Tumor-to-tumor metastases: latent renal cell carcinoma discovered after elective surgical resection of a convexity meningioma.

Abstract Background: Tumor-to-tumor metastases are extremely rarely reported lesions which usually involve an indolent lesion hosting a more aggressive neoplasm. We present an unusual initial manifestation of a previously unknown clear cell renal cell carcinoma as a tumor-to-tumor metastasis in a typical meningothelial meningioma. Case report: A 73-year old patient with transient left slight monoparesis was addressed to our Neurosurgical Department after being evaluated by his general practitioner and passing a cerebral MRI which revealed a right frontotemporal mass attached to the meninge. At presentation, no deficits were identified; therefore an elective surgery was proposed. Histological analysis revealed a typical meningothelial meningioma containing a metastatic clear cell renal cell carcinoma. Additional thoraco-abdominal computer tomography identified a 6 cm diameter lesion within the right kidney with radiological features highly suggestive of a primary clear cell renal cell carcinoma. Conclusion: Our case highlights the need for a specialized neuropathological approach to clinical and imagistic indolent meningiomas, as they may require important differential diagnosis that can highly impact the treatment and follow-up of brain tumor patients.