Medulloblastoma

Medulloblastomas are the most common malignant brain tumour of childhood. They most commonly present as midline masses in the roof of the 4th ventricle with associated mass effect and hydrocephalus. Treatment typically consists of surgical resection, radiation therapy, and chemotherapy, with the prognosis strongly influenced by surgical resection, presence of CSF metastases at the time of diagnosis, and expression of the c-erbB-2 (HER2/neu) oncogene.

Although medulloblastoma has been classically thought of as a single entity it is becoming increasingly evident that there are a number of distinct molecular subgroups with, albeit overlapping, clinical, histological and imaging features 8. This has been reflected in the 2016 update of the WHO classification of CNS tumours, which recognizes four molecular subgroups. 

These molecular subgroups have been named WNT, SHH, Group 3 and Group 4 8. Perhaps counterintuitively what most of us think of as the typical medulloblastoma (midline tumour in early childhood) is group 4. Further information on the subtypes of medulloblastoma are available in the links below and in the article classification of medulloblastomas.

Overall medulloblastomas account for 12-25 % of all paediatric CNS tumours, and 30-40% of paediatric posterior fossa tumours 1,7. They are also seen in adults, but only account for 0.4-1.0% of adult brain tumours 1. Since there are many more adults than children, 14-30% of all medulloblastomas are found in adults.

Taken as a group, there is a moderate male predilection with a M:F ratio of 2:1, although this is only true of group 3 and 4 tumours 8

They usually present in childhood with 77% of cases before the age of 19. The median age of diagnosis is 9 years. When diagnosed in adulthood, they typically present in the 3rd and 4th decades and are more likely to arise in atypical locations (see below). When they present in adulthood, there is often a better prognosis. 

Importantly age of presentation and gender ratio is influenced by tumour genomics 7-9:

  • WNT
    • children and adults (not seen in infancy)
    • M:F 1:1
  • SHH
    • infants and adults (rare in children)
    • M:F 1:1
  • Group 3
    • infants and children (rare in adults)
    • M > F
  • Group 4
    • typically children (rare in infants)
    • M:F 2:1

Growth of these very cellular tumours is often rapid and accounts for their relatively rapid clinical onset. Typically, presentation occurs over a few weeks with features that are dominated by symptoms of raised intracranial pressure as a result of obstructive hydrocephalus 7

In approximately 40% of patients there is evidence of CSF seeding at the time of diagnosis 7.

The tumours in general tend to be extremely cellular and is an example of a small round blue cell tumour which results in predictable imaging features. They are categorised as CNS primitive neuroectodermal tumours (WHO grade IV).

Medulloblastomas are associated with a number of syndromes, including:

The radiographic features are strongly influenced by histological type and molecular subtype of the tumour. Many of the imaging characteristics can, however, be remembered by thinking of medulloblastoma as a small round blue cell tumour

Overall the vast majority (94%) of medulloblastomas arise in the cerebellum and the majority of these, from the vermis (75%). They tend to protrude into the fourth ventricle from its roof, and may even grow directly into the brainstem 1,7. This pattern is particularly common in group 3 and group 4, and in some SHH subgroup tumours 10

Other areas are less common, and are seen more frequent in older children and adults. In such cases the tumour is also more likely to be poorly marginated and demonstrate larger cyst formation 7. Adult medulloblastomas are usually located laterally, in the cerebellar hemispheres, with only 28% centred in the vermis; these are most commonly of the SHH subgroup 10

Cerebellar peduncle is almost exclusively seen in the relatively indolent WNT subgroup 8-10

CT

On CT, medulloblastomas appear as a mass arising from the vermis, resulting in effacement of the fourth ventricle / basal cisterns and obstructive hydrocephalus. 

They are usually hyperdense (90%) and cysts formation/necrosis is common (40-50%), especially in older patients. Calcification is seen in 10-20% of cases 7.

Enhancement is present in over 90% of cases and is usually prominent 7.

MRI
  • T1
    • hypointense to grey matter
  • T1 C+ (Gd)
    • overall 90% enhance, often heterogeneously
    • group 4 tumours tend to enhance less 10
  • T2/FLAIR
    • overall are iso to hyperintense to grey matter
    • heterogeneous due to calcification, necrosis and cyst formation
    • surrounding oedema is common 10
  • DWI/ADC
    • restricted diffusion (low ADC values)
  • MR spectroscopy
    • elevated choline
    • decreased NAA
    • may show a taurine peak 5

MRI is able to delineate the fourth ventricle and subarachnoid space to a much greater degree than CT. Although medulloblastomas project into the fourth ventricle, unlike ependymomas they do not usually extend into the basal cisterns 7.

As CSF seeding is common at presentation, imaging with contrast of the whole neuraxis is recommended to identify drop metastases and leptomeningeal spread. Although rare, extraneural spread is reported.

So if all this sounds confusing, that's because it is. Molecular subgroups, histology, location, appearance and demographics all interact, but this notwithstanding, you can make some fairly robust predictions based on imaging when taking all of these together. Location is the key to this approach. 

  • cerebellar peduncle
  • cerebellar hemisphere
    • very likely SHH subgroup and therefore intermediate prognosis
    • likely desmoplastic/nodular/medulloblastoma with extensive nodularity (MBEN)
  • midline
    • may be group 3, group 4 or SHH
    • typically infants with poorly defined tumour, with prominent enhancement, likely group 3 (or SHH) and therefore worst prognosis
    • typically children with well defined tumours, with mild or no enhancement, likely group 4 and therefore slightly better prognosis
    • adults with variably defined and variably enhancing tumours, are likely SHH (or group 4)

Treatment typically consists of surgical resection, radiation therapy, and chemotherapy. In general the tumours are quite radiosensitive.

Prognosis depends on complete surgical resection, and presence of CSF metastases at the time of diagnosis, which are generally common in infants and children (~25%) and uncommon in adults (~2%) 1

Expression of the c-erbB-2 (HER2/neu) oncogene is useful in staging of medulloblastomas. Increased c-erbB-2 expression reflects an increase in the proliferative activity of a tumour (widely used in breast cancer staging).

  • no CSF metastases, complete surgical resection and negative c-erbB-2 expression: 5-year-survival 100%
  • no CSF metastases, complete surgical resection and positive c-erbB-2 expression: 5-year-survival 54%
  • CSF metastases and/or incomplete surgical resection: 5-year-survival 20%

New genomic classification is also useful in predicting prognosis 7-9:

  • WNT: very good
  • SHH: infants good, others intermediate
  • group 3: poor
  • group 4: intermediate

In the paediatric population consider:

In the adult population consider:

Share article

Article information

rID: 5335
Section: Pathology
Synonyms or Alternate Spellings:
  • Medulloblastomas

Support Radiopaedia and see fewer ads

Cases and figures

  • Drag
    Figure 1: gross pathology
    Drag here to reorder.
  • Drag
    Case 1
    Drag here to reorder.
  • Drag
    Case 2: in an adult
    Drag here to reorder.
  • Drag
    Case 3: with drop metastasis
    Drag here to reorder.
  • Drag
    Case 4: T1 C+ : in an adult
    Drag here to reorder.
  • Drag
    Case 5: T1 C+
    Drag here to reorder.
  • Drag
    Case 6
    Drag here to reorder.
  • Drag
    Case 7
    Drag here to reorder.
  • Drag
    Case 8: low ADC in tumour
    Drag here to reorder.
  • Drag
    Case 9
    Drag here to reorder.
  • Drag
    Case 10
    Drag here to reorder.
  • Drag
    Case 11
    Drag here to reorder.
  • Drag
    Case 12
    Drag here to reorder.
  • Drag
    Case 13
    Drag here to reorder.
  • Drag
    Case 14
    Drag here to reorder.
  • Drag
    Case 15
    Drag here to reorder.
  • Drag
    Case 16
    Drag here to reorder.
  • Drag
    Case 17
    Drag here to reorder.
  • Drag
    Case 18
    Drag here to reorder.
  • Drag
    Case 19
    Drag here to reorder.
  • Drag
    Case 20
    Drag here to reorder.
  • Drag
    Case 21
    Drag here to reorder.
  • Drag
    Case 22
    Drag here to reorder.
  • Drag
    Case 23
    Drag here to reorder.
  • Drag
    Case 24
    Drag here to reorder.
  • Drag
    Case 25
    Drag here to reorder.
  • Drag
    Case 26
    Drag here to reorder.
  • Drag
    Case 27
    Drag here to reorder.
  • Updating… Please wait.
    Loadinganimation

    Alert accept

    Error Unable to process the form. Check for errors and try again.

    Alert accept Thank you for updating your details.