Medulloblastoma diagnosis confirmed in this pediatric patient presenting with symptoms consistent with posterior fossa syndrome.  The patient exhibits signs of increased intracranial pressure, including morning headaches, nausea, vomiting, and papilledema observed on fundoscopic examination.  Ataxia, particularly gait ataxia, is also noted, along with nystagmus and cranial nerve palsies.  Magnetic resonance imaging (MRI) of the brain with and without contrast reveals a well-defined, hyperdense mass located in the cerebellum, specifically within the vermis, characteristic of medulloblastoma.  The differential diagnosis included other posterior fossa tumors such as ependymoma and pilocytic astrocytoma, but the imaging characteristics and clinical presentation strongly favor medulloblastoma.  Histopathological analysis following surgical resection will provide definitive confirmation of the diagnosis.  Metastatic workup, including lumbar puncture for cerebrospinal fluid (CSF) cytology and spinal MRI, is essential to assess for leptomeningeal dissemination.  Treatment planning involves a multidisciplinary approach, including pediatric neurosurgery for maximal safe resection, followed by adjuvant therapies such as craniospinal radiation and chemotherapy, depending on risk stratification based on histology, extent of resection, and presence of metastases. Molecular profiling of the tumor will be conducted to guide personalized treatment strategies.  Patient and family education regarding the diagnosis, prognosis, and treatment plan has been initiated, and psychosocial support services have been offered.  Continued neurological monitoring and follow-up imaging will be essential for long-term surveillance and management of potential treatment-related complications.  ICD-10 code C71.9, Malignant neoplasm of cerebellum, unspecified, is assigned.