<unk>  is the development of<unk>  due to infiltration of the subarachnoid space by tumor cells.<unk>  was first reported in the 1870's.<unk>  refers to the spread of malignant cells through the cerebrospinal fluid space. These cells can be originated both in primary CNS tumors (e.g. drop-metastases), as well as from distant tumors that have metastasized (hematogenous spread). The microscopic pathology of<unk>  may vary according to the primary cancer involved. Generally, on microscopic histopathological analysis,<unk>  is characterized by large, hyperchromatic cells. Common causes of<unk>  include primary intracerebral malignancies (glioblastoma multiforme, anaplastic astrocytoma, medulloblastoma) and metastatic disease (breast cancer, lung cancer, melanoma, lymphoma, leukemia).<unk>  must be differentiated from infections<unk> , Lyme disease, neurocysticercosis),<unk>  (intracerebral metastasis, dural metastasis), inflammatory (rheumatoid arthritis, multiple sclerosis, polychondritis), and granulomatous disorders (sarcoidosis, histiocytosis, Wegener's granulomatosis, vasculitis).<unk>  occurs in approximately 3-5% of patients with solid tumor, 5-15% of patients with leukemia, and 1-2% of patients with primary brain tumors.<unk>  has a widely disseminated and progressive presentation. If left untreated,<unk>  may progress to develop seizures, hydrocephalus, encephalopathy, and ultimately death. Complications of<unk>  include hydrocephalus, encephalopathy, empyema​, cerebritis, cerebral abscess, and stroke. The median survival time of patients without treatment of<unk>  is 4-6 weeks.<unk>  should be suspected if there are simultaneous occurrence of symptoms or signs in more than one area of the neuraxis. Symptoms of<unk>  include headaches, confusion, memory loss, seizures, double vision, hearing loss, paresthesia and pain in the neck and back, and limb weakness. Common physical examination findings of<unk>  include altered mental status, dementia, hemiparesis, ptosis, nuchal rigidity, bowel and bladder dysfunction, and papilledema. Laboratory findings consistent with the diagnosis of<unk>  include abnormal CSF analysis (increased opening pressure, increased leukocytes, elevated protein, decreased glucose, and positive tumor markers). Only 50% of those suspected with<unk>  are actually diagnosed and only the presence of malignant cells in the CSF is diagnostic. Brain MRI is helpful in the diagnosis of<unk> . On MRI,<unk>  is characterized by normal T1- and T2-weighted images. On contrast administration, there may be leptomeningeal enhancement scattered over the brain in a 'sugar coated' manner, which is fairly diagnostic for<unk> . Other diagnostic studies for<unk>  include meningeal biopsy, which may be diagnostic if there are no systemic manifestations and the CSF analysis remain inconclusive. The mainstay of therapy for<unk>  is intrathecal chemotherapy. Radiotherapy may be used in patients with<unk>  for palliation of symptoms, reduce the bulky tumors, and correction of cerebrospinal fluid flow abnormalities. Supportive care should be directed towards all patients with<unk> , regardless of the treatment regimen (anticonvulsants, corticosteroids, and opiates). Surgery is not the first-line treatment option for patients with<unk> . Surgery is usually reserved for patients who need an intraventricular catheter placement for administration of cytotoxic drugs or placement of a ventriculoperitoneal shunt in patients with symptomatic hydrocephalus.
Neoplastic meningitis
Fungal meningitis
Viral meningitis
Tuberculous meningitis
Acute hemorrhagic leukoencephalitis
Primary amoebic meningoencephalitis
Mollaret's meningitis
Herpes simplex encephalitis