What Are the Types of Meningioma? Grades and Characteristics

Meningioma is the term used for tumors that develop from the membrane structures called the meninges, which surround the brain and spinal cord. Meningiomas do not consist of a single tumor type. They can be divided into different subtypes and grades based on their cellular characteristics, growth behavior, molecular changes, and risk of recurrence. Therefore, in a patient diagnosed with meningioma, not only the presence of the tumor but also its grade and characteristics are important for treatment and follow-up planning.

Although the majority of meningiomas are slower-growing tumors, some types may grow more rapidly and have a tendency to recur after treatment. Prof. Dr. Ömür Günaldı emphasizes the importance of evaluating the pathological grade, imaging characteristics, the patient’s neurological condition, and the tumor’s relationship with critical structures, in addition to its size and location.

What Is a Meningioma?

Meningiomas develop from cells associated with the meninges surrounding the central nervous system. Although they do not originate from the brain tissue itself, as they grow, they may put pressure on brain tissue, nerves, or blood vessels and cause neurological symptoms.

Some meningiomas may remain very small and cause no symptoms for years. These tumors may be discovered incidentally during a brain MRI performed for another reason.

In contrast, as the tumor grows, symptoms such as headache, epileptic seizures, vision problems, balance disorders, loss of strength, or speech problems may occur.

What Are the Types of Meningioma?

Meningiomas can be divided into different subtypes according to their cellular structures seen under the microscope and their molecular characteristics. In the current classification, not only microscopic appearance but also certain molecular changes are important in determining the tumor grade.

The main meningioma subtypes may include meningothelial, fibrous, transitional, psammomatous, angiomatous, microcystic, secretory, clear cell, chordoid, and other less common types.

These names may seem complicated to patients. The most important point is determining the tumor grade in the pathology report and identifying characteristics that may affect the risk of recurrence.

Prof. Dr. Ömür Günaldı states that pathological evaluation contributes to planning the postoperative follow-up program and, when necessary, additional treatments.

What Are the Grades of Meningioma?

According to the World Health Organization classification, meningiomas are primarily evaluated under three grades:

• WHO Grade 1 meningioma
• WHO Grade 2 meningioma
• WHO Grade 3 meningioma

As the grade increases, the tumor may generally have a greater likelihood of showing more aggressive biological behavior and recurring after treatment. However, the clinical course is not the same for every patient.

What Is a WHO Grade 1 Meningioma?

WHO Grade 1 meningiomas constitute the majority of meningiomas and generally tend to grow more slowly.

These tumors may sometimes remain without significant growth for years. In some small and asymptomatic Grade 1 meningiomas, regular imaging follow-up may be preferred instead of immediate surgery.

Different Histological Subtypes May Be Seen Within Grade 1

Meningothelial Meningioma: This is one of the classic histological appearances of meningiomas. The tumor cells show characteristics similar to cells associated with the meninges.

Fibrous Meningioma: Also called fibrous or fibroblastic meningioma, this type may show more prominent spindle-shaped cells and connective tissue characteristics.

Transitional Meningioma: This is a type of meningioma in which meningothelial and fibrous characteristics may occur together. It may also be referred to as a “mixed meningioma.”

Psammomatous Meningioma: In this type, calcified structures called psammoma bodies may be prominent. In some tumors, calcification may also be detected on imaging studies.

Angiomatous Meningioma: This is one of the meningioma subtypes in which vascular structures are prominent.

Microcystic Meningioma: It has a distinctive histological appearance characterized by prominent small spaces between cells on microscopic examination.

Secretory Meningioma: This is a less common meningioma subtype in which the cells may show features resembling secretory structures.

Although Grade 1 tumors generally have a lower tendency to recur, this does not mean that they will never recur. Whether the tumor can be completely removed and its location are also important for long-term follow-up.

Prof. Dr. Ömür Günaldı emphasizes that even in low-grade meningiomas, regular follow-up should be continued according to the individual characteristics of the patient.

What Is a WHO Grade 2 Meningioma?

WHO Grade 2 meningiomas may have a higher potential for recurrence or progression compared with Grade 1 tumors.

During pathological examination, increased mitotic activity, invasion into brain tissue, and certain histological characteristics may be considered when determining the grade. In the current classification, certain molecular findings are also important for diagnosis and grading.

When a Grade 2 diagnosis is made, postoperative follow-up is generally planned more closely. Depending on the extent of surgical removal of the tumor and other risk factors, radiotherapy may also be considered for some patients through a multidisciplinary approach.

Clear Cell Meningioma

Clear cell meningioma is a specific type of meningioma associated with certain molecular characteristics. It may show different biological behavior compared with some other low-grade meningiomas.

Chordoid Meningioma

This is a histological subtype that may be characterized by cord-like cellular arrangements. All current pathological criteria are taken into account when determining the exact grade of the tumor.

Prof. Dr. Ömür Günaldı states that postoperative follow-up is particularly important in Grade 2 meningiomas and that the frequency of follow-up should be determined according to the pathological and surgical characteristics of the tumor.

What Is a WHO Grade 3 Meningioma?

WHO Grade 3 meningiomas are a group of meningiomas that may show more aggressive biological behavior. They may grow more rapidly and have a higher tendency to recur after treatment compared with lower-grade tumors.

In the current WHO classification, the presence of certain specific molecular changes may also result in a meningioma being classified as Grade 3.

Treatment of Grade 3 meningiomas is generally not limited to surgery alone. Depending on the patient’s condition, additional treatments such as radiotherapy may be considered after surgery, and closer imaging follow-up may be performed.

How Is the Grade of a Meningioma Determined?

Determining the exact grade of a meningioma is primarily based on pathological examination. Tumor tissue removed during surgery is examined under a microscope by a pathologist, and molecular tests may be used when necessary.

During the evaluation, the appearance of the tumor cells, their division activity, their relationship with surrounding brain tissue, and certain molecular changes may be taken into consideration.

Although MRI images may provide some clues about the behavior of the tumor, the exact WHO grade cannot be determined by imaging alone.

Prof. Dr. Ömür Günaldı states that evaluating preoperative imaging together with the postoperative pathology results is important for planning subsequent treatment and follow-up.

Why Is the Location of a Meningioma Important?

In meningiomas, the anatomical location of the tumor is as important as its grade.

For example, a tumor located close to the outer surface of the brain and more accessible surgically does not have the same surgical characteristics as a meningioma located at the skull base near important nerve and vascular structures.

According to their location, meningiomas may be described as convexity, parasagittal, falx, sphenoid wing, olfactory groove, and skull base meningiomas.

The location of the tumor may also affect the symptoms that occur in the patient.

What Is a Skull Base Meningioma?

Skull base meningiomas may develop in complex anatomical regions located at the lower part of the brain. These areas may contain the optic nerves, nerves that control eye movements, major blood vessels, and other cranial nerves.

Therefore, treatment planning for skull base meningiomas is based not only on the size of the tumor but also on its relationship with critical anatomical structures.

In some cases, attempting to remove the entire tumor may create a high risk to neurological functions. In such patients, safe surgical limits and complementary treatments may be considered when necessary.

Prof. Dr. Ömür Günaldı states that one of the primary goals of meningioma surgery is to achieve tumor control while preserving the patient’s neurological functions as much as possible.

Does the Grade of a Meningioma Affect Treatment?

Yes. The WHO grade of a meningioma is one of the important factors in determining the treatment and follow-up approach. However, treatment decisions are not made based on grade alone.

• WHO grade of the tumor
• Size of the tumor
• Location in the brain
• Growth rate
• Patient’s age
• Overall health condition
• Presence or absence of neurological symptoms
• Whether the tumor can be completely removed
• Previous treatments
• Molecular and pathological characteristics

Therefore, different treatment or follow-up approaches may be used for two patients with meningiomas of the same grade.

Do Meningiomas Require Surgery?

Not every meningioma requires surgery. Some small tumors that do not cause symptoms and show no growth on follow-up imaging may be monitored with regular MRI scans.

Surgical treatment may be considered if the tumor grows, causes neurological symptoms, or puts pressure on important surrounding structures.

The goal of surgery is to safely remove the tumor whenever possible. However, in tumors closely associated with critical blood vessels or nerves, the extent of surgery is determined with patient safety in mind.

Prof. Dr. Ömür Günaldı emphasizes that meningioma surgery should be planned individually for each patient and that detailed evaluation of the anatomical characteristics of the tumor is important when making surgical decisions.

Can Meningioma Recur?

Meningiomas may grow again after treatment. The likelihood of recurrence depends on many factors.

In general, higher-grade meningiomas have a greater tendency to recur. In addition, whether the tumor can be completely removed, its biological characteristics, and its location may also affect the risk of recurrence.

Therefore, even if surgery has been successfully performed, it is important to continue MRI follow-up examinations at intervals determined by the doctor.

Can the Grade of a Meningioma Change Over Time?

A recurrent meningioma may not always have exactly the same characteristics as the original tumor. In some cases, changes in the biological or pathological characteristics of the tumor may occur over time.

Therefore, in some meningiomas that require repeat surgery, it may be important to perform another pathological examination of the newly removed tissue.

Why Are the Type and Grade of a Meningioma Important?

In the diagnosis of meningioma, it is not sufficient to classify the tumor simply as “benign” or “malignant.”

Today, meningiomas are evaluated by considering their histological characteristics, WHO grade, molecular changes, anatomical location, and clinical behavior together.

These details help determine the frequency of follow-up, the surgical approach, and, when necessary, additional treatments such as radiotherapy.

As also emphasized by Prof. Dr. Ömür Günaldı, the goal in meningioma treatment is not only to evaluate the mass seen on imaging but also to consider the biological behavior of the tumor together with the individual characteristics of the patient.