Symptoms of brain metastases
Approximately two-thirds of brain
metastases are symptomatic at some point. Symptoms are
caused by increased intracranial pressure, and/or focal
irritation or destruction of brain tissue.
Increased intracranial pressure can be
caused by tumor growth, swelling (edema) induced in the
adjacent brain tissue, obstruction of cerebral spinal fluid
pathways (hydrocephalus) or a combination of these effects.
Typically, patients may experience nonspecific symptoms such
as headache, nausea, vomiting, mental status change and
lethargy.
Focal irritation or destruction of
brain tissue produces varied symptoms, such as seizures,
paralysis, visual impairment, epileptic seizures, gait
disturbances or other neurologic deficits, depending on the
specific location of the metastatic lesion.
How brain metastasis is diagnosed
When a patient presents with any of
the symptoms described above, doctors generally recommend a
brain imaging study.
There are two primary choices for such
imaging:
CT scanners use X-rays projected from
a hollow tube to produce cross-sectional images, or slices,
of almost any part of the body. These images depict the
brain tissue in high detail, unlike the routine X-rays
commonly used to evaluate a patient for a broken bone. When
a brain tumor is suspected, intravenous iodinated contrast
(dye) is often injected into the patient immediately prior
to the CT scan. This special dye enhances visualization of
abnormalities, such as tumors, on the scan. During the CT
scan, the patient lies still on a table that slides into a
large, circular opening in the scanning machine. As the
table moves through the doughnut-like opening of the CT
scanner, a series of X-ray beams pass through the body from
many different directions.
Another type of imaging tool commonly
used to diagnose brain metastases is magnetic resonance
imaging. MRI uses a strong magnetic field and radio waves,
rather than X-rays, to produce detailed images of soft
tissue organs, such as the brain. Specialized detectors in
the computerized MRI scanner record and process fluctuations
in the intensity of radio waves, thereby making it possible
to generate a series of cross-sectional images that can be
interpreted by doctors. Most patients diagnosed with an
abnormality on a CT scan will typically undergo an MRI as
well.
During an MRI scan, the patient must
lie flat on a table that slides into the bore (tunnel-like
structure) of the scanner. Individuals suffering from
claustrophobia (fear of small, enclosed spaces) may have
difficulty undergoing an MRI, but with mild sedatives, most
patients can be imaged. In the occasional patient for whom
claustrophobia is more severe, an "open" MRI (i.e., one that
is not enclosed), can be used for imaging. A typical scan of
the brain takes approximately 30 minutes. As with CT,
contrast is usually injected to improve the visibility of
most tumors. Unlike the dye used with CT scans, MRI contrast
(gadolinium) does not contain iodine, and allergies to it
are extremely rare. Because of the extremely powerful
magnetic field that exists within the scanner, MRI cannot be
used on patients with pacemakers or other surgically
implanted metal devices. MRI centers should routinely ask
patients about their medical history to establish the safety
of MRI in each patient.
Treatment options for brain metastases
The various treatment options that are
available for treating brain metastases will be discussed in
the following sections. In arriving at a specific treatment
plan, both the doctor and patient need to consider the
precise location(s) of the metastatic tumor(s), patient age,
tumor type, status of the cancer in other parts of the body,
and general health of the patient.
Oral steroid medication
Treatment with oral steroids (e.g.,
Decadron, dexamethasone, prednisone) is an important part of
the management of almost all patients with brain metastases.
Metastatic tumors very frequently cause brain edema, or a
breakdown in the blood-brain barrier. This phenomenon
results in an abnormal accumulation of fluid in the tissue
of the brain. Brain edema is harmful because it causes the
brain to function abnormally or leads to an increase in
pressure within the cranium, often manifested by headaches.
By stabilizing the blood-brain barrier, steroids reduce
swelling and its associated symptoms. In the short term,
such therapy can be very effective for treating swelling.
However, steroids alone are rarely an adequate longer-term
treatment for brain metastases. This is because larger doses
of steroids are needed over time to maintain a therapeutic
effect, and as the dosage is increased, disabling side
effects become increasingly apparent. The potential side
effects of steroid use need to be discussed with the
prescribing doctor.
Surgery
Clinical studies have shown that
surgery is beneficial for managing select patients with
brain metastases.
The most widely accepted indication for conventional surgery
is for patients who have:
-
A single metastatic tumor
located in an area of the brain that is safely
accessible by open surgery
-
No evidence of cancer
elsewhere in the body. Aggressive surgical removal
of the metastatic tumor in such favorable situations
results in better outcomes compared to radiation
therapy. Only very rarely is removal of more than
one brain metastasis indicated. When a diagnosis of
metastasis cannot be established by imaging alone,
or the origin of the tumor is in doubt, removal of
the brain metastases has the advantage of providing
pathological material (tissue samples) for a
definitive diagnosis. The risks of surgical removal
vary considerably depending on the health of the
patient and location of the tumor. A thorough
discussion of potential risks with the treating
surgeon is always warranted prior to any surgical
intervention.
Whole brain radiotherapy
Radiation therapy has been a mainstay
of treatment for brain metastases for many years. It is
often referred to as whole brain radiotherapy and involves
daily administration of radiation to the brain over a period
of several weeks. The treatment takes advantage of the fact
that cancer cells are more prone to radiation injury than a
normal brain. Traditionally, whole brain radiation therapy
has been the primary mode of treatment for the vast majority
of patients with brain metastases. Whole brain radiotherapy
can produce significant shrinkage of many brain metastases
tissue, and in doing so, relieve a patient's symptoms.
However, such treatment often does not completely eliminate
the tumors, and recurrence is not uncommon. Meanwhile, there
are significant, albeit oftentimes subtle, cognitive side
effects to whole brain radiotherapy that become increasingly
apparent over time. Spreading treatment over longer periods
of time may alleviate some of the injury to normal brain
tissue that is induced by radiation therapy.
In recent years, a growing body of
clinical evidence has emerged suggesting that whole brain
radiotherapy may be withheld, or at least delayed, in those
patients with three or less brain metastases that have been
treated with stereotactic radiosurgery (discussed below).
This finding is important because radiosurgery involves
selective targeting of only the tumor with radiation,
whereas whole brain radiotherapy irradiates the entire
brain. As a result, the use of radiosurgery alone alleviates
much of the risk of damaging the normal brain with
radiation. While the strategy of avoiding whole brain
radiotherapy is being pursued more and more, it remains a
point of debate whether it is best to treat with
radiosurgery alone or in combination with conventional
radiation. The risks and benefits of these different
strategies should be discussed in detail with the patient's
radiation oncologist and neurosurgeon.
Although there are several types of devices used to
administer radiosurgery, the principle of delivering a high
dose of radiation to a precisely localized target is the
same. Some technologies, like the Gamma Knife, use
radioactive cobalt as a source of ionizing radiation. A
linear accelerator produces the radiation in other devices.
Regardless of the source of radiation, nearly all methods of
radiosurgery use stereotactic frames that are anchored to
the patient's skull with invasive aluminum or titanium
screws. The frame serves to accurately localize the tumor in
space and immobilize the patient's head. The CyberKnife® is
the only radiosurgery device that does not require such a
frame for precise targeting. As a result, this instrument
uniquely enables doctors treating gliomas to divide a large
radiosurgical dose into more than one stage or
fraction-staged radiosurgery. Staged CyberKnife radiosurgery
is of particular benefit to patients who have previously
received large doses of conventional radiation therapy and
patients with gliomas near critical areas of the brain.
Radiosurgery
Radiosurgery is an important therapy
for the treatment of metastatic brain tumors. This procedure
enables doctors to focus a high dose of radiation on a tumor
while minimizing radiation exposure to surrounding normal
tissue. Radiosurgery involves the precise delivery of
multiple beams of radiation, such that each beam enters the
body from a different angle and passes through the tumor.
This makes it possible to "concentrate" the radiation at the
point of beam intersection (at the tumor) while giving the
rest of the brain only a small overall dose. The accuracy
with which radiosurgery is targeted minimizes the risk of
harming surrounding healthy tissue, and, as a result, larger
and more effective doses of radiation can be administered.
These unique advantages of radiosurgery make possible the
most precise and aggressive radiation treatment available
for brain metastases. Meanwhile, unlike whole brain
radiotherapy, which must be administered daily over several
weeks, radiosurgery treatment can usually be completed in
one to five sessions. Radiosurgery can be used alone to
treat brain metastases, or in conjunction with surgery or
whole brain radiotherapy, depending on the specific clinical
circumstances.
Radiosurgery is a widely accepted treatment for a single
metastatic brain tumor that cannot be safely removed by
traditional surgical techniques. It is also used frequently
when a patient has more than one metastatic tumor, a
condition that usually precludes surgical treatment. In
addition, many clinical series have now shown that
radiosurgery may be as effective as traditional surgery for
the eradication of single metastatic brain tumors, whether
the tumor can be safely removed by surgical means. Finally,
radiosurgery can also be used in conjunction with surgery to
eliminate another inoperable tumor or to treat a tumor that
persists or recurs following a surgical removal.
The advantage of radiosurgery over traditional surgery is
that no skull opening, or craniotomy, is required, and as a
result, there is no surgical trauma to the normal brain.
Furthermore, the recovery time from radiosurgery is much
shorter than that from standard surgery. Because
radiosurgery does not require a patient to be put under
general anesthesia (which entails a breathing tube),
radiosurgery is an important alternative to surgery for
patients who are not in otherwise good health. Finally, it
is much easier to treat more than one metastasis with
radiosurgery than it is with conventional surgery.