Your pathology report for atypical meningioma, WHO grade 2

By Jason Wasserman MD PhD FRCPC
July 15, 2025

An atypical meningioma is a type of brain tumour that starts in the meninges, the protective layers that cover the brain and spinal cord. It is classified as WHO grade 2, which means it is more aggressive than a WHO grade 1 meningioma but less aggressive than a WHO grade 3 anaplastic meningioma.

Atypical meningiomas grow faster than WHO grade 1 meningiomas, have a higher risk of coming back (recurrence) after treatment, and may invade nearby tissues, such as the brain or skull. They still rarely spread to other parts of the body and can often be managed successfully with surgery and, in some cases, radiation therapy.

What are the symptoms of an atypical meningioma?

The symptoms of an atypical meningioma depend on where the tumour is located and how much pressure it places on the brain or spinal cord. Common symptoms include:

  • Headaches.

  • Seizures.

  • Weakness, numbness, or difficulty with coordination.

  • Vision or hearing problems.

  • Changes in memory, personality, or thinking.

Some tumours are found incidentally during imaging for another reason.

What is the difference between a meningioma and an atypical meningioma?

A meningioma refers to a tumour that arises from the meninges. Most meningiomas are WHO grade 1, meaning they are grow slowly and are unlikely to come back after complete removal.

An atypical meningioma is a WHO grade 2 tumour. It still starts in the same location, but it shows more aggressive features under the microscope, such as:

  • A higher number of mitotic figures (dividing tumour cells).

  • Growth into nearby brain tissue (brain invasion).

  • Unusual patterns of growth.

Because of these features, atypical meningiomas are more likely to grow back after treatment than grade 1 meningiomas. They may also grow faster and require closer follow-up and additional treatment, such as radiation therapy.

Is an atypical meningioma a cancerous tumour?

Atypical meningiomas are not considered malignant (cancerous) in the same way as grade 3 meningiomas or other aggressive brain cancers. However, they are more aggressive than WHO grade 1 meningiomas and have a higher chance of recurrence.

For this reason, they are sometimes referred to as “borderline” or “intermediate-grade” tumours. While they rarely spread outside the brain, they can cause serious problems depending on their location and growth.

With treatment and regular follow-up, many people with atypical meningioma can live long, healthy lives.

How is an atypical meningioma diagnosed?

Atypical meningioma is diagnosed after surgical removal of the tumour. A pathologist examines the tumour under a microscope and uses specific criteria to determine if it is WHO grade 2. Imaging tests like MRI or CT scans may suggest that a tumour is more aggressive, but only microscopic examination can confirm the diagnosis.

What does an atypical meningioma look like under the microscope?

Atypical meningiomas may look similar to WHO grade 1 meningiomas but show certain features that make them more likely to grow quickly or come back.

To be diagnosed as atypical, the tumour must have at least one of the following:

  • Increased mitotic activity (tumour cells dividing more frequently than normal).

  • Brain invasion (tumour cells pushing into the brain tissue).

  • Or at least three of the following additional features:

    • High cell density.

    • Small, tightly packed tumour cells.

    • Prominent nucleoli (dark-staining centers of the nuclei).

    • Sheet-like growth (tumour cells growing in large uninterrupted areas).

    • Areas of necrosis (tumour cell death).

The tumour cells may also show mild variation in shape and size, but they usually do not look highly abnormal.

What is brain invasion?

Brain invasion means that tumour cells have grown past the meninges and into the nearby brain tissue. This is an important feature in the diagnosis of atypical meningioma, even if the tumour looks otherwise benign. Tumours with brain invasion have a higher risk of recurrence and may require closer follow-up and additional treatment.

What is the treatment for an atypical meningioma?

Treatment typically begins with surgery to remove as much of the tumour as possible. In many cases, especially if the tumour was not completely removed or has brain invasion, doctors may also recommend:

  • Radiation therapy, such as external beam radiation, to lower the risk of recurrence.

  • Regular MRI scans to monitor for regrowth.

Chemotherapy is rarely used for this type of tumour unless it transforms into a more aggressive type or cannot be treated with surgery or radiation.

What does margin status mean?

After surgery, the pathologist examines the margins (edges) of the tissue removed to determine if any tumour cells are present at the edge:

  • A negative margin means no tumour cells are seen at the edge, suggesting the tumour was completely removed.

  • A positive margin means tumour cells were found at the edge, which increases the risk of recurrence.

Margin status helps your doctor decide whether additional treatment, such as radiation, may be needed.

What is the prognosis for atypical meningioma?

The prognosis for atypical meningioma is generally good, especially if the tumour is completely removed and followed by appropriate treatment. However, compared to WHO grade 1 meningiomas, atypical meningiomas often show:

  • Higher chance of coming back after treatment (recurrence rate is 30–50%)

  • Faster growth rate.

  • Greater need for long-term follow-up and, in some cases, additional treatment like radiation.

Factors that may affect prognosis include:

  • How much of the tumour was removed during surgery.

  • Whether the tumour invaded the brain.

  • The number of dividing cells seen under the microscope.

  • The tumour’s location and size.

Even after successful treatment, lifelong monitoring with periodic imaging (MRI scans) is usually recommended.

Questions to ask your doctor

  • Was the tumour completely removed?

  • Do I need radiation after surgery?

  • How often should I have follow-up imaging?

  • What are the chances the tumour will come back?

  • What symptoms should I watch for?

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