Diagnosing brainstem glioma involves careful evaluation of symptoms, detailed imaging studies, and sometimes tissue sampling to determine the exact nature of the tumor and guide treatment decisions.
Who Should Undergo Diagnostics and When to Seek Medical Attention
If you or your child experience certain warning signs that affect brain function, it’s important to seek medical attention promptly. Because brainstem gliomas—tumors that develop in the area connecting the brain to the spinal cord—can grow quickly in some cases, symptoms may appear suddenly and worsen over just days or weeks. In other situations, symptoms develop slowly and may be overlooked for months.[1][9]
Common warning signs include persistent headaches, especially those that are most severe in the morning and improve throughout the day. Problems with eye movement, such as double vision or difficulty controlling eye muscles, are frequently among the first symptoms to appear. Weakness or numbness on one side of the face or body, difficulty speaking or swallowing, problems with balance and coordination, and progressive weakness in the arms or legs all warrant medical evaluation. Children may also show changes in handwriting quality, failure to thrive, or unusual drowsiness and behavioral changes.[4][15]
Brainstem gliomas occur most commonly in children, particularly those between ages 5 and 10, representing about 10 to 20 percent of all brain tumors in this age group. However, adults can also develop these tumors, though they are far less common in people over 16 years old.[1][10]
Diagnostic Methods for Identifying Brainstem Glioma
Medical History and Physical Examination
The diagnostic process begins when a physician records your complete medical history and conducts a thorough physical examination to understand your symptoms. This initial assessment helps establish what problems you’re experiencing and how they might be related to brain function.[4][15]
A neurological examination is a specialized assessment that evaluates whether your brain, spinal cord, and nerves are working correctly. During this exam, your doctor will check several important functions, including your vision, hearing, balance, coordination, strength, and reflexes. They may also test sensation in different parts of your body and observe how you walk and move. Problems with any of these functions can provide clues about where a tumor might be located and how it’s affecting the brainstem.[4][14]
Magnetic Resonance Imaging (MRI)
If your physician suspects a brain tumor or other abnormality based on your symptoms and examination, imaging tests are typically the next step. Magnetic resonance imaging, or MRI, is the preferred and most important diagnostic tool for brainstem gliomas. An MRI scan can identify the specific area in the brainstem where the tumor originates and often provides enough information to make a diagnosis without any other procedures.[1][4]
The MRI uses powerful magnets and radio waves to create detailed pictures of your brain’s soft tissues. During the scan, you lie still inside a large tube-shaped machine that takes multiple images from different angles. Sometimes a contrast dye is injected into a vein before or during the scan to help certain structures show up more clearly. The entire process is painless, though the machine can be noisy and some people feel uncomfortable in the enclosed space.[4]
MRI scans are particularly valuable because they can show the tumor’s size, exact location, and relationship to surrounding brain structures. They can also reveal whether the tumor appears to be growing in one focused area or spreading throughout the brainstem. This distinction is crucial because focal brainstem gliomas—tumors that stay in one area—behave very differently from diffuse intrinsic pontine gliomas (DIPG), which spread throughout the brainstem tissue.[1][11]
Other Imaging Studies
While MRI is the primary imaging tool, other scans may occasionally be used. Computed tomography, or CT scans, use X-rays and computer processing to create cross-sectional images of the brain. CT scans are faster than MRI and may be used in emergency situations or when MRI is not available. However, they provide less detailed images of brainstem structures compared to MRI.[3]
Biopsy Procedures
In many cases, especially with tumors in the pons (the middle portion of the brainstem), the appearance on MRI is so characteristic that doctors can make a diagnosis without removing tissue for examination. This approach has been common historically because the brainstem is a small, delicate area packed with vital structures that control essential body functions, making surgery risky.[1][11]
However, medical centers like UCSF now routinely perform biopsies of brainstem tumors when feasible to obtain more detailed information. A biopsy is a procedure to remove a small sample of tumor tissue for laboratory analysis. This tissue can confirm the diagnosis and, importantly, allow doctors to analyze specific features of the tumor, such as genetic mutations, that may inform treatment decisions.[1][11]
When the tumor’s appearance on imaging is unusual or doesn’t fit the typical pattern of brainstem glioma, a neurosurgeon will discuss the possibility of surgical removal or at least performing a biopsy. The biopsy procedure typically involves making a small opening in the skull and using image guidance to insert a thin needle to the tumor location. The tissue sample is then sent to specialists called neuropathologists, who examine it under a microscope to determine the exact type of cells present and how aggressive they appear.[16]
Tissue Analysis and Grading
When tissue is obtained, either through biopsy or surgery, laboratory analysis provides crucial information about the tumor. Brainstem gliomas are typically astrocytomas, tumors that arise from star-shaped support cells in the brain called astrocytes. These tumors are graded on a scale from I to IV, with grade I being the least aggressive and grade IV being the most aggressive.[1][3]
The grading is based on how the cells look under the microscope, including features like cell shape abnormalities, how fast the cells are dividing, whether new blood vessels are forming, and whether areas of dead tissue (necrosis) are present. Grade I tumors are considered benign and slow-growing. Grade II tumors can grow more quickly, especially in the brainstem. Grade III and IV tumors are considered high-grade, meaning they grow rapidly and are more difficult to treat.[3]
Modern diagnosis also includes molecular profiling, which means analyzing the tumor’s genetic characteristics. Certain genetic changes, called mutations, can significantly affect how the tumor behaves and responds to treatment. For example, specific mutations in genes like H3 K27M are associated with more aggressive brainstem gliomas. Understanding these molecular features helps doctors predict outcomes and may reveal opportunities for targeted therapies.[3][13]
Distinguishing Brainstem Glioma from Other Conditions
Part of the diagnostic process involves ruling out other conditions that might cause similar symptoms. The combination of your symptom pattern, neurological examination findings, and MRI appearance usually makes the diagnosis clear. However, doctors must sometimes consider other possibilities, including different types of brain tumors, infections, inflammatory conditions, or blood vessel abnormalities in the brainstem region.[4]
The specific pattern of symptoms helps distinguish brainstem problems from issues in other parts of the brain or nervous system. For instance, the classic combination of cranial nerve problems (such as facial weakness or eye movement difficulties), coordination problems, and long tract signs (weakness or numbness in the arms or legs) strongly suggests a brainstem location.[10]
Diagnostics for Clinical Trial Qualification
If you’re considering participation in a clinical trial—a research study testing new treatments—additional diagnostic testing may be required beyond what’s needed for standard care. Clinical trials use specific criteria to determine which patients can enroll, and these criteria often include particular diagnostic test results.[3]
For brainstem glioma trials, enrollment criteria typically require confirmation of the diagnosis through MRI imaging that clearly shows a tumor in the brainstem. Some trials may require tissue confirmation through biopsy, particularly trials testing treatments that target specific genetic mutations. In these cases, the biopsy tissue must be tested to prove that your tumor carries the genetic change the experimental treatment is designed to target.[13]
Additional baseline testing is often required before starting a clinical trial. This may include detailed blood tests to check your overall health and organ function, particularly kidney and liver function, since these organs process many medications. Some trials require testing of your heart function through an electrocardiogram (ECG) or other cardiac assessments. Your general performance status—how well you can carry out daily activities—is also typically assessed using standardized rating scales.[13]
Molecular testing of tumor tissue has become increasingly important for clinical trial enrollment. Many newer trials focus on treating tumors with specific genetic characteristics, so determining your tumor’s molecular profile through laboratory analysis of biopsy tissue is essential. This testing looks for particular gene mutations, chromosomal changes, or protein markers that might make the tumor responsive to experimental therapies.[3][13]
Some clinical trials for diffuse intrinsic pontine glioma (DIPG) have been designed specifically to test treatments targeting the H3 K27M mutation that’s common in these aggressive tumors. To qualify for such trials, patients need biopsy confirmation showing their tumor carries this specific mutation. This is one reason why more medical centers now recommend biopsy even for tumors that were traditionally diagnosed by imaging alone—the tissue provides access to potentially beneficial clinical trials.[13]
