A 2-year-old boy is brought to the physician by his parents, who complain that their son continually loses his balance. They also report that his speech seems more slurred. Physical examination confirms the truncal ataxia and wide-based gait. The child appears lethargic, and there is bobbing of the head while he is sitting. Muscle tone is normal. This patient may have a midline tumor in which anatomic portion of the brain?

The neuroectoderm may (albeit infrequently) give rise to a neoplasm of neuronal heritage. These tumors occur most often in childhood, and their cellular composition is usually primitive. An example is medulloblastoma, which arises in the cerebellum, generally in the first decade of life. This entity is usually situated in the vermis. Its growth is rapid and regional infiltration is extensive. Children with medulloblastoma are first seen with cerebellar dysfunction or hydrocephalus. Tumors in the other areas do not ordinarily produce the symptoms described.Diagnosis: Medulloblastoma