Serious infections of the central nervous system: encephalitis, meningitis, and brain abscess.

Central nervous system infections in adolescents range from the diffuse cerebritis of encephalitis to the regional inflammation of meningitis, and very focal disease of brain abscess. Clinical presentations reflect this wide spectrum, with encephalitis primarily characterized by altered mental status, meningitis by fever, headache, and neck stiffness, and brain abscess manifesting localizing findings. Encephalitis and viral meningitis are frequently caused by the seasonal enteroviruses and arboviruses, while most adolescent bacterial meningitis is due to Neisseria meningitidis and Streptococcus pneumoniae. The microbiology of brain abscess reflects underlying host risk factors. Gram-positive cocci are seen in patients with congenital heart disease, while respiratory flora including anaerobes are associated with sinus or otic disease. Lumbar puncture to characterize and culture the CSF remains the optimal test for the diagnosis and management of encephalitis and meningitis, while CT-guided needle biopsy may be both diagnostic and therapeutic for brain abscesses. New diagnostic tests include the use of PCR. A variety of safe and effective treatment regimens exists for most bacterial infections as well as for some herpesvirus infections. New vaccines are under study to further control bacterial meningitis.