Non-invasive assessment of ventricular shunt function using tympanic membrane displacement measurement technique

A technique which was originally developed for measuring cochlear fluid pressure, has been under trial for the past two years as a means of assessing ventricular shunt function. The principle of the technique has been reported in previous papers (1, 2, 3) and has been shown to provide a reliable measure of intracranial pressure (ICP) in terms of induced displacement of the tympanic membrane. This study concentrates on the assessment of shunt blockage in spina bifida patients who subsequently underwent shunt revision. The tympanic displacement technique is shown to be of value to this patient group in three respects. Firstly as a research technique to study group-averaged ICP measurements where the ICP needs to be known but invasive measurements cannot be justified. Secondly for assessing shunt dysfunction in individual patients and, finally, in determining the success of shunt revision surgery. The technique was found to be extremely sensitive to relative changes in ICP with shunt revision or any subsequent blockage. The technique is more reliable diagnostically in instances where the patients act as their own controls and a comparison with baseline measurements can be made. Three case reports are illustrated which were selected from those patients tested to emphasise the importance of serial measurements of ICP over period of several days post-revision. The tympanic displacement technique is shown to provide a practical and acceptable method by which this can be undertaken.