![]() In any case, there is no evidence that MRI-based screening improves outcomes when compared to contrast-enhanced CT yet so many institutions continue to employ CT as the initial test of choice. However, current MRI technology has been shown to be more sensitive than CT and is the preferred imaging of choice. Often the first line of imaging, contrast-enhanced CT was previously thought to be equivalent to MRI for the detection of metastases. ![]() The size threshold at which metastases develop edema varies depending on histology (from 4 to >30 mm) with those from the gastrointestinal tract developing edema at the smallest diameter 15. It is important to note, however, that when metastases are small they often do not have any surrounding oedeam. Most larger metastases are surrounded by vasogenic edema due to poorly formed new blood vessels that mimic the microcirculation of the primary tumor and in some instances the degree of edema can be striking. Both lung and breast cancers can also occasionally hemorrhage, and as they are far more common primaries than the classically hemorrhagic tumors, they should also be considered. Metastases that classically hemorrhage include melanoma, renal cell carcinoma, choriocarcinoma and thyroid cancer. HemorrhageĬertain malignancies are more susceptible to hemorrhage which can aid in suggesting a primary malignancy. Similarly, although cerebral metastases are often thought of as being multiple, ~50% are seemingly solitary at diagnosis and in a minority of cases, no known or identifiable malignancy is present even after examination of the body with other modalities 4,13,14. 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 any where in the neuraxis. Their histological appearance will, of course, depend on the primary tumor. Typically well-demarcated except for melanoma metastases. Typically metastases are relatively well-demarcated from the surrounding parenchyma, and usually, there is a zone of peritumoural edema out of proportion with the tumor size. 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. Parenchymal blood flow is an important determinant of the distribution of metastases: 80% of metastases localize to the cerebral hemispheres, 15% localize to the cerebellum, and 3% localize to the basal ganglia 8. Often these tumors can be found at the grey/white matter junction. Gastrointestinal tract adenocarcinomas (the majority colorectal carcinoma)Ī population-based study of 169,444 cancer patients from 1973 to 2001 in Detroit revealed that overall, 10% of patients diagnosed with one of these five primaries went on to develop brain metastases. Specifically, 19.9% of lung cancers, 6.9% of melanomas, 6.5% of renal cancers, 5.1% of breast cancers and 1.8% 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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