Infratentorial Multinodular and Vacuolating Neuronal Tumor or Multinodular and Vacuolating Posterior Fossa Lesions of Unknown Significance? Clinico-Radiologic Findings from 2 Cases

Multinodular and Vacuolating Neuronal Tumor-like Lesion of the Spinal Cord: Two Case Reports

We describe 2 cases of a spinal cord lesion with imaging features closely resembling those described in supratentorial multinodular and vacuolating neuronal tumor (MVNT) or infratentorial multinodular and vacuolating posterior fossa lesions of unknown significance. Multiple well-delineated nonenhancing T2-hyperintense intramedullary cystic ovoid nodules were visualized within the white matter of the spinal cord, including some immediately abutting the gray matter. No alterations in signal intensity or morphology were detected in a follow-up. Moreover, no relevant clinical symptoms attributable to the lesions were present. We describe these lesions as presumed MVNT, and we therefore use the term MVNT-like spinal cord lesions.

Case report: Rare case of multinodular and vacuolar neuronal tumors in the cerebellum

Multinodular and vacuolar neuronal tumor (MVNT) is a rare and benign neuroepithelial tumor. Most reports describe tumors located in the cerebral hemisphere. A literature review found that 15 cases were located in the posterior cranial fossa, but all lacked pathological evidence. In this case, a patient sought medical attention due to insomnia and irritability. Neuroepithelial tumors were found in the imaging, and the patient underwent radiation therapy. Three years later, malignant tumors were found upon imaging examination. After surgical resection and pathological testing, MVNT occurring in the cerebellum was diagnosed. MVNT is rare in the cerebellum, and direct imaging diagnosis becomes difficult after treatment. Therefore, our report of this case helps to further accurate understanding of the imaging, pathological, and molecular genetic changes occurring before and after MVNT treatment, and will improve the accuracy of pre-treatment diagnosis and reduce the likelihood of overtreatment.

Major Changes in 2021 World Health Organization Classification of Central Nervous System Tumors

The World Health Organization (WHO) published the fifth edition of the WHO Classification of Tumors of the Central Nervous System (WHO CNS5) in 2021, as an update of the WHO central nervous system (CNS) classification system published in 2016. WHO CNS5 was drafted on the basis of recommendations from the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy (cIMPACT-NOW) and expounds the classification scheme of the previous edition, which emphasized the importance of genetic and molecular changes in the characteristics of CNS tumors. Multiple newly recognized tumor types, including those for which there is limited knowledge regarding neuroimaging features, are detailed in WHO CNS5. The authors describe the major changes introduced in WHO CNS5, including revisions to tumor nomenclature. For example, WHO grade IV tumors in the fourth edition are equivalent to CNS WHO grade 4 tumors in the fifth edition, and diffuse midline glioma, H3 K27M-mutant, is equivalent to midline glioma, H3 K27-altered. With regard to tumor typing, isocitrate dehydrogenase (IDH)-mutant glioblastoma has been modified to IDH-mutant astrocytoma. In tumor grading, IDH-mutant astrocytomas are now graded according to the presence or absence of homozygous CDKN2A/B deletion. Moreover, the molecular mechanisms of tumorigenesis, as well as the clinical characteristics and imaging features of the tumor types newly recognized in WHO CNS5, are summarized. Given that WHO CNS5 has become the foundation for daily practice, radiologists need to be familiar with this new edition of the WHO CNS tumor classification system. Online supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article. ^©RSNA, 2022.