Systemic cancer metastasis in a meningioma: report of two cases and review of the literature.

"Tumour-to-tumour" phenomenon is a rare event; meningioma has been reported as the most common primary intracranial tumour to harbour metastases, the majority of which arise from breast and lung carcinomas. Several hypotheses have been previously proposed to explain this occurrence, but the exact mechanisms responsible for the development of metastases in meningiomas are not known. Magnetic resonance imaging (MRI) and spectroscopy could be useful to hypothesize this uncommon event, but its preoperative diagnosis remains highly difficult. Two patients are reported, with breast and renal carcinoma metastases in an intracranial meningioma. Pathogenetic mechanisms and neuroimaging features are discussed. A brief review of the literature is presented.