areas of caseous necrosis (HE).

FIGURE 6.5

Tuberculous meningitis/encephalitis. A. Thick gelatinous exudate fills the basal cisterns B. Macrosection of the infundibulum shows massive granulomatous exudate in the subarachnoid space (Cresyl violet). C. Subarachnoid exudate shows lymphoplas-macytic infiltrations, Langhans'-type multinucleated giant cells, and epithelioid cells, and areas of caseous necrosis (HE).

FIGURE 6.6

Tuberculoma. A. Macrosection of a cherry-sized tuberculoma surgically excised from the cerebellum of a 32-year-old man. B. Multiple microtubercles with (C) Langhans'-type multinucleated giant cells (HE).

FIGURE 6.6

Tuberculoma. A. Macrosection of a cherry-sized tuberculoma surgically excised from the cerebellum of a 32-year-old man. B. Multiple microtubercles with (C) Langhans'-type multinucleated giant cells (HE).

Most viruses, after replication in distant organs, reach the nervous system via the bloodstream during a temporary phase of viremia. A few viruses reach the neural tissue along peripheral nerves, through retrograde axonal transport.

Once the viruses reach the neural tissue, they can afflict it in several ways. Most viruses evoke an acute aseptic inflammation of the leptomeninges, brain, and/ or spinal cord. Some latent viruses, when reactivated, produce either an acute inflammatory or a slowly progressive inflammatory/demyelinating disease. Other viruses (teratogenic) produce malformations in the fetuses of infected pregnant women, and a few viruses (oncogenic) are apt to produce neoplasms.

0 0

Post a comment