Quantitative assessment of the tympanic membrane displacement test in children and adolescents with shunted hydrocephalus : reproducibility of tympanic membrane displacement test measurements in children with shunted hydrocephalus

Samuel, Madan (1999) Quantitative assessment of the tympanic membrane displacement test in children and adolescents with shunted hydrocephalus : reproducibility of tympanic membrane displacement test measurements in children with shunted hydrocephalus. University of Southampton, Doctoral Thesis.

Abstract

The aim of this study is to procure a quantitative measure of the intracranial pressure by tympanic membrane displacement test by comparing volume displacement of the tympanic membrane on acoustic stapedial contraction with direct intracranial pressure measurement. The study also defines the sensitivity and specificity of the test as a diagnostic modality and assesses the test's reproducibility.

The tympanic membrane displacement test was first introduced clinically as an audiometric technique in the assessment of intracranial pressure in hydrocephalics in 1987. A pilot study in 1989 qualitatively showed that consistent results could be obtained in young patients with benign intracranial hypertension with hydrocephalus.

A prospective comparative evaluation of 68 clinical episodes of shunt malfunction was assessed by tympanic membrane displacement test and direct intracranial pressure measurement via the Rickham ventriculostromy reservoir in 40 patients (mean age 13.3 years) with shunted hydrocephalus between January 1995 and June 1996.

In addition, 31 clinical episodes of shunt malfunction were evaluated by serial tympanic membrane displacement test and direct intracranial pressure measurement in 8 shunted hydrocephalic children between January 1995 and Feb 1996.

The patients were classified into three groups by tympanic membrane displacement test and direct intracranial pressure measurement as raised intracranial pressure, low intracranial pressure and normal intracranial pressure. The inter-rater agreement between the groups was very good, κ=0.88, with a P value of <0.001. The sensitivity of the test was 93%, specificity was 100%, positive predictive value was 100% and negative predictive value was 73%. The test was reproducible.

The objective measure of the tympanic membrane displacement for raised intracranial pressure was -200nl or less and for low intracranial pressure was +200nl or greater. The tympanic membrane displacement test is a reliable, reproducible, non-invasive investigation for the assessment of intracranial pressure in shunted hydrocephalics. It can be used on regular bases as a routine test, thereby reducing the need for invasive intracranial pressure monitoring. The test may well provide a useful serial guide to intracranial pressure abnormalities in children with shunted hydrocephalus.

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