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1Otolaryngology - Head and Neck Surgery, Case Western Reserve University
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This video shows how to surgically obstruct the guinea pig's endolymphatic duct to produce endolymphatic hydrops.
Megerian, C. A., Heddon, C., Melki, S., Momin, S., Paulsey, J., Obokhare, J., et al. Surgical Induction of Endolymphatic Hydrops by Obliteration of the Endolymphatic Duct. J. Vis. Exp. (35), e1728, doi:10.3791/1728 (2010).
Surgical induction of endolymphatic hydrops (ELH) in the guinea pig by obliteration and obstruction of the endolymphatic duct is a well-accepted animal model of the condition and an important correlate for human Meniere's disease. In 1965, Robert Kimura and Harold Schuknecht first described an intradural approach for obstruction of the endolymphatic duct (Kimura 1965). Although effective, this technique, which requires penetration of the brain's protective covering, incurred an undesirable level of morbidity and mortality in the animal subjects. Consequently, Andrews and Bohmer developed an extradural approach, which predictably produces fewer of the complications associated with central nervous system (CNS) penetration.(Andrews and Bohmer 1989)
The extradural approach described here first requires a midline incision in the region of the occiput to expose the underlying muscular layer. We operate only on the right side. After appropriate retraction of the overlying tissue, a horizontal incision is made into the musculature of the right occiput to expose the right temporo-occipital suture line. The bone immediately inferio-lateral the suture line (Fig 1) is then drilled with an otologic drill until the sigmoid sinus becomes visible. Medial retraction of the sigmoid sinus reveals the operculum of the endolymphatic duct, which houses the endolymphatic sac. Drilling medial to the operculum into the area of the endolymphatic sac reveals the endolymphatic duct, which is then packed with bone wax to produce obstruction and ultimately ELH.
In the following weeks, the animal will demonstrate the progressive, fluctuating hearing loss and histologic evidence of ELH.
Part 1: Anesthesia and preparation for surgery
Part 2: Incision and exposure of the bony occiput
Part 3: Drilling the temporo-occipital suture
Figure 2 The area to be drilled partially overlies the temporo-occipital suture.
Part 4: Obstruction of the Duct
Part 5: Post-Operative Care
The guinea pig is put in an incubator to maintain body temperature and checked at 30 minute intervals until awake and able to maintain a sternal position. The animal is inspected for respiration rate and body color. This center uses enrofloxacin (0.2 mL at 22.7 mg/mL, subcutaneously) and buprenorphine (0.05 mL at 0.3mg/mL, subcutaneously) for post-operative infection prophylaxis and pain control, respectively. Analgesic is given once on the day of surgery and twice on post-operative day one and two. Although antibiotics are not necessary for aseptic surgery, a five-day, twice a day course of prophylactic antibiotics may be givenonce on post-operative day three.
Complications and Management
In the weeks following surgical obstruction of the endolymphatic duct, the animal subject experiences fluctuating sensorineural hearing loss as measured by auditory evoked brainstem response. A sample of auditory brainstem response (ABR) recording is shown in Figure 3. The left ear serves as an unoperated control.
Figure 3: ABR threshold levels at 16 kHz from a guinea pig 28 weeks post-surgery. The threshold for the left (unoperated) ear is 30 db SPL and for the right (operated) ear is close to 70 dB.
Histological examination of the cochlea also shows distension of Reissner's Membrane (Figure 4).
Figure 4: Distension of Reissner s Membrane is a typical finding in ELH. Measurable distension of the basilar membrane may or may not be present.
Experiments on animals were performed in accordance with the guidelines and regulations set forth by the Institutional Animal Care and Use Committee at Case Western Reserve University.
This work was supported in part by a grant from the American Otological Society to CAM and by a grant from the University Hospitals Case Medical Center to KNA and CAM. We would like to thank Jeff Churney at Focus Medical Group, Inc. (Hinckley, OH) for providing us with a microscope camera. Video production services provided courtesy of Fusion Creative Marketing, Inc. (Valdosta, GA) We thank Jonathan Frankel and Alex Levitt at CWRU for their comments during the preparation of the video.
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