Atypical Meningioma: Understanding Your Pathology Report

By Jason Wasserman MD PhD FRCPC
April 27, 2026

An atypical meningioma is a type of meningioma that is more aggressive than a grade 1 (benign) meningioma but less aggressive than a grade 3 meningioma. Meningiomas develop from meningothelial cells in the meninges, the thin layers of tissue that cover and protect the brain and spinal cord. Like all meningiomas, atypical meningiomas are dural-based tumors — they grow attached to the dura (the tough outer layer of the meninges) and sit on the surface of the brain rather than within it. This extra-axial location means the tumor can usually be separated from the brain at surgery, which is the main treatment.

Atypical meningiomas are classified as World Health Organization (WHO) grade 2. The grade is assigned when the tumor shows specific microscopic features suggesting it is growing more actively than a grade 1 meningioma, when it invades the underlying brain, or when two specific molecular changes are identified. Compared with grade 1 meningiomas, atypical meningiomas are more likely to come back after surgery, often require radiation therapy in addition to surgery, and need closer long-term monitoring. Compared with grade 3 (anaplastic) meningioma, they are less aggressive and generally have a better prognosis.

This article will help you understand the findings in your pathology report — what each term means and why it matters for your care. For a broader overview of meningioma including all grades, histologic subtypes, and locations, see the main meningioma article.

What are the symptoms of atypical meningioma?

The symptoms of atypical meningioma depend on where the tumor is growing, its size, and how quickly it grows. Atypical meningiomas tend to grow faster than grade 1 meningiomas, so symptoms can develop more quickly, but many patients still present with a gradual onset of neurological symptoms over weeks to months. Some tumors are discovered on imaging performed for another reason.

Common symptoms include:

• Headaches — often worse in the morning or with activities that increase pressure inside the head.
• Seizures — particularly for tumors over the surface of the brain.
• Weakness or numbness on one side of the body — usually on the opposite side to the tumor.
• Changes in vision or hearing — with tumors near the optic nerves or inner ear.
• Balance problems or difficulty walking — with tumors near the cerebellum or brainstem.
• Changes in personality, behavior, or memory — particularly with frontal lobe tumors.

Atypical meningiomas can arise anywhere along the meninges. The most common locations are the cerebral convexities (the outer surface of the brain), the falx cerebri (the midline fold between the two halves of the brain), the skull base, and less commonly the spinal canal. Tumor location affects both the symptoms and the complexity of surgery.

What causes atypical meningioma?

For most people diagnosed with atypical meningioma, the exact cause is not known. The tumor develops through a series of genetic changes that accumulate in meningothelial cells over time. Atypical meningiomas tend to have more of these changes than grade 1 meningiomas, which is reflected in their more aggressive behavior.

Several factors are known to increase the risk:

• Ionizing radiation — prior radiation to the head, especially in childhood, clearly increases the risk of developing a meningioma, including higher-grade tumors.
• Male sex — unlike grade 1 meningiomas, which are much more common in women, atypical meningiomas are slightly more common in men.
• Older age — the risk of higher-grade meningioma increases with age.

A small number of atypical meningiomas develop in the setting of an inherited condition. Inherited conditions are caused by a genetic change that is present in every cell of the body from birth and can be passed from parent to child. Inherited conditions associated with atypical meningioma include:

• Neurofibromatosis type 2 (NF2) — caused by a change in the NF2 gene. People with NF2 often develop multiple meningiomas across all grades, vestibular schwannomas, and other nervous system tumors, usually at a younger age than sporadic cases.
• BAP1 tumor predisposition syndrome — caused by a change in the BAP1 gene. This syndrome is associated with rhabdoid and high-grade meningiomas, as well as mesothelioma, melanoma of the eye and skin, and kidney cancer.
• SMARCE1-associated meningioma syndrome — caused by a change in the SMARCE1 gene. This condition specifically predisposes to clear cell meningioma, which is automatically classified as grade 2, and is most often diagnosed in younger patients.

Germline (inherited) genetic testing and genetic counselling are recommended when a patient has multiple meningiomas, when an atypical meningioma is diagnosed at a young age, or when tumor testing identifies loss of BAP1 or SMARCE1.

How common is atypical meningioma?

Atypical meningiomas account for approximately 15–30% of all meningiomas. They are more common in adults and are slightly more common in men than in women, which distinguishes them from grade 1 meningiomas, which occur predominantly in women. Like grade 1 meningiomas, they become more common with age.

How is the diagnosis made?

The diagnosis of atypical meningioma usually begins when imaging of the brain — most often magnetic resonance imaging (MRI) — reveals a dural-based mass. Atypical meningiomas typically appear as well-defined, contrast-enhancing masses attached to the dura. Compared with grade 1 meningiomas, they are more likely to show irregular or lobulated borders, evidence of brain invasion (where the tumor appears to push into the underlying brain), increased swelling (edema) in the surrounding brain, and spontaneous necrosis (dark areas on imaging where tumor cells have died). CT scanning often reveals calcifications within the tumor. Although these imaging features can suggest a higher-grade tumor, the grade can only be determined by examining the tissue under the microscope.

The diagnosis is confirmed after a tissue sample is examined by a pathologist. In most cases, tissue is obtained during surgery to remove the tumor. A neurosurgeon opens the skull through a craniotomy and removes as much of the tumor as can be safely taken out. When the tumor is not safely removable, a smaller stereotactic biopsy is performed instead.

Under the microscope, atypical meningioma is a tumor of meningothelial cells that shows one or more of the following features that distinguish it from a grade 1 meningioma. The first is increased mitotic activity — more tumor cells are caught in the act of dividing than expected. The WHO 2021 classification standardized the measurement of mitotic activity to mitotic figures per square millimeter; a count of 2.5 or more mitotic figures per square millimeter is one criterion for grade 2. The second defining feature is brain invasion, which means tumor cells are extending directly into the underlying brain tissue rather than simply pushing against it. Brain invasion is a powerful predictor of recurrence and automatically places a meningioma into grade 2 regardless of all other features. The third route to a grade 2 diagnosis is the presence of at least three out of five specific microscopic features: unusually high cellularity (a dense packing of tumor cells), small cells with a high ratio of nuclear size to cytoplasm, prominent nucleoli (small dense structures visible inside the tumor cell nuclei), sheet-like growth without the normal architectural organization seen in grade 1 tumors, and spontaneous necrosis (areas of dead tumor not explained by surgical injury). Two histologic subtypes — chordoid meningioma and clear cell meningioma — are automatically classified as grade 2 regardless of whether any of these features are present, because of their inherently higher recurrence risk.

To confirm the diagnosis, the pathologist uses immunohistochemistry (a laboratory test that uses antibodies to detect specific proteins in the tumor cells) and, increasingly, molecular testing. SSTR2A and EMA confirm the meningothelial origin of the tumor. Ki-67, a marker of how rapidly tumor cells are dividing, is often elevated in atypical meningiomas and supports the higher grade. The results of molecular testing, particularly for TERT promoter mutation and CDKN2A/B homozygous deletion, are sometimes essential to finalize the grade, because the presence of either change upgrades a tumor to WHO grade 3 even when the microscopic features would otherwise support grade 2.

WHO grade

WHO grade 2 (atypical) is an intermediate grade — more aggressive than grade 1 (benign) meningioma but less aggressive than grade 3 meningioma. The grade tells patients and their treatment team how likely the tumor is to come back after surgery and whether additional treatment such as radiation is needed.

It is worth understanding how grade 2 is assigned, because a patient’s pathology report may describe features that sound alarming even for a tumor that ultimately receives the same grade 2 classification. All of the following result in a grade 2 diagnosis:

• Increased mitotic activity alone — ≥2.5 mitotic figures per square millimeter.
• Brain invasion alone — regardless of other microscopic features.
• Three or more of five specific microscopic features — high cellularity, small crowded cells, prominent nucleoli, sheet-like growth, or spontaneous necrosis.
• Chordoid or clear cell histologic subtype — automatically grade 2 regardless of other features.

Two molecular findings — a TERT promoter mutation or homozygous deletion of CDKN2A/B — automatically upgrade a tumor to WHO grade 3. This means that a tumor appearing to be grade 2 by its microscopic features alone may be reclassified as grade 3 once molecular results are available. The pathology report should document which of the above criteria were met and whether molecular testing was performed.

Extent of resection (Simpson grade)

For atypical meningioma, the extent to which the tumor is removed during surgery is one of the strongest predictors of whether the tumor will come back, and directly influences whether radiation therapy is recommended afterward. The pathology and operative reports often describe the extent of resection using the Simpson grade, a five-point scale where lower numbers indicate more complete removal:

• Simpson grade 1 — complete removal of the tumor together with the attached dura and any involved bone.
• Simpson grade 2 — complete removal of the tumor, with coagulation (cautery) of the attached dura.
• Simpson grade 3 — complete removal of the tumor, but the attached dura is left in place untreated.
• Simpson grade 4 — partial removal of the tumor.
• Simpson grade 5 — biopsy or decompression only.

For atypical meningiomas, even a Simpson grade 1 or 2 resection (the most complete removal) is associated with a recurrence rate of 30–40% over five years, which is substantially higher than for completely removed grade 1 tumors. This is why radiation therapy is often recommended after surgery for atypical meningiomas regardless of the completeness of removal. With Simpson grade 3 or 4 resections, the recurrence risk is considerably higher, and the case for adjuvant radiation becomes stronger.

Biomarker and molecular testing

Molecular testing is increasingly performed for atypical meningiomas, particularly when the diagnosis is borderline between grade 2 and grade 3, when the tumor recurs, or when a high-risk molecular profile would change treatment decisions. The results can refine the grade, predict recurrence risk more precisely than microscopic features alone, and identify tumors that may be eligible for clinical trials.

TERT promoter mutation

Mutations in the TERT promoter region are found in about 5–6% of grade 2 meningiomas and are associated with dramatically shorter time to recurrence and worse survival. When a TERT promoter mutation is identified, the tumor is automatically reclassified as WHO grade 3, regardless of its microscopic appearance. This is one of the most important molecular results in meningioma pathology and is one of the reasons molecular testing has become routine for atypical tumors.

CDKN2A and CDKN2B

CDKN2A and CDKN2B are tumor suppressor genes that slow cell division. When both copies of these genes are lost (a change called homozygous deletion), tumor cells grow more freely and the tumor behaves aggressively. Like a TERT promoter mutation, homozygous deletion of CDKN2A and/or CDKN2B automatically upgrades the tumor to WHO grade 3. Testing is performed using next-generation sequencing with copy-number analysis or fluorescence in situ hybridization (FISH).

H3K27me3 loss

H3K27me3 is a chemical modification on a histone protein that helps control which genes are turned on or off. Loss of H3K27me3 protein expression on immunohistochemistry is not a formal WHO grading criterion but is an important prognostic marker in atypical meningioma: tumors that have lost H3K27me3 have a significantly higher risk of recurrence than those that retain it. Your pathology report may describe H3K27me3 as retained or lost.

NF2

The NF2 gene is the most commonly mutated gene in meningiomas overall. NF2 alterations are detected by next-generation sequencing and copy-number analysis. Their presence does not change the WHO grade in isolation but may be noted as part of the molecular profile and can prompt consideration of germline testing if features of neurofibromatosis type 2 are present clinically.

SMARCE1 and BAP1

Loss of nuclear SMARCE1 protein on immunohistochemistry supports a diagnosis of clear cell meningioma and should prompt germline testing for SMARCE1 mutations, particularly in younger patients. Loss of BAP1 protein is associated with rhabdoid morphology and aggressive behavior, and should similarly prompt germline testing for BAP1 tumor predisposition syndrome.

DNA methylation profiling

DNA methylation profiling compares the tumor’s methylation pattern to a large reference database and can classify meningiomas into molecular risk groups that predict recurrence more accurately than WHO grade alone. This testing is increasingly used in specialized centers, particularly for borderline or recurrent cases, and may help resolve diagnostic uncertainty when microscopic and molecular findings are inconsistent.

For more information about biomarker and molecular testing across all cancer types, visit the Biomarkers and Genetic Testing section.

What is the prognosis?

Atypical meningioma has an intermediate prognosis — substantially better than grade 3 meningioma but with a meaningfully higher risk of recurrence than grade 1. Ten-year relative survival is approximately 90%, but the chance of the tumor coming back depends on several interacting factors.

Recurrence rates after surgery vary considerably:

• After complete removal (Simpson grade 1 or 2) — approximately 30–40% recurrence within five years.
• After partial removal (Simpson grade 3 or 4) — substantially higher recurrence rates, often 50% or more within five years.
• With adjuvant radiation therapy — recurrence rates are lower than with surgery alone, though the magnitude of benefit depends on the extent of resection and molecular profile.

Several features are associated with a higher risk of recurrence or faster progression:

• Brain invasion — one of the strongest predictors of recurrence in grade 2 meningioma.
• Higher mitotic activity — tumors with mitotic counts at the higher end of the grade 2 range tend to recur earlier.
• High Ki-67 index — a high proportion of actively dividing cells suggests a more aggressive tumor.
• Loss of H3K27me3 — associated with significantly shorter time to recurrence.
• TERT promoter mutation or CDKN2A/B homozygous deletion — these findings upgrade the tumor to grade 3 and are associated with the worst outcomes.
• Incomplete surgical removal — Simpson grade 3 or 4 resection.
• Skull-base location — these tumors are often harder to remove completely than convexity tumors.
• Recurrent tumor — meningiomas that come back after initial treatment tend to behave more aggressively with each recurrence.

What happens after the diagnosis?

Atypical meningioma is managed by a multidisciplinary team that typically includes a neurosurgeon, a neuro-oncologist, a radiation oncologist, a neuropathologist, and a neuroradiologist. Other members of the team may include a neurologist for seizure management, a neuro-ophthalmologist for tumors near the optic nerves, an endocrinologist for tumors near the pituitary gland, and a geneticist or genetic counsellor when an inherited condition is suspected.

Surgery

Surgery is the first and primary treatment for most atypical meningiomas. The goal is the most complete removal that can be achieved safely — ideally a Simpson grade 1 or 2 resection, including removal of the attached dura. Complete removal reduces the risk of recurrence and improves the chance that radiation alone will be sufficient to control any residual microscopic disease. When the tumor involves the skull base or critical nerves and blood vessels, complete removal may not be possible without unacceptable risk of neurological injury. In these cases, a planned subtotal removal followed by radiation is the typical approach.

Radiation therapy

Radiation is an important part of treatment for most atypical meningiomas. Whether radiation is given immediately after surgery or reserved for recurrence depends on the completeness of resection, the tumor’s molecular profile, and the practices of the treating center.

• Adjuvant radiation after complete resection — the evidence base is evolving, but many centers recommend radiation even after complete removal of atypical meningiomas because of the high recurrence risk. The ROAM/EORTC-1308 clinical trial studied this question specifically and found that adjuvant radiation significantly improved progression-free survival after gross total resection of WHO grade 2 meningioma.
• Adjuvant radiation after incomplete resection — strongly recommended when the tumor was not completely removed, given the high recurrence rate with incomplete resection alone.
• Stereotactic radiosurgery — a single high dose of focused radiation delivered in one session. Used for smaller tumors or residual disease after surgery.
• Fractionated radiation — multiple smaller doses given over several weeks. Used for larger tumors, tumors involving the skull base, or when high doses near critical structures require dose distribution across sessions.

Systemic therapy

No systemic therapy (chemotherapy, hormone therapy, or targeted drugs) has been established as a standard treatment for atypical meningioma. For tumors that recur after surgery and radiation and cannot be safely re-operated, options sometimes include bevacizumab (a drug that reduces blood vessel growth), somatostatin analogues, and targeted therapies based on specific molecular findings identified in the tumor. Clinical trials are an important option for patients with recurrent or progressive atypical meningioma.

Follow-up

Long-term follow-up with regular MRI scans is essential because atypical meningiomas can come back months or years after initial treatment — sometimes after a period of apparent stability. The interval and duration of follow-up imaging depend on the WHO grade, the extent of resection, whether radiation was given, and whether high-risk molecular features were identified. Typical surveillance involves MRI every 6 months for the first several years, with longer intervals if the tumor remains stable. Long-term effects of the tumor and its treatment — including seizures, cognitive changes, hormonal effects, and the late effects of radiation — are managed by the multidisciplinary team as needed.

Questions to ask your doctor

• What histologic subtype is my tumor — chordoid, clear cell, or atypical by microscopic features — and how was the grade 2 diagnosis made?
• Did the tumor invade the brain, and how does that affect my risk of recurrence?
• What was the Simpson grade of my surgery — was the tumor completely removed, and was the dura removed as well?
• Were any molecular tests performed, and did the results show a TERT promoter mutation or CDKN2A/B deletion?
• Was H3K27me3 staining performed, and was it retained or lost?
• Do you recommend radiation therapy, and if so, what type — stereotactic radiosurgery or fractionated radiation?
• If radiation is not recommended now, under what circumstances would it be considered in the future?
• Should I be referred for genetic counselling or germline genetic testing?
• How often will I need MRI scans, and for how long?
• What symptoms should I watch for that might suggest the tumor is coming back?
• How will any seizures be managed, and will I be able to drive?
• Are there clinical trials available for my type of meningioma?
• What are the expected long-term effects of the tumor and its treatment on cognitive function, vision, hormones, and quality of life?
• What supportive care services are available — neuropsychology, rehabilitation, endocrinology, and mental health support?

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