A Rare Presentation of Colon Carcinoma Metastasis Within a Meningioma: A Case Report and Literature Review.

Colon carcinoma with brain metastasis is a rare presentation. This presentation is more unusual and unique when the single brain metastatic lesion has two different types of tumors. This rare phenomenon is known as a tumor-to-tumor metastasis. A meningioma usually hosts lung and breast cancers within it. However, colon carcinoma metastasis into meningiomas has rarely been reported. An 86-year-old man presented with neurological symptoms and was found to have a brain mass. The search for primary lesions was negative as the chest, abdomen, and pelvis CT scan was insignificant. When the brain lesion's pathology revealed a composite mass of adenocarcinoma and a meningioma, further investigation with a colonoscopy revealed a colonic mass as the primary metastasis lesion. This unique presentation and pathology emphasize the importance of a comprehensive investigative approach to finding the primary lesions and consideration of such a phenomenon in these lesions.