SHAKEN BABY syndrome has only recently been recognised by experts as a form of child abuse. Vigorous shaking can cause brain damage in the same way as banging a baby's head against a hard surface. But because it leaves no bruise or mark, it is harder to detect.

Shaking causes damage when the tiny veins inside the skull supplying blood to the brain become torn and start to bleed. A baby's head is big for its body, it has weak neck muscles and its brain is pliable and mobile within the skull. It is therefore more vulnerable than an adult brain.

Blood leaks into the space between the membranes, or meninges, surrounding the brain, forming a subdural haemorrhage. In some cases this may cause no problems but in others it can have serious effects. Symptoms may range from temporary lethargy or feeding difficulties to more serious problems.

A major bleed that leads to swelling and increased pressure on the brain can cause death or long-term disability. A study in the British Medical Journal, published last month, suggested that 200 babies a year are killed or suffer permanent disability as a result of being shaken, often because their parent or carer has been unable to console their crying.

The BMJ estimate was based on a study of 33 babies treated for brain haemorrhages in Wales and Bristol. Only 14 were thoroughly medically examined on admission and doctors from the University of Wales and Southmead Hospital, Bristol, warned that many cases of child abuse may be being missed. Nine of the babies died and 15 had a profound disability. Abuse was eventually confirmed in 21 cases and a further six were said to be "highly suggestive" of abuse.

The Royal College of Paediatrics has undertaken its own study of shaken baby syndrome and is collecting details of all babies diagnosed with brain haemorrhages. The study is due to conclude later this year.