The child typically becomes listless, with repeated episodes of vomiting, and a morning headache, which may lead to a misdiagnosis of gastrointestinal disease or migraine. Soon after, the child will develop a stumbling gait, truncal ataxia, frequent falls, diplopia, papilledema, and sixth cranial nerve palsy. Positional vertigo and nystagmus are also frequent, and facial sensory loss or motor weakness may be present. Decerebrate attacks appear late in the disease. Extraneural metastasis to the rest of the body is rare, and when it occurs, it is in the setting of relapse, more commonly in the era prior to routine chemotherapy. Pathogenesis
Medulloblastomas are usually found in the vicinity of the fourth ventricle, between the brainstem and the cerebellum. Tumors with similar appearance and characteristics originate in other parts of the brain, but they are not identical to medulloblastoma.Although medulloblastomas are thought to originate from immature or embryonal cells at their earliest stage of development, the cell of origin depends on the subgroup of medulloblastoma. WNT tumors originate from the lower rhombic lip of the brainstem, while SHH tumors originate from the external granular layer.Currently, medulloblastomas are thought to arise from cerebellar stem cells that have been prevented from dividing and differentiating into their normal cell types. This accounts for the histologic variants seen on biopsy. Both perivascular pseudorosette and Homer Wright pseudorosette formations are highly characteristic of medulloblastomas and are seen in up to half of cases.
The addition of radiation to the entire neuraxis and chemotherapy may increase the disease-free survival. Some evidence indicates that proton beam irradiation reduces the impact of radiation on the cochlear and cardiovascular areas and reduces the cognitive late effects of cranial irradiation. This combination may permit a 5-year survival in more than 80% of cases. The presence of desmoplastic features such as connective tissue formation offers a better prognosis. Prognosis is worse if the child is less than 3 years old, degree of resection is inadequate, or if any CSF, spinal, supratentorial, or systemic spread occurs. Dementia after radiotherapy and chemotherapy is a common outcome appearing two to four years following treatment. Side effects from radiation treatment can include cognitive impairment, psychiatric illness, bone growth retardation, hearing loss, and endocrine disruption. Increased intracranial pressure may be controlled with corticosteroids or a ventriculoperitoneal shunt. A new approach to monitor tumor development and treatment response by liquid biopsy is promising, but remains challenging. Chemotherapy
Chemotherapy is often used as part of treatment. Evidence of benefit, however, is not clear as of 2013. A few different chemotherapeutic regimens for medulloblastoma are used; most involve a combination of lomustine, cisplatin, carboplatin, vincristine, or cyclophosphamide. In younger patients (less than 3–4 years of age), chemotherapy can delay, or in some cases possibly even eliminate, the need for radiotherapy. However, both chemotherapy and radiotherapy often have long-term toxicity effects, including delays in physical and cognitive development, higher risk of second cancers, and increased cardiac disease risks.