Cerebral collision tumor vs. tumor-to-tumor metastasis. Case series with a literature review

Aim of the study. In this paper, we aim to provide a comparative analysis of collision tumors and tumor-to-tumor metastases (TTM). Material and methods. We present 3 patients with suspected meningiomas who were later found to have dual tumors — two of whom presented with TTM and a third with a collision tumor. Clinical history, imaging, surgical findings, and histopathological evaluation were analyzed and compared with the literature. Results. Patient 1, a 65-year-old woman, was diagnosed with a collision tumor comprising a meningothelial meningioma and metastatic lung adenocarcinoma. Patient 2, a 66-year-old woman, had a TTM of a meningioma infiltrated by neuroendocrine carcinoma. Patient 3, a 64-year-old man, had a TTM of glioblastoma multiforme and meningioma. Conclusions and clinical implications. Collision tumors consist of two adjacent, separate lesions, whereas TTM occurs when one tumor metastasizes into another. Neuroimaging alone cannot reliably distinguish collision tumors from TTM; histopathological and immunohistochemical evaluations are essential, as differentiating between the two has implications for staging, treatment, and prognosis. Even when a single lesion is suspected, neuropathologists should examine brain tumors meticulously, as identifying a hidden component can fundamentally alter diagnosis and clinical management.