Benign vs Malignant Brain Tumours

Benign and malignant brain tumours differ in two ways that decide treatment: spread and removability. A benign brain tumour is a non-cancerous growth that never spreads elsewhere in the body and, in most cases, can be removed completely by surgery. A malignant brain tumour is a cancer: it can spread within the nervous system to the spine and usually cannot be removed completely.

Dr. Sonal Gupta, Principal Director & HOD Neuro and Spine Surgery, Fortis Hospital, Shalimar Bagh, New Delhi, India, starts her account of brain tumours with that distinction. Her framework for referring doctors runs in a clear order: understand where the tumour arises and whether it is benign or malignant, recognise the symptoms that justify a scan, confirm the diagnosis with imaging and biopsy, and then match the treatment to the tumour. This guide sets out the classification and its consequences; the companion articles cover brain tumour headache red flags and when to scan and brain tumour surgery versus radiosurgery in depth.

What is a brain tumour?

A brain tumour is an abnormal growth of cells inside the skull, in the same way that a tumour elsewhere in the body is an abnormal growth of cells in that organ. Dr. Gupta describes three places a brain tumour can arise from:

• The skull bone that covers the brain.
• The meninges, the membranes that wrap the brain.
• The brain tissue itself.

Within the benign group, she names three origins:

• Meningiomas arise from the meninges, the covering membranes of the brain.
• Nerve sheath tumours arise from the sheaths of the nerves that run beneath the brain. Because these nerves sit at the base of the skull, these growths are classed as skull base tumours.
• Pituitary tumours arise from the pituitary gland, the hormone-producing gland at the base of the brain.

Benign vs malignant brain tumours: the key differences

A benign brain tumour is a non-cancer tumour that does not spread and can usually be removed completely; a malignant brain tumour is a cancer that can spread and usually cannot. Dr. Gupta frames treatment goals around that difference.

The reason a malignant tumour often cannot be fully removed is biological, not technical. Diffusely infiltrating cancers such as high-grade gliomas can never be removed completely: microscopic cancer cells are always left behind in the surrounding brain, even when every visible part of the tumour has been taken out. This is why surgery for a malignant tumour is usually followed by further treatment rather than being the whole plan.

Benign tumours are different. The primary aim of an operation for a benign tumour is to take the whole tumour out. Where a very large benign tumour cannot safely be removed in one sitting, or a fragment remains attached to a nerve, Dr. Gupta uses staged surgery or radiosurgery (highly focused radiation delivered without an incision) to finish the job, as described in the companion treatment article.

Can a scan tell benign from malignant?

Not with certainty. Dr. Gupta explains that CT, MRI and MR spectroscopy (an MRI technique that measures the chemical make-up of tissue) together distinguish benign from malignant tumours with an accuracy of about 90%. Only a biopsy, the examination of tumour tissue under the microscope, confirms whether a tumour is benign or malignant and establishes its grade. Grade describes how aggressive the tumour cells look, and it shapes every decision that follows surgery.

Symptoms, by contrast, cannot make this distinction at all. A headache, a seizure or weakness in a limb indicates that a tumour may be present; it says nothing about whether that tumour is benign or malignant.

Primary vs secondary brain tumours

The second axis of classification is where the tumour started: inside the skull, or elsewhere in the body.

• Primary brain tumours begin inside the skull, in the brain tissue or its coverings.
• Secondary brain tumours, also called brain metastases, are cancers that have spread to the brain from elsewhere in the body.

Among primary brain tumours, about 70% are non-malignant, chiefly meningiomas and pituitary tumours, and about 30% are malignant. In adults, brain metastases from cancers elsewhere are more common than primary brain tumours; Dr. Gupta noted that about 25% of people with cancer will develop spread of that cancer to the brain.

For metastases, her principle for surgery is restrictive and clear. An operation is advised only when there is a single large tumour in the brain, or when there are several tumours but one of them is life-threatening. The logic is that surgery is reserved for the tumour that is either too large to leave or dangerous enough to threaten life on its own.

What causes brain tumours

For most patients, the exact cause of a brain tumour is not known. Dr. Gupta is direct on this point: only a few factors are known to precipitate a brain tumour.

• Radiation exposure. Excessive radiation exposure, including high-dose X-rays, can cause brain tumours.
• Genetic predisposition. In a small number of families, one member has a particular type of tumour and other family members go on to develop the same type. Family history is a recognised risk factor, but genes play the major role in only very few patients.
• HIV infection. A very small proportion of people who are HIV positive are predisposed to certain types of brain tumour. The best-established example is primary central nervous system lymphoma, a cancer of immune cells that is strongly associated with weakened immunity.
• Previous head injury. Dr. Gupta notes that a very small number of patients who have had a head injury develop a meningioma 5 to 10 years later.

Brain tumours can occur at any age, from newborns to older adults.

The most common brain tumours in adults and children

The most common primary brain tumours in adults are meningioma, pituitary tumours and astrocytic tumours including glioblastoma, with oligodendroglioma a less common glioma; in children, they are astrocytoma, medulloblastoma, ependymoma and brainstem glioma. The tumour types differ sharply between the two groups.

In adults, the most common primary brain tumours Dr. Gupta lists are:

• Astrocytoma, a tumour of the star-shaped supporting cells of the brain (astrocytes), ranging from slow-growing to highly aggressive forms.
• Meningioma, usually benign, arising from the meninges.
• Pituitary tumours, usually benign, arising from the hormone-producing gland at the base of the brain.
• Oligodendroglioma, a less common tumour of the cells that produce the insulating myelin around nerve fibres.

In children, the most common primary brain tumours are:

• Medulloblastoma, a malignant tumour that arises in the cerebellum at the back of the brain.
• Astrocytoma, which in children is frequently low grade.
• Ependymoma, a tumour of the cells lining the fluid-filled spaces (ventricles) of the brain.
• Brainstem glioma, a tumour of the brainstem, the part of the brain that controls breathing, swallowing and eye movements.

Dr. Gupta's guidance on children is that a brain tumour is identified in the same way as in an adult, and the operation itself is the same. The difference lies in radiotherapy and chemotherapy, which have to be modified according to the child's age. For a fuller picture of childhood brain and other solid tumours, see Dr. Arun Singh Danewa's guide to childhood solid tumours.

Brain tumour symptoms that warrant a scan

Brain tumour symptoms depend on three things: the size of the tumour, its type and its location in the brain. A small tumour in a critical area can cause more trouble than a large one in a quieter region. When symptoms suggest a tumour, the patient needs a CT scan or an MRI.

Not every headache is a brain tumour. Dr. Gupta identifies specific headache characteristics that should prompt a scan, including headache that is worse in the early morning, headache aggravated by coughing, sneezing or exercise, and headache relieved by vomiting. Seizures, vision or hearing problems, paralysis, memory loss and changes in behaviour or personality are also on her list. The full set of red flags, the imaging sequence and the specific advice for newborns and adults with a first seizure are covered in the companion article on headache red flags and diagnosis.

How brain tumours are treated

Dr. Gupta describes four treatment modalities: surgery, radiotherapy, chemotherapy and radiosurgery. Options include each of these alone or a combination of treatments, chosen according to whether the tumour is benign or malignant, how large it is and where it sits.

Two technologies define her surgical practice: computer-assisted neuronavigation, which locates the tumour during the operation and makes keyhole surgery possible, and a high-end, surgeon-controlled robotic microscope that helps remove the tumour without damaging the surrounding brain. For malignant tumours, she adds a genetic study of the tumour and, where appropriate, targeted immunotherapy to surgery, radiotherapy and chemotherapy. How these options are chosen, including when radiosurgery is the better first step and when it is not, is the subject of the companion article on surgery versus radiosurgery. Indicative prices for tumour removal are listed on the craniotomy and brain tumour excision cost page.

Brain and spine services at Fortis Hospital, Shalimar Bagh

Dr. Gupta heads the neurosurgery department at Fortis Hospital, Shalimar Bagh, which is equipped for complex brain and spine surgery. The department's work extends well beyond brain tumours:

• Brain: brain tumour treatment, stroke treatment, paediatric neurosurgery including shunts (tubes that drain excess fluid from the brain), brain infections, epilepsy surgery, and deep brain stimulation for Parkinsonism.
• Spine: treatment of all spine diseases, including keyhole spine surgery for disc problems and spine fractures, microscopic surgery for benign and cancerous spine tumours, tuberculosis infections of the spine, and spine injuries.

Questions from international doctors, on epilepsy surgery, newborn screening, surgical complications and specific patient cases, are answered in the Live Discussion with Dr. Sonal Gupta. More on the specialty is collected on the neuro and spine surgery hub.