Benign Brain Tumors

What "benign" means for a brain tumor

In most of the body, "benign" means harmless. In the brain it is more nuanced. A benign brain tumor:

• is made of cells that look relatively normal under the microscope (low grade, usually WHO grade 1)
• grows slowly and does not spread to other organs
• has clear borders, so it can often be removed completely

But it can still be serious, because a growing mass inside the rigid skull raises pressure and can press on vital structures. Some benign tumors sit in places that make surgery difficult. A few can recur or, rarely, become more aggressive. Benign tumors are more common than malignant primary brain tumors in adults.

Common types

Meningioma

Meningiomas grow from the membranes covering the brain and spinal cord. They are the most common primary brain tumor, especially in women and older adults. Many are small and found by chance. Larger ones cause headaches, seizures, weakness or vision problems depending on their location.

Pituitary adenoma

Pituitary adenomas grow in the pituitary gland at the base of the brain. They may make excess hormones, causing conditions such as prolactinoma (absent periods, milky nipple discharge, low libido), acromegaly (growth hormone) or Cushing's disease (cortisol). Larger tumors press on the optic nerves, causing loss of side vision in both eyes.

Vestibular schwannoma (acoustic neuroma)

An acoustic neuroma grows on the nerve from the inner ear to the brain. It causes gradual hearing loss in one ear, ringing (tinnitus) and imbalance. Tumors on both sides suggest neurofibromatosis type 2.

Other benign tumors

• Craniopharyngioma: near the pituitary, mostly in children and older adults, affecting vision, growth and hormones.
• Hemangioblastoma: in the back of the brain, sometimes linked to von Hippel-Lindau disease.
• Pilocytic astrocytoma: a low-grade tumor most common in children, often curable with surgery.
• Choroid plexus papilloma and colloid cysts: can block fluid flow and cause hydrocephalus.

Symptoms

Symptoms depend on the size and location of the tumor rather than whether it is benign.

From raised pressure:

• headaches, often worse in the morning or with coughing or bending
• nausea and vomiting
• blurred vision from swelling of the optic nerve
• drowsiness

From local pressure:

• seizures
• weakness or numbness on one side
• speech or language problems
• vision changes, including loss of side vision
• one-sided hearing loss and imbalance
• personality, behavior or memory changes
• hormone problems with pituitary tumors

Many benign tumors cause no symptoms and are found on scans done for other reasons.

Causes and risk factors

Most have no known cause. Known risk factors include:

• previous radiation to the head
• inherited conditions such as neurofibromatosis types 1 and 2, von Hippel-Lindau disease and multiple endocrine neoplasia type 1
• for meningiomas: female sex and older age

Mobile phone use has not been shown to cause brain tumors.

Diagnosis

• Neurological examination: strength, reflexes, coordination, vision fields and hearing.
• MRI with contrast: the main test. It shows the tumor's size, location and features.
• CT scan: useful for calcification and bone involvement, or if MRI is not possible.
• Hormone blood tests for pituitary tumors.
• Visual field testing and hearing tests for tumors near the optic or hearing nerves.
• Biopsy: sometimes needed to confirm the type, usually at the time of surgery.

Treatment

Watchful waiting

Small tumors without symptoms, particularly meningiomas and small acoustic neuromas, are often monitored with MRI scans every 6 to 12 months at first, then less often if stable.

Surgery

Surgery aims to remove the whole tumor safely. Complete removal often cures benign tumors. Techniques include:

• craniotomy: opening part of the skull
• endoscopic surgery through the nose for most pituitary tumors
• image guidance and nerve monitoring to protect vital areas

Radiation

• Stereotactic radiosurgery (such as Gamma Knife or CyberKnife): a precise, high dose of radiation in one or a few sessions, used for small tumors or leftover tumor after surgery.
• Fractionated radiation therapy: smaller daily doses for larger tumors or those near sensitive structures.

Medicines

• Dopamine agonists (cabergoline, bromocriptine) shrink most prolactinomas without surgery.
• Medicines that block growth hormone or cortisol for other hormone-secreting pituitary tumors.
• Anti-seizure medicines for seizures.
• Steroids to reduce swelling around the tumor.
• Hormone replacement if the pituitary is underactive after treatment.

Outlook

The outlook for most benign brain tumors is good, especially when the tumor can be completely removed. Some people have lasting effects, such as hearing loss after acoustic neuroma treatment, seizures, or hormone deficiencies after pituitary surgery. Some tumors, particularly meningiomas, can recur, so long-term follow-up scans are recommended.

Frequently asked questions

Is a benign brain tumor dangerous?

It can be. Although it is not cancer and does not spread, it can press on the brain, nerves or blood vessels inside the closed skull. This can cause headaches, seizures, vision loss or other problems. Many small benign tumors, however, never cause symptoms and only need monitoring.

What are the symptoms of a benign brain tumor?

Symptoms depend on location: headaches worse in the morning, seizures, weakness, vision or hearing loss, balance problems, personality changes and hormone problems. Many benign tumors grow slowly and cause no symptoms for years.

Can a benign brain tumor become cancerous?

Rarely. Most benign brain tumors stay benign. A small proportion, such as some meningiomas, can recur and occasionally become more aggressive over time. That is why follow-up MRI scans are recommended even after treatment.

Does a benign brain tumor always need surgery?

No. Small tumors without symptoms are often monitored with regular MRI scans. Prolactinomas usually shrink with medicine. Surgery or radiosurgery is recommended when a tumor causes symptoms, is growing, or is in a location where growth would be dangerous.