Cellular Origin

John Cleland, an anatomy professor in Glasgow in 1864, made an initial observation of two tumors that seemed to take their origin from the arachnoid, not the dura mater [6]. Schmidt, in 1902, and subsequently Cushing & Weed, in 1915, reported similar findings that these tumors seemed to arise from the arachnoid.

Currently, it is thought that meningiomas originate from specialized cells of the arachnoid granulations, called "arachnoid cap cells", but other possibilities include arachnoidal fibroblasts, or meningoblasts that are theoreti-

cal precursor cells of the meninges. Whether arachnoid cap cells are derived from the neural crest or the mesoderm remains unclear as cap cells may exhibit both mesenchymal and epithelial characteristics. Factors supporting the origin of meningiomas from arachnoid cap cells, particularly for the meningothelial variety, include histological and ultrastructural similarities between the tumor and cap cells. These include: the formation of whorls by the cells in-vivo and in-vitro, complex intertwining cell processes, the presence of intracellular junctions, named desmosomes, and an abundance of intracellular intermediate filaments that stain positive for vimentin. Fibroblastic and transitional benign varieties may have additional features that are similar to the fibroblasts found in deeper layers of the arachnoid adjacent to the subarachnoid space.

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