CNS malignancies, as a group, are the most common solid tumor and the second most common malignancy of childhood, comprising about 17% of all malignancies during childhood and adolescence. National Cancer Institute (NCI) statistics show that approximately 2,200 U.S. children younger than 20 years are diagnosed annually with invasive CNS tumors. Astrocytomas account for about 50%; medulloblastomas and primitive neuroectodermal tumors account for about 25%; and other gliomas and ependymomas comprise the rest. Unlike adults and older children (older than 10 years of age), who have primarily supratentorial brain tumors, young children have an increased likelihood of malignancies in the cerebellum and brainstem. Medulloblastoma, which arises within the cerebellar vermis or within the hemispheres, is the most common malignant brain tumor in children, with about 400 new cases in U.S. children every year.

Most patients with cerebellar tumors will present with ataxia. Defined as impaired coordination of movement and balance, ataxia is associated with dysfunction of the cerebellum or of the sensory or motor pathways connecting to it. A physician must be aware of a child’s developmental milestones to determine if a patient is ataxic or exhibiting age-appropriate “clumsiness.” Other conditions that may be confused with ataxia include muscle weakness, myopathic or neuropathic; spasticity; or movement disorders. A careful neurologic exam is needed to distinguish these general causes. The differential diagnosis for ataxia is broad and includes head trauma, Guillain-Barré syndrome, a vascular event, hydrocephalus, labyrinthitis, certain medications, seizures, conversion disorders, and infratentorial tumors.

The occurrence of a worsening headache, nausea, or vomiting, particularly on awakening, should raise the concern for increased intracranial pressure that may be secondary to a CNS lesion or tumor. Other conditions that may present with increased intracranial pressure include traumatic brain injury, hydrocephalus, arteriovenous malformation, pseudotumor cerebri and intracranial infections. Because a lumbar puncture (LP) may result in brain herniation in patients with elevated intracranial pressure, a computed
tomography (CT) scan must be obtained prior to the LP in a child with a headache.

The most common cause of intermittent headache and vomiting in pediatrics is migraine. Migraine headaches are usually hemicranial; throbbing or pulsating; associated with abdominal pain, nausea, or vomiting; and resolve with rest. They may be associated with an aura, and a family history of migraines is found in 80% of the patients. Other common headaches are cluster or stress-related headaches, but they are not typically accompanied by nausea. A complete neurologic exam should be performed in any child presenting with a headache, vomiting, and ataxia. In a large tertiary care center study, no patient with a normal neurologic examination had a brain tumor on neuroimaging.