A tumor is any mass caused by abnormal or uncontrolled growth of cells. Tumors in the brain are categorized according to several factors, including where they're located, the type of cells involved, and how quickly they're growing. Some of the most common factors are:
- Low-grade vs. high-grade: Usually, low-grade tumors are slow-growing, while high-grade tumors are fast-growing and aggressive. High-grade tumors can invade nearby tissue or spread elsewhere in the body, and are more likely to recur after treatment. They are generally associated with a worse outlook.
- Localized vs. invasive: A localized tumor is confined to one area and is generally easier to remove, as long as it's in an accessible part of the brain. An invasive tumor has spread to surrounding areas and is more difficult or impossible to remove completely.
- Primary vs. secondary: Primary brain tumors originate in the brain. Secondary brain tumors are made up of cells that have spread (metastasized) to the brain from somewhere else in the body. In children, most brain tumors are primary.
There are many different types of pediatric brain tumors, ranging from those that can be cured with minimal therapy to those that cannot be cured even with aggressive therapy. Some of the most common include, but are in no way limited to:
Astrocytomas
Astrocytomas originate from star-shaped brain cells known as astrocytes. There are four major subtypes of astrocytomas:
- Juvenile pilocytic astrocytoma (grade 1)
- Fibrillary astrocytoma (grade 2)
- Anaplastic astrocytoma (grade 3)
- Glioblastoma multiforme (grade 4)
Low-grade astrocytomas (grades 1 and 2) in kids are highly curable because they usually grow slowly, don't spread, and usually are fairly easy to remove unless found in areas where surgery would be difficult (like the optic nerve). After surgery, there's a chance that chemotherapy or radiation won't be needed.
High-grade astrocytomas (grades 3 and 4) are more aggressive, more invasive, and more difficult to treat. Treatment usually includes surgery, chemotherapy, and radiation.
An important feature in determining the outlook for patients with astrocytomas is location, because this directly affects the chance for a cure. Tumors that can be completely removed surgically are much more likely to be cured, while those that can't be completely removed are, in general, less curable.
Brain stem glioma
The brain stem, located deep in the back of the brain, consists of the midbrain, pons, and medulla. These structures coordinate all of the brain's messages. They also control many of the body's autonomic functions (the autonomic nervous system is responsible for controlling many of the body processes we almost never need to think about, like breathing, digestion, sweating, and shivering).
A tumor that develops in any area of the brain stem is called a brain stem glioma. Tumors that occur in the pons (pontine gliomas) are the most common but are often the most difficult to treat. Tumors that occur in the midbrain and medulla are less common but usually more easily treated.
Symptoms of a pontine glioma may come on suddenly and worsen very quickly. These may include:
- Double vision
- Turning in of one eyeball
- Drooping of the eyelid or one side of the face
- Trouble swallowing
- Trouble speaking and walking
Midbrain tumors may cause similar eye symptoms, along with headaches and vomiting. This is due to increased pressure in the head caused by a blockage of cerebrospinal fluid, the fluid that surrounds and cushions the brain and spinal cord.
Tumors of the medulla are associated with swallowing problems and limb weakness. Because the brain stem is an area of the brain that generally can't tolerate surgery, brain stem gliomas are usually treated with radiation (high-energy X-rays that kill cancer cells) and chemotherapy.
Ependymoma tumors
Ependymoma tumors originate in brain cells that produce cerebrospinal fluid.
They mostly develop in children under age 5. Ependymomas are classified according to their location, and most do not spread (metastasize) to other areas of the body.
Those located in the top part of the head are called supratentorial. This type of tumor is associated with symptoms such as nausea, vomiting, and headaches from increased pressure within the brain, as well as weakness and vision problems.
Tumors found in the back of the head are more common. These are called infratentorial, and are also associated with nausea, vomiting, and headache, as well as trouble with coordination.
Supratentorial ependymomas often can be cured by surgery alone, while infratentorial ependymomas usually require much more aggressive treatment with surgery, chemotherapy, and radiation.
Ependymomas are treated primarily with surgery and radiation therapy. If the tumor can be completely removed, patients with ependymomas may need no additional treatments. However, some completely removed ependymomas and most incompletely removed ependymomas will require further treatment – usually radiation therapy and sometimes also chemotherapy.
Ependymomas can also be found in the spinal cord.
Primitive neuroectodermal tumors (PNETs)
Primitive Neuroectodermal Tumors (PNET) are a group of tumors that can occur anywhere in the brain, but whose cells look very similar under a microscope. Types of PNETs include
- Medulloblastoma
- Posterior fossa PNET
- Supratentorial PNET
- Pineoblastoma
All of these tumors are able to metastasize through the cerebrospinal fluid that surrounds the brain and the spinal cord. Medulloblastomas, by definition, can only occur in the posterior fossa or cerebellum (back part of the brain), while primitive neuroectodermal tumors can occur anywhere in the brain or spinal cord. These cancers are highly sensitive to chemotherapy and radiation therapy, so modern treatment regimens are usually curative. Although treatment regimens are effective, late side effects of therapy can be a significant problem.
PNET symptoms generally depend on their size and location, but common ones include:
- Headaches, nausea, and vomiting (especially in the morning) caused by increased pressure in the head
- Weakness in the arms and legs
- Vision problems
- Seizures
- Trouble with balance and coordination
Even though PNETs require aggressive treatment, including surgery, chemotherapy, and radiation therapy, recent medical advances have made a cure possible for the majority of children who have them.
Optic nerve gliomas
Optic nerve gliomas affect vision. The optic nerve sends signals to the brain about what the eye sees. A tumor that occurs along this pathway is called an optic nerve glioma. These tumors mostly affect kids under age 10; those with the genetic condition neurofibromatosis type 1 (which causes tumors to grow on nerve tissue) have an increased risk of developing them.
The most typical symptom is progressive vision loss. With slow-growing tumors, this may be hard to spot at first – especially in younger children who can't describe what they're seeing. With fast-growing tumors (or less aggressive ones that have reached a large size), vision problems will eventually become apparent.
Kids also may start tilting their heads or experiencing what appears to be developmental delays such as clumsiness during walking, speech difficulties, or behavior changes. A condition called nystagmus (when the eyeballs appear to "jitter" involuntarily) also might appear. Sometimes, if the tumor is pressing on the pituitary gland, growth problems can result.
Optic nerve gliomas are usually treated with chemotherapy, although radiation also can be used. Most kids do well with treatment, and further vision loss is usually prevented.
Craniopharyngiomas
Craniopharyngiomas are low-grade tumors that arise in the middle of the brain near the pituitary gland. As a result of their location, many patients have endocrinologic (hormone) problems when the tumor is diagnosed and after it is treated.
While craniopharyngiomas can be cured with surgery alone, most pediatric centers do not attempt total removal of the tumor at diagnosis unless it can be accomplished without injury to the sensitive surrounding structures. Total removal of the tumor without consideration of these surrounding structures can cause permanent hormone deficiencies that can be difficult to manage.
Therefore, for most patients, only partial removal of the tumor is done at diagnosis, followed by radiation therapy for any remaining tumor. This approach usually results in effective treatment of the tumor without causing lifelong hormone deficiencies.
Germ Cell Tumors
These brain tumors usually arise from two special areas in the middle of the brain – the areas around the pituitary and pineal glands. Germ cell tumors include two main types, germinomas and nongerminomatous germ cell tumors.
Germinomas are sensitive to chemo and radiation therapy and both are usually used to help achieve an excellent cure rate. Nongerminomatous germ cell tumors include several different types of tumors which, in general, are not as curable as germinomas. Nongerminomatous germ cell tumors are treated with surgery, chemotherapy, and radiation therapy.