In order to understand what a glioblastoma is we have to first appreciate the different cell types that compose healthy brain tissue. Brain tissue has both neurons and glia. Neurons are the "action" cells of the brain. They send messages to and from different regions of the brain and spinal cord to cause a specific bodily response. Glia are the "helper" cells of the brain. They ensure that neurons stay healthy.
A glioblastoma is a malignant brain tumor that arises from a specific type of glial cell known as an "astrocyte". Glioblastomas are not only the most common astrocytic tumor, but they are also the most common primary brain tumor!
It is important to realize that there are less malignant tumors that arise from astrocytes (discussed in other articles). Many of these tumors have a much better prognosis, which is why it is important to distinguish glioblastomas from their more benign counterparts.
The first distinguishing characteristic is neovascularization. Neovascularization is a fancy medical term used to describe the proliferation of blood vessels within the tumor. As the tumor grows, it requires new vessels to feed it oxygen and nutrients; the process of neovascularization allows the tumor to obtain these essential factors so that it can continue to grow.
Interestingly, as the tumor expands, sections of it will get choked off from its own blood supply. The end result is that part(s) of the tumor actually dies. This is referred to as "necrosis", which is a common finding in glioblastoma.
One of the most distinguishing features of glioblastomas is when cancerous astrocytes "line up" and outline areas of necrosis in a process known as pseudopalisading (see image below).
Glibolastoma is therefore characterized by the following pathological characteristics: prominent microvascular proliferation (ie: development of new blood vessels within the tumor), mitosis (ie: an indicator of cell division/growth), and necrosis (ie: areas of dead tumor); pseudopalisading necrosis is a specific form of necrosis shown in the above image that is a hallmark of glioblastomas.
Glioblastomas may present with any number of signs and/or symptoms depending on their location within the brain. Lesions that are located on the left side of the brain may cause problems with speech. Tumors in the areas of the brain that control motor movement may cause weakness. Additionally, tumors that arise in the frontal lobes may cause odd behavioral changes. Some patients present with seizures, and others with only a dull headache.
An official diagnosis of glioblastoma can only be made when a pathologist looks at a sample of the tumor under a microscope. These samples are typically obtained by a neurosurgeon who resects or biopsies the tumor.
However, glioblastomas also have typical features seen on imaging studies such as MRI. For example, these tumors will "rim-enhance" when a contrast material such as gadolinium is infused into the patient during the scan. Rim enhancement is a result of the contrast material leaking out of all of the blood vessels present within the tumor. It is important to note that other diseases such as abscesses, lymphomas, and other infections can also cause rim-enhancing lesions.
Another useful study known as MR spectroscopy measures the relative amounts of different molecules present within an abnormal area. In a glioblastoma the amount of lactate, choline, and lipid are all increased. Lactate is a marker of brain tissue that is not receiving enough oxygen, which is common in necrotic tumor areas. Choline is a molecule that is present in cell membranes. When neurons are rapidly dividing, which is what occurs in tumors, the amount of choline present also increases. A different molecule known as N-acetyl aspartate (NAA) is present in mature cells. Therefore, unlike lactate and choline levels, NAA is decreased in tumors because these cells are "immature" (ie: poorly differentiated).
Treatment combines a mixture of surgery, radiation therapy, and different chemotherapeutic drugs, the most common being temozolomide (Temodar®). Surgery is only useful when a significant amount of the tumor can be removed. Despite optimal treatment the prognosis for patients with glioblastoma remains extremely poor.
It is also highly important to treat the edema that frequently surrounds the tumor. Steroids, most commonly dexamethasone (Decadron®), are used to decrease the amount of edema, which usually improves symptoms.
Patients are often started on an anti-seizure medication such as levetiracetam (Keppra®) or phenytoin (Dilantin®).
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