Brain Tumor classfication - A comprehensive guide

Brain Tumor Classification: A comprehensive Guide

Brain tumors are complex and challenging to diagnose, making an accurate classification essential for effective treatment. In this comprehensive guide, let’s embark on a journey with UpSurgeOn to unravel the intricacies of these growths in the human brain. This guide provides the framework for categorizing brain tumors, thereby supporting surgeons in optimizing patient outcomes 

A brain tumor is a growth of abnormal cells in the brain or near it [1] [2]. There are various types of brain tumors, and they can develop in different parts of the brain or skull, including the brain tissue, protective lining, underside of the brain (skull base), brainstem, sinuses, nasal cavity, and other areas [2].

Brain tumors can be classified based on five categories: the origin of the tumor, Glial & Non-Glial, historical classification, molecular classification and grading

1. Origin of the brain tumor 

Brain Tumor detection with Surgical simulator and Navigation tool
Brain Tumor detection with Surgical simulator and Navigation tool. Source: UpSurgeOn

There are more than 150 different types of brain tumors documented. However, they can be broadly categorized into two main groups:

  1. Primary Brain Tumors: These tumors originate in the brain itself. They can be either benign (noncancerous) or malignant (cancerous). 
  • Benign Tumors: These tumors are non-cancerous and tend to grow slowly. They often have well-defined borders and do not invade surrounding brain tissue. While benign brain tumors can still be harmful, they are generally easier to remove surgically, and the chances of recurrence are lower.
  • Malignant Tumors: Malignant brain tumors, also known as brain cancer, are aggressive and can invade surrounding brain tissue. They often lack well-defined borders, making complete surgical removal more challenging. Additionally, malignant tumors can spread to other parts of the brain or even to distant organs, making them more difficult to treat.
  1. Secondary (metastatic) Brain Tumors: These tumors start in other parts of the body and spread to the brain. They are always malignant. Common primary cancers that can metastasize to the brain include lung, breast, and colon cancers [3].

2. Glial & Non Glial 

Brain and Tumor Dissection on UpSurgeOn surgical simulator. Source: UpSurgeOn

Brain tumors can be classified into two main categories: glial and non-glial tumors. 

  • Glial tumors:  Glial brain tumors, also known as gliomas, originate from the glial cells in the brain and spinal cord. Glial cells are the supportive cells of the nervous system and play a crucial role in maintaining the health and function of neurons. There are three main types of glial cells:
  • Astrocytes: These cells provide structural support to neurons, help regulate the chemical environment of the brain, and form the blood-brain barrier.
  • Oligodendrocytes: These cells produce myelin, a fatty substance that insulates and protects nerve fibers, allowing for efficient transmission of electrical signals.
  • Ependymal cells: These cells line the ventricles of the brain and the central canal of the spinal cord, producing cerebrospinal fluid (CSF) and helping to circulate it.
  • Non-glial tumors:  Non-glial brain tumors are tumors that develop from cells in the brain that are not glial cells. These tumors can originate from various structures within the brain, including nerves, blood vessels, and the covering of the brain (meninges) [3] [4]. These tumors can be either benign (non-cancerous) or malignant (cancerous).

3. Historial classification 

Brain tumors can be classified based on their histological characteristics, which involve the microscopic appearance of the tumor cells and their resemblance to different cell types. The World Health Organization (WHO) classification system is commonly used for this purpose [57]. Here are the major categories of brain tumors based on their histological classification:

  • Tumors of neuroepithelial tissue: This is the largest category and includes various types of gliomas, such as astrocytomas, ependymomas, and oligodendrogliomas.
  • Tumors of peripheral nerves: These tumors develop in the nerves outside the brain and spinal cord, such as schwannomas and neurofibromas.
  • Tumors of meninges: Meningiomas are the most common type of tumor that originates in the meninges, the protective membranes surrounding the brain and spinal cord.
  • Tumors of the sellar region: These tumors occur in the area of the brain called the sella turcica, which houses the pituitary gland. Pituitary tumors are the most common type in this category.
  • Germ cell tumors: These tumors develop from the cells that give rise to sperm or eggs. They can occur in the brain, pineal gland, or other parts of the body.
  • Lymphomas: Lymphomas are cancers that originate in the lymphatic system, but they can also affect the brain and spinal cord.
  • Metastatic tumors: These tumors are secondary tumors that have spread to the brain from other parts of the body, such as the lungs, breast, or colon.

The histological classification of brain tumors is important for determining the appropriate treatment approach and predicting the tumor’s behavior and prognosis [7].

4. Molecular classification 

Molecular classification is a more recent approach that takes into account the unique genetic and molecular characteristics of brain tumors. This classification system helps in understanding the tumor’s behavior, predicting its response to treatment, and developing targeted therapies. The 2021 WHO Classification of Tumors of the Central Nervous System introduced major changes to advance the role of molecular diagnostics in CNS tumor classification [5]. The classification includes categories such as: 

  • Diffuse Gliomas: Diffuse gliomas are divided into adult-type diffuse gliomas and pediatric-type diffuse gliomas. Adult-type diffuse gliomas are further classified into three groups based on the presence of specific molecular alterations: astrocytoma, isocitrate dehydrogenase (IDH) mutant; oligodendroglioma, IDH mutant and 1p/19q codeleted; and glioblastoma, IDH wild type. Pediatric-type diffuse gliomas are classified as low-grade or high-grade based on their molecular features [8].
  • Circumscribed Astrocytic Gliomas: Circumscribed astrocytic gliomas are a new “supercategory” introduced in the 2021 WHO classification. They include tumors such as pilocytic astrocytoma, pleomorphic xanthoastrocytoma, and subependymal giant cell astrocytoma. These tumors are defined by specific molecular alterations and have distinct clinical and histopathological features [9].
  • Ependymal Tumors: Ependymal tumors are now classified based on the integration of anatomical location, histopathology, and molecular alterations. This classification allows for a more precise diagnosis and better understanding of the clinical behavior of these tumors [9].
  • Embryonal Tumors: The molecular classification of embryonal tumors has led to the identification of new tumor entities. For example, CNS neuroblastoma with FOXR2 activation (CNS NB-FOXR2), CNS Ewing sarcoma family tumor with CIC alteration (CNS EFT-CIC), CNS high-grade neuroepithelial tumor with MN1 alteration (CNS HGNET-MN1), and CNS high-grade neuroepithelial tumor with BCOR alteration (CNS HGNET-BCOR) are newly recognized tumor types with distinct molecular and clinical features [9].

5. Grading 

Brain tumors can also be categorized into different types based on their grading, which indicates the aggressiveness and growth potential of the tumor cells. The grading system may vary depending on the type of brain tumor, but the most commonly used system is the World Health Organization (WHO) classification, which assigns grades ranging from I to IV [1012].

  • Grade I: These tumors are the least aggressive and have cells that closely resemble normal brain cells. They grow slowly, and they are often considered benign. Examples include pilocytic astrocytomas and gangliogliomas.
  • Grade II: The cells in Grade II tumors look less like normal cells compared to Grade I tumors. These tumors are considered low-grade and have a higher chance of recurring or progressing to a higher grade over time. Examples include diffuse astrocytomas and oligodendrogliomas.
  • Grade III: Tumors in this category, also known as anaplastic tumors, have cells that look very different from normal cells and are actively growing. They are considered high-grade and have a more aggressive nature. Examples include anaplastic astrocytomas and anaplastic oligodendrogliomas.
  • Grade IV: These tumors have cells that look the most abnormal and tend to grow quickly. They are highly aggressive and often referred to as glioblastomas. Glioblastomas are the most common and deadliest type of primary brain tumor.

In addition to the WHO grading system, other classification systems such as Kernohan grade and St. Anne/Mayo grade have been used in the past, but the WHO classification is the most widely accepted and used today [13].


Our hope is that this guide has not only provided a comprehensive understanding of brain tumor classification but also served as a beacon of empowerment. Armed with this knowledge, medical professionals can make informed decisions, and patients can face their challenges with greater resilience and understanding. UpSurgeOn is your trusted partner on the journey of improving patient outcomes. Our surgical simulation technologies were created with the mission of empowering surgeons to do their mission with confidence, precision and skill. Let’s embark on the journey to explore the transformative power of surgical simulation with UpSurgeOn and stay ahead in the ever-evolving field of surgery!


  1. Brain tumor – Symptoms and causes – Mayo Clinic. (2023, April 21). Mayo Clinic.
  2. Brain tumors and brain cancer. (n.d.). Johns Hopkins Medicine.
  3. Brain tumors – Classifications, symptoms, diagnosis and treatments. (n.d.).
  5. Louis, D. N., Perry, A., Wesseling, P., Brat, D. J., Cree, I. A., Figarella-Branger, D., … & Ellison, D. W. (2021). The 2021 WHO classification of tumors of the central nervous system: a summary. Neuro-oncology23(8), 1231-1251.
  6. Kleihues, P., Burger, P. C., & Scheithauer, B. W. (1993). The new WHO classification of brain tumours. Brain Pathology, 3(3), 255–268.
  7. Bruce, J. N., MD. (n.d.). Brain Cancer staging: Grading of central nervous system tumors.
  8. Berger, T., Wen, P. Y., Lang‐Orsini, M., & Chukwueke, U. (2022). World Health Organization 2021 Classification of Central Nervous System Tumors and Implications for therapy for Adult-Type Gliomas. JAMA Oncology, 8(10), 1493.
  9. Smith, H., Wadhwani, N. R., & Horbinski, C. (2022). Major features of the 2021 WHO classification of CNS tumors. Neurotherapeutics, 19(6), 1691–1704.
  10. Grades of brain tumours. (n.d.).
  11. Diagnosis and Grading of brain Tumors – Siteman Cancer Center. (2021, July 22). Siteman Cancer Center.
  12. Staging and grading brain cancer and brain tumors. (n.d.). Roswell Park Comprehensive Cancer Center.
  13. Grading Brain Tumors | SEER training. (n.d.).

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