Subependymoma - atypical
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There is a heterogeneously enhancing mass that occupies the inferior fourth ventricle and extends through the foramen Magendie to lie posterior to the cervicomedullary junction.
The mass is mildly hyperintense to cortex on T2, with multiple small T2 hyperintense foci that suppress on FLAIR, as well as containing multiple rounded foci of signal loss on 2D MERGE sequence which may represent calcifications or blood product or both. The ADC values within the enhancing component of the mass are approximately 1560mm2/s, although, given the amount of T2* signal loss, these values should be interpreted with caution. No increased CBV (the same caution due to T2* effects should be exercised) identified and MR spectroscopy is non-contributory (not shown).
The medulla and cervicomedullary junction are mildly anteriorly displaced with partial effacement of the premedullary cistern. There is no obstructive hydrocephalus.
There is an enhancing 8mm mass within the floor of the left anterior cranial fossa with associated dural tail that is favored to be extra-axial and likely a small meningioma. Non-specific periventricular white matter T2/FLAIR hyperintensities are most in keeping with changes of chronic small vessel ischemia.
Conclusion: Enhancing mass within the inferior fourth ventricle with extension through the foramen Magendie but without hydrocephalus. The appearance is most consistent with an ependymoma. In this age group a subependymoma is also worth considering although size and imaging appearances would be atypical. Other entities (e.g. metastases, choroid plexus papilloma and hemangioblastoma) are all thought to be far less likely. Probable small meningioma arising from the floor of the left anterior cranial fossa.
The patient went on to have a craniotomy and excision of the mass.
Sections show a variably cellular glioma composed of monotonous tumor cells set within a dense fibrillary stroma. Tumor cells demonstrate round nuclei with granular chromatin and inconspicuous nucleoli. There are scattered foci of dystrophic calcification present. No perivascular pseudorosettes, nuclear atypia or mitoses are seen. No necrosis or microvascular proliferation are seen. There is no evidence of malignancy.
FINAL DIAGNOSIS: Subependymoma (WHO grade I).