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Page 8 of 15 Dasgupta et al. J Transl Genet Genom 2018;2:15. I https://doi.org/10.20517/jtgg.2018.21
[31]
value for WNT-subgroup medulloblastoma. Dasgupta et al. reported the longest tumor dimension to be <
4 cm in > 35% of WNT-subgroup tumors compared to > 4 cm in > 80% of patients of other subgroups. The
presence of cyst or cavity (71%) and perilesional edema (53%) can also be encountered frequently in adult
[28]
WNT-subgroup medulloblastoma .
SHH SUBGROUP MEDULLOBLASTOMA
This subgroup comprising nearly 30% of all medulloblastomas is the most heterogeneous molecular
subgroup in terms of genetic aberrations, histologic features, clinical presentation, and outcomes [4-6] .
Normal cerebellar development is highly dependent on SHH signaling; however, unrestricted SHH activity
can lead to medulloblastoma tumorigenesis. The 5-year overall survival in patients with SHH-subgroup
medulloblastoma ranges from 50%-85% depending upon age at diagnosis, histological subtype, presence of
[3,6]
metastases, and underlying molecular genetic abnormalities . A large proportion (> 50%) of SHH-pathway
[5,6]
medulloblastomas show desmoplastic histology with extensive nodularity seen almost exclusively in this
subgroup; remaining tumors show either classic or LCA histology. They are seen at comparable frequency in
males and females, but have a unique bimodal age incidence with most cases involving infants (< 3 years) or
adults (> 18 years).

Anatomic location
SHH-pathway medulloblastomas are known to arise from granule neuron precursor cells in the external
granular layer of the cerebellum [32,33] and often associated with a lateralized hemispheric location. In the
[21]
series by Teo et al. , 9 of 17 (53%) SHH tumors were located laterally in the cerebellar hemispheres. Because
of the lateralized location, these tumors are often seen to be away from the brainstem with distinct space
appreciated between the tumor margin and the dorsal brainstem. A similar observation was reported by
[23]
Wefers et al. , with only 10 of 21 (48%) SHH-pathway medulloblastomas having any contact with the
brainstem. They further noted that for hemispheric location, SHH-subgroup tumors were relatively more
rostral (superior) compared to more caudal (inferior) location for WNT-subgroup tumors, and no specific
[28]
predilection in non-WNT/non-SHH tumors. In a large cohort of adult medulloblastomas , exclusive
cerebellar location was reported in 40 of 64 (63%) SHH-pathway tumors, with only 11 (17%) SHH-tumors
[28]
being limited to midline vermian location. Zhao et al. also reported that 48% of adult SHH-subgroup
medulloblastoma burden exclusively in the rostral cerebellum with only 25% of SHH-subgroup tumors
having any brainstem contact, mostly with the cuneate nucleus. On comparing the anatomic location of
adult SHH-subgroup tumors with their infantile and childhood counterparts, the proportion of patients
with cerebellar hemispheric location increased with age and was seen in 13%, 56%, and 63% of infantile,
[31]
childhood, and adult SHH-medulloblastoma respectively. Dasgupta and colleagues , also reported
lateralized hemispheric location in 29 of 44 (66%) patients with SHH-subgroup medulloblastoma including
rising proportion of patients with hemispheric tumors with increasing age at initial diagnosis. Thus,
lateralized location was seen in 72% of adults (≥ 18 years) with SHH-pathway medulloblastoma compared to
only 27% hemispheric location in the infantile age group (< 3 years), who continue to have predominantly
midline SHH-subgroup tumors. Hemispheric location was seen in nearly 60% of childhood SHH-pathway
medulloblastoma. The authors also reported superior location abutting and/or reaching the tentorium as a
specific imaging feature of SHH-subgroup medulloblastoma seen in 48% of patients, as opposed to only 6%
for all other subgroups.

Contrast-enhancement pattern
The degree and pattern of contrast-enhancement have been reportedly variable in SHH-pathway
[24]
medulloblastoma. Lastowska et al. reported 7 of 8 SHH-subgroup tumors to be associated with contrast
uptake, which was more frequent compared to other subgroups. Although most adult patients (91%)
with SHH-pathway medulloblastoma do show moderate or intense contrast enhancement, nearly 9%
[31]
[28]
of patients may show minimal or no enhancement at all . Dasgupta et al. reported some contrast-