High levels of lactate dehydrogenase in cerebrospinal fluid are often associated with bacterial meningitis. Choroid plexuses appear in the ventricles which produce cerebrospinal fluid. The choroid plexus mediates the production of cerebrospinal fluid (CSF). Isoniazid reaches therapeutic concentrations in serum, cerebrospinal fluid, and within caseous granulomas. This box contains three elements&colon; brain, intracranial blood and cerebrospinal fluid. The choroid plexus has the important function of producing cerebrospinal fluid. The CNS is protected by the cranium, vertebral column, meninges, cerebrospinal fluid. Diagnosis is based on blood or cerebrospinal fluid testing. The cerebrum contains the ventricles where the cerebrospinal fluid is produced and circulated. Neurologists frequently perform lumbar punctures to assess characteristics of a patient's cerebrospinal fluid. The presence of white blood cells in cerebrospinal fluid is called pleocytosis. Leptomeningeal carcinomatosis occurs when the cancer cells invade and proliferate in the cerebrospinal fluid. It is a common contaminant in blood and cerebrospinal fluid cultures. This rupture can cause the nasal cavity to fill with cerebrospinal fluid. These cisterns are filled with cerebrospinal fluid.