Communication between the Perilymphatic Scalae and Spiral Ligament Visualized by in vivo MRI

Abstract

We evaluated the transport of Gadolinium-diethylenetriaminepentaacetate-bismethylamide (Gd-DTPA-BMA) through the round window (RW) membrane into the perilymphatic space with 4.7-T MRI in an animal study and 1.5-T MRI in humans. After administration of Gd-DTPA-BMA onto the intact RW membrane of guinea pig, Gd-DTPA-BMA uptake was observed in the basal turn and part of the second turn within 40 min. The scala tympani, scala vestibuli, the fibrous part of the spiral ligament and semicircular canal all showed uptake of Gd-DTPA-BMA. All turns of the cochlea were filled with Gd within 10 min in the perforated RW membrane administration group and within 30 min in the intravenous administration group. In patients who accepted middle ear injection of Gd-DTPA-BMA, uptake was observed within 2 h in the basal turn and semicircular canal. After 12 h the apex did still not show any uptake. Gd-DTPA-BMA is transported from the RW to the semicircular canal, the scala tympani and scala vestibuli without passing the helicotrema.

Direct Entry of Gadolinium into the Vestibule Following Intratympanic Applications in Guinea Pigs and the Influence of Cochlear Implantation

“…Prior studies have reported higher levels in scala vestibuli than scala tympani (Zou et al 2005. Several possibilities have been postulated to explain this including a connection to calcium channels (Zou et al 2005) and the potential additional passage through the annular ligament around the stapes footplate (Zou et al 2005; however, no one has yet interpreted their findings quantitatively.…”

“…When performed at different times after application, this allows a more complete picture of drug distribution in the ear as a function of distance and time to be established. In previous studies, the technique has generally been used to document the Gd distribution qualitatively (Zou et al , 2005Counter et al 2003), but in this study, we have analyzed the data semiquantitatively. The analysis leads us to the novel conclusion that in most ears, the observed distribution of Gd-DTPA cannot be accounted for solely by entry from the RW niche into ST through the RW membrane, with subsequent local redistribution from ST to SV in the basal turn.…”

“…Several possibilities have been postulated to explain this including a connection to calcium channels (Zou et al 2005) and the potential additional passage through the annular ligament around the stapes footplate (Zou et al 2005; however, no one has yet interpreted their findings quantitatively. A Calculated Gd levels in ST and SV, respectively, when all drug enters through the RW membrane.…”

“…Analysis of clinical studies showed that only low levels of gentamicin reached cochlear regions responsible for the hearing of speech frequencies . The slow distribution of substances along the ear has been supported by magnetic resonance imaging (MRI) studies that have demonstrated gadolinium takes hours to diffuse beyond the second cochlear turn (Zou et al 2005) and by measurements of the spread of chemical markers along ST Ma 2001, Salt et al 2007) which are consistent with distribution being dominated by passive diffusion. The question of the relative distribution of drugs within the cochlea and vestibular system over time has not been assessed quantitatively, which was one of the aims of this study.…”

“…A number of prior studies have used similar methodology but have only made qualitative assessments of gadolinium distribution in the ear (Zou et al , 2005Counter et al 2003). In this study, semi-quantitative measurements derived from MR images allowed different regions of the inner ear with different treatments, such as cochlear implantation, to be compared across groups of animals.…”