Brain metastases are secondary brain tumours, that have metastasised to the brain from a primary malignancy elsewhere in the body. They are made up of the same cell type as that of the primary tumour.
Brain metastases are the most common intracranial tumours in adults (10 times more common than primary tumours), but are very rare in children <14 years of age.
The most common sites of primary malignancies of brain metastases:
- Lung cancer - the most common
- Breast cancer
- Malignant melanoma
- Renal cell carcinoma
- Colorectal cancer
- Pancreatic cancer
- Testicular cancer
😷 Presentation
These tumours tend to be located in the cerebral hemispheres, the cerebellum or the brainstem.
Symptoms have an acute or subacute onset based on the rapidity of growth of the tumour:
- Weight loss
- Seizures
- Focal neurological deficit depending on which part of the parenchyma is compressed
- Cognitive deficit/change in mental status
- Headaches
🔍 Investigations
- 🥇 Contrast-enhanced CT:
- Pre-contrast imaging: the mass may be isodense, hypodense or hyperdense (classically melanoma) compared to normal brain parenchyma.
- Following administration of contrast: enhancement can be intense, punctate, nodular or ring-enhancing if the tumour has outgrown its blood supply.
- MRI without contrast
- 🏆 Gadolinium-enhanced MRI - indicates well-circumscribed tumours.
- Small metastases: homogeneous enhancement (the entire tumour has the same intensity on the image, which is usually iso- or hypointense on T1 MRI)
- Large metastases: ring enhancement due to central necrosis (hypointense centre on T1, with a hyperintense ring around it if there is contrast)
Often, imaging might also show:
- Haemorrhage
- Vasogenic oedema/perifocal oedema
Certain malignancies are more susceptible to haemorrhage which can aid in suggesting a primary malignancy. Metastases that classically haemorrhage include melanoma, renal cell carcinoma, choriocarcinoma and thyroid cancer. Both lung and breast cancers can also occasionally haemorrhage, and as they are far more common primaries than the classically haemorrhagic tumours, they should also be considered.
Most larger metastases are surrounded by vasogenic oedema due to poorly formed new blood vessels that mimic the microcirculation of the primary tumour.
🧰 Management
Management of brain metastases is based on the primary tumour type, extent of metastasis, and individual patient factors.
Unfortunately, patients with brain metastases typically have a mean survival of one month without treatment. With treatment, the mean age of survival is still less than one year, although in some patients with solitary metastases longer survival may occur.
- Anticancer therapies - this typically involves a combination of systemic and local therapy:
- Systemic therapy: chemotherapy immunotherapy, and/or targeted agents.
- Local therapy: radiosurgery, radiotherapy, and/or surgical resection.
- Limited brain metastases: surgical resection or stereotactic radiosurgery (e.g., Gamma Knife, CyberKnife, proton beam).
- Extensive brain metastases: stereotactic radiosurgery and/or whole-brain radiotherapy (WBRT)
- Tumours causing mass effect: consider surgical resection.
- Supportive care
- Glucocorticoids (dexamethasone) as needed, to reduce tumour oedema and raised ICP.
- Palliative care for patients with a high primary tumour burden and a poor functional status.
Options for surgery include the following: