AQP4 and anaplastic astrocytoma: AQP4 expression was high in WHO I pilocytic astrocytomas (perhaps because of their peculiar vessel morphology, with a microvascular proliferation and for the presence of glomeruloid bodies), in WHO III anaplastic astrocytomas, and in WHO IV glioblastomas (the most aggressive forms of primary brain tumors), whereas WHO II tumors showed significantly lower AQP4 levels.