Olfactory Groove Meningioma

Our Specialists for Olfactory Groove Meningioma

Olfactory groove meningiomas grow slowly in one of the most forgiving-looking parts of the brain — until they don't. By the time most patients notice something is wrong, the tumor is often already large and pressing on the optic nerves, the frontal lobes, and the major arteries that feed them. Getting all of it out, through the right corridor, is the difference between a cure and a complication.

Peleg Horowitz, M.D., Ph.D.

Co-Director, Pituitary & Neuroendocrine Disorders Program

Dr. Horowitz is a skull base and neuro-oncology surgeon who also serves as Director of Quality and Associate Program Director for the Neurological Surgery residency. His laboratory research has identified novel genes driving meningioma and pediatric glioma formation, with work published in Nature Genetics and PNAS, and is funded by the DoD Neurofibromatosis Research Program. He holds a PhD in neuroscience from Northwestern and completed residency at Brigham and Women's/Boston Children's with a skull base fellowship at MD Anderson. Dr. Horowitz co-directs UChicago's anterior skull base program and routinely tailors the corridor for olfactory groove meningiomas — bifrontal, unilateral subfrontal, supraorbital keyhole, or endoscopic endonasal — to the specific anatomy of each tumor. His laboratory has also published on the molecular drivers of meningioma formation, which increasingly informs how we decide on adjuvant treatment after resection.

Rohaid Ali, M.D.

Director, Endoscopic Neurosurgery

Dr. Ali is Director of Endoscopic Neurosurgery at UChicago, specializing in minimally invasive keyhole approaches to skull base and intracranial lesions. His practice focuses on endoscopic techniques for pituitary and skull base tumors, using narrow corridors through the nose or small cranial openings to reach deep lesions with minimal disruption of surrounding tissue. As Director of Endoscopic Neurosurgery at UChicago, Dr. Ali leads the endoscopic endonasal program — the minimally invasive corridor through the nose that is often the right answer for smaller, midline olfactory groove meningiomas that have already eroded into the cribriform plate. He works in a combined two-surgeon, four-handed technique with our otolaryngology skull base partners for these cases.

Bakhtiar Yamini, M.D.

Vice Chair for Academic Affairs; Director, Neurosurgical Oncology

Dr. Yamini is a brain tumor surgeon and scientist who serves as Vice Chair for Academic Affairs and Director of Neurosurgical Oncology at UChicago. In the operating room, he uses advanced imaging and navigation tools for stereotactic biopsy, laser ablation, and image-guided maximal resection. In his lab, he runs NIH-funded research into why some tumors resist treatment and into biodegradable nanoparticle vectors that deliver drugs directly to CNS tumors. Dr. Yamini directs neurosurgical oncology at UChicago and sees anterior skull base meningioma patients in combined clinic with radiation oncology and neuro-oncology, so the plan for an olfactory groove meningioma — observation, surgery, radiosurgery, or a combination — is made by the whole team on the same day. His laboratory also investigates the molecular biology of brain tumors, including drivers of meningioma recurrence.

What Is an Olfactory Groove Meningioma?

An olfactory groove meningioma is a tumor that grows from the meninges — the thin protective lining of the brain — right over the cribriform plate and planum sphenoidale, the bony floor of the front of the skull. That floor is the roof of your nasal cavity and sits directly under the undersurface of the frontal lobes. These tumors tend to push the frontal lobes up and backward as they grow, and eventually they reach down toward the optic nerves and the arteries supplying the front of the brain.

About 10% of all intracranial meningiomas arise in this location, which makes olfactory groove meningiomas one of the more common anterior skull base tumors. Like most meningiomas, they are usually benign (WHO grade 1 in roughly 90% of cases), they grow slowly over years, and they do not invade the brain itself. What makes them tricky is not the tumor biology — it's the real estate. A few millimeters separate the tumor from the optic nerves, the olfactory nerves, and the anterior cerebral arteries that feed both frontal lobes.

Because the frontal lobes can accommodate a tumor for a surprisingly long time, many olfactory groove meningiomas are already large at the time of diagnosis — it is not unusual for them to be 4, 5, or even 6 centimeters across when first discovered. The size and the lateral reach of the tumor are the biggest factors that decide which surgical approach is right for you.

What Does It Feel Like?

Olfactory groove meningiomas are famous for presenting late. The frontal lobes — especially the undersurface — tolerate slow compression unusually well, and the early symptoms are subtle enough that they're often attributed to aging, stress, or depression. When symptoms do appear, they usually come in three patterns.

Loss of smell (anosmia)

• Gradual loss of the sense of smell, usually in both nostrils, because the tumor stretches and destroys the olfactory nerves that run along its undersurface
• A related dulling of taste (most of what we call taste is actually smell)
• Many patients only notice the anosmia when someone else points it out — or when they fail to notice a gas leak, smoke, or spoiled food

Frontal lobe syndrome

• Personality change — apathy, loss of initiative, flat affect, or, less commonly, disinhibition and impulsivity
• Slowed thinking, trouble planning or following through on tasks
• Memory lapses and new difficulty with concentration
• Family members often describe the patient as "not themselves" for months or years before the diagnosis — these changes are routinely mistaken for depression or early dementia

Visual symptoms

• Gradual loss of vision in one eye, often in a pattern the patient describes as a graying or dimming rather than blurring
• The classic Foster-Kennedy syndrome — optic atrophy (nerve damage) in one eye from direct tumor compression, combined with papilledema (swelling of the optic disc) in the other eye from raised pressure inside the skull
• Headaches, especially in the forehead, that get worse with coughing, straining, or lying flat
• New-onset seizures in a minority of patients

Any combination of unexplained loss of smell, a personality change, and a vision problem deserves an MRI. Catching an olfactory groove meningioma before the optic nerves and frontal lobes are permanently injured is far easier than trying to reverse the damage afterward.

How Is It Diagnosed?

The diagnosis almost always starts with MRI of the brain with and without contrast. Olfactory groove meningiomas have a very recognizable appearance: a rounded or lobulated mass sitting on the floor of the front of the skull, enhancing brightly with contrast, and typically showing a dural tail along the cribriform plate and planum sphenoidale. MRI also tells us exactly where the optic nerves, anterior cerebral arteries, and optic chiasm are in relation to the tumor — the details that determine which surgical corridor is safest.

A CT scan is almost always added, because CT shows bone in a way MRI cannot. It tells us whether the tumor has caused hyperostosis (thickening) or erosion of the cribriform plate, whether there is extension down into the ethmoid sinuses or nasal cavity, and whether the frontal sinus is in the surgical path. CT angiography or MR angiography maps the anterior cerebral arteries (the A2 segments), which are often draped over the top of these tumors and must be preserved.

A formal ophthalmology evaluation with visual acuity, visual fields, and optic nerve assessment is essential before surgery. Subtle field defects are often the first objective sign of optic nerve compression, and establishing a baseline matters for tracking recovery after surgery. Formal olfactory testing is sometimes added when preserving smell is a realistic goal.

The definitive diagnosis — the pathologic confirmation that a tumor is a meningioma and its WHO grade — is made after surgery, when the tissue is examined under the microscope. Today, molecular testing is increasingly part of that workup: specific genetic changes can upgrade a meningioma's grade and change recommendations about adjuvant radiation.

Types of Olfactory Groove Meningioma

Olfactory groove meningiomas are grouped less by their microscopic subtype (they are almost all benign WHO grade 1) and more by their size and their relationship to nearby structures. That anatomy is what actually drives the surgical plan.

By size

• Small (less than 3 cm) — often discovered incidentally on an MRI ordered for something else. For carefully selected patients, these can sometimes be watched; when surgery is needed, minimally invasive options like a supraorbital keyhole or, in select cases, an endoscopic endonasal approach are on the table.
• Medium (3-5 cm) — usually symptomatic, often with anosmia and mild frontal symptoms. Most can be removed through a unilateral transcranial corridor with very good results.
• Large and giant (greater than 5 cm) — these are the classic late-presenting tumors. They typically require a more generous transcranial exposure (either bifrontal or a wider unilateral subfrontal) to safely separate the tumor from the optic nerves, the A2 segments, and both frontal lobes.

By relationship to the superior sagittal sinus and A2 arteries

• Tumors that push the anterior cerebral arteries up and over the back of the mass are more technically demanding — the A2 branches must be carefully dissected off the tumor capsule so they are not kinked or torn during removal.
• Tumors that extend posteriorly toward the anterior edge of the superior sagittal sinus require venous mapping ahead of time; injury to the sinus in this region can cause hemorrhage or venous infarction.

By relationship to the optic chiasm

• More posterior tumors reach the tuberculum sellae and optic chiasm, and the planning overlaps with a separate category of skull base meningioma (tuberculum sellae meningioma). For these, decompression of the optic nerves is the first priority.

By extension into the nasal cavity or sinuses

• A subset of tumors erode through the cribriform plate into the ethmoid sinuses and nasal cavity. This is where the endoscopic endonasal approach shines — because the tumor is already in the nose, removing it from below, along with the involved bone and dura, can be more direct than coming from above.
• Tumors with significant lateral extension over the orbits, or that wrap around the optic nerves and A2 arteries laterally, are generally better addressed through a transcranial corridor, where those structures can be seen and protected directly.

How Is It Treated?

Should this tumor come out at all?

For a small, asymptomatic olfactory groove meningioma found incidentally — especially in an older patient with other medical problems — the right answer is sometimes to watch it with serial MRIs at 6 months, then yearly. For any tumor that is symptomatic, growing on imaging, or pressing on the optic apparatus, surgery is the treatment of choice, because complete removal is usually curative.

The surgical corridor — choosing the right approach

There is no single best operation for olfactory groove meningioma. The corridor is chosen based on tumor size, its lateral reach, how far it extends down into the nose, its relationship to the A2 arteries and optic nerves, and the patient's goals around smell and vision preservation.

Bifrontal craniotomy

A traditional bifrontal approach — opening the bone across both sides of the forehead — gives the widest possible view of the anterior skull base and is particularly useful for large and giant tumors or tumors with significant bony involvement of the cribriform plate on both sides. It allows complete removal of the dural attachment and involved bone in a single piece (a Simpson grade 1 resection). The trade-off is a larger exposure and, in older series, a somewhat higher rate of minor complications than unilateral approaches.

Unilateral subfrontal or frontolateral craniotomy

For most tumors, we can remove the entire lesion through a unilateral craniotomy — either a subfrontal approach from directly above the eyebrow or a frontolateral approach from just behind it. A pooled analysis of more than 1,000 patients showed that unilateral corridors have lower overall complication rates than bifrontal approaches while still achieving equivalent rates of complete resection, even for sizeable tumors. The unilateral approach also tends to do better at preserving the olfactory nerve on the uninvolved side.

Supraorbital "keyhole" craniotomy

For smaller and medium-sized tumors that don't extend far laterally, a supraorbital keyhole — a small, roughly 3 cm craniotomy hidden in the eyebrow — offers a minimally invasive corridor to the anterior skull base. Meta-analyses report gross total resection rates around 85% for olfactory groove meningiomas removed this way, with minimal frontal lobe retraction and excellent cosmetic results. It is not the right approach for a 6 cm giant — but for the right tumor and the right patient, it is a powerful option.

Endoscopic endonasal approach

For carefully selected tumors — particularly those that are smaller, that sit in the midline without wide lateral extension, and that have already eroded through the cribriform plate into the nose — a purely endoscopic endonasal approach can remove the tumor from below, through the nostrils, without any skin incision or brain retraction. The trade-offs are real: the endonasal approach sacrifices olfaction on the involved side, has a higher rate of cerebrospinal fluid (CSF) leak than transcranial approaches, and is not the right choice for tumors that extend laterally beyond the optic nerves or that encase the A2 arteries. When offered to the right patient, though, it can shorten recovery and improve visual outcomes.

Protecting vision and the arteries

Whichever corridor we choose, the same principles apply: early internal decompression of the tumor (taking the bulk out from the inside) so the capsule can be collapsed away from the optic nerves, sharp microsurgical dissection to separate the tumor from the A2 arteries without kinking or coagulating them, and meticulous skull base reconstruction with a vascularized flap to keep CSF where it belongs. Intraoperative navigation, high-field microscopes, and (for endonasal cases) endoscopic visualization are standard parts of our anterior skull base setup.

Radiation therapy — when, and when not

For WHO grade 1 tumors that are completely removed, radiation is not needed. For residual tumor that could not be safely removed, for grade 2 (atypical) tumors, or for recurrences, stereotactic radiosurgery (a single focused dose, usually Gamma Knife) or fractionated radiation are excellent adjuncts. Long-term control rates for radiosurgery applied to residual benign meningiomas approach 90%.

What Are the Outcomes?

For olfactory groove meningiomas, outcomes are driven by three things: how much of the tumor is removed (the Simpson grade), whether the optic nerves are decompressed in time, and whether the A2 arteries and their small branches stay intact. When complete removal is achieved, most patients are essentially cured, and the large majority of preoperative visual and cognitive deficits improve.

A few things are worth emphasizing. First, the biggest predictor of long-term control is whether the tumor and its dural attachment are completely removed the first time — which in turn depends on the surgical corridor and the surgeon's comfort operating around the optic apparatus and A2 arteries. Second, the frontal lobe changes that many patients describe — apathy, slowed thinking, loss of initiative — usually improve significantly after the tumor is decompressed, though the timeline can stretch over many months. Third, even with a Simpson grade 1 resection, late recurrences do happen; regular MRI follow-up for at least 10 years is part of the plan.

The single most important thing you can control is the experience of the team doing your operation. Olfactory groove meningiomas are uncommon enough that a center's cumulative volume makes a real difference — in choosing the right corridor, in protecting your vision, and in getting you to a cure on the first attempt.

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