Medulloblastoma is one of the most common malignant childhood brain tumors, typically arising in the posterior fossa, particularly in the cerebellum. According to the World Health Organization (WHO) classification, medulloblastomas are part of the Embryonal Tumor group and are classified as WHO Grade 4, indicating a highly aggressive tumor with a significant propensity for dissemination.
Medulloblastomas account for approximately 20% of all pediatric brain tumors. They are rare in adults, often referred to as “medulloblastoma adult” in clinical contexts. This tumor can disseminate through the cerebrospinal fluid (CSF) to both the brain and spinal cord, a process known as drop metastasis.
Histopathological and Molecular Classification of Medulloblastoma
Modern classification integrates both histological and molecular features.
1. Histopathological Subtypes
1.Classic Medulloblastoma
Most common subtype.
Small, densely packed, round tumor cells with high mitotic activity.
2.Desmoplastic / Nodular Medulloblastoma
More frequent in infants under 3 years and in adults.
Better prognosis compared to the classic subtype.
3.Large Cell / Anaplastic Medulloblastoma
The most aggressive form.
High risk of recurrence and CSF dissemination.
2. Molecular Subgroups (WHO 2021)
- WNT-activated Medulloblastoma: Generally the best prognosis. More common in children; low risk of CSF metastasis.
- SHH-activated Medulloblastoma: More common in infants and adults. Prognosis worsens in the presence of TP53 mutations.
- Group 3 Medulloblastoma: Often associated with MYC amplification. Poor prognosis and high likelihood of CSF dissemination.
- Group 4 Medulloblastoma: The most common molecular subtype. Intermediate prognosis.
Symptoms and Clinical Presentation
Due to its posterior fossa location, medulloblastoma frequently leads to hydrocephalus and increased intracranial pressure. The most common symptoms include:
Headache and morning vomiting (signs of increased intracranial pressure)
Gait disturbances and imbalance (cerebellar ataxia)
Dizziness
Blurred or double vision (6th cranial nerve compression)
Irritability and cognitive decline in children
Back pain and bowel/bladder dysfunction in cases with spinal drop metastases
Diagnostic Methods
Medulloblastoma diagnosis relies on a combination of clinical suspicion, imaging, and histopathology. Medulloblastoma radiology:
Magnetic Resonance Imaging (MRI): Brain MRI shows a posterior fossa mass with contrast enhancement.
Spinal MRI is required to detect CSF dissemination (drop metastases).
Cerebrospinal Fluid (CSF) Analysis: Performed after surgery to avoid tumor seeding.
Detection of malignant cells confirms leptomeningeal spread.
Histopathological and Molecular Testing: Definitive diagnosis is based on surgical resection or biopsy.
Molecular subgrouping guides prognosis and therapy selection.
Medulloblastoma Treatment Approaches
Management requires a multidisciplinary team, including pediatric neurosurgery, oncology, and radiation oncology.
1. Microsurgical Resection (Primary Treatment)
Goal: Maximal safe tumor resection
Gross total resection improves prognosis.
Functional preservation is critical due to cerebellar and brainstem proximity.
2. Radiotherapy
Standard in children older than 3 years and adults.
Craniospinal irradiation (CSI) is performed to eliminate microscopic CSF metastases.
Dose reduction is possible in low-risk patients; proton therapy helps spare healthy tissue.
3. Chemotherapy
Common agents: Vincristine, cisplatin, lomustine (CCNU), cyclophosphamide
In infants, intensive chemotherapy is used to delay radiotherapy and reduce long-term side effects.
Therapy is personalized based on molecular subgroup and risk status.
The Role of Neuro-Oncology Tumor Boards
Neuro-oncology tumor boards bring together specialists from neurosurgery, oncology, neuroradiology, pathology, endocrinologist and radiation therapy to discuss individual cases. These interdisciplinary meetings enhance treatment planning, foster personalized care, and have been linked to prolonged survival and better quality of life.