Mixed mesenchymal differentiation in meningiomas.

Five intracranial meningiomas showing mixed mesenchymal differentiation are described. Three contained cartilage, three contained bone, four contained hyaline fibrous strands or nodules which in two instances were calcified, three contained angiomatous areas, one contained pericytoma-like areas, four contained pleomorphic and sometimes multinucleate giant cells, and one contained a mucoid matrix including spheroidal cells superficially resembling chordoma. The importance of recognising such tumours is emphasised as they can be misdiagnosed as metastatic deposits, particularly in a frozen section.