What is Edward Kennedy's diagnosis?

Senator Kennedy will undergo radiation therapy after his surgery

The news that veteran US Senator Edward Kennedy has contracted brain cancer has focused public attention on gliomas - the form of malignant tumour with which he has been diagnosed.

Gliomas - which are more likely to occur in older people - are one of the most common types of brain tumour.

They account for some 42% of all brain tumours, and 77% of malignant brain tumours.

Like other cancers, gliomas are made up of abnormal cells which multiply and spread through the affected area, causing pain and restricting bodily function.

But unlike some cancers, malignant brain tumours rarely spread to other organs.

Language and movement

Doctors have categorised several subtypes of glioma, and rate them on a numerical scale according to how aggressive they appear to be.

Mr Kennedy's glioma is located in the parietal section of the upper-left side of his brain.

This area of the brain governs the body's movement and ability to understand language.

Mr Kennedy has undergone surgery to have the cancerous cells taken out.

Gliomas 42% of all brain tumours are gliomas 77% of all malignant brain tumours are gliomas Glioma patients over the age of 70 have lower survival rates

"With malignant tumours like this you need to remove as much as you safely can," says Dr Anthony Caputy, Professor of Neurosurgery at George Washington University.

"Senator Kennedy's surgeons will have used a number of 'neuronavigation techniques' to map out the cancerous areas of his brain," he adds.

"They can stimulate his brain, either with electrical signals or by bringing him back to consciousness and performing language tests on him. Using imaging devices, they are then able to map out the areas that are healthy."

With the surgery complete, Mr Kennedy will now undergo a course of radiation, as well as chemotherapy, in an attempt to eradicate all traces of the cancerous material.

No details have been given as to Mr Kennedy's prospects for recovery, although doctors say that glioma patients over the age of 70 have a much lower survival rate.

Some 13,070 Americans will die as a result of brain or nervous system cancers this year, and 21,810 people overall will develop them, according to the American Cancer Society.