Brain tumours are the second commonest type of cancer in children and adolescents; with leukaemia, they make up over 50% of cancers diagnosed in patients under the age of 15. Surgical resection is the most common treatment for paediatric brain tumours, as for adult ones, and if the whole tumour can be removed the prognosis is good. Paediatric neurosurgery, however, is an exceptionally delicate and complex procedure, even more so than neurosurgery in adults. The interior of the brain is "a sphere with few landmarks" and it is very challenging to remove all diseased tissue precisely while sparing the surrounding normal tissue. The pre-operative MRI scans that are in routine use for neurosurgery in all developed countries do not provide a complete solution, because the brain moves as soon as the head is opened and further shift occurs as the tumour is resected, making navigation inaccurate.

The most up-to-date MRI technology, however, allows images of the brain to be updated regularly during surgery, providing guidance that is analogous to that provided by car satellite navigation systems. Since December 2009, the Alder Hey Children's Hospital in Liverpool, UK, has been able to offer this intra-operative magnetic resonance imaging to its young brain tumour patients, using a 3-Tesla scanner and a guidance system from the specialist imaging technology company Brainlab. This was the first such facility for children to be installed in Europe and only the second in the world.

The system was described by Sasha Burn, a consultant paediatric neurosurgeon at Alder Hey hospital, and Chris Davis of BrainLab at a Royal Society of Medicine meeting to discuss medical innovations on 24 February 2011. "The facility to update MRI scans during an operation removes the problem of brain shift, and reduces the likelihood that a highly skilled surgeon will damage healthy tissue by mistake or leave tumour tissue untouched", said Burn. Davis illustrated the extent of the latter problem by quoting clinical research suggesting that on average 25% of operations on brain tumours fail to remove the whole of the tumour.

Davis described the BrainSuite intra-operative MRI system, which uses technology for updating images that was first developed in the computer gaming industry, in detail. Each installation is built to order to fit the requirements of a specific client. The operation begins based on pre-operative images and then when the time is right an intra-operative MRI scan is performed with the wound still open. The new images from this scan are then uploaded onto the navigation system giving precise an accurate guidance mid-operation. The system installed at Alder Hey is a two-room one, with the scanner in a different room from the operating theatre; in other systems, such as one in London, all the equipment is installed in a single room and the patient rotates into the magnet. "Future intra-operative MRI machines are likely to provide images that update in real time, but we're not quite there yet", said Davis.

The intra-operative MRI scanner at Alder Hey is now being used to treat at least one paediatric brain tumour patient a week, ranging from babies to young adults who were diagnosed as children and who can remain under the care of the children's hospital until their early twenties. It can be used for all types of brain tumour, even diffuse ones. "This type of guidance will always help surgeons, even when the tumour boundaries are poorly defined", said Burn. Although it is still too early to measure long-term outcomes, surgeons and their young patients are already seeing benefits as the number of cases where second or subsequent resections are required has been substantially reduced.