Walsh & Hoyt: Parenchymal Metastases

The brain parenchyma is affected much more frequently by direct hematogenous metastasis of distant neoplasms than by extension of tumor that has metastasized to the adjacent bone of the skull. Tumor cells reach the brain through the arterial circulation, most commonly from the lung, by either a primary lung cancer or a lung metastasis. They most commonly involve the gray-white junction. This appears to be due to a narrowing of vessels with slowing of blood flow in that location. The location of metastases in the brain roughly correlates with the blood flow to that area. Metastases are found in the cerebral hemispheres (80%), in the cerebellum (15%), and 5% in the brainstem. The incidence of multiple metastases when using enhanced MRI scanning approximates 70%. The true incidence of intracranial hematogenous metastases in patients with cancer varies greatly depending on the bias of the investigator, but the frequency is generally in the range of 2040%.