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.

Part 1: Anesthesia and preparation for surgery
<ol>
 <li>An adult, female Duncan-Hartley guinea pig from Charles River International Laboratories, Inc. (Wilmington, MA) is anesthetized with ketamine 60 mg/kg and xylazine 12 mg/kg intramuscularly.</li>
 <li>Petroleum lubricant is applied to the eyes to protect the animal from corneal injury due to drying.</li>
 <li>The animal is shaved from the top of the head to the shoulders and between the ears.</li>
 <li>The shaved area is prepped in a sterile fashion first with 7.5% povidone-iodine followed by 70% ethyl alcohol.</li>
 <li>The animal is placed onto an operating table with warming blanket and onto a platform that elevates the head and flexes the neck. The head of the animal is directed away from the surgeon. Adequate flexion of the neck is required in order to adequately expose the occipital ridge.</li>
 <li>The animal is draped in a sterile fashion.</li>
</ol>
Part 2: Incision and exposure of the bony occiput
<ol>
 <li>Bupivacaine plus epinephrine (Marcaine) 0.25% is applied along the prospective incision site (midline dorsal skin incision along the occiput). This causes local vasoconstriction, limiting bleeding, and provides lasting post-operative analgesia after the animal wakes.</li>
 <li>Midline dorsal skin incision is made on the scalp along the occiput. <img src="/files/ftp_upload/1728/1728fig1.jpg" alt="Figure 1" /> Figure 1: Skin incision is made along the dorsal midline, as shown above.</li>
 <li>To gain adequate exposure, the skin is retracted laterally by placing a small curved hemostat on each side of the incision.</li>
 <li>A horizontal incision is made along the neck muscle to expose the bony occiput. At this stage the animal may twitch despite adequate anesthesia due to transection of the greater occipital nerve. Spinal cord transection is a danger with horizontal incision into the suboccipital region. This complication can be avoided by ensuring that underlying bone is always felt underneath the scalpel blade.</li>
 <li>With the suboccipital musculature incised to the bone, a third hemostat is used to retract the superior muscle edge. This hemostat is held in place by the surgical assistant.</li>
 <li>A Lempert periosteal elevator is used to expose the temporo-occipital suture.</li>
 </ol>
 Part 3: Drilling the temporo-occipital suture
 <ol>
 <li>Upon exposure of the temporo-occipital suture (Figure 2), an otologic drill with 1.5 mm diamond burr is used to drill inferio-laterally to the suture. </li>
 <li>Below the outer table of the skull, the spongy texture of the diplo&euml; (The intervening cancellous bone between tables of the skull) will become visible. Once the diplo&euml; has been drilled away, the inner table of the skull appears, along with a faint blue hue that is the sigmoid sinus.</li>
 <li>The margins of the sigmoid sinus are defined without penetrating the vessel. </li>
 <li>Once the bone overlying the sigmoid sinus has been sufficiently thinned, higher magnification is utilized and a straight pick is used to carefully remove the bone overlying the sigmoid sinus.</li>
 </ol>
 <img src="/files/ftp_upload/1728/1728fig2.jpg" alt="Figure 2" /> Figure 2 The area to be drilled partially overlies the temporo-occipital suture.
 Part 4: Obstruction of the Duct
 <ol>
 <li>The skeletonized sigmoid sinus is retracted medially to reveal the operculum. </li>
 <li>A 0.5 mm diamond burr is used to drill medial to the operculum and into the endolymphatic sac and duct. </li>
 <li>The endolymphatic duct is then packed with bone wax using a straight pick. </li>
 <li>The skull defect is then reinforced with Gelfoam (Pfizer, New York, NY). </li>
 <li>4-0 POLYSORB (United States Surgical, Norwalk, CT) suture is used to bring the muscle together. There is then a seamless transition to a subcutaneous suture technique for closing the skin incision. With this closure there is no need to remove sutures afterward and there is no risk that the animal will claw at the site and pull out a suture.</li>
 </ol>
 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
 <ol>
 <li>Respiratory depression The surgeon should always be aware of the animal s respirations. If breathing slows or stops, discontinue surgery and visually inspect for thoracic movement. If the animal is experiencing respiratory difficulty or labored breathing, check that the mouth and airway are not occluded. </li>
 <li>Sigmoid sinus penetration Use Gelfoam and compression along with the suction tip until bleeding is stopped.</li>
 <li>Dural penetration Cover the defect with Gelfoam.</li>
 <li>Vestibular damage Do not drill more than 1 mm lateral to the sigmoid sinus. Doing so risks injuring the posterior semicircular canal, which would invalidate all data for the guinea pig. </li>
 </ol>

<ol>
	<li>Andrews, J. C., Bohmer, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+surgical+approach+to+the+endolymphatic+sac+and+the+cochlear+aqueduct+in+the+guinea+pig.">The surgical approach to the endolymphatic sac and the cochlear aqueduct in the guinea pig.</a> Am J Otolaryngol. 10, 61-66 (1989).</li><li>Kimura, R., Schuknecht, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membranous+hydrops+in+the+inner+ear+of+the+guinea+pig+after+obliteration+of+the+endolymphatic+sac.">Membranous hydrops in the inner ear of the guinea pig after obliteration of the endolymphatic sac.</a> Pract Otolaryngol. , (1965).</li></ol>

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.

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.
 <a href="http://jove.unicartagenaproxy.elogim.com/files/ftp_upload/1728/1728fig4.jpg"><img border="0" src="/files/ftp_upload/1728/1728fig3tmb.jpg" alt="FIgure 3" /></a> Figure 3: ABR threshold levels at...

surgical induction of endolymphatic hydrops by obliteration of the endolymphatic duct

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.

Watch this Scientific Journal Video about Surgical Induction of Endolymphatic Hydrops by Obliteration of the Endolymphatic Duct at JoVE.com

Surgical Induction of Endolymphatic Hydrops by Obliteration of the Endolymphatic Duct

This video shows how to surgically obstruct the guinea pig's endolymphatic duct to produce endolymphatic hydrops.

Surgical induction of endolymphatic hydrops (ELH) in the guinea pig by obliteration and obstruction of the endolymphatic duct is a well-accepted animal ...

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Biology

11.4K Views.  Case Western Reserve University. This video shows how to surgically obstruct the guinea pig's endolymphatic duct to produce endolymphatic hydrops.

Video: Surgical Induction of Endolymphatic Hydrops by Obliteration of the Endolymphatic Duct

Canalostomy As a Surgical Approach to Local Drug Delivery into the Inner Ears of Adult and Neonatal Mice

Local delivery of therapeutic drugs into the inner ear is a promising therapy for inner ear diseases. Injection through semicircular canals (canalostomy) has been shown to be a useful approach to local drug delivery into the inner ear. The goal of this article is to describe, in detail, the surgical techniques involved in canalostomy in both adult and neonatal mice. As indicated by fast-green dye and adeno-associated virus serotype 8 with the green fluorescent protein gene, the canalostomy facilitated broad distribution of injected reagents in the cochlea and vestibular end-organs with minimal damage to hearing and vestibular function. The surgery was successfully implemented in both adult and neonatal mice; indeed, multiple surgeries could be performed if required. In conclusion, canalostomy is an effective and safe approach to drug delivery into the inner ears of adult and neonatal mice and may be used to treat human inner ear diseases in the future.

Here we describe canalostomy procedure which allows local drug delivery into the inner ears of adult and neonatal mice through the semicircular canal with minimum damage to hearing and vestibular function. This method can be used to inoculate viral vectors, pharmaceuticals, and small molecules into the mouse inner ear.

Local delivery of therapeutic drugs into the inner ear is a promising therapy for inner ear diseases. Injection through semicircular canals (canalostomy) ...

Genetics

A Revised Surgical Approach to Induce Endolymphatic Hydrops in the Guinea Pig

Endolymphatic hydrops is an enlargement of scala media that is most often associated with Meniere&#39;s disease, though the pathophysiologic mechanism(s) remain unclear. In order to adequately study the attributes of endolymphatic hydrops, such as the origins of low-frequency hearing loss, a reliable model is needed. The guinea pig is a&#160;good model because it hears in the low-frequency regions that are putatively affected by endolymphatic hydrops. Previous research has demonstrated that endolymphatic hydrops can be induced surgically via intradural or extradural approaches that involve drilling on the endolymphatic duct and sac. However, whether it was possible to create an endolymphatic hydrops model using an extradural approach that avoided dangerous drilling on the endolymphatic duct and sac was unknown. The objective of this study was to demonstrate a revised extradural approach to induce experimental endolymphatic hydrops at 30 days post-operatively by obliterating the endolymphatic sac and injuring the endolymphatic duct with a fine pick. The sample size consisted of seven guinea pigs. Functional measurements of hearing were made and temporal bones were subsequently harvested for histologic analysis. The approach had a success rate of 86% in achieving endolymphatic hydrops. The risk of cerebrospinal fluid leak was minimal. No perioperative deaths or injuries to the posterior semicircular canal occurred in the sample. The presented method demonstrates a safe and reliable way to induce endolymphatic hydrops at a relatively quick time point of 30 days. The clinical implications are that the presented method provides a reliable model to further explore the origins of low-frequency hearing loss that can be associated endolymphatic hydrops.

This article demonstrates an extradural approach to obliterate the guinea pig endolymphatic sac and injure the endolymphatic duct with a fine pick in order to induce experimental endolymphatic hydrops.

Endolymphatic hydrops is an enlargement of scala media that is most often associated with Meniere&#39;s disease, though the pathophysiologic mechanism(s) ...

Neuroscience

A Revised Method for Inducing Secondary Lymphedema in the Hindlimb of Mice

Animal models are of paramount importance in the research of lymphedema in order to understand the pathophysiology of the disease but also to explore potential treatment options. This mouse model allows researchers to induce significant lymphedema lasting at least 8 weeks. Lymphedema is induced using a combination of fractioned radiotherapy and surgical ablation of lymphatics. This model requires that the mice get a dose of 10 Gray (Gy) radiation before and after surgery. The surgical part of the model involves ligation of three lymph vessels and extraction of two lymph nodes from the mouse hindlimb. Having access to microsurgical tools and a microscope is essential, due to the small anatomical structures of mice. The advantage of this model is that it results in statistically significant lymphedema, which provides a good basis for evaluating different treatment options. It is also a great and easily available option for microsurgical training. The limitation of this model is that the procedure can be time consuming, especially if not practiced in advance. The model results in objectively quantifiable lymphedema in mice, without causing severe morbidity and has been tested in three separate projects.

This animal model enables researchers to induce statistically significant secondary lymphedema in the hindlimb of mice, lasting at least 8 weeks. The model can be used to study the pathophysiology of lymphedema and to investigate novel treatment options.

Animal models are of paramount importance in the research of lymphedema in order to understand the pathophysiology of the disease but also to explore ...

Medicine

Intrathecal Application of a Fluorescent Dye for the Identification of Cerebrospinal Fluid Leaks in Cochlear Malformation

In cases of cerebrospinal fluid (CSF) leaks, reliable detection of their origins is needed to seal the leak sufficiently and prevent complications, such as meningitis. A method is presented here using intrathecal administered fluorescein in a clinical case of bilateral congenital ear malformation. A fluorescent dye is administered intrathecally to achieve intraoperative visualization of CSF leaks. The dye is applied 20 min before surgery, and concentration of 5% is used. Per every 10 kg of body weight, 0.1 mL of the fluid is applied intrathecally. The fluorescein is visualized using a fully digital microscope. The origin of the fluid leak is identified in the stapes footplate. During primary surgery, it is sealed, and cochlea implantation is performed for hearing restoration. In this specific case, 6 weeks later, the implant was explanted due to acute meningitis, and the electrode array was left as a spacer. Postoperatively, in the aural smear, &#946;-transferrin was detected. During a revision mastoidectomy, dislocated coverage of the leak was found. The stapes was removed and oval window sealed. Five days after revision surgery, no &#946;-transferrin was detected in the aural smear. During the revision of cochlea implantation 6 months later, intact coverage of the oval niche was observed. Thus, intrathecal fluorescein application proves to be a reliable tool for the detection of CSF leaks. It facilitates the orientation in malformations and complicated or unknown surgical situs. In the literature, its use is described for CSF fistulas in endonasal surgery but is rarely described in skull base and mastoid surgeries. The method has been used successfully in several cases with CSF leaks, and the results confirm the feasibility of safely accessing the origin of the leak.

Intrathecally applied fluorescein is used to achieve intraoperative visualization of CSF leaks. This protocol describes a lumbar puncture, the application of 5% fluorescein, and intraoperative visualization using a fully digital microscope.

In cases of cerebrospinal fluid (CSF) leaks, reliable detection of their origins is needed to seal the leak sufficiently and prevent complications, such ...

Endaural Endoscopic Atticoantrotomy (Retrograde Mastoidectomy) using a Constant Suction Bone-drilling Technique

Endoscopic middle ear surgery is a widely employed minimally invasive surgical technique to address middle ear and mastoid pathology. Bone drilling is the main technical challenge of endoscopic middle ear surgery. The accompanying video describes the detailed protocol of a constant-suction bone-drilling technique and the procedure of endaural exclusive endoscopic atticoantrotomy (retrograde mastoidectomy) using this technique. The main components of this bone-drilling technique include a soft and flexible suction tube, which is placed into the tympanic cavity to provide constant suction, and a soft sleeve, which is wrapped around the drill shaft to prevent the high-speed rotating shaft from damaging the lens of the endoscope. With these simple modifications, the traditional otological electrodrill can be used for drilling a tiny endaural incision in endoscopic middle ear surgery. Based on this bone-drilling technique, endaural endoscopic atticoantrotomy (retrograde mastoidectomy) can be successfully established for the removal of various amounts of bone, depending on the extent of the lesion. The short-term postoperative outcome seems promising.

Endaural Endoscopic Atticoantrotomy Retrograde Mastoidectomy using a Constant Suction Bone-drilling Technique

In this paper, we present the protocol and short-term outcomes of endaural exclusive endoscopic atticoantrotomy using a constant suction bone-drilling technique.

Endoscopic middle ear surgery is a widely employed minimally invasive surgical technique to address middle ear and mastoid pathology. Bone drilling is the ...

An Integrated (Microscopic/Endoscopic) Dissection Ear Surgery Course

Traditionally, otologic surgical training consisted of microscopic cadaveric dissections. However, during the last decades the endoscope has significantly changed the surgical perspective in the otologic field. Thus, the modern ear and lateral skull base surgeon should master the entire spectrum of endoscopic and microscopic approaches, with the aim of tailoring the procedure and guaranteeing the best possible functional outcome. This work proposes a step-by-step guided and illustrated dissection course, including indications for the setup of the cadaver lab and the integration of the microscope and endoscope to enhance the use of both instruments. The alternation of the endoscope and microscope allows the novice to train the correct handling of the instruments in the surgical field under both optical views. This aspect is of utmost importance since it is not advisable to start off a technique without practicing the other one, as both are important and complementary in the modern otologic surgery setting.

An Integrated Microscopic/Endoscopic Dissection Ear Surgery Course

Traditionally, otologic surgical training consisted of microscopic cadaveric dissections. However, during the last decades the endoscope has significantly ...

Endoscopic Cholesteatoma Surgery

Implementation of endoscopes in cholesteatoma surgery resulted in considerable changes in the management of cholesteatoma in the last two decades. Compared to the microscopic approach with an excellent but straight-line view and limited illumination, the introduction of endoscopes provides a wide-angled panoramic view. Moreover, angled lenses allow the surgeon to visualize the middle ear and its hidden recesses through a transcanal, minimally-invasive approach. The endoscope enables the surgeon to remove limited cholesteatoma of the middle ear and its recesses using an exclusive endoscopic technique by taking advantage of these benefits. This reduces the rate of residual disease and sparing external incisions and excessive temporal bone drilling as in a transmastoid approach. Since transcanal endoscopic access is mainly a one-handed technique, it implies the need for specific procedures and technical refinements. This article describes a step-by-step guide as a surgical manual for endoscopic removal of epitympanic cholesteatoma. Different techniques for cholesteatoma dissection and bone removal for epitympanectomy, including curettage and powered instruments such as drills and ultrasonic devices with their outcomes, are discussed. This may offer ear surgeons insight into technical refinements and the latest technological developments and open the horizon for different techniques.

The present protocol describes a step-by-step guide for the complete endoscopic removal of epitympanic cholesteatoma with different techniques for cholesteatoma dissection and bone removal for epitympanectomy.

Implementation of endoscopes in cholesteatoma surgery resulted in considerable changes in the management of cholesteatoma in the last two decades. ...

Endolymphatic Duct Blockage as a Surgical Treatment Option for M&#233;ni&#232;re's Disease

Endolymphatic duct blockage is a relatively new treatment option for M&#233;ni&#232;re's disease, aiming to reduce vertigo attacks while sparing hearing and equilibrium. After a regular mastoidectomy, the posterior semicircular canal is identified, and Donaldson's line is determined. This is a line through the horizontal semicircular canal, crossing the posterior semicircular canal. The endolymphatic sac is usually found at this site under the posterior semicircular canal. The bone of the endolymphatic sac and the dura are thinned until the sac is skeletonized, after which the endolymphatic duct is identified. The duct is then blocked with a titanium clip. Using a computerized tomography (CT) scan, the position is confirmed. Follow-up visits take place 1 week, 6 weeks and 1 year after surgery. To this day, only one prospective trial assessing this method has been conducted, comparing this new method to endolymphatic sac decompression. Results of the duct blockage are promising, with 96.5% of the patients free of vertigo after 2 years. However, further research is required.

Endolymphatic duct blockage is a relatively new surgical method for patients suffering from M&#233;ni&#232;re's disease. Following a regular mastoidectomy, the endolymphatic duct is identified and ligated using a regular titanium hemoclip. The effectiveness of this procedure is currently being assessed in a randomized trial.

Endolymphatic duct blockage is a relatively new treatment option for M&#233;ni&#232;re's disease, aiming to reduce vertigo attacks while sparing hearing ...

Surgical Treatment of an Endolymphatic Sac Tumor

Endolymphatic sac tumors (ELST) are low-grade papillary adenocarcinoma originating from the endolymphatic sac. Usually slow-growing, with local aggressiveness and a low risk of distant metastases, ELST can be sporadic but also frequently associated with von Hippel Lindau disease. The current treatment of ELST is primarily surgical resection. A 55-year-old woman accessed our otologic tertiary level referral center for a sudden worsening of hearing loss in her left ear and vertigo. A magnetic resonance (MRI) and computer tomography scan study subsequently showed a mass in the petrous bone; hence, the presence of an ELST was hypothesized. After embolization of the mass, the patient underwent surgical removal of the lesion. The resection of the mass was done through a translabirinthine approach, with an uneventful procedure. No residual disease remained after surgery. After 24 months of radiologic follow up with MRI, there are no signs of recurrence disease. This paper reports the management of this sporadic ELST, as well as the follow up results, providing clinicians this protocol for the handling of such a challenging otologic skull base surgery and rare disease.

Here, we discuss clinical and radiological features of endolymphatic sac tumors and report the methodology and results of a surgical removal in a case in care at our otologic referral center.

Endolymphatic sac tumors (ELST) are low-grade papillary adenocarcinoma originating from the endolymphatic sac. Usually slow-growing, with local ...

Dissection of the Endolymphatic Sac from Mice

The study of mutant mouse models of human hearing and balance disorders has unraveled many structural and functional changes which may contribute to the human phenotypes. Although important progress has been done in the understanding of the development and function of the neurosensory epithelia of the cochlea and vestibula, limited knowledge is available regarding the development, cellular composition, molecular pathways and functional characteristics of the endolymphatic sac. This is, in large part, due to the difficulty of visualizing and microdissecting this tissue, which is an epithelium comprised of only one cell layer. The study presented here describes an approach to access and microdissect the endolymphatic sac from the wild-type mouse inner ear at different ages. The result of a similar dissection is shown in a pendrin-deficient mouse model of enlargement of the vestibular aqueduct. A transgenic mouse with a fluorescent endolymphatic sac is presented. This reporter mouse can be used to readily visualize the endolymphatic sac with limited dissection and determine its size. It can also be used as an educational tool to teach how to dissect the endolymphatic sac. These dissection procedures should facilitate further characterization of this understudied part of the inner ear.

This study describes how to dissect the endolymphatic sac from the inner ear of the mouse at different ages. The result of a similar dissection is shown in an Slc26a4-null mouse model of enlargement of the endolymphatic sac. A transgenic mouse with a fluorescent reporter expressed in the endolymphatic sac is presented as a model to readily visualize the endolymphatic sac, and educational tool.

The study of mutant mouse models of human hearing and balance disorders has unraveled many structural and functional changes which may contribute to the ...