B. Nageris et al., A HUMAN TEMPORAL BONE STUDY OF CHANGES IN THE BASILAR-MEMBRANE OF THEAPICAL TURN IN ENDOLYMPHATIC HYDROPS, The American journal of otology, 17(2), 1996, pp. 245-252
We observed that some temporal bones with endolymphatic hydrops (EH) s
howed varying degrees of basalward displacement (towards the scala tym
pani) of the basilar membrane (BM) in the apical turn of the cochlea.
In some, the BM was adherent to the bony wall of the scala tympani (i.
e., the interscalar septum). Such mechanical distortion of the BM coul
d conceivably alter cochlear mechanics and lead to sensorineural heari
ng loss. The results of a systematic evaluation of 234 temporal bones
to characterize, quantify and determine the functional significance of
this observation are presented. Four groups of bones were evaluated:
normal (N = 78), presbycusis (N = 96), Meniere's disease (N = 23), and
EH secondary to labyrinthitis (N = 37). The incidence of extreme disp
lacement of the BM in the apical turn such that it adhered to the inte
rscalar septum was 52% in Meniere's disease, 57% in EH secondary to la
byrinthitis, 10% in presbycusis, and 1% in normals. These differences
were significant and could not be explained on the basis of age, sex,
post-mortem time, or artifact of technique or processing. Displacement
of the BM was not observed in other turns of the cochlea. Its pathoge
nesis is not known, but may be related to atrophy of the spiral ligame
nt. It is likely that such BM displacement results in sensorineural he
aring loss. However, our data and theoretical analyses both indicate t
hat such a loss will be restricted to frequencies below 100 Hz and tha
t this pathologic change alone is not likely to cause appreciable hear
ing loss at clinically tested frequencies of 250 Hz and higher. Hence,
even though this pathologic finding is common in endolymphatic hydrop
s, it cannot explain the low-frequency hearing loss observed in Menier
e's disease.