Olfactory Groove Meningioma

Olfactory groove meningiomas are noncancerous tumors located on the skull base beneath the frontal lobes. These tumors can affect surrounding structures and require surgical removal to protect neurological function and vision. The experience of the surgical team is essential to achieving optimal outcomes during these procedures.

What Is Olfactory Groove Meningioma?

An olfactory groove meningioma is a tumor that grows from the meninges right over the cribriform plate and planum sphenoidale, the bony floor of the front of the skull. It sits directly under the undersurface of the frontal lobes. About 10% of all intracranial meningiomas arise here.

Like most meningiomas, they are usually benign (WHO grade 1 in roughly 90% of cases) and grow slowly. Because the frontal lobes can accommodate a tumor for a surprisingly long time, many are already 4-6 cm at diagnosis.

At a Glance

Olfactory groove meningiomas are benign tumors (WHO grade 1 in ~90% of cases) that grow from the dura overlying the cribriform plate
Because they grow silently, many are already 4-6 cm at diagnosis — with classic symptoms of loss of smell, personality change, and visual decline
Complete removal is curative for most patients, with 10-year recurrence-free survival above 85% after Simpson grade 1 resection
We tailor the approach — bifrontal, unilateral subfrontal, supraorbital keyhole, or endoscopic endonasal — to each tumor
Protecting vision and the arteries feeding the frontal lobes is the single biggest factor in a good outcome

Symptoms

Loss of smell (anosmia)

Gradual loss of the sense of smell, usually in both nostrils
Many patients only notice it when someone else points it out

Frontal lobe syndrome

Personality change — apathy, loss of initiative, flat affect, or disinhibition
Slowed thinking, trouble planning or following through on tasks
Family members often describe the patient as 'not themselves' for months or years

Visual symptoms

Gradual loss of vision in one eye — often described as graying or dimming
Foster-Kennedy syndrome — optic atrophy in one eye, papilledema in the other
Headaches, especially in the forehead

Any combination of unexplained loss of smell, personality change, and vision problem deserves an MRI.

Diagnosis

MRI of the Brain (With and Without Contrast)

Classic appearance: a rounded or lobulated mass sitting on the floor of the front of the skull, enhancing brightly with contrast, with a dural tail.

CT Scan

Shows bone detail — hyperostosis or erosion of the cribriform plate, extension into the ethmoid sinuses or nasal cavity.

CT or MR Angiography

Maps the anterior cerebral arteries (A2 segments), which are often draped over the top of these tumors.

Formal Ophthalmology Evaluation

Visual acuity, visual fields, and optic nerve assessment before surgery to establish a baseline.

Molecular Testing

After surgery, specific genetic changes can upgrade a meningioma's grade and change recommendations about adjuvant radiation.

Types

By Size

Small (<3 cm) — often incidental; supraorbital keyhole or endoscopic endonasal approaches possible
Medium (3-5 cm) — usually symptomatic; most can be removed through a unilateral transcranial corridor
Large/giant (>5 cm) — typically require bifrontal or wider unilateral subfrontal exposure

By Relationship to A2 Arteries

Tumors that push anterior cerebral arteries over the back of the mass are more technically demanding.

By Extension into the Nasal Cavity

A subset erodes through the cribriform plate into the ethmoid sinuses — where the endoscopic endonasal approach shines.

Treatment

Bifrontal Craniotomy

Widest possible view of the anterior skull base; particularly useful for large/giant tumors or with significant bilateral bony involvement. Allows complete Simpson grade 1 resection.

Unilateral Subfrontal or Frontolateral Craniotomy

For most tumors. Lower overall complication rates than bifrontal while achieving equivalent rates of complete resection.

Supraorbital 'Keyhole' Craniotomy

Small ~3 cm craniotomy hidden in the eyebrow. Meta-analyses report gross total resection rates ~85% for olfactory groove meningiomas. Excellent cosmetic results.

Endoscopic Endonasal Approach

For carefully selected tumors — smaller, midline, without wide lateral extension, that have eroded through the cribriform plate. Higher CSF leak rate; not for laterally extending tumors.

Radiation Therapy

Not needed for WHO grade 1 completely removed. Stereotactic radiosurgery for residual tumor, grade 2, or recurrences. Long-term control rates approach 90%.

Outcomes

Outcome	Typical result	What to know
Gross total resection (transcranial)	~90-95%	Simpson grade 1 or 2 achievable in most cases
Gross total resection (endoscopic endonasal)	~70-85%	Best for smaller, midline tumors
Visual improvement when affected	~60-80%	Higher after endonasal decompression in selected cases
Preservation of olfaction (transcranial, unilateral)	~30-50%	Best when preoperative smell preserved on uninvolved side
5-year recurrence-free survival (complete resection)	>90%	Very good when Simpson 1 achieved
10-year recurrence (modern series)	~5-15%	Long-term MRI follow-up essential

The biggest predictor of long-term control is whether the tumor and dural attachment are completely removed the first time.

References

Nakamura M, et al. Olfactory groove meningiomas: clinical outcome and recurrence rates. Neurosurgery. 2008;62(6 Suppl 3):1224-1232. PMID: 18695543
Koutourousiou M, et al. Endoscopic endonasal surgery for olfactory groove meningiomas: outcomes in 50 patients. Neurosurg Focus. 2014;37(4):E8. PMID: 25391163
Bamimore MA, et al. Smell outcomes in olfactory groove meningioma resection: systematic review and meta-analysis. World Neurosurg. 2022;160:22-32. PMID: 35033688
Khan DZ, et al. The endoscope-assisted supraorbital 'keyhole' approach for anterior skull base meningiomas: updated meta-analysis. Acta Neurochir. 2021;163(3):661-676. PMID: 32889640
Goldbrunner R, et al. EANO guideline on the diagnosis and management of meningiomas. Neuro-Oncology. 2021;23(11):1821-1834. PMID: 34181733

Our Specialists

Peleg Horowitz, MD, PhD

Neurosurgery

Bakhtiar Yamini, MD

Neurosurgery

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