Metastatic tumors are the most common tumor of the brain—ten times more common than primary brain tumors! Up to 70% of the time, multiple metastatic brain tumors are present during imaging and can be innumerable.
Shockingly, the average survival of a patient with brain metastases receiving maximal intervention is less than one year. Maximal intervention includes surgery, radiation therapy, and chemotherapy.
Often, the impacts of a metastatic brain tumor on the central nervous system (CNS) can be controlled, but the systemic disease progresses and eventually becomes fatal. However, long-term survival can occur under specific circumstances, particularly with certain subsets of cancers.
Patients with certain characteristics and comorbidities tend to experience a worse prognosis with a metastatic brain tumor:
- Over 65 years of age
- Incapacity (a poor ability to care for themselves)
- Systemic disease that is widespread
- Multiple metastases (diffuse cerebral disease)
Metastases in the spine usually involve the bony elements rather than the nervous tissue. However, from there the tumors may compress the neural elements. Spinal cord compression can result from a tumor growing into the spinal canal, a bone prolapsing into the spinal canal, or deformed pathological fractures. Rarely, you may see an intraparenchymal tumor that involves the tissue of the spinal cord.
The most common primary cancers with brain metastases are lung, breast, renal cell, gastrointestinal (GI), and melanoma cancers.
When should you consider a metastatic CNS tumor as a possible diagnosis?
Signs and symptoms
Patients may relate to a history of increasing headaches. This is a common finding (but nonspecific).
A new-onset seizure is one of the more common presentations. A new-onset seizure in an adult should always raise the suspicion of a brain tumor and should lead to brain imaging.
Patients may present with progressive focal deficits in movement, speech, vision, or sensation depending on the tumor location. Obviously, the location of the tumor in the nervous system will dictate the type of symptoms.
A patient can be asymptomatic if the tumor arises in non-eloquent tissue such as the frontal lobe. Such tumors may be discovered incidentally on brain imaging for other reasons (e.g., screening of a patient with known cancer). However, as the tumor (or the surrounding edema) grows in size it will begin to cause neurological symptoms, increased intracranial pressure with related headaches, and eventually nausea, vomiting, and lethargy.
Patients with metastases in the spine often present with new and severe pain, pathological fracture, or progressive neurological deficits (usually myelopathic in nature). Pain is generally the most common presentation, and it can be incapacitating in nature.
Neurological deficits will generally involve paraparesis or quadriparesis, depending on the location of the tumor in the spine. Generally, neurological progression is gradual over days or weeks (but can be rapid).
What do you do if you suspect a metastatic CNS tumor?
If you suspect metastases when viewing a computed tomography (CT) of the brain, obtain contrast magnetic resonance imaging (MRI). Magnetic resonance imaging is far more sensitive for defining multiple metastases than CT imaging.
As a screening tool, MRI is therefore preferable to CT imaging. When suspicion is high, MRI with and without intravenous (IV) contrast is also preferred. In some patients, dozens of small metastatic lesions may become apparent on MRI.
Brain metastases usually enhance and are generally associated with surrounding edema. Solitary lesions may be difficult to distinguish from some high-grade glial tumors, abscesses, strokes, and multiple sclerosis (MS) pathologies, although various MRI sequences may help with the diagnosis.
Magnetic resonance imaging uses a variety of settings to generate various sequences that interpret the signal coming from the tissue in different ways. Various sequences can bring out certain tissue qualities better than others. For example, edema is better seen on T2- and proton-weighted images, old blood is better seen on gradient-echo images, and infarct or dead tissue is better seen on diffusion-weighted and apparent diffusion coefficient (ADC) map sequences. Certain sequences can help differentiate pathologies such as strokes, abscesses, and MS from tumors, but a definitive pathological diagnosis cannot be made by imaging.
If you discover a metastasis in the spine, image the remainder of the spine and brain to look for other lesions. Multiple lesions are not uncommon.
With the discovery of a new brain or spine lesion (suspicious for metastasis) in a previously healthy patient, obtain a thorough medical history, and perform a full neurological exam.
Obtain a complete blood count (CBC), metabolic panel, urine analysis, coagulation assay, liver function tests in all patients, and a prostate-specific antigen level in men. These are general screens that may offer some hints regarding a possible primary tumor.
If a primary tumor has not been identified, obtain a CT of the chest, abdomen, and pelvis to look for one. This will generally be ordered with oral and IV contrast. Include a mammogram for women, and a bone scan for patients with apparent bone lesions.
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- Bhangoo, SS, Minskey, ME, Kalkanis, SN, et al. 2011. Evidence-based guidelines for the management of brain metastases. Neurosurg Clin N Am. 22: 97-104. PMID: 21109154
- Olsen JJ, Kalkanis SN, Ryken, TC, et al. 2019. Guidelines for the treatment of adults with metastatic brain tumors. Congress of Neurological Surgeons. https://www.cns.org/
- Tse, V. 2018. Brain metastases. Medscape. https://emedicine.medscape.com/