The fluid that bathes the brain and spinal cord is called ‘cerebrospinal fluid’ or ‘CSF’, and is produced in the fluid-filled spaces of the brain (the ‘ventricles’) before being absorbed over the surface of the brain. About a pint of CSF is produced each day and if a blockage occurs in the passages that drain CSF from the centre of the brain, the consequences can be life-threatening (‘acute hydrocephalus’). However, some other patients develop a chronic form of hydrocephalus, caused by poor re-absorption of CSF.
Normal pressure hydrocephalus is a rare condition affecting the elderly, which is characterised by deterioration in walking and balance, and if untreated, progresses to cause dementia and urinary incontinence. It involves enlarged ventricles in the brain, but perhaps counterintuitively, it does not reflect increased pressure within these fluid spaces. No-one fully understands why it happens, but there is a well-established, effective and safe treatment. This involves the insertion of a ‘shunt’ which carries fluid from the centre of the brain into the abdominal cavity, where it is absorbed. A large proportion of patients selected for this treatment improve following it (approximately 70%).
It is unclear who will respond to a shunt, and this results in both patients receiving intervention who do not benefit from it (and being exposed to all the associated risks), and a reluctance in the wider medical community to refer patients for the treatment.
The current gold standard test for determining response to the treatment is insertion of a drain into the spinal canal and drainage of about 400ml of CSF with various assessments before and after. The problem with this test is that it is invasive, requires a hospital stay, involves rare but significant risks, and is not completely reliable. A number of supplemental tests have been proposed, which are less invasive, and may, either individually (or taken together) improve diagnostic accuracy, and/or eliminate the need for lumbar drainage. These include:-
- Looking at the pressure changes over time in the spinal canal (the ‘ICP waveform’);
- Looking in detail at the brain scans of patients to identify a series of features that constitute ‘DESH’;
- Measuring the resistance to re-absorption of CSF through a test called an infusion study.
Our aim is to look at which of these tests best predicts response to a shunt in a large group of patients who have been treated at our institution over the last 20 years. We would also like to survey the available literature on supplemental tests and present this as a systematic review. Further to this, we would like to start a pilot study looking at the predictive value of subtle changes in the pattern of pressure changes in the brains of patients with NPH who respond to a shunt, compared to those who do not.
We would like to present the results of this work at an international conference for specialists working in this area to disseminate it and foster collaborations for future work. The ultimate goal of our group is to perform a study that involves changing the treatment of patients (called a ‘trial’) but this will need to be underpinned by the ‘observational’ studies described above.