Which cell type is the primary origin of meningiomas, the most common primary brain tumors in adults?

Meningiomas arise primarily from the cells of the meninges, which are the protective membranes surrounding the brain and spinal cord. Specifically, these tumors originate from the arachnoid cap cells, which are a type of meningeal cell. Meningiomas are the most common primary brain tumors in adults, highlighting the significance of these meningeal cells as the source of the tumor.

Understanding the origin of meningiomas is crucial in both their diagnosis and treatment, as well as in understanding the biologic behavior of these tumors. Their meningeal origin often explains their characteristic growth patterns, as they commonly displace rather than invade adjacent brain tissue, and are usually well-circumscribed.

The other cell types mentioned do not give rise to meningiomas. Astrocytes are glial cells involved in forming gliomas, endothelial cells line blood vessels, and melanocytes are pigment-producing cells in the skin and not related to meningeal tumors. Thus, the correct answer is supported by the primary cellular origin of meningiomas within the meningeal structure.