The brain is located in a privileged position in the human body. It is protected from trauma by a hard skull and from blood-borne infections by the blood-brain barrier, an anatomical barricade to the passage of large bacteria or substances into the brain's cerebrospinal fluid. Despite its protective effects, microbes can sometimes bypass the barrier and cause infectious diseases of the brain.
Meningitis
Meningitis is the inflammation of the meninges, the thin tissue covering surrounding the brain. It is most commonly caused by bacteria and viruses. The symptoms of meningitis include fever, neck stiffness, headache, photophobia (aversion to bright lights) and vomiting. A lumbar puncture with microscopic examination of the spinal fluid for the presence of white blood cells (the cells that fight off infection) is necessary to diagnose meningitis. Patients with bacterial meningitis can become critically ill; they need prompt attention, including support of vital signs and treatment with antibiotics. Viral meningitis usually causes milder symptoms and may only need pain and fever control and fluids. The one virus that requires aggressive therapy is the herpes virus, which can cause both meningitis and encephalitis.
Encephalitis
Encephalitis is an acute inflammation of the brain. Just like meningitis, it can be caused by bacteria and viruses, although viral encephalitis is far more common. The herpes virus is a common cause of this illness, but other viral illnesses, such as influenza infection, can result in encephalitis. Patients with encephalitis have symptoms of meningitis, and can also have changes in mental status such as confusion, lethargy, visual changes, loss of consciousness and coma. Seizures are another common symptom of encephalitis. Younger children and infants might just have fever, irritability and poor feeding. Lumbar puncture can help in the diagnosis, though it does not always detect the condition. Imaging studies such as brain MRI usually shows changes in the brain consistent with the disease. Treatment is symptomatic, but antiviral therapy can be useful in the treatment for herpes encephalitis.
Brain Abscess
An abscess is a collection of pus, bacteria and other immune system debris in the brain. Abscesses are usually caused by the body's reaction trying to contain an infection by either a bacteria or a fungus. This causes swelling, which can limit the blood supply to the brain and result in seizure or a stroke. The symptoms of abscess can be similar to the other brain infections. Treatment for brain abscesses include IV antibiotics and, occasionally, surgical treatment.
