The appearance of brain metastases is variable depending on their size, location and histology, and they can mimic other pathologies such as high-grade gliomas and infections.Īlthough they most often occur at the grey-white matter junction or in the arterial watershed areas, they can occur essentially anywhere in the neuraxis. Their histological appearance will depend on the primary tumor. Typically well-demarcated except for melanoma metastases. Typically metastases are relatively well-demarcated from the surrounding parenchyma, and there is usually a zone of peritumoural edema out of proportion with the tumor size. Parenchymal blood flow is an important determinant of the distribution of metastases 8: Often these tumors can be found at the grey/white matter junction. This can lead to presentation with cerebral metastases, even with quiescent systemic disease. In patients with known malignancies, the brain can sometimes act as a reservoir for metastatic disease as traditional chemotherapy regimens can have poor permeability through the blood-brain barrier. However, up to 60-75% of patients can be asymptomatic at the time of imaging 9. These patients can commonly present with headaches, seizures, mental status alterations, ataxia, nausea and vomiting, and visual disturbances. Gastrointestinal tract adenocarcinomas (the majority are colorectal carcinoma)Ī population-based study of 169,444 cancer patients from 1973-2001 in Detroit revealed that overall, 10% of patients diagnosed with one of these five primaries went on to develop brain metastases. Specifically, 20% of lung cancers, 7% of melanomas, 7% of renal cancers, 5% of breast cancers and 2% of colorectal cancers metastasized to the brain 3. The true incidence of brain metastases is unknown, but recent estimates are as high as 200,000 cases per year in the United States alone 1.įive primary tumors account for 80% of brain metastases 2: Consequently, the term "cerebral metastases" is a synonym for "brain metastases". As the cerebrum corresponds to the majority of the brain volume and thus receives most of its blood supply, it is more common for metastatic lesions to appear in the cerebral parenchyma. The term brain technically includes the cerebrum, the cerebellum and the brainstem.
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