medulloblastomas

Medulloblastoma is a malignant embryonal tumor of the cerebellum and the most common malignant brain tumor in children. It typically arises in the posterior fossa, often in the midline cerebellar vermis, and can produce hydrocephalus with symptoms of increased intracranial pressure. It is much less common in adults.

Clinical presentation usually includes morning headaches, nausea or vomiting, gait instability, truncal ataxia, and signs of raised intracranial pressure. Younger children may present with irritability or macrocephaly if hydrocephalus develops. Spread through the cerebrospinal fluid can occur, leading to drop metastases along the neuraxis.

Medulloblastomas are now categorized by histology and molecular biology. Histologically, they are classic embryonal tumors; large cell and anaplastic variants are recognized. Molecularly, four major groups have been defined: WNT-activated, SHH-activated, Group 3, and Group 4. WNT-activated tumors generally have the best prognosis, SHH-activated tumors show variable outcomes, and Group 3 tumors are often associated with worsened prognosis, while Group 4 has an intermediate outlook. Molecular grouping informs risk stratification and, in some centers, treatment decisions.

Diagnosis is supported by magnetic resonance imaging, which typically shows a midline cerebellar mass that enhances with contrast and may cause fourth ventricle obstruction. CSF cytology may reveal tumor cells if the CSF is sampled.

Treatment centers on maximal safe surgical resection, followed by adjuvant therapy. Standard management includes craniospinal irradiation with a posterior fossa boost and may include chemotherapy, especially in children, to reduce or delay radiation exposure. Long-term follow-up includes monitoring for recurrence and treatment-related effects, such as neurocognitive and endocrine problems. Prognosis depends on age, extent of resection, metastatic spread, and molecular subgroup.