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Medulloblastoma, WNT-activated is the least common type of medulloblastoma and has by far the best prognosis, with the vast majority achieving cure with appropriate therapy. They are usually seen in children and, to a lesser degree, adults. They typically arise from the region surrounding the foramen of Luschka and middle cerebellar peduncle.
NB: WNT is a combination of the words "wingless" and "integrated".
WNT tumors account for only 11% of all medulloblastomas, and have, unlike group 3 and 4 tumors, no particular predilection for males, with M:F of 1:2 5.
The majority of these tumors are encountered in children (peak incidence 7-14 years of age) with a substantial minority occurring in adults 1,5. They are, however, almost never diagnosed in infants 1,5.
WNT-activated tumors arise from progenitor cells of the lower rhombic lip mossy fiber neuron lineage that migrate laterally along the anterior extramural migratory streams. This accounts for the location of these tumors 5,6:
foramen of Luschka: 75%
fourth ventricle: 70%
cisterna magna: 30%
cerebellopontine angle cistern: 20%
WNT-activated tumors are almost invariably (97%) of classic histology, with the remainder being of anaplastic morphology 1,2,5. Interestingly even those with anaplastic histology have a good prognosis, which is not the case with other subgroups 2.
Most WNT-activated medulloblastomas are sporadic, most frequently the result of mutations of CTNNB1, which encodes for beta-catenin, or monosomy 6, although numerous other mutations have been described 2,5. Rarely, these tumors are encountered in patients with Turcot syndrome, who have a mutation of the APC gene 2.
Interestingly, and helpful in preoperative assessment, WNT-activated medulloblastomas have a distinct predilection for the cerebellar peduncle, bulging into the cerebellopontine angle, which is not usually encountered in other molecular subgroups. They tend to have prominent contrast enhancement 3.
For more details on radiographic features please refer to the general article on medulloblastomas.
Treatment and prognosis
Surgery is the first line of therapy (as is the case in all medulloblastoma groups) with the aim being histological proof, molecular subtyping and maximal tumor resection, with adjuvant therapy depending on an overall risk profile (see general article on medulloblastoma) 2.
The incidence of CNS metastatic disease in the WNT-activated group at diagnosis is uncommon, found in only 10% of children, and not seen in adults 1.
WNT tumors have a much better prognosis than all other subtypes of medulloblastoma, in all age groups, but this is especially the case in children with long-term survival of almost 100% 5