A brain tumor is a mass of abnormal cells that is growing in or around the brain. It develops when abnormal cells multiply for unknown reasons. Benign and malignant are terms used to describe brain tumors. Benign brain tumors are usually slow growing and have distinct borders and a normal appearance under a microscope. Malignant tumors are considered brain cancer. They tend to invade healthy areas of the brain and may grow rapidly. A benign tumor may be considered malignant if it is located in a critical area of the brain or its size is life-threatening.
Primary brain tumors start within the brain. Secondary or metastatic brain tumors come from cells which have broken away from cancers within the body and traveled to the brain. Metastatic brain tumors are always considered malignant since they evolve from cancerous cells and grow rapidly.
What Causes a Brain Tumor?
Brain tumors are usually caused by a change in genetic structure, such as mutated or missing genes. This results in abnormal cells. If abnormal cells have malignant potential, they will form a tumor when they multiply.
Changes in genetic structure may be inherited, caused by the environment, or both. Overall, a low percentage (5%) of primary brain tumors are associated with inherited genes alone. However, certain types of brain tumors, such as glioblastoma multiforme, are often associated with inherited genes.
High-dose ionizing radiation, used to treat brain tumors, may on rare occasions be associated with the production of secondary brain tumors. This most often occurs from radiation treatments that are given over time. People exposed to certain chemicals, such as petrochemicals, pesticides and formaldehyde, appear to be at higher risk of developing a malignant brain tumor than those who are not exposed. In laboratory experiments, some viruses caused brain tumors in animals. It is unknown whether viruses can cause brain tumors in humans. While the general public believes that electromagnetic fields may be connected to brain tumors, there is no research showing such a relationship.
There are many environmental and genetic factors that can cause brain tumors. However, in most cases, we just don't know what causes a brain tumor.
Tumors are graded based on their microscopic appearances. The grade indicates the level of malignancy. Tumors are graded on their mitotic index (growth rate), vascularity (blood supply), presence of a necrotic (dead cells) center, invasive potential (border distinctness) and similarity to normal cells.
Malignant tumors may contain several grades of cells. The most malignant grade of cell found determines the grade for the entire tumor, even if most of the tumor is a lower grade.
In the World Health Organization grading system, grade I tumors are the least malignant. These tumors grow slowly and microscopically appear almost normal. Surgery alone may be effective for grade I tumors. However, even a grade I tumor may be life-threatening if it is inaccessible for surgery. Grade I tumors are often associated with long-term survival.
Grade II tumors grow slightly faster than grade I tumors and have a slightly abnormal microscopic appearance. These tumors may invade surrounding normal tissue, and may recur as a grade III or higher tumor.
Grade III tumors are malignant. These tumors contain actively reproducing abnormal cells and invade surrounding normal tissue. Grade III tumors frequently recur, often as grade IV tumors.
Grade IV tumors are the most malignant and invade wide areas of surrounding normal tissue. These tumors reproduce rapidly, appear very unusual under the microscope and are necrotic in the center. Grade IV tumors cause new blood vessels to form, to help maintain their rapid growth.
Types of Treatment
Various treatments may be used to treat a malignant brain tumor. The type and number of treatments given are dependent upon many factors, including the size of the tumor, its growth rate and the symptoms the patient is experiencing. Patients should realize that there is more than one way to treat their tumors and should seek medical centers where many options and a continuum of treatments are available.
Surgical biopsies of brain tumors are no longer considered absolutely necessary because of the development of new imaging techniques. With the current scanning abilities of CT and MRI scans using contrast dyes, a brain tumor may be diagnosed as malignant or benign without opening the skull for a biopsy. There has always been controversy over whether the act of obtaining a biopsy may allow the spread of cancerous cells to other areas of the brain.