Background: Tumor-to-tumor metastasis is a rare, but well-reported, curiosity in which one type of primary neoplasm metastasizes to another primary tumor type within the same person. Often there are limited clinical consequences and the condition is an incidental finding identified only on microscopic examination of a resected specimen.
Objective: To report two examples of benign meningiomas in which metastatic tumor deposits from the patient's hematopoietic neoplasm to the meningioma caused significant peritumoral edema, necessitating semiemergent surgical resection. Clinical suspicion in both patients was an atypical or anaplastic meningioma due to the edema.
Results: One patient had multiple myeloma associated with extensive necrosis within his otherwise benign convexity meningioma; first diagnosis of his IgG, kappa-restricted plasma cell dyscrasia was made from this tumor-to-tumor meningioma specimen. Subsequent workup revealed systemic disease. The second patient carried a diagnosis of marginal zone lymphoma but then presented 5 years later with symptoms referable to a large dural-based mass with significant surrounding edema, prompting surgical removal. Dural marginal zone lymphoma was identified within epidural, intradural, and subdural spaces, in the same location as an underlying benign meningioma.
Conclusions: Although rare, neurosurgeons should be aware of the entity of tumor-to-tumor metastasis as, in large series, meningiomas are the third most frequent recipient tumor type and pituitary adenomas, the fifth most frequent, probably reflecting their rich vascularity. In examples where the donor tumor type is a hematopoietic neoplasm, significant edema can be produced by the tumor-to-tumor metastasis.
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