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Medulloblastoma is a most common pediatric malignant primary brain tumor (cancer) originating in the part of the brain that is towards the back and the bottom, on the floor of the skull, in the cerebellum or posterior fossa. The brain is divided into two main parts, the larger cerebrum on top and the smaller cerebellum below towards the back. They are separated by a membrane called the tentorium. Tumors that originate in the cerebellum or the surrounding region below the tentorium are therefore called infratentorial. Historically medulloblastomas have been classified as a PNET (primitive neuroectodermal tumour), however it is now known that medulloblastoma is distinct from supratentorial PNET's and are no longer considered similar entities. Medulloblastomas are non-invasive rapidly growing tumors that, unlike most brain tumors, spread through the cerebrospinal fluid (CSF) and frequently metastasize to different locations along the surface of the brain and spinal cord. The cumulative relative survival rate for all age groups and histology follow-up was 60%, 52%, and 32% at 5 years, 10 years, and 20 years, respectively, with children doing better than adults.〔 ==Signs and symptoms== Signs and symptoms are mainly due to secondary increased intracranial pressure due to blockage of the fourth ventricle and are usually present for 1 to 5 months before diagnosis is made. The child typically becomes listless, with repeated episodes of vomiting, and a morning headache, which may lead to a misdiagnosis of gastrointestinal disease or migraine. Soon after, the child will develop a stumbling gait, frequent falls, diplopia, papilledema, and sixth cranial nerve palsy. Positional dizziness and nystagmus are also frequent and facial sensory loss or motor weakness may be present. Decerebrate attacks appear late in the disease. Extraneural metastasis to the rest of the body is rare, and when it occurs is in the setting of relapse, more commonly in the era prior to routine chemotherapy. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Medulloblastoma」の詳細全文を読む スポンサード リンク
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