An infiltrating glioma is a primary brain tumor originating from the brain’s supportive cells, known as glial cells. These tumors are defined by their characteristic growth pattern: the cells do not form a distinct, encapsulated mass. Instead, the cancerous cells spread individually, weaving through healthy brain tissue, which makes the tumor borders indistinct and surgical removal challenging. Gliomas are classified based on the specific type of glial cell from which they arise, such as astrocytes or oligodendrocytes.
Defining Infiltrating Glioma and Classification
Infiltrating gliomas in adults primarily arise from astrocytes (astrocytomas) and oligodendrocytes (oligodendrogliomas). These tumors are formally classified using the World Health Organization (WHO) grading system, which assigns a grade from 2 to 4 based on the tumor’s potential for aggressive growth. Grade 1 tumors are typically non-infiltrating and are not included in this category.
Modern classification relies heavily on molecular genetics, which provides a more accurate prediction of tumor behavior than histology alone. The most significant molecular marker is the status of the Isocitrate Dehydrogenase (IDH) enzyme, which is often mutated in these tumors. Tumors with the IDH mutation generally carry a more favorable prognosis compared to IDH-wildtype tumors.
The current WHO classification integrates this molecular data to define three major groups of adult diffuse gliomas.
Major Groups of Adult Diffuse Gliomas
Astrocytoma, IDH-mutant: Defined by the presence of the IDH mutation but without the 1p/19q co-deletion.
Oligodendroglioma, IDH-mutant and 1p/19q-codeleted: Characterized by both the IDH mutation and the complete loss of chromosomal arms 1p and 19q.
Glioblastoma, IDH-wildtype: The most aggressive group, a highly malignant tumor that lacks the IDH mutation.
This molecular-based classification system is important because the specific combination of IDH and 1p/19q status directly dictates the choice of treatment and indicates the patient’s long-term outlook. The WHO grade is assigned within these molecular groups; for instance, Glioblastoma, IDH-wildtype, is always assigned a WHO grade 4.
Identifying Symptoms and Diagnostic Methods
The symptoms of an infiltrating glioma are highly variable, depending on the tumor’s size, location, and speed of growth. General symptoms often arise from increased intracranial pressure. This can manifest as headaches, often worse in the morning, and may be accompanied by nausea and vomiting.
Many patients first present with new-onset seizures, which occur because tumor cells disrupt the brain’s normal electrical activity. If the glioma is located in specialized areas, it can cause specific neurological deficits. For example, a tumor in the parietal lobe might cause difficulty with speech or coordinating movements, while one in the occipital lobe could lead to visual disturbances.
The diagnostic process begins with a detailed neurological examination. If a brain tumor is suspected, the primary imaging test is Magnetic Resonance Imaging (MRI). MRI provides high-resolution images that help determine the tumor’s exact size, location, and characteristics, such as whether it is spreading diffusely.
A definitive diagnosis requires obtaining a tissue sample through either a biopsy or surgical resection. This tissue is examined by a neuropathologist to determine the cell type, WHO grade, and to perform molecular testing for IDH mutation and 1p/19q co-deletion. This molecular information is necessary to finalize the precise diagnosis and plan the therapeutic strategy.
Current Treatment Approaches
The management of an infiltrating glioma typically involves a combination of surgery, radiation therapy, and chemotherapy, tailored to the tumor’s molecular profile and grade. The first step, when feasible, is surgical resection. The goal is to achieve maximal safe resection, removing as much of the tumor as possible without causing new neurological deficits.
The infiltrating nature of these tumors makes complete removal virtually impossible, as microscopic cells extend beyond visible boundaries. To help neurosurgeons distinguish tumor from healthy tissue, advanced techniques are employed. These include fluorescence guidance, where a compound makes tumor tissue glow under specific light, or an awake craniotomy, which allows the surgical team to test patient function in real-time.
Following surgery, or as a primary treatment, radiation therapy targets and destroys residual tumor cells. Radiation uses high-energy beams directed precisely at the tumor location, often delivered in small daily doses over several weeks. Advancements like proton therapy help minimize the dose reaching surrounding healthy brain structures.
Chemotherapy is an integral component, often administered concurrently with radiation. The most common drug is Temozolomide (TMZ), an oral agent that sensitizes tumor cells to radiation effects. Chemotherapy use depends heavily on molecular findings; for example, certain high-grade gliomas may receive a combination of drugs like Procarbazine, Lomustine, and Vincristine (PCV). For aggressive tumors like Glioblastoma, IDH-wildtype, the standard of care is maximal surgical resection followed by radiation and Temozolomide.
Understanding Prognosis and Follow-Up Care
The prognosis for an infiltrating glioma varies widely and depends on several factors established during diagnosis. The most significant factors are the WHO grade, the extent of surgical resection achieved, and the molecular status of the tumor. Tumors that are IDH-mutant generally have a more favorable prognosis and longer overall survival compared to IDH-wildtype tumors.
Following primary treatment, long-term surveillance is necessary to monitor for tumor recurrence. This follow-up care primarily involves regular Magnetic Resonance Imaging (MRI) scans, often scheduled at frequent intervals during the first few years. The goal of consistent imaging is to detect recurrence early, when it may be more manageable with further intervention.
Supportive care is a major component of long-term management, addressing persistent neurological deficits or symptoms caused by the tumor or its treatment. Patients may require various forms of rehabilitation, including physical therapy, occupational therapy, or speech therapy. Managing chronic symptoms, such as persistent seizures, requires ongoing specialized medication and care.