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Medulloblastoma is a highly malignant brain tumour that commonly arises in children, though it can also occur in adults. It originates in the cerebellum or posterior fossa, the part of the brain responsible for balance, coordination, and other motor functions.

About

• Commonest tumour in children

Aetiology

• A malignant primitive neuroectodermal tumour
• Posterior fossa tumour are seen more commonly in children
• It is a primitive neuroectodermal tumour (PNET)
• May spread through CNS and very rarely metastasise to bone.

Histological Subtypes

• Classic Medulloblastoma: The most common form, characterized by sheets of small, round, blue cells with hyperchromatic nuclei.
• Desmoplastic/Nodular Medulloblastoma: Features nodular regions and reticulin-free zones, typically associated with a better prognosis.
• Large Cell/Anaplastic Medulloblastoma: A more aggressive variant with large, pleomorphic cells and a poorer prognosis.
• Medulloblastoma with Extensive Nodularity: Characterized by nodules with abundant reticulin fibers, often seen in infants.

Molecular Subgroups

• WNT-activated Medulloblastoma:
  • Characteristics: Generally has the best prognosis with a 5-year survival rate of about 90%.
  • Genetics: Mutations in the WNT signaling pathway.
  • Location: Frequently located in the midline of the cerebellum.
• SHH-activated Medulloblastoma:
  • Characteristics: Intermediate prognosis.
  • Genetics: Mutations in the Sonic Hedgehog (SHH) pathway.
  • Location: Often arises in the cerebellar hemispheres.
• Group 3 Medulloblastoma:
  • Characteristics: Poor prognosis, often associated with MYC amplification.
  • Genetics: High rates of metastasis at diagnosis.
  • Location: Commonly found in the midline of the cerebellum.
• Group 4 Medulloblastoma:
  • Characteristics: Intermediate prognosis, the most common molecular subtype.
  • Genetics: Often has an isochromosome 17q abnormality.
  • Location: Similar to Group 3, often found in the midline.

Clinical

• Hydrocephalus, Cerebellar signs, Spread to the spinal cord
• Midline so present with gait and truncal ataxia and nystagmus

Investigations

• Magnetic Resonance Imaging (MRI) is the imaging modality of choice for medulloblastoma due to its superior soft-tissue contrast and ability to provide detailed images of the brain.
  • T1-Weighted Imaging (with and without contrast): Medulloblastomas typically appear as isointense to hypointense on T1-weighted images. After contrast administration, the tumour often shows heterogeneous enhancement.
  • T2-Weighted Imaging: The tumour usually appears hyperintense on T2-weighted images, providing clear delineation of the tumour's margins and surrounding edema.
  • FLAIR (Fluid-Attenuated Inversion Recovery): Useful for detecting peritumoural edema and non-enhancing tumour components.
• Computed Tomography (CT): are less commonly used for medulloblastoma but can be helpful in certain situations.
  • Emergency Situations: CT is often the first imaging modality used in an emergency setting, especially if MRI is not immediately available.
  • Bone Involvement: CT is superior to MRI in detecting bone involvement or calcifications within the tumour.
  • Hydrocephalus: CT can quickly assess the presence of hydrocephalus, a common complication of medulloblastoma due to obstruction of cerebrospinal fluid (CSF) pathways.
• Positron Emission Tomography (PET) often combined with CT (PET/CT), can be used in specific cases to assess the metabolic activity of the tumour:
  • Metastasis Detection: PET can help identify metastases, particularly in the spinal cord, which may not be easily detected on MRI or CT alone.
  • Assessing Treatment Response: PET is useful in evaluating the tumour’s metabolic response to therapy, with reduced uptake indicating a good response.
• Spinal MRI: Given that medulloblastoma can metastasize via the cerebrospinal fluid (CSF), spinal MRI is often performed to check for drop metastases along the spinal cord. Whole Spine MRI performed at diagnosis and during follow-up to assess the entire spinal cord for metastatic disease.

Management

• Surgical excision, Radiation, Chemotherapy
• Depends on the tumour's molecular subgroup, location, and the patient's age and overall health.
• Aggressive tumour and recurrence is possible