Brain Tumor Diagnosis: How Pathologists Identify Tumor Types and Guide Treatment

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• Initial Tissue Examination Under Microscope
• Immunohistochemistry Staining for Tumor Subtypes
• Molecular Diagnostics for Complex Cases
• Diagnostic Report Process for Clinicians
• Common Brain Tumor Types Identified
• When Advanced Testing Is Needed
• Full Transcript

Initial Tissue Examination Under Microscope

Dr. Sebastian Brandner, MD, describes how brain tumor diagnosis begins when neurosurgeons send biopsy samples to pathology laboratories. The tissue undergoes fixation and processing before being sliced into thin sections mounted on glass slides. "We dye the cells so nuclei, cytoplasm and neuron processes become visible under microscopy," explains Dr. Brandner. This first examination determines whether the sample contains an intrinsic brain tumor (like glioma), extrinsic growth (such as meningioma or metastasis), or non-tumor conditions like inflammation.

Immunohistochemistry Staining for Tumor Subtypes

About 60-70% of cases require immunohistochemical staining - specialized dye tests performed by automated machines. "These stains reveal molecular markers that help classify glioma subtypes and other tumors," notes Dr. Brandner. The neuropathology team reviews these stained slides after 24 hours, gaining critical details about tumor behavior and origin. This second diagnostic step proves particularly valuable for intrinsic brain tumors that require precise classification for treatment planning.

Molecular Diagnostics for Complex Cases

For approximately 10% of challenging cases, especially certain gliomas, Dr. Brandner's team employs molecular diagnostics. "We extract DNA from tumor tissue for quantitative PCR or microarray testing," he explains. These advanced techniques identify genetic mutations and chromosomal abnormalities that influence prognosis and therapy options. While only 1% of tumors require this level of analysis, molecular profiling has become essential for personalized treatment approaches in neuro-oncology.

Diagnostic Report Process for Clinicians

All diagnostic findings compile into comprehensive reports that pathologists authorize electronically. "Our database immediately shares results with hospital clinicians," says Dr. Brandner. The reports integrate microscopic observations, immunohistochemistry patterns, and molecular data when available. This systematic documentation ensures neurosurgeons, oncologists and neurologists receive complete diagnostic information to guide patient care decisions.

Common Brain Tumor Types Identified

Dr. Sebastian Brandner, MD, emphasizes the importance of distinguishing between primary and metastatic brain tumors during diagnosis. Common categories include gliomas (originating from brain glial cells), meningiomas (arising from meningeal tissues), and secondary cancers that spread from other organs. Accurate classification directly impacts treatment strategies, with gliomas often requiring different approaches than metastatic tumors or benign growths.

When Advanced Testing Is Needed

The neuropathology expert explains that molecular testing becomes crucial when standard methods yield uncertain results. "We pursue additional diagnostics when we need absolute clarity about tumor behavior," states Dr. Brandner. These situations frequently involve gliomas where genetic markers like IDH mutations or 1p/19q codeletion significantly affect prognosis and treatment response. The combination of traditional pathology with modern molecular techniques provides the most accurate brain tumor diagnoses available today.

Full Transcript

Dr. Anton Titov, MD: Let's start with brain tumors. Sometimes brain tumors are diagnosed clinically. Neurosurgeons usually remove the tumor, then the material from the tumor gets into your hands. Brain tumor biopsy gets to the pathologist. Could you please walk us through this? How do you diagnose brain tumors? How do you establish brain tumor molecular diagnosis?

Dr. Sebastian Brandner, MD: Neurosurgeons send us tumor material. Everything else they expect us to solve for them. We help not only them, but also the oncologists, the neurologists, and the patient. After we receive the tumor sample material, it is fixed in a fixative. This tumor material is processed and becomes something that we can cut into very thin slices, resulting in slides like this.

Dr. Sebastian Brandner, MD: You can see here the specimens are mounted in the center of the slide. It goes to another procedure where we dye the cells so the nuclei, the cytoplasm, and the neuron processes look distinctive under the microscope. After that, the actual diagnostic procedure starts.

Dr. Sebastian Brandner, MD: We look through the microscope first to identify what type of brain tumor it is.

Dr. Anton Titov, MD: Is it an intrinsic brain tumor or an extrinsic brain tumor such as meningioma or metastasis? Or is it something entirely different? Is it inflammation?

Dr. Sebastian Brandner, MD: Sometimes we get material from the spine that is actually not a brain tumor as such. We then have to send the tumor to other specialists because it's often soft tissue tumors.

Dr. Sebastian Brandner, MD: Back to brain tumors: under the microscope we make the first decision about what type of brain tumor it is. That clearly defines and determines what we do next. We then order a number of stains that tell us more about the nature of the tumor.

Dr. Anton Titov, MD: What type of glioma is it? What subtype?

Dr. Sebastian Brandner, MD: So we order the second round of special stains. Today it is all done on a machine. These special stains are called immunohistochemistry or immunohistochemical staining. A day later they arrive again on our microscope desk. We discuss and look at them, which gives us a fairly clear idea of what we are dealing with.

Dr. Sebastian Brandner, MD: I would say the very first step—just looking at the stained slide—is what we do with all brain tumor biopsies. In our hands, 60-70% of those brain biopsies require the second step of immunostaining. It's important for intrinsic brain tumors like gliomas and many other types of tumors.

Dr. Sebastian Brandner, MD: After that, we have a very good idea about nearly all brain tumors. But probably 10% of tumors require additional diagnostic tests, especially gliomas. So we look further because we want to find the precise diagnosis and really go into detail.

Dr. Sebastian Brandner, MD: That is the last step, called molecular diagnostics. This is done entirely differently—it leaves the domain of pathology and goes into molecular biology. Tissues of the tumor are taken from the blocks or slides, then prepared so we can extract the nucleic acids, the DNA.

Dr. Sebastian Brandner, MD: This material is then subjected to molecular pathology tests. We usually do a quantitative PCR, and in rare cases we also do DNA microarray investigations. This last step is probably done in 1% of the tumors when all other tests don't give us sufficient clarity of the brain tumor diagnosis.

Dr. Sebastian Brandner, MD: All that brain tumor diagnostic information is then put into a report. The report is typed up on a computer connected to a database.

Dr. Anton Titov, MD: The database then feeds back that information to the clinical teams.

Dr. Sebastian Brandner, MD: We authorize the report electronically to be released. It goes straight away to the hospital's clinicians, who can review the brain tumor diagnosis report. But that's not the end of the diagnostic process.

Dr. Sebastian Brandner, MD: Precise brain tumor diagnosis starts with microscopic examination of stained brain tumor tissue. Is it a metastatic or primary brain tumor? Is it meningioma or glioma?