Hydrocephalus and the status of endolymphatic membranes in temporal bones of children

Abstract

Homeostasis of the intralabyrinthine fluids is considered to be essential for normal functioning of the inner ear. Disturbances in the intralabyrinthine fluids can be caused by alterations in composition, or changes in volume secondary to resorption or from exchanges between intra- and extralabyrinthine fluid compartments. Carlborg et al demonstrated, in cats, that increased cerebrospinal fluid pressure can be transferred via the cochlear aqueduct to the perilymphatic compartment (Carlborg et al. 1992). Clinically Moss showed, by the tympanic membrane displacement technique, that hydrocephalus can influence hearing in children (Moss et al. 1989). Transmission of fluid and associated pressures between the perilymphatic and subarachnoid spaces demands a patent cochlear aqueduct, but in histologic studies the patency of the cochlear aqueduct in humans is still controversial. In previous studies (Palva, Dammert 1969; Wlodyka 1978) patency was reported to be age-dependent whereas a recent study did not show statistical correlation between age and patency (Merchant, Gopen, 1995), although in most mammals (Böhmer 1993; Carlborg et al. 1992) and in infants the cochlear aqueduct always seems to be open (Palva 1970). In histologic studies the status of the intralabyrinthine fluids is assumed by the position of the endolymphatic membranes. Bulging of Reissner’s membrane is described as endolymphatic hydrops which suggests an excess of endolymph. The opposite situation of retraction (collapse) of Reissner’s membrane and the saccule has been described in adult patients (Fraysse et al. 1988; Fernandez 1958), however its significance is not known. Hypothetically, it seems possible that increased intracranial pressure would produce retraction of the endolymphatic membranes. We therefore conducted this study to answer the following questions:

• 1. What is the patency of the intralabyrinthine fluid pathways in the temporal bones of children?

• 2. Are there histopathologic findings that indicate pressure changes in the inner ear from hydrocephalus?