Ossified metaplastic meningiomas: A systematic review on a rare subset of "brain stones".

•Metaplastic meningiomas are rare entities, and intracranial osseous subtype are even more rare.•Gross total resection is considered the best treatment choice.•Differential diagnosis is mandatory, including osteoma, osteoblastoma, and calcified giant aneurysms.•This rare entity must be considered in a global approach and tailored surgical technique.