Chordomas are rare and low-grade malignant solid tumours, despite their histologically benign appearance, that arise in the bone from embryonic notochordal vestiges of the axial skeleton, a mesoderm-derived structure that is involved in the process of neurulation and embryonic development. Chordomas occurring in the skull base tend to arise in the basiocciput along the clivus. Three major morphological variants have been described (classical, chondroid, and atypical/dedifferentiated). The pathogenesis and molecular mechanisms involved in chordoma development remain uncertain. From a pathological standpoint, the microenvironment of a chordoma is heterogeneous, showing a dual epithelial-mesenchymal differentiation. These tumours are characterised by slow modality of biologic growth, local recurrence, low incidence of metastasis rates, and cancer stem cell (CSC) phenotype. The main molecular findings are connected with brachyury immunoexpression and activation of the downstream Akt and mTOR signalling pathways. The differentiation between typical and atypical chordomas is relevant because the tumoural microenvironment and prognosis are partially different. This review provides an insight into the recent and relevant concepts and histochemical markers expressed in chordomas, with special emphasis on dedifferentiated chordomas and their prognostic implications.

Medulloblastoma (MB) is a highly aggressive soft tissue neoplasm, classified as a primitive neuroectodermal tumor. It is the most common posterior fossa tumor in children, but occurs rarely in adults. MB accounts for approximately 20% of all primary central nervous system (CNS) tumors of childhood, while its incidence is around 1% of adult brain tumors. Most often it occurs in the cerebellum. We report a case of multicentric MB involving the bilateral cerebellopontine angle (CPA) and right cerebellar hemisphere. The tumor showed isointensity on T1/T2-weighted images, and slight hyperintensity on T2-weighted fluid-attenuated inversion-recovery (FLAIR) images. The MB had restricted diffusion on diffusion-weighted images (DWI). It was not easy to make an accurate diagnosis before biopsy. The lesion in our patient presented with atypical MR image features of medulloblastoma. To our knowledge, this is the first case of bilateral CPA MB.