The micrograph shows a tumor with numerous vascular structures and intervening stromal cells without mitotic figures. These findings are consistent with a hemangioblastoma. The presence of cytoplasmic vacuoles within stromal cells containing lipid or glycogen results in a "clear cell" appearance on routine histochemistry. This is a "benign" tumor (WHO grade I) and while complete resections are often curative, these lesions can sometimes carry a notable amount of associated morbidity or even mortality, depending on their location.
Typical imaging findings often show a cystic component with an enhancing mural nodule. Tumors larger than 1 cm commonly have a cystic component. Given that these tumors account for ~10% of posterior fossa tumors, obstructive hydrocephalus is not uncommon.
Hemangioblastomas are associated with loss of function mutations in the von Hippel-Lindau (VHL) gene, at the chromosome 3p25 locus. It is therefore no surprise that individuals with VHL disease (an autosomal dominant disorder) have a heightened risk of developing these tumors. Patients with VHL carry one abnormal copy of the gene and then suffer a somatic mutation or deletion of the other allele resulting in tumor formation. Accordingly, all patients diagnosed with hemangioblastomas should be tested for VHL disease as 25% of patients with hemangioblastomas will have VHL disease. Patients with VHL often have multiple hemangioblastomas evident on imaging at the time of their initial presentation as ~ 2/3 of VHL patients will develop hemangioblastomas. These patients are also at increased risk of developing additional tumors and therefore require serial lifetime monitoring MRI scans. Sporadic hemangioblastomas will often (but not always) have two somatic deleterious mutations in VHL.
Posterior fossa tumors, such as ependymoma and medulloblastoma, are more common in children than in adults. In the adult population, posterior fossa tumors are often due to metastasis from a systemic malignancy. Non-neoplastic disorders that can lead to posterior fossa mass lesions in the adult population include abscesses, vascular malformations (including mycotic aneurysms) and demyelinating/immune/inflammatory lesions. Posterior fossa meningiomas and stage IV gliomas can have similar clinical manifestations but would have different imaging features and different histopathologic findings.
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