Brain Stem Gliomas are the most common pediatric brain tumor and are typically low-grade pilocytic astrocytomas that may occur in the cerebellum or brain stem.

• Gliomas commonly present with focal neurologic deficits (FND) caused by mass effect; these may progress over the course of months as the tumor grows larger and affects additional brain regions.

DDX: Arnold-Chiari malformations:

• rare congenital malformations that typically present in infancy with feeding and breathing problems, myelomeningocele, and progressive hydrocephalus, imaging shows downward displacement of the cerebellar vermis.
• Some Arnold-Chiari malformations present in adolescence with mostly bilateral cranial nerve palsies, weakness and cerebellar dysfunction caused by the downward displacement of the cerebellar tonsils and consequent brainstem compression.
• However, this 7-year-oid patient's unilateral deficits are more consistent with a brain stem glioma...and gliomas are more common than Arnold-Chiari malformations.