Abstract:
Although inflammation is considered a major contributor to the development of ear disease and hearing disorders, most of the information is derived from acute animal studies and little is known about the progression of dynamic inflammatory disease in the living inner ear. Purpose: To chronically study the intact inner ear we have developed acquisition methods for magnetic resonance imaging of the intact and damaged cochlea and have investigated the evolution of dynamic changes in vascular permeability in cochlear tissues associated with inflammation in the same animal. Methods: To induce cochlear inflammation guinea pigs (GPs, n=4) were sensitised by bacterial lipopolysaccharide (LPS,0.8mg/kg) followed 24 hours later by bilateral LPS intra-tympanic injection (30μl). Two animals were treated with saline as a control. Anaesthetised GPs were scanned 4, 7, 10 and 14 days after inducing inflammation using a 4.7T MRI system combined with the use of a contrast agent (Gadodiamide, 500mmol/L, Gd) injected intravenously (femoral vein 1.5mmol/kg). Animals were scanned at fixed 1.5min intervals post-injection over a maximum of 70min and the rate of Gd uptake into cochlear tissues estimated as an index of vascular permeability. The rate of signal enhancement (Gd uptake) increased (3.5-fold) in the inflamed cochlea on day 4 and decreased to normal by 14 days indicating a reversible increase in vascular permeability with inflammation. Conclusion: These results demonstrate quantitative reversible changes in cochlear vascular permeability with inflammation and demonstrate the feasibility of using MR imaging to investigate dynamic, chronic changes in cochlear vascular perfusion in an animal model. This study was approved by the University of Auckland Animal Ethics Committee.