Olfactory Groove Meningioma — Symptoms, Diagnosis, Treatment, and Prognosis

Most readers benefit from reviewing this Quick Summary together with the sections on Symptoms of Olfactory Groove Meningioma, Diagnosis, Surgical Treatment, Radiation Therapy, and Treatment Decision-Making. Later sections provide more detailed explanations intended for patients seeking a deeper understanding before important treatment decisions are made.

What Is an Olfactory Groove Meningioma

An olfactory groove meningioma (OGM) is a meningioma that arises from the meninges in the olfactory groove region of the anterior skull base, just above the nasal cavity. As it enlarges, it may extend to adjacent parts of the anterior skull base.

Most meningiomas arise from specialized cells within the arachnoid layer, often called arachnoid cap cells. When genetic changes occur in these cells, they may begin to multiply abnormally and gradually form a tumor. Unlike tumors that originate inside the brain tissue, olfactory groove meningiomas grow outside the brain, attached to the dura mater of the anterior skull base. As they enlarge, they typically compress the surrounding frontal lobes without directly invading the brain tissue. Because of this growth pattern, they often remain well-defined masses, although large tumors may come into contact with nearby arteries and the optic nerves, compress them, and in some cases become firmly adherent to these structures. The skull base bone at the site of tumor origin is often thickened (hyperostosis), reflecting tumor involvement of the underlying bone.

Olfactory groove meningiomas represent approximately 8–10% of intracranial meningiomas. Because of their location beneath the frontal lobes, they may become quite large before they are discovered.

Meningiomas occur approximately two to three times more frequently in women than in men. They are also rare in children, representing less than 2% of all pediatric brain tumors.

In many patients, the tumor grows slowly and initially produces few symptoms. One of the earliest manifestations is often a disturbance of smell or gradual loss of smell (anosmia) due to compression of the olfactory nerves. Because this change may develop slowly and many patients do not immediately notice it, the tumor can continue to enlarge for years before other symptoms appear. As the tumor grows further, patients may develop headaches, personality or behavioral changes related to frontal lobe compression, progressive cognitive slowing, visual disturbances if the optic pathways become involved, and occasionally seizures.

Image: Olfactory groove meningioma and meningiomas of other locations

Biological Classification of Meningiomas

The biological behavior of olfactory groove meningiomas is determined through histopathological analysis using the World Health Organization (WHO) classification.

Three main categories are recognized:

• WHO grade I — benign meningioma. This is the most common form, representing roughly 80–85% of meningiomas. These tumors typically grow slowly and often remain stable for long periods. When completely removed surgically, the chance of recurrence is relatively low.
• WHO grade II — atypical meningioma. Atypical meningiomas account for approximately 10–15% of cases in surgical series. These tumors show increased cellular activity and a higher likelihood of recurrence after surgery. After complete tumor removal, some patients may be managed with MRI follow-up rather than immediate radiation therapy.
• WHO grade III — malignant (anaplastic) meningioma. These tumors are rare, representing roughly 1–3% of cases. They grow more aggressively, recur more frequently, and usually require combined treatment with surgery and radiation therapy.

Although histological grade is important, clinical outcome also depends strongly on tumor location, the relationship to the frontal lobes, olfactory nerves, optic nerves, and anterior cerebral vessels, and the possibility of complete surgical removal.

You can read more about other brain tumors on our Brain Tumors page.

Genetic and Biological Causes

Most olfactory groove meningiomas arise from sporadic genetic mutations that occur during life rather than inherited genetic disorders. At the molecular level, tumor development usually results from two main biological mechanisms:

• inactivation of tumor suppressor genes, which normally prevent uncontrolled cell growth
• activation of oncogenic signaling pathways, which stimulate cell proliferation

The most frequently involved gene is NF2, located on chromosome 22. Loss of function of this gene disrupts normal cell growth control and allows tumor formation. Other molecular alterations identified in meningiomas include mutations involving genes such as TRAF7, AKT1, SMO, and KLF4, while additional less common alterations may involve genes such as PIK3CA or TERT.

The only clearly established environmental risk factor is exposure to ionizing radiation, particularly during childhood.

Meningiomas occur approximately two to three times more frequently in women than in men, suggesting that hormonal influences may play a role in tumor development and growth.

Although most meningiomas arise sporadically, a small proportion occur in the context of inherited genetic syndromes. The best known example is neurofibromatosis type 2 (NF2). Patients with NF2 may develop multiple meningiomas in different intracranial and spinal locations.

How Olfactory Groove Meningiomas Grow and Affect the Brain

Olfactory groove meningiomas usually grow slowly over many years. Because they arise outside the brain tissue, they affect the brain mainly through compression and do not infiltrate the brain. In the early stages, the tumor mainly compresses the olfactory bulbs and olfactory tracts. With further growth over time, it may gradually extend upward and begin to compress the inferior surfaces of the frontal lobes. Large olfactory groove meningiomas may also extend posteriorly toward the optic nerves, optic chiasm and anterior cerebral arteries.

Studies following patients with untreated meningiomas have shown that a substantial proportion of tumors remain stable for long periods. Among tumors that do grow, the increase in size is usually slow and gradual, often measured in millimeters per year rather than rapid expansion.

Another important mechanism is peritumoral brain edema, a form of swelling in the surrounding brain tissue caused by leakage of fluid from nearby blood vessels. This swelling increases intracranial pressure and often worsens symptoms.

Together with the very enlarged tumor itself, this edema can produce a mass effect, meaning that the expanding lesion compresses and displaces normal brain structures. Because the skull is a rigid, closed cavity with limited space for expansion, increasing pressure may eventually force parts of the brain to shift from their normal position. In severe cases, this may lead to brain herniation, which is a dangerous stage of mass effect.

Image: A meningioma growing from the coverings of the brain and compressing surrounding parts of the brain, without infiltrating them.

Symptoms of Olfactory Groove Meningioma

The symptoms caused by olfactory groove meningiomas depend mainly on tumor size, surrounding edema, and involvement of nearby structures.

Typical symptoms may include:

•gradual loss of smell (anosmia)- often affecting both sides. This is usually the earliest symptom because the tumor initially compresses the olfactory (smell) nerves. The change typically develops slowly and often goes unnoticed by the patient. If the tumor remains small or stops growing, this may remain the only symptom. If the tumor continues to enlarge over time, additional symptoms listed below may appear years later as the tumor and surrounding edema become more significant.
• headaches, especially when the tumor becomes larger
• personality or behavioral changes, such as apathy, irritability, disinhibition, or poor judgment
• progressive decline in concentration, memory, or executive function
• visual disturbances, particularly if the tumor grows posteriorly toward the optic nerves or optic chiasm
• seizures, especially in larger tumors irritating the frontal lobes
• gait imbalance or generalized slowing, sometimes seen in advanced cases
• urinary incontinence or marked cognitive decline, occasionally in very large bilateral frontal tumors

Because frontal lobe compression may develop slowly, some patients are first evaluated for psychiatric, cognitive, or personality-related changes before the tumor is discovered on imaging.

Image: The olfactory nerve (CN I) — consisting of numerous nerve fibers originating in the roof of the nasal cavity, entering the skull through the cribriform plate, and terminating via relay pathways in the evolutionary oldest part of the brain. Read more on these pages about brain anatomy and the anatomy of the cranial nerves.

Diagnosis of Olfactory Groove Meningioma

The most important diagnostic test is MRI of the brain with contrast.

During this examination, the patient lies inside the MRI scanner while magnetic fields generate highly detailed images of the brain. A contrast agent injected through a vein highlights tumor tissue.

MRI allows physicians to determine:

• tumor size
• precise location along the anterior skull base
• relationship to the frontal lobes
• relationship to the optic nerves, optic chiasm, and anterior cerebral vessels
• presence of surrounding brain edema
• possible extension toward the ethmoid region or skull base bone

Olfactory groove meningiomas typically appear as well-defined extra-axial tumors attached to the dura of the anterior cranial fossa, often with strong contrast enhancement and sometimes with a dural tail.

Image: A T1-weighted contrast-enhanced MRI shows a large olfactory groove meningioma in three planes as a bright (enhancing) tumor.

The final diagnosis is confirmed through histopathological analysis after surgery or biopsy.

However, several other conditions may occasionally produce similar imaging findings and should be considered in the differential diagnosis.

These include:

• other anterior skull base meningiomas, such as planum sphenoidale meningiomas
• dural metastases
• solitary fibrous tumor / hemangiopericytoma
• esthesioneuroblastoma extending intracranially in selected skull base cases
• sinonasal or skull base tumors with intracranial extension

Although MRI is the main imaging method used to diagnose olfactory groove meningiomas, CT scans may provide useful additional information. CT is particularly helpful in evaluating hyperostosis, skull base bone changes, calcification, and extension toward the paranasal sinuses. In selected cases, vascular imaging may also be required to assess the relationship of the tumor to the anterior cerebral arteries.

Monitoring Without Treatment: When an Olfactory Groove Meningioma is Only Observed

Not all olfactory groove meningiomas require immediate treatment.

Observation may be considered when:

• the tumor is small
• the patient has no clear neurological symptoms
• imaging shows little or no growth over time
• there is little or no surrounding edema
• there is no significant compression of the frontal lobes or optic pathways
• the patient is elderly or has serious medical conditions increasing surgical risk

Follow-up generally involves MRI examinations every 6–12 months initially. If a small tumor shows documented growth and remains at a safe distance from the optic nerves, treatment may in selected cases be performed with stereotactic radiosurgery (SRS) rather than surgery.

However, observation must be individualized carefully in this location. Even slowly growing bigger tumors may eventually cause subtle cognitive or behavioral deterioration, and some patients do not notice progressive loss of smell or frontal lobe dysfunction until the tumor becomes large. For this reason, the decision to observe rather than treat depends not only on tumor size, but also on growth trend, edema, cognitive symptoms, visual risk, and overall clinical context.

Symptomatic Treatment

Medications are often used to control complications caused by the tumor.

• Brain swelling (edema) is commonly treated with corticosteroids, most often dexamethasone, which reduces edema in the surrounding brain tissue.
• Seizures are treated with antiepileptic medications, such as levetiracetam or other modern antiseizure drugs.

These medications may stabilize the patient temporarily but do not eliminate the tumor itself.

Headache is common, particularly in larger tumors associated with significant edema or raised intracranial pressure. Headache in patients with small meningiomas does not necessarily mean that the tumor is the cause. Many patients have common primary headache disorders such as tension-type headache, migraine, or cervicogenic headache, which are frequent in the general population and may occur independently of the tumor. For this reason, the type of headache should be carefully evaluated and defined before attributing the symptoms to the meningioma, and the presence of headache alone is usually not a sufficient reason to recommend immediate surgical removal of a small, otherwise asymptomatic tumor.

Olfactory Groove Meningioma and Cognitive or Behavioral Change

Unlike many tumors that produce obvious focal neurological deficits early, olfactory groove meningiomas may first present with changes in personality, initiative, emotional control, or judgment.

Because the tumor compresses the frontal lobes, some patients may gradually become:

• more apathetic
• less organized
• emotionally blunted
• socially disinhibited
• forgetful or mentally slowed

Family members often notice these changes before the patient does.

This clinical pattern is important because it may delay diagnosis. In some patients, the tumor is first suspected only after progressive changes in daily functioning, work performance, or interpersonal behavior become obvious.

Surgical Treatment of Olfactory Groove Meningiomas

Surgery remains the primary treatment for symptomatic or progressively growing olfactory groove meningiomas. The procedure is usually performed through a craniotomy, which involves temporarily removing a portion of the skull to access the tumor.

In most cases the operation proceeds through several stages:

• Skin incision and craniotomy
The scalp is opened using a carefully planned incision, usually placed behind the hairline when possible for cosmetic reasons. A bone flap is created to expose the anterior cranial base and the dura overlying the tumor. Various craniotomy approaches (e.g., pterional, bicoronal, and subfrontal) can be used for olfactory groove meningioma surgery, depending on the tumor size, its dominant growth direction, and the surgeon’s preference, as shown in the image below.

• Opening of the dura
The dura mater is carefully opened to expose the tumor and surrounding frontal lobe structures.

• Internal tumor debulking
Whenever possible, the surgeon first attempts to control or detach the tumor from its dural attachment, because meningiomas receive much of their blood supply from dural vessels. The tumor is then reduced from the inside, most often using an ultrasonic aspirator (CUSA). This internal debulking decreases tumor volume and pressure, making subsequent dissection safer.

• Microsurgical dissection
The remaining peripheral parts of the tumor are then gradually separated from the surrounding brain tissue, blood vessels, and preserved olfactory structures, and especially from the optic nerves and anterior cerebral arteries if the tumor extends posteriorly. These residual portions of the tumor are removed piece by piece under microsurgical visualization.

• Treatment of the dural attachment
Because the tumor arises from the dura of the anterior skull base, the involved dura is usually removed or coagulated whenever possible to reduce recurrence risk.

• Removal of infiltrated bone when present
Some olfactory groove meningiomas produce hyperostosis or infiltration of the anterior skull base bone. In such cases, abnormal bone may need to be drilled away, and in selected situations skull base reconstruction may be required.

• Dural reconstruction and closure
After tumor removal, the dura is reconstructed if necessary. The bone flap is replaced, and the scalp is closed.

The main goals of surgery are:

• safe tumor removal
• decompression of the frontal lobes
• protection of the optic nerves and major arteries
• reduction of recurrence risk
• preservation of neurological function

In many patients, preoperative loss of smell is already permanent, and restoration of olfaction after surgery is often limited, especially when the tumor has already severely compressed or destroyed the olfactory structures.

Image: Various locations and sizes of craniotomies can be used for olfactory groove meningioma surgery, depending on the tumor’s size, its dominant growth direction, or the surgeon’s preference.

Image: The image illustrates a craniotomy. Both the skin incision and the skull opening are performed within the hair-bearing area of the scalp. The dura is opened to expose the brain as part of the surgical approach to the tumor. After the procedure, the bone flap is secured and the scalp is reconstructed, ensuring no cosmetic defect remains after healing. The same principles apply to the craniotomies shown in the image above regarding olfactory groove meningioma surgery.

Image: Stages of surgical removal of a meningioma. After craniotomy and opening of the dura, image (a) shows the dark brown meningioma. Image (b) illustrates its separation from the brain, blood vessels, and other normal tissues, followed by its piecemeal reduction. Image (c) shows the removal of the remaining peripheral parts of the meningioma. Image (d) shows the condition after the meningioma has been completely removed. These same surgical principles are also applied in the surgery of olfactory groove meningiomas

Modern Surgical Technologies

Modern neurosurgery employs several technologies to increase precision and safety.

• Neuronavigation systems function as intraoperative GPS, allowing the surgeon to navigate within the skull with millimeter accuracy.
• Ultrasonic aspirators (CUSA) fragment and aspirate tumor tissue while preserving surrounding blood vessels and nerves.
• Intraoperative neurophysiological monitoring may be used in selected cases, depending on tumor extension and nearby critical structures.
• Microsurgical magnification allows careful dissection from arteries, optic pathways, and frontal lobe surfaces.

These technologies significantly improve precision and reduce risk during surgery.

In selected cases, preoperative embolization may be considered, but this is less common and depends on the vascular supply of the tumor.

Endoscopic Surgery for Olfactory Groove Meningiomas

In addition to classical microsurgical craniotomy, some olfactory groove meningiomas may be removed using an endoscopic endonasal approach.

This technique accesses the tumor through the nasal cavity and skull base, avoiding a standard cranial opening. It is mainly considered for selected midline anterior skull base tumors, especially when their anatomical extension is favorable for this route. Importantly, the endoscopic endonasal approach necessarily sacrifices olfactory function because it traverses the cribriform plate; patients who retain any residual smell should be informed of this before selecting this route.

The basic steps of endoscopic surgery usually include:

• endonasal access through the nasal cavity
• removal of part of the skull base bone to expose the dura
• opening of the dura covering the tumor
• internal debulking of the tumor
• careful separation of the tumor from surrounding structures
• removal of the tumor in fragments
• reconstruction of the skull base defect, usually with vascularized tissue flaps to reduce the risk of cerebrospinal fluid leakage

Potential advantages of endoscopic surgery include:

• no large scalp incision
• no standard craniotomy
• direct midline access from below
• limited brain retraction

However, this approach is suitable only for a minority of olfactory groove meningiomas. The endoscopic endonasal approach is mainly used for small to medium-sized midline tumors located at the cribriform plate or planum sphenoidale, especially when the tumor grows predominantly downward toward the skull base and does not extend far laterally over the frontal lobes or surround major arteries. Many tumors of this size may also be technically suitable for stereotactic radiosurgery (SRS) if they demonstrate growth but remain relatively small and are not producing significant brain compression. In current practice, only a minority of olfactory groove meningiomas are treated using a purely endoscopic endonasal approach, roughly around 10–15% in selected surgical series.

Important limitations include:

• difficulty removing large lateral tumor extensions
• limited control when the tumor surrounds important arteries
• challenges in managing extensive dural attachment or infiltrated bone
• increased risk of CSF leakage if skull base reconstruction is not adequate

For these reasons, microsurgical craniotomy remains the most common treatment for many olfactory groove meningiomas, especially larger tumors or tumors with more complex extension.

The choice between microsurgical and endoscopic approaches depends on tumor size, extension, vascular relationships, skull base anatomy, and the experience of the surgical team.

Image: Many skull base tumors, such as meningiomas, pituitary adenomas, and others, can be removed without a craniotomy using an endoscopic endonasal approach.

Extent of Tumor Removal — Simpson Classification

The completeness of tumor removal is classified using the Simpson grading system.

• Simpson Grade I — complete removal of the tumor and its dural attachment
– recurrence risk approximately 5–10% over long-term follow-up
– probability of needing another intervention ~3–5%

• Simpson Grade II — tumor removed, dural attachment coagulated
– recurrence risk approximately 10–20%
– probability of further treatment ~5–10%

• Simpson Grade III — tumor removed but dura left intact
– recurrence risk approximately 20–30%
– probability of additional treatment ~10–20%

• Simpson Grade IV — subtotal removal
– recurrence risk approximately 40–60%
– additional treatment often required in 30–50%

• Simpson Grade V — biopsy or decompression only
– tumor progression expected in most patients
– further definitive treatment usually necessary

In olfactory groove meningiomas, the extent of removal may be influenced by the relationship of the tumor to the optic apparatus, anterior cerebral arteries, frontal skull base, and bone infiltration.

Radiation Therapy for Olfactory Groove Meningiomas

Radiation therapy is used when complete surgical removal is not possible, when tumors recur, or when a small residual tumor remains after surgery. It may also be considered for small tumors that demonstrate clear growth during imaging follow-up, particularly when surgery carries increased risk.

Typical radiation doses for meningiomas are:

• 12–16 Gy delivered in a single session in stereotactic radiosurgery (SRS), typically used for small olfactory groove meningiomas, usually smaller than about 2.5–3 cm in diameter, especially when the tumor does not produce significant frontal lobe compression and is located at a safe distance from the optic nerves and optic chiasm. It is also commonly used for small residual tumors after surgery.
• 50–54 Gy in fractionated radiotherapy, delivered over several weeks. This approach is used less often for olfactory groove meningiomas and is usually considered when surgery is not possible or when radiosurgery is unsuitable due to tumor size or proximity to the optic nerves.

Radiation therapy can effectively stop tumor growth in many patients. Modern radiation techniques provide long-term tumor control in approximately 85–95% of benign meningiomas, especially when small tumors are treated with stereotactic radiosurgery.

Sometimes even relatively small tumors may be unsuitable for single-session radiosurgery if they lie very close to the optic nerves or optic chiasm, because these structures tolerate only limited radiation exposure. In olfactory groove meningiomas, however, the more common limitation for radiosurgery is tumor size, since many tumors are already large when diagnosed and produce significant frontal lobe compression or edema.

In tumors located close to the optic pathways, fractionated radiation is often preferred over single-session radiosurgery because it may reduce the risk of radiation injury to vision.

In some patients with small residual tumor near the optic pathways or major arteries, careful MRI surveillance may be preferred over immediate radiation if the remnant is stable and asymptomatic.

The final treatment decision is usually made by a multidisciplinary team, including a neurosurgeon, radiation oncologist, and neuroradiologist.

Planned subtotal resection followed by radiosurgery is less common for olfactory groove meningiomas, because many tumors can be safely removed completely. In most cases, a small residual tumor is left only when the surgeon encounters dense adherence to critical arteries or optic structures during surgery.

Recurrence of Olfactory Groove Meningiomas

The likelihood of recurrence depends on tumor grade and completeness of removal.

• After complete removal of benign meningiomas, recurrence occurs in approximately 5–10% of cases over 10–15 years.
• After subtotal removal, recurrence rates may reach 20–40%.
• Atypical meningiomas recur in approximately 30–40% of cases.
• Malignant meningiomas may recur in 50–80% of patients.

Because recurrence may occur many years after treatment, long-term MRI follow-up is essential.

When an olfactory groove meningioma recurs, treatment decisions depend on several factors:

• tumor growth rate
• tumor size
• relationship to the optic apparatus and skull base arteries
• previous treatments
• patient symptoms
• histological grade

Not all recurrences require immediate treatment. Some small stable recurrences can be monitored, while others require surgery, radiation, or both.

Observation of Small Recurrences

Small recurrent olfactory groove meningiomas that show minimal or no growth may initially be managed with MRI surveillance.

Observation is most commonly chosen when:

• the recurrent tumor is small
• the patient has no neurological or visual symptoms
• imaging shows slow or stable growth
• the recurrence is located in a higher-risk surgical area

Follow-up usually involves MRI every 6–12 months.

Repeat Surgery

Surgical reoperation is considered when:

• the recurrent tumor causes neurological, cognitive, or visual symptoms
• imaging shows significant growth
• the tumor is accessible for safe removal
• mass effect on the frontal lobes becomes clinically important

Repeat surgery aims to remove the recurrent tumor and, when possible, its dural attachment.

However, reoperation may be more technically demanding because:

• scar tissue from the previous surgery may be present
• arteries, optic structures, or frontal lobe surfaces may already be displaced
• previous skull base reconstruction may alter normal anatomy

Radiation Therapy for Recurrence

Radiation therapy is frequently used for recurrent olfactory groove meningiomas, particularly when complete reoperation is not feasible.

Radiation may be recommended when:

• residual tumor remains after surgery
• recurrence occurs after previous surgery
• the tumor lies in a surgically difficult skull base location
• the tumor shows atypical or malignant histology

Two main radiation approaches are used:

• fractionated radiotherapy, typically delivering 50–54 Gy
• stereotactic radiosurgery, usually delivering 12–16 Gy in a single focused treatment

When recurrent tumor lies close to the optic nerves or optic chiasm, fractionated treatment is often safer than single-session radiosurgery.

Treatment Strategy by Tumor Grade

Management also depends strongly on the WHO tumor grade.

• WHO grade I meningiomas. Recurrence may be managed with observation, repeat surgery, or radiosurgery, depending on tumor growth and symptoms.
• WHO grade II (atypical) meningiomas. These tumors recur more frequently. Postoperative radiotherapy is often recommended, particularly after incomplete tumor removal, although some patients may be managed with close MRI follow-up after complete resection.
• WHO grade III (malignant) meningiomas. These aggressive tumors typically require postoperative radiotherapy regardless of the completeness of surgical removal, together with close imaging follow-up.

Long-Term Monitoring

Because olfactory groove meningiomas may recur many years after treatment, long-term follow-up is essential.

Typical surveillance includes:

• annual MRI for several years after treatment
• longer imaging intervals if the tumor remains stable

Early detection of recurrence allows treatment before major neurological, cognitive, or visual deterioration develops.

Experimental and Targeted Therapies

Several medications have been studied for recurrent or progressive meningiomas when surgery and radiotherapy are no longer sufficient. These include bevacizumab, as well as drugs acting on molecular pathways such as AKT or SMO inhibitors. Somatostatin-receptor–based treatments such as octreotide and combinations including everolimus have also been investigated.

However, current evidence remains limited, and surgery and radiation therapy remain the main treatments for most olfactory groove meningiomas.

When Expert Opinions May Differ

In many patients diagnosed with olfactory groove meningioma, different specialists may recommend different treatment strategies. This is common in neurosurgery and does not necessarily mean that one opinion is correct while another is wrong.

Treatment decisions depend on multiple clinical factors, including:

• tumor size
• tumor location and skull base extension
• growth rate observed on MRI
• presence of surrounding edema or mass effect
• patient age and overall health
• presence or absence of neurological symptoms
• degree of visual risk
• relationship of the tumor to important arteries and optic pathways
• tumor grade if histological diagnosis is already known

Because these factors interact in complex ways, reasonable specialists may arrive at different conclusions regarding the safest management strategy.

Observation vs. Early Surgery

One of the most common differences in opinion occurs when an olfactory groove meningioma is discovered incidentally on MRI and the patient has no obvious symptoms. Some specialists recommend active surveillance, particularly when the tumor is small and shows no signs of growth. Others may recommend earlier surgery, especially if the tumor is located in a position where further growth could later threaten the frontal lobes, optic pathways, or major vessels.

Differences in Surgical Strategy

Even when surgery is recommended, surgeons may disagree about the optimal operative strategy. One surgeon may aim for maximal removal including the involved dura and abnormal bone, while another may prefer a more conservative removal if the tumor is densely adherent to critical arteries or the optic apparatus.

Similarly, some tumors may be approached through microsurgical craniotomy, while others may be considered for endoscopic endonasal surgery in carefully selected cases.

Surgery vs. Radiation Therapy

Another area where opinions may differ involves the use of radiation therapy. Some specialists recommend surgery first, followed by radiation only if residual tumor remains. Others may recommend primary radiation in carefully selected small tumors or in patients with increased surgical risk.

These differences usually reflect different risk assessments, particularly regarding vision, skull base anatomy, and long-term tumor control.

How Prognosis Depends on Tumor Grade, Location, and Extent of Removal

The prognosis of olfactory groove meningioma depends primarily on the biological grade of the tumor, its anatomical relationships, and the extent to which it can be safely removed.

In most patients, olfactory groove meningiomas are WHO Grade I tumors, which usually grow slowly and have a favorable long-term prognosis when treated appropriately.

Functional recovery after treatment varies depending on the structures that were compressed before surgery.

Sense of smell (olfaction). Because the tumor usually compresses the olfactory nerves early, loss of smell is common at diagnosis. When smell has already been completely lost before surgery, recovery is uncommon. However, partial improvement of smell may occur in approximately 10–30% of patients, particularly when olfactory function was only partially impaired before treatment.

Cognitive and behavioral symptoms. Many patients develop subtle frontal lobe symptoms such as slowed thinking, reduced concentration, personality changes, or decreased motivation. After tumor removal and relief of brain compression, significant improvement in cognitive or behavioral symptoms occurs in about 60–80% of patients, although recovery may take several months.

Vision. Visual disturbances may occur when the tumor compresses the optic nerves or optic chiasm. If visual loss is mild and compression is relieved early, visual improvement is observed in roughly 50–70% of patients. When visual impairment has been severe or long-standing, recovery is less likely.

Tumor control is generally very good for benign tumors. When complete or near-complete removal is achieved, long-term tumor control is typically above 85–90%. In cases where a small residual tumor remains, additional treatment with stereotactic radiosurgery or radiotherapy can often provide effective long-term control.

Overall prognosis is most favorable in patients with benign tumors, limited brain edema, preserved vision, and safe near-complete tumor removal. Prognosis is generally less favorable in higher-grade tumors, very large tumors causing severe frontal lobe compression, or cases where only limited tumor removal is possible.

Can an Olfactory Groove Meningioma Become Life-Threatening?

Yes, an olfactory groove meningioma can become life-threatening, although this is not the usual course in most patients.

Most of these tumors grow slowly, and many remain stable for years without causing major neurological problems. However, if the tumor becomes large enough, it may produce severe pressure on both frontal lobes, marked edema, increased intracranial pressure, significant cognitive deterioration, visual compromise, or in extreme cases brain herniation.

The danger therefore does not arise only from the biological nature of the tumor itself, but from its mass effect on vital brain structures.

This risk is higher in:

• large tumors
• tumors with extensive frontal edema
• tumors extending toward the optic pathways or major arteries
• higher-grade meningiomas

For this reason, even though olfactory groove meningiomas are usually benign, they should never be considered harmless solely on the basis of histological grade. Their real clinical significance depends on tumor size, location, rate of growth, and effect on surrounding brain structures.

Frequently Asked Questions About Olfactory Groove Meningioma