Snapshot A 5-year-old boy presents to his pediatrician with headache, nausea, and 2 episodes of emesis. His symptoms began approximately 1 month ago and his headache is most prominent in the morning. The patient also reports some mild fevers and chills. On physical exam, the patient has a wide-based gait with impaired heel-to-toe walking. Fundoscopy demonstrates bilateral papilledema. An MRI brain with intravenous contrast demonstrates a heterogenous midline lesion with hydrocephalus. Introduction Overview neuroepithelial primary central nervous system (CNS) tumor arising from the posterior fossa Epidemiology Incidence most common malignant primary brain tumor in pediatric patients more common in males and in patients between the age of 1-10 Etiology Pathogenesis Upregulation in WNT signaling Presentation Symptoms signs of increased intracranial pressure such as morning headaches nausea vomiting Physical exam in midline lesions (e.g., cerebellar vermus lesion) truncal ataxia (e.g., broad-based gait) in cerebellar hemisphere lesions appendicular ataxia (e.g., impaired finger-to-nose testing) Imaging MRI with and without intravenous contrast indication imaging study of choice for brain cancer Studies Making the diagnosis based on clinical presentation and radiographic findings on CNS imaging (MRI, CT) Differential Pilocytic astrocytoma differentiating factor cystic appearance on MRI Treatment Includes resection, radiation, and chemotherapy Complications Preoperative neurological deficits due to hydrocephalus and intracranial posterior fossa lesion Prognosis Depends on a variety of factors such as age of diagnosis, residual deficits post procedure, histopathology, and biological/molecular markers