A glioma is a tumor that originates in the brain or spinal cord from glial cells, which support and nourish nerve cells. Unlike tumors that are clearly contained, an infiltrative glioma is defined by its method of growth. Its cancerous cells spread into and mix with the surrounding healthy brain tissue, lacking a distinct border. This growth pattern makes it challenging to manage, as tumor cells can migrate along white matter tracts and blood vessels to different brain regions.
Glioma Classification and Grading
Infiltrative gliomas are categorized using the World Health Organization (WHO) classification system, which incorporates the tumor’s histological features and its molecular genetics. This system grades tumors on a scale from lower-grade (less aggressive) to high-grade (more aggressive), which helps predict their behavior. The classification relies on molecular markers for a more precise diagnosis.
The main types of adult diffuse gliomas are identified by the glial cell they most resemble: astrocytes or oligodendrocytes. Astrocytomas originate from astrocyte cells, while oligodendrogliomas arise from oligodendrocyte cells. Grade II and Grade III gliomas are considered lower-grade, though Grade III tumors grow more rapidly. Grade IV gliomas, known as glioblastoma, are the most common and aggressive high-grade primary brain tumors in adults. The latest WHO classification refines these categories, distinguishing an “astrocytoma, IDH-mutant” from a “glioblastoma, IDH-wildtype,” highlighting the importance of genetic information.
Recognizing the Symptoms
The symptoms of an infiltrative glioma are not determined by the tumor type but by its size and, most importantly, its location within the brain. As the tumor grows, it exerts pressure on surrounding brain tissue, leading to a variety of possible symptoms. The location dictates the specific neurological functions that may be affected.
A tumor located in the frontal lobe, for instance, might cause changes in personality, mood, or behavior, as well as weakness on one side of the body. If a glioma develops in the temporal lobe, it could lead to seizures, memory problems, or difficulties with speech. Tumors in the parietal lobe can affect sensation, coordination, and spatial awareness, while those in the occipital lobe may cause vision problems. The overall increase in pressure inside the skull can produce general symptoms like persistent headaches, unexplained nausea and vomiting, and confusion.
The Diagnostic Process
The diagnostic journey for an infiltrative glioma begins with a neurological exam. During this assessment, a physician tests vision, hearing, balance, coordination, strength, and reflexes. These tests help identify functional deficits that might point to a specific area of the brain being affected.
Following the physical exam, imaging studies are the primary tool for visualizing the brain’s structure. Magnetic Resonance Imaging (MRI) is the preferred method because it provides detailed pictures of soft tissues. A contrast agent is often injected into a vein before the scan to highlight the tumor, making its size, shape, and location clearer.
A definitive diagnosis requires a biopsy, which involves the surgical removal of a small piece of the tumor tissue for laboratory analysis. Pathologists examine the tissue sample to confirm that it is a glioma and to determine its histological features. Molecular and genetic testing of the biopsy sample has become standard practice to identify specific genetic markers. This analysis provides information about the tumor’s likely behavior and its potential response to different treatments. These markers include IDH mutations, 1p/19q co-deletion, and MGMT promoter methylation status.
Standard Treatment Approaches
The treatment for an infiltrative glioma is personalized, guided by the tumor’s type, grade, and molecular profile, as well as the patient’s age and overall health. A multi-modal approach combining several therapies is the standard of care. This strategy is designed to address the challenges posed by the tumor’s infiltrative nature.
Surgery is often the first step in treatment. The primary goal is “maximal safe resection,” which means removing as much of the tumor as is safely possible without harming brain tissue responsible for important functions. Because these tumors spread into surrounding tissue, complete removal is often not possible. Reducing the tumor’s bulk can alleviate symptoms caused by pressure on the brain and make subsequent treatments more effective.
Following surgery, radiation therapy is commonly used to target and destroy any remaining tumor cells. It involves delivering controlled doses of high-energy rays to the tumor area over several weeks to slow the tumor’s regrowth. Chemotherapy is another pillar of treatment and is often administered at the same time as radiation. The oral medication temozolomide is a frequently used chemotherapy drug for gliomas.
In addition to these standard treatments, newer therapies are available. Tumor-Treating Fields (TTFields) is a non-invasive therapy that uses low-intensity electrical fields delivered by a portable device worn on the scalp. These electrical fields are designed to disrupt the division of cancer cells, inhibiting tumor growth. This therapy is often used with maintenance chemotherapy after initial treatment with surgery and radiation.