What to know about an olfactory groove meningioma

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An OGM is a slow-growing, benign tumor that doctors often diagnose during brain scans for unrelated symptoms. It develops in the meninges.

The meninges are three protective layers that cover the brain, including:

• Dura mater: This is the tough, thick outer layer.
• Arachnoid mater: This is the thin middle membrane.
• Pia mater: This delicate, innermost layer follows the shape of the brain.

Sometimes, clusters of cells grow from the arachnoid mater through the dura mater and into the space around the eye. These are called arachnoid cap cells and are usually harmless. OGMs and other meningiomas can develop from these cells. An OGM develops in a groove at the base of the skull.

According to a 2022 case report, OGMs are a rare type of meningioma that accounts for around 4–18% of meningioma diagnoses and 2% of all brain tumors overall.

They are more common in females than males. In the United States, OGMs may develop in around 0.008% of females and 0.003% of males yearly.

However, the American Cancer Society considers meningiomas to be the most common type of brain tumor, even though they do not strictly occur inside the brain.

OGMs do not often cause symptoms until they reach at least 4 centimeters. Once OGMs reach this size, they may compress areas of the brain and nervous system, including the optic nerve and the frontal lobe.

When they occur, symptoms most commonly include the following:

• reduced or absent sense of smell — anosmia
• headaches
• personality changes

Other symptoms might include:

• vision problems
• seizures
• high blood pressure in the skull

Tumors develop as a result of changes in the genes that inform cells to grow and divide. These might occurs due to:

• errors as cells split
• damage to the DNA of the cells from outside sources
• genes that parents pass on to children

However, the underlying causes of these gene changes remain unclear. Several factors might increase a person’s risk for OGMs, including:

• genetic conditions that cause excessive tumor growth, which might include:
  • neurofibromatosis type 2
  • schwannomatosis – a rare form of neurofibromatosis
  • Gorlin syndrome
• radiation-linked factors, such as:
  • radiation therapy for other conditions
  • exposure to ionizing radiation
• hormonal factors, including:
  • hormone replacement therapy
  • exposure to sources of hormones outside of the body
  • breast cancer
  • the use of oral birth control
• having obesity
• alcohol use disorder

No strong evidence suggests that using a cell phone or experiencing head trauma can increase a person’s risk of developing OGM.

A doctor often does not recommend treatment for individuals with a small OGM or a tumor that does not cause symptoms. They may advise continued observations.

A doctor may also arrange checkups and monitor the growth of the tumor every 6 months through scans.

According to a 2023 systematic review, treating OGMs aims to:

• relieve compression on the frontal lobe
• restore vision and sense of smell
• remove all of the tumor to prevent it from returning

Surgeons can achieve this through two possible surgical procedures: craniotomy and endoscopic endonasal approach (EEA).

A craniotomy involves removing a section of the skull, and EEA involves entering through the nose to perform surgery on the brain or top of the spine.

Both procedures may require a hospital stay of around 5–7 days and roughly 2–3 weeks of recovery at home.

Doctors may also propose stereotactic radiation therapy for people, depending on the location of the tumor.

Craniotomy

Craniotomy involves the following:

• removing part of the skull
• completing necessary surgical procedures
• reattaching the skull

For people with an OGM, a surgeon will remove part or all of the tumor where possible while preserving the surrounding brain tissue.

EEA

This type of surgery involves inserting a lighted, flexible tube called an endoscope through the nose. During the procedure, a neurosurgeon and an ear, nose, and throat surgeon work together to remove the tumor.

A 2018 review concluded that EEA surgery is effective for small OGM tumors that have already removed a person’s sense of smell. This procedure may also be helpful alongside craniotomy surgery for tumors that return after treatment and move into the nose.

Stereotactic radiation therapy

A doctor may also request this procedure if the tumor is not close to the eye or nerves or if the individual’s age or overall health means they are not likely to tolerate surgery well. However, this is not an extended course of radiation therapy, as with some cancers. Instead, doctors will often give a single dose of high powered radiation therapy in one session.

People who receive stereotactic radiation will often be able to return to most typical activities within a week, although they might not experience immediate improvements in their sense of smell. Radiation therapy might cause nausea, headaches, and fatigue as side effects.

Most people with an OGM have a good outlook and remain tumor-free for 5 years. A 2018 study found that in a sample of 43 people who received treatment for an OGM, the tumor returned within 5 years for 11.6% of the participants.

The study authors identified certain factors and features of the tumor that may make recurrence more likely, including:

• swelling, or edema, around the tumor
• a soft texture in the tumor instead of hard tissue
• an overgrowth of bony tissue near the tumor — hyperostosis
• thickening of the dura mater around the tumor — dural tail sign

A 2021 analysis followed the symptoms of 17 people who underwent OGM resection. The researchers found that people showed overall cognitive impairment straight after the procedure but that this improved in most areas over the next year.

However, scores ranking cognitive flexibility, memory, inhibition, and attention remained lower after a year than the average scores of people without an OGM.

An OGM develops in the brain’s outer layer and grows along the nerves connecting the brain to the nose. They grow slowly and may not show symptoms for years. However, this rare, benign tumor can affect vision, sense of smell, and cognition.

Treatment often involves removing part or all of the tumor, either through open surgery on the skull or via the nose. Most people recover fully and have a good outlook. However, the tumor returns for some people.