Magnetic Resonance Imaging of the Development of Otitis Media with Effusion Caused by Functional Obstruction of the Eustachian Tube

Abstract

In this study, magnetic resonance imaging (MRI) was used to define in vivo the effect of experimental functional obstruction of the eustachian tube (ET) on vascular permeability and the development of middle ear (ME) effusion. After collection of baseline data for ME pressure and MRI, the right tensor veli palatini muscle of 10 cynomolgus monkeys was injected with botulinum toxin A to induce ET obstruction. The left tensor veli palatini muscle was injected with saline in 4 monkeys. Right and left ME pressures and compliances were measured twice daily over a follow-up period of 36 days, and MRI scanning sessions including administration of a contrast agent, gadopentetate dimeglumine, were repeated on days 3, 6, 11, 15, 21, 29, and 36 in 6 animals and on days 15, 21, 29, and 36 in 4 animals. Two right ears did not develop underpressures, 5 developed persistent underpressures, and 3 developed underpressures that resolved. No changes in MRI parameters were noted for the ears that did not develop underpressures, but a progressive brightening of the ME on T2-weighted images, indicative of the development of inflammation and effusion, was noted for the others. Also, an increasing rate of transfer of the contrast agent between the vascular and ME compartments, indicative of increasing vascular permeability, was observed to track the temporal changes in ME pressure. These results support a causal relationship between ET dysfunction, ME underpressures, increased vascular permeability, and otitis media with effusion

Mucosal Surface Area Determines the Middle Ear Pressure Response Following Establishment of Sniff-Induced Underpressures

“…Because experimental and clinical studies show the initiation of ME pathologies at underpressures of approximately -200 mmH 2 O (ref. ambient) (22)(23)(24), pressure-regulating mechanisms would, by definition, maintain ME pressure in excess of that critical value. Gradient-driven, volume gas transfers during active openings of the ET at greater than a specified frequency (dependent upon extant gradients, gas exchange constants and volume transfers) will maintain ME pressure in excess of the critical value, while lesser frequencies of tubal openings will allow quasi-stable ME pressures below the critical value.…”

Prevention of Otitis Media With Effusion by Repeated Air Inflation in a Monkey Model

“…6,7 Two 40-mm 2 circular areas over the mastoid and petrous portions of the temporal bone in the axial image, and a 20-mm 2 rectangular area over the ME in the coronal image were defined. Signal intensity values for all regions were calculated and then normalized as their ratio to the concurrent value of a reference solution.…”

“…Botulinum toxin (5 U/kg of botulinum toxin type A; Sigma Chemical Co, St Louis, Mo) in a volume of 0.1 to 0.2 mL was injected into the right tensor veli palatini muscle to induce functional ET obstruction and, as a control, the left muscle was injected with 0.1 to 0.2 mL of a saline solution as previously described. 7 Twice daily, all monkeys were sedated (intramuscular injection of ketamine hydrochloride, 10 mg/kg) and tympanometry (model GSI 33, Grasen Stadler Middle Ear Analyzer; Grasen Stadler, Melford, NH) was performed bilaterally. Then, air or sham inflation was done if the right ME pressure was −100 mm H 2 O or less.…”

“…The MRI protocol included a T1-weighted spin echo scout scan (echo time = 16 milliseconds, repetition time = 400 milliseconds, acquisition matrix = 256 ϫ 192 pixels, slice thickness = 3 mm, slice gape = 1 mm), and T2-weighted fast spin echo axial and coronal oblique scans (echo time = 96 milliseconds, repetition time = 2200 milliseconds, acquisition matrix = 256 ϫ 256 pixels, slice thickness = 3 mm, slice gap = 0 mm) of the animal's head, which was positioned within an extremity coil. 7 If the right ME pressure on the day of MRI was −100 mm H 2 O or less, inflation as per group assignment was done following the MRI. If the postinflation ME pressure was increased, repeated tympanograms were done at 5-minute intervals, and then the MRI protocol was repeated.…”

“…Hypothetically, introducing gas into the ME by passively forcing the ET to open should resupply the volume gas loss due to transmucosal exchange, and thereby prevent the development of the threshold underpressure (Ϸ-200 H 2 O) that is required for fluid transudation and effusion accumulation. 7,12 However, in a recent experiment that controlled for most of the above listed confounding factors, ME inflation with the inert gas argon, did not prevent the development of OME in monkeys with functional ET obstruction. 6 In this study, an identical experimental model was used, but the inflation protocol was revised to include an earlier onset of treatment (prior to the development of the critical underpressure), a greater inflation frequency (twice per day), and a more standard inflation method (Politzer air bag).…”