Medulloblastoma, SHH-activated

Medulloblastoma - sonic hedgehog (SHH) subgroup tumours are malignant tumours of the central nervous system. They are the second most common medulloblastoma subgroup (after group 4) and are approximately as common as group 3. They are found most commonly in adults and infants, but infrequently in children. Although they can arise from the vermis of the cerebellum, as is typical for group 3 and 4, they are most frequently are located laterally within the cerebellar hemispheres. 

Epidemiology

SHH subgroup tumours account for approximately 27% of all medulloblastomas, and have, unlike group 3 and 4, have no particular predilection for males, with a ~1:1 male to female ratio ^1-2. 

They are most frequently encountered in adults (>16 years) and infants (<4 years) but are uncommon in children ^1-2. 

Pathology

SHH medulloblastomas can demonstrate various histologies, with classic, large large cell/anaplastic and desmoplastic/nodular/medulloblastoma with extensive nodularity (MBEN) all encountered ². 

Importantly, almost all desmoplastic/nodular/medulloblastoma with extensive nodularity (MBEN) tumours are SHH subtype ². 

Radiographic features

The radiographic features of SHH subgroup tumours are variable depending on, to a degree depending on histological subtype. 

When they are of classic or large cell / anaplastic/anaplastic histology and located in the midline, they are essentially indistinguishable from group 3 and group 4 tumours ³. 

The desmoplastic/nodular/medulloblastoma with extensive nodularity (MBEN) tumours, on the other hand, tend to beoccur in the lateral parts of the cerebellar hemispheres ³. 

For more details on radiographic features, please refer to the general article on medulloblastomasmedulloblastoma. 

Treatment and prognosis

Surgery is the first line of therapy (as is the case in all subgroups) with the aim being histological proof, molecular subtyping and maximal tumour resection, with adjuvant therapy depending on an overall risk profile (see general article on medulloblastoma) ². 

The incidence of CNS metastatic disease in the SHH subgroup at diagnosis is relatively common in infants (17%) and children (22%) but is uncommon in adults ¹. 

SHH tumours have intermediate prognosis compared to other subtypes of medulloblastoma; that is, better than group 3 tumours, but significantly worse  than WNT subtypes ¹:

• 77% 10-year overall survival of  in infants
• 51% 10-year overall survival of  in children
• 35% 10-year overall survival of  in adults

Prognosis is also influenced by histological subtype.