QUANTITATIVE ASSESSMENT OF INTRACRANIAL-PRESSURE BY THE TYMPANIC MEMBRANE DISPLACEMENT AUDIOMETRIC TECHNIQUE IN CHILDREN WITH SHUNTED HYDROCEPHALUS

The objective of this prospective study was to compare the clinical fe atures at presentation, tympanic membrane displacement test results an d direct intracranial pressure measurements in children with shunted h ydrocephalus to procure a quantitative measure of the intracranial pre ssure by tympanic membrane displacement test. A prospective comparativ e evaluation of 61 clinical episodes of shunt malfunction was assessed by volume displacement of the tympanic membrane and direct intracrani al pressure measurements in 40 patients with shunted hydrocephalus bet ween January 1995 and June 1996. The volume displacement of the tympan ic membrane (Vm) on stapedial contraction was inward for raised intrac ranial pressure in 27 episodes and ranged from -120nl to -506nl (mean = -250nl). This was confirmed by direct intracranial pressure monitori ng, which ranged from 23 to 40 mm Hg (mean = 29 mm Hg). The tympanic m embrane displacement test measurement in 30 episodes of low intracrani al pressure ranged from +263nl to +810nl (mean = +530nl), and this was corroborated by direct intracranial pressure measurement ranging from 1 to 6 mm Hg (mean = 3.8 mm Hg). The normal baseline Vm values obtain ed when the subjects were asymptomatic ranged from +58nl to +175nl (me an = +115nl). The tympanic membrane displacement test as a non-invasiv e diagnostic tool in predicting changes in intracranial pressure had a sensitivity of 93% and specificity of 100%. The predictive value of t he test was 100%, and the negative predictive value was 73%. The kappa statistical analysis was used to measure the agreements between the g roups. The strength of the agreement was very good, k = 0.88 and the P value was < 0.001. The objective measure of intracranial pressure by tympanic membrane displacement test with the Vm value of -200nl and mo re negative was indicative of raised intracranial pressure and a Vm va lue of +200nl and greater, for low intracranial pressure. The intracra nial pressure measurements made on an individual subject basis were re liable and accurate. The test can therefore be used for regular assess ment of shunted hydrocephalics to enable correlation of intracranial p ressure with symptoms in individual patients.