Because of this, medulloblastomas are typically only classified as grade IV.

因为这一特征，髓母细胞瘤通常只被分为IV级。

Overall, the most common malignant tumor is a medulloblastoma, which typically forms in or around the cerebellum, adjacent to the fourth ventricle.

总体而言，最常见的儿童恶性脑肿瘤是髓母细胞瘤；它们通常在第四脑室旁的小脑内或周围形成。

Histologically, medulloblastomas often have a feature called Homer-Wright rosettes, which are dense tangles of neurons and neuroglial cells, surrounded by ring-like structures formed by tumors cells.

组织学方面，髓母细胞瘤常具有一种特征，Homer-Wright菊形团：即肿瘤细胞核围绕着密集缠结在一起的神经细胞和神经胶质细胞突起排列。

Now, while medulloblastoma may be the most common malignant tumor, the most common primary pediatric tumor is a type of astrocytoma called a juvenile pilocytic astrocytoma.

尽管髓母细胞瘤可能是最常见的恶性肿瘤，最常见的儿童原发脑肿瘤是一种星形细胞瘤，称为青少年毛细胞型星形细胞瘤。

For example, as pinealomas, medulloblastomas, and ependymomas enlarge - the mass of the tumor can compress nearby ventricles blocking the flow of cerebrospinal fluid which causes swelling, called hydrocephalus.

例如，随着松果体瘤、髓母细胞瘤与室管膜瘤的增大，巨大的肿瘤可以压迫一旁的脑室，阻断脑脊液的流动，从而引起组织肿胀，称为脑水肿。