Updated: Sep 8, 2008
Metastasis to the brain is the most feared complication of systemic cancer and the most common intracranial tumor in adults. The incidence of brain metastasis is rising with the increase in survival of cancer patients. Currently, cancer patients live longer as a result of important advances in cancer diagnosis and management, and in particular, the widespread use of MRI to detect small metastases. Approximately 40% of intracranial neoplasms are metastatic. Multiple, large autopsy series suggest that, in order of decreasing frequency, lung, breast, melanoma, renal, and colon cancers are the most common primary tumors to metastasize to the brain.[1,2 ]
Brain metastases are an increasingly important cause of morbidity and mortality in cancer patients. Thus, brain metastasis presents a therapeutic challenge for the treating physician and is an emotionally and physically debilitating event for the patient. Early diagnosis and aggressive treatment of brain metastasis may result in remission of brain symptoms and may enhance the quality of the patient's life and prolong survival. The radiologist plays a primary role in the management of cancer patients by helping detect, localize, and diagnose the lesion.
For excellent patient education resources, visit eMedicine's Cancer and Tumors Center. Also, see eMedicine's patient education article Brain Cancer.
Metastatic spread to the brain through blood circulation occurs mostly via arterial circulation; (2) less often, it occurs via the Batson venous plexus (pelvic and GI tumors). Most metastases are round, well-demarcated lesions located at the junction of gray and white matter.[3 ]Leakage from tumor vessels results in an extensive zone of edema surrounding the tumor.
Before entering the brain, arterial blood must pass through the lungs, where larger aggregates of tumor cells are filtered out in the capillaries; as a result, many emboli traveling to the brain via the arterial route originate either from a primary lung tumor or a metastatic site in the lung. However, single tumor cells may pass through the capillaries of the lung, and larger tumor emboli may pass from the venous circulation to the arterial circulation through a persistently patent foramen ovale between the right and left atrium of the heart.
Metastatic tumor growth in the brain depends on complex organotropic factors, as well as passive vascular delivery of tumor cells. Lesions are located in the cerebrum (80-85%), in the cerebellum (10-15%), and in the brain stem (3-5%). Slightly more than 50% of the time, metastases are multiple, not solitary; primary melanoma, as well as primary lung and breast tumors, are more likely to produce multiple metastases.
Intracranial metastases may be categorized by location as skull, dura, leptomeninges, and parenchymal brain metastases. Lesions of the brain and leptomeninges account for 80% of intracranial metastases. Meningeal carcinomatosis most commonly occurs in patients with breast carcinoma and malignant melanoma; less commonly, it occurs in patients with lymphoma, leukemia, and other tumors. Patients usually present with headache, vague neurologic complaints, and one or more cranial nerve palsies.
Approximately 170,000 cancer patients develop brain metastases annually. Intracranial metastases are seen in approximately 24% of patients who die from cancer (as reported in different series, the rate varies from 11-35%).
The prognosis for patients with brain metastases typically is poor. Therapeutic considerations must be individualized; there are many relevant factors, including the patient's neurologic status, the extent of systemic tumor, the number and location of brain metastases, and the sensitivity of the tumor to radiation and chemotherapy. Patients with the best prognostic indicators often die within 18-24 months. Of particular relevance to imaging is the fact that for patients with a solitary brain metastasis who undergo treatment by surgical resection, the survival rate after 1 year is approximately doubled. Most available treatment is palliative; however, consideration should be given to prolonging the patient's quality of life through specific therapy to the brain.
Brain metastases demonstrate the same predilection for gender that the primary tumors do. Lung cancer is the most common source of metastases in male patients, whereas breast cancer is the most common source in female patients. As the frequency of lung cancer in women increases, it may become the most common primary tumor to metastasize to the brain in women as well.
The incidence of brain metastases as determined on the basis of age parallels that of primary systemic tumors. Most brain metastases occur in patients 35-70 years of age.
Approximately two thirds of brain metastases are symptomatic at some point. Symptoms primarily are caused by (1) increased intracranial pressure resulting in headache, nausea, vomiting, confusion, and lethargy and (2) focal irritation or destruction of neurons resulting in hemiparesis, visual field defects, aphasia, focal seizures, ataxia, and other focal neurologic signs or deficits.
The most common symptoms, in order of decreasing frequency, are headache, focal weakness, and mental status changes. Symptoms typically are of gradual onset. However, if seizures are excluded, 5-10% of patients develop other acute symptoms. An acute strokelike presentation may occur and often is precipitated by hemorrhage into the tumor.
Hemorrhage is present in 3-14% of metastases; it is most often seen in metastases from melanoma, choriocarcinoma, and renal, thyroid, lung, breast, and germ-cell tumors. Bronchogenic metastases are the most common hemorrhagic lesions because they occur in much greater numbers. Generalized or focal seizures may occur in 20% of patients with brain metastases.
Different primary tumors spread to the brain at different points in the disease course. The median latent interval between the initial diagnosis of a primary tumor and the diagnosis of brain metastases varies from 6-9 months for lung cancer and from 2-3 years for melanoma, breast, and colon cancer. In 20% of patients, metastases are detected during diagnosis of the primary tumor; in 50% of patients, they are detected within 1 year of the diagnosis.
In 5-10% of cancer patients, brain metastasis is the first clinical manifestation of systemic cancer. Lung carcinoma is the primary tumor in 45% of those in whom the primary site is discovered.
Surgical resection is the preferred treatment for patients with one apparent metastasis detected on enhanced CT or MRI. Radiosurgery is a simple, effective, noninvasive, cost-effective method of treating surgically inaccessible lesions; it is a therapeutic option in 2-6 of cases of brain metastases.
With regard to screening for intracranial metastases, no consensus has been reached concerning when to use CT or MRI for initial staging evaluation of a patient with cancer. However, brain MRI for patients with primary cancers that frequently metastasize to the brain (eg, bronchogenic carcinoma) is probably cost effective. Numerous studies have shown that contrast-enhanced MRI detects 2-3 times as many lesions as contrast-enhanced CT, especially lesions less than 5 mm in diameter. In addition, approximately 20% of patients with solitary metastatic lesions on CT show multiple lesions on MRI. The decision to perform imaging for patients with other cancers is made on the basis of the clinical evaluation.
In the presence of multiple cerebral metastases from an unknown primary source, a limited search for the primary tumor is of value; such a search includes a chest radiograph, breast examination and mammography, and abdominal ultrasound (US). An extensive search for an occult malignancy is unrewarding. Surgery may be required for patients presenting with a solitary intracranial tumor or to search for a possible primary tumor.
It has been shown that treatment with dexamethasone leads to a reduction in evidence on MRI of peritumoral edema and, occasionally, a lessening in the extent of contrast enhancement. If a lesion is found and a definitive diagnosis cannot be established, biopsy should be performed.
Surgical removal of the lesion is indicated for single or solitary brain metastasis in patients with good systemic performance status, because surgery is both diagnostic and therapeutic.
Patients with multiple brain metastases or poor systemic performance status are possible candidates for whole-brain radiation therapy or radiosurgery.[4,5 ]
Most patients with a known primary tumor undergo imaging studies when neurologic signs and symptoms develop. MRI with contrast enhancement currently is the procedure of choice, because MRI is more sensitive and specific than other imaging modalities in determining the presence, location, and number of metastases. Contrast-enhanced CT is used widely because of its accessibility and low cost.[6 ]
Approximately one third of patients operated on for a single cerebral metastasis diagnosed with contrast-enhanced CT probably have more than one lesion. Contrast-enhanced MRI is more sensitive than CT in detecting the number of cerebral metastases.
Medical care is influenced significantly by the additional information gained from gadolinium-enhanced MR studies. If a solitary metastasis is found, definitively ruling out the presence or absence of additional lesions is important for diagnosis and for deciding upon possible surgical management. Standard-dose or high-dose gadolinium-enhanced MRI may demonstrate additional lesions that suggest metastatic disease. Use of magnetization transfer with single-dose gadolinium administration is roughly equivalent to triple-dose, postcontrast, spin-echo imaging in detecting lesions and lesion conspicuity.
Brain, Abscess
Brain, Hypertensive Hemorrhage
Brain, Lymphoma
Brain, Stroke
Meningioma, Brain
Other problems or factors to consider include the following:
Skull radiograms may detect multiple lytic or sclerotic deposits when the metastatic process involves the cranium. Lung and breast tumors are the most common primary malignancies to affect the skull. Multiple lytic lesions secondary to multiple myeloma tend to be uniformly small. Blastic metastases are seen in patients with primary prostate cancer or in patients who have undergone treatment for breast cancer. Calcifications are uncommon in metastases but do occur in primary adenocarcinoma, osteogenic sarcoma, and lung and breast carcinoma. Plain radiographs are not helpful in detecting metastatic disease of the brain.
Multiple lytic or blastic lesions are highly suggestive of a metastatic process. Solitary lesions must be differentiated from other pathologic processes affecting the skull vault.
Normal anatomic variants, such as emissary vein, arachnoid granulation, and bone island, may mimic a metastatic lesion in a known cancer patient. Use of CT with bone windows may eliminate false diagnoses.
Metastases frequently are multiple; they are seen at the junction of gray and white matter, usually with significant surrounding edema (see Images 2-3). CT findings are as follows[7,8 ]:
Contrast-enhanced CT is effective in detecting major leptomeningeal spread (see Image 8). Contrast-enhancing subdural or epidural metastases may be seen, usually secondary to calvarial lesions (see Image 10). Of breast, lung, prostate, and renal-cell neoplasms, 5% metastasize to the calvarium; of these, 15% extend into the subdural space.
On findings of multiple, enhancing solid lesions at the gray matter–white matter junction and prominent surrounding edema in a patient with known primary cancer, a diagnosis of metastases may be confidently made. Approximately 90% of patients with a history of cancer who present with a single supratentorial lesion have brain metastases.
Patients with multiple lesions are even more likely to have metastatic disease. Before undergoing definitive therapy, patients who are found to have a single metastasis on contrast-enhanced CT should undergo a contrast-enhanced MRI examination, if facilities for such an examination are available.
Routine cranial CT is useful in the staging of cancer in the patient with non – small-cell lung cancer; cranial CT has a sensitivity of 92%, a specificity of 99%, and an accuracy of 98% in detecting brain metastases. Contrast-enhanced CT is perhaps the best method to identify calvarial metastases. In studies comparing contrast-enhanced CT with contrast-enhanced MRI, approximately 20% of patients who demonstrated a single lesion on CT demonstrated multiple lesions on MRI. Mostly, the lesions missed on contrast-enhanced CT were smaller (<2 cm in diameter) and were located next to the bone in a frontotemporal location. Dural-based metastases may mimic meningioma.
Multiple lesions (see Images 4-5) with marked vasogenic edema (see Image 1) and mass effect are typically seen in patients with brain metastases.[9,10,11,12,13,14 ]MRI findings are as follows:
The usefulness of diffusion-weighted and perfusion-weighted imaging and proton-MR spectroscopy in the initial diagnosis of brain metastases has not been established.
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy.
NSF/NFD has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.
Gadolinium-enhanced MRI is superior to contrast-enhanced CT in the diagnosis of brain metastases. Gadolinium-enhanced MRI has the following advantages:
High-dose gadoteridol (ProHance) is better able to detect additional smaller lesions than routine-dose gadopentetate dimeglumine (Magnevist). Detection of additional lesions is important when considering surgical treatment of a solitary lesion. Magnetization transfer used with routine-dose gadolinium contrast is closely comparable to the high-dose technique.
On imaging, dural-based metastases (see Image 6) may resemble meningioma. Leptomeningeal carcinomatosis (see Image 7) may resemble chronic meningitis; however, an appropriate history or detection of primary cancer may be sufficient for establishing the diagnosis. Leptomeningeal enhancement may occur after the administration of radiation or following extra-axial hemorrhage; it may also occur below a craniotomy site. Single or multiple ring-enhancing lesions with edema may resemble infectious processes. Solitary lesions resemble primary brain tumors.
US has no role in the diagnosis of brain metastases. Intraoperative US may help in the surgical removal of brain metastases.
Currently, nuclear medicine studies are not employed routinely as primary imaging techniques for detecting intracranial metastatic disease.
Typical findings are multiple intracerebral areas of increased activity. The standard isotope used is technetium Tc 99m. On isotope whole-body bone scans, calvarial metastases may appear as multiple focal areas of increased activity. With whole-body 18-fluorodeoxyglucose (FDG) positron emission tomography (PET) used in cancer staging, intracerebral metastases may appear as areas of increased metabolism.[15,16,17,18 ]
Radionuclide studies are sensitive but are highly nonspecific. In studies involving a small number of patients, FDG-PET demonstrated low sensitivity and low specificity. Currently, FDG-PET is not considered superior to CT or MRI in the initial evaluation of suspected brain metastases.
In older reports, radionuclide imaging was reported to detect intracerebral metastases in approximately 90% of patients, but the findings were nonspecific. Neoplasm, inflammation, vascularity, or trauma may cause the abnormal uptake. FDG-PET has been reported to detect approximately two thirds of brain metastases resulting from systemic cancer.
Angiography currently is not used as a primary diagnostic procedure for metastatic disease. Rarely, preoperative angiography and embolization of large hypervascular metastases from renal and thyroid cancer may be useful.
Angiography is useful in evaluating tumor vascularity in selected metastatic lesions before biopsy is performed.
The results of angiography are nonspecific in the diagnosis of metastases.
Endovascular procedures employing particles or surgical gelatin (Gelfoam) may be used for presurgical or palliative embolization of hypervascular tumors.[19 ]
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brain metastases, brain metastasis, brain cancer, systemic cancer, brain carcinoma, metastasis, metastases, intracranial metastasis, intracranial metastases, metastatic cancer, metastatic brain cancer, metastasis detection, metastasis imaging
Anil Khosla, MBBS, Assistant Professor, Department of Radiology, Section of Neuroradiology, Mallinckrodt Institute of Radiology, Washington University School of Medicine, Veterans Affairs Medical Center of St Louis
Anil Khosla, MBBS is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, American Society of Neuroradiology, North American Spine Society, and Radiological Society of North America
Disclosure: Nothing to disclose.
Jeffrey L Creasy, MD, Associate Professor, Associate Section Head, Division of Neuroradiology, Director, Neuroradiology Fellowship, Department of Radiology, Vanderbilt University
Jeffrey L Creasy, MD is a member of the following medical societies: American College of Radiology, American Society of Neuroradiology, and Radiological Society of North America
Disclosure: Nothing to disclose.
Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.
Robert L DeLaPaz, MD, Director, Professor, Department of Radiology, Division of Neuroradiology, Columbia University
Robert L DeLaPaz, MD is a member of the following medical societies: American Society of Neuroradiology, Association of University Radiologists, and Radiological Society of North America
Disclosure: Nothing to disclose.
Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute
Robert M Krasny, MD is a member of the following medical societies: American Roentgen Ray Society and Radiological Society of North America
Disclosure: Nothing to disclose.
James G Smirniotopoulos, MD, Professor of Radiology, Neurology, and Biomedical Informatics, Chairman, Department of Radiology and Radiological Sciences, Uniformed Services University of the Health Sciences
James G Smirniotopoulos, MD is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, American Society of Head and Neck Radiology, American Society of Neuroradiology, American Society of Pediatric Neuroradiology, Association of University Radiologists, and Radiological Society of North America
Disclosure: Nothing to disclose.
Management of brain metastases: role of radiotherapy alone or in combination with other treatment modalities.
Program in Evidence-based Care - State/Local Government Agency [Non-U.S.]. 2004 Mar 30. 35 pages. NGC:003529
Pre-irradiation evaluation and management of brain metastases.
American College of Radiology - Medical Specialty Society. 1999 (revised 2005). 7 pages. NGC:004635
Single brain metastasis.
American College of Radiology - Medical Specialty Society. 1999 (revised 2006). 7 pages. NGC:005132
Multiple brain metastases.
American College of Radiology - Medical Specialty Society. 1999 (revised 2006). 8 pages. NGC:005553
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