Leptomeningeal cancer (also called  leptomeningeal carcinomatosis, leptomeningeal disease (LMD), leptomeningeal metastasis, neoplastic meningitis, meningeal metastasis and meningeal carcinomatosis) is a rare complication of cancer in which the disease spreads from the original tumor site to the meninges surrounding the brain and spinal cord. This leads to an inflammatory response, hence the alternative names neoplastic meningitis (NM), malignant meningitis, or carcinomatous meningitis. The term leptomeningeal (from the Greek lepto, meaning fine or slight) describes the thin meninges, the arachnoid and the pia mater, between which the cerebrospinal fluid is located. The disorder was originally reported by Eberth in 1870.It occurs with cancers that are most likely to spread to the central nervous system. The most common cancers to include the leptomeninges are breast cancer, lung cancer, and melanomas because they can metastasize to the subarachnoid space in the brain which offers a hospitable environment for the growth of metastatic tumor cells. Individuals whose cancer has spread to an area of the brain known as the posterior fossa have a greater risk of developing a leptomeningeal cancer. The condition can also arise from primary brain tumor like medulloblastoma. Leptomeningeal disease is becoming more evident because cancer patients are living longer and many chemotherapies cannot reach sufficient concentrations in the spinal fluid to kill the tumor cells. Signs and symptoms
The most common symptoms of leptomeningeal cancer is pain and seizures. The other symptoms may include headaches (usually associated with nausea, vomiting, light-headedness), gait difficulties from weakness or ataxia, memory problems, incontinence, sensory abnormalities.
In some cases, symptoms may include double vision, numb chin, back pain, leg weakness, sphincter-related problems, hydrocephalus, loss of urine control, and difficulty walking. Depending on where the tumor cells settle, leptomeningeal cancer can cause almost any neurological problem. Other symptoms that are less common cranial nerve abnormalities, spinal symptoms such as limb weakness and paresthesia, and bowel and bladder dysfunction. Diplopia is the most common symptom of cranial nerve dysfunction. Trigeminal sensory or motor loss, cochlear dysfunction, and optic neuropathy are also common findings. Spinal signs and symptoms include weakness, dermatomal or segmental sensory loss, and pain in the neck, back, or following radicular patterns.3 affected domains of neurological function:

Cerebral hemisphere (15%)
Cranial Nerves (35%)
Spinal cord and roots (60%)Signs reported:

headache
mental status change
confusion
cognitive impairment
seizures
hemiparesis
gait instability

Related Diseases
Parenchymal Disease occurs in 30-40% of those diagnosed with NM. The disease associated with the main functioning body of an organ, in this case the brain. acute cerebellar ataxia is a rare initial presenting feature of NM, particularly in gastric cancer. Paraneoplastic cerebellar degeneration (PCD) is a well-known cause of cerebellar ataxia associated with neoplastic disorders, and commonly, with positivity for various anti-neuronal antibodies. Bilateral sensorineural hearing loss caused by complications with the vestibulocochlear nerves from onset of NM 
Subacute Confusion: when functioning of the brain such as cognition deteriorates but at a less rapid rate than that of acute confusion

Causes
Leptomeningeal carcinomatosis occurs when the cancer cells invade the cerebrospinal fluid and spread throughout the central nervous system.