Metastases

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Diagnosis Definition

Brain metastases are the most common malignant intracranial tumors in adults
Most are due to hematogenous dissemination
They are most commonly intraparenchymal in adults and skull/dural-based in children
The most common origins are lung cancer, followed by breast cancer, malignant melanoma, renal cell carcinoma, and colon cancer

Imaging Findings

Brain metastases vary in signal on MRI but are generally low signal on T1 and high signal on T2 and FLAIR sequences
Hemorrhage is indicated by blooming artifact seen on gradient echo (GRE) or susceptibility weighted imaging (SWI) sequences and is most commonly seen in melanoma, choriocarcinoma, renal cell carcinoma, thyroid cancer, and some types of bronchogenic carcinoma
Melanoma metastases can be hyperintense on T1 due to T1 shortening from melanin or hemorrhage
Surrounding edema and mass effect are common
Almost all metastases will enhance with contrast, which can appear solid or ring-like
Skull metastases are best seen on CT as sclerotic or lucent lesions and on MRI as infiltration and loss of normal T1 bright fat in the diploic space
Highly cellular metastases typically have restricted diffusion on diffusion-weighted MRI

Pearls

Contrast-enhanced MRI detects 2-3 times as many metastases as contrast-enhanced CT, especially lesions that are less than 5 mm in diameter
Approximately 20% of patients with solitary metastatic lesions on CT show multiple lesions on MRI
Most brain metastases are multiple, but 30% of metastases are solitary and may be confused with primary brain tumors

References

Barajas RF, Cha S. Metastasis in adult brain tumors. Neuroimaging Clin N Am 2016; 26(4):601-620
Al-Okaili RN, Krejza J, Wang S, Woo JH, Melhem ER. Advanced MR imaging techniques in the diagnosis of intraaxial brain tumors in adults. RadioGraphics 2006; 26(Suppl 1):S173–89

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