In the differential diagnosis we have a variety of posterior fossa see tumors like the pilocytic astrocytoma (PA) (its main differential), the gangliogliomas and gangliocytomas, meduloblastoma, the pleomorphic xanthoastrocytoma which is almost always hemispheric and the papillary glioneuronal tumor, the last one being usually hemispheric.

The PA is also a WHO grade 1 tumor whit a strong association to type 1 neurofibromatosis with a peak in the first 2 decades of life (9-10 years old patients) being the most common primary brain tumor of childhood, they present as an expansive mass whit symptoms coming from the compression of adjacent structures.  On image they range from large cysts with a brightly enhancing mural nodule: 67%, heterogeneous, mixed solid and multiple cysts and central necrosis and completely solid, all 3 with a vivid enhancement after contrast, being a key point to differentiate it from RGNT

Meduloblastoma is the most common malignant brain tumor in children having four groups in the 2016 who classification and new subgroups in the 2021 revision based on DNA-methylation profiling and transcriptome profiling. On image they show higly DWI restriction making its point of differenciation from RGNT 

In conclusion RGNT is a rare posterior fossa tumor that attires a lot of attention when diagnosed due to its striking image presentation, although pathology is the only definitive diagnostic test, images help guiding the management and complementary studies needed, investigation is still on the making of new treatments for this condition, and to have it in our scope when reading brain MRI is a most.