Primary Sonic Hedgehog–activated dorsal brainstem medulloblastoma and ipsilateral cerebellar atrophy in an adult

Abstract

Medulloblastoma (MB) that arises outside the cerebellum from cells of the dorsal brainstem is rare. The most common subtype of MB in the dorsal brainstem is the Wingless (WNT) subtype that contains activating mutations in the WNT pathway effector CTNNB1. Ipsilateral cerebellar hemi-atrophy with a brainstem tumour is a finding that is usually documented with brainstem gangliogliomas as a possible specific imaging sign. We present a case of a 23-year-old female with progressive headache, imbalance on walking, double vision and difficulty in swallowing for a year. Magnetic resonance imaging demonstrated a mass with prominent restricted diffusion on the dorsal surface of the lower brainstem with ipsilateral cerebellar atrophy. The final histopathological diagnosis was a Sonic Hedgehog (SHH)-activated and TP53 wild-type primary lower dorsal brainstem MB. Primary SHH-activated TP53 wild-type dorsal brainstem MB is extremely rare, and as far as we know, the association of the tumour with ipsilateral cerebellar hemi-atrophy in an adult has never been reported. MB should be included in the differential diagnosis of focal dorsal brainstem tumours, even in the presence of ipsilateral cerebellar hemi-atrophy.

DDX3X Suppresses the Susceptibility of Hindbrain Lineages to Medulloblastoma

“…The great majority of WNT-medulloblastomas are located in and around the cerebellar pontine angle and infiltrate the brainstem (Patay et al, 2015;Perreault et al, 2014); however, around 10% of cases do not involve the brainstem, with rare WNT-medulloblastomas being confined solely to the cerebellum (Di Giannatale et al, 2016). Similarly, while the majority of SHH-medulloblastomas are lateralized within the cerebellar hemispheres, a small proportion are found outside of the cerebellum, with rare cases being confined to the brainstem (Demir et al, 2019). It is noteworthy that patient age, tumor location and DDX3X mutational status are tightly correlated among human SHH-medulloblastomas: only 2% of SHHmedulloblastomas arising in patients aged <18 years mutate DDX3X and the majority are found in the cerebellar midline; conversely, 52% of adult SHH-medulloblastomas mutate DDX3X and almost all these tumors are located within the cerebellar hemispheres.…”

Magnetic Resonance Imaging of Unusual Neoplasms Related to Foramen of Luschka: A Review for Differential Diagnosis

“…Imaging differential diagnoses include medulloblastoma, brain metastases, ependymoma, and primary parenchymal lymphoma. 6 Ipsilateral cerebellar atrophy has been found in brainstem gangliogliomas. 7 …”