Hi, my name is Chris Edden. I'm a researcher at Case Western Reserve University in the Department of Otolaryngology head and neck Surgery. Today I'll be describing the surgical blockade of the endo lymphatic duct in the Guinea pig, which produces endo, lymphatic hydros and is used to model many errors, disease related ear pathology.Ando.
Lymphatic hydros is a swelling of the endo, lymphatic compartment of the cochlea and is a key histological marker for knee's disease. Here you see a cross-sectional picture of a normal cochlea with two peri lymphatic compartments, the scale of phony and scale of hasibe, and a non dilated scale of media, which is continuous with the endo lymphatic duct, the structure we're operating on within weeks of the surgical procedure, the scale edia becomes dilated as indicated here, and reisner's membrane becomes distended. The animals also undergo progressive fluctuating hearing loss on the surgical ear.
Just as in many air's disease, surgical induction of hydros in the Guinea pig has been the gold standard animal model for human Meniere's disease since it was first described in 1965 by Robert Kor and Harold Schneck. Although the procedure was initially performed using a more invasive intradural approach, our center prefers an extradural approach because it results results in less morbidity and mortality for the animal. The following is a description of the materials, animal care and surgical approach necessary for successful and humane performance of this rather intricate procedure.
First, I'll describe the surgical materials needed. The animal is an adult female, Duncan Hartley, albino Guinea pig from Charles River International Laboratories Incorporated. For room preparation and sterile setup, you'll need sterile surgical attire, an operative microscope with sterile cover and Mars, small fenestrated drape, intraoperative warming pad suction apparatus.
A number five, suction, a number 40 suction sterile saline, stainless steel basin, and a head holder. For anesthesia, you'll need ketamine 60 milligrams per kilogram and xylazine 12 milligrams per kilogram Preoperatively. You'll need a petroleum based I lubricant an electric shaver, Betadine, and 70%ethyl alcohol intraoperatively, you'll need 0.6 milliliters of 0.25%marking a number 11 disposable safety scalp, three curved hemostats, a lier periosteal elevator, WEX cell surgical spears and otologic drill, A 1.5 millimeter diamond burr and a 0.5 millimeter diamond burr.
A straight pick a bone curette, a 10 cc syringe bone wax gel foam four oh absorbable suture with a P 13 cutter needle, addin forceps, diamond jaw needle driver, and suture scissors. For post-op care, you'll need a clean cage with warming pad. Point two mls of inter floxacin at 22.7 milligrams per milliliter.
Point zero five milliliters of buprenorphine 0.3 milligrams Per milliliter. First anesthetize the Guinea pig With ketamine 60 milligrams per kilogram and xylazine 12 milligrams per kilogram intramuscularly. This regimen allows for 60 to 90 minutes of anesthesia without respiratory depression, which is usually plenty of time for the performance of this procedure.
After anesthetizing the animal, a petroleum-based lubricant is applied to the eyes. Next, the back of the head is shaved with electric clippers from the upper thoracics to the top of the head. Then the site is prepped with Betadine, followed by alcohol.
Now the animal is ready for surgery. My name is Dr.Cliff McGillion. I am a professor of Otolaryngology Head and neck Surgery here at Case Western Reserve University Hospitals in Cleveland and the director of Otology and Neurotology.
What I want to talk to you today about is the surgical technique for inducing endo lymphatic hydros in the Guinea pig. We go extraorally and expose the sigmoid sinus and just anterior to the sigmoid sinus and lateral to the sigmoid sinus. We find the O perm of the endo lymphatic system and remove the duct material and the sac material and actually drill out the duct under direct visualization.
The most important part I think of the procedure is skeletonizing the sigmoid sinus and then medial that and directly visualizing the O curriculum of the endo lymphatic duct. Once the surgical site is prepared, the animal is transferred to the OR and placed onto a head holder. The neck is flexed to give adequate exposure of the occipital ridge and draped in a sterile fashion for the health and safety of the animal.
Observe the same sterile technique that will be required for a human patient in order to maintain adequate body temperature during the procedure, be sure that a warming pad is placed under the operative surface before first incision. Marking is injected around the surgical site. The surgical procedure is begun by making a midline dorsal skin incision on the scalp Along the occiput to gain Adequate exposure, retract the skin by placing a hemostat on each side of the incision, electrocautery will not be necessary as the Guinea pig has a robust hemostatic mechanism.
Next, a horizontal incision is made along the neck muscle. To expose the bony occiput, A well-placed incision may immediately expose the temporal occipital suture line as shown here. Transection of the greater occipital nerve that commonly underlies the muscle may make the animal twitch.
Despite adequate anesthesia when cutting through the muscle, it is important to feel the bone underneath the blade. If not, the incision may be too low, which could risk spinal cord transection once through the neck muscle. A third hemostat is used to grasp the superior portion of the incision and is held in place by the surgical assistant.
Blunt dissection is used to expose the occipital bone. Remember to stay on the right side of the external occipital crest at all times and that the left ear serves as a control. In this model, A lumper periosteal elevator is then used to further expose the cranium and expose the external occipital crest and temporal occipital suture line Drilling with a 1.5 millimeter diamond burb begins just inferior to the suture line.
The goal is to expose the posterior foss auraura and the sigmoid sinus. All drilling must stay on or inferior to the temporal occipital seizure line At all times. Keep a number five suction tube to suction the blood.
Also have an assistant keep the field irrigated with sterile saline. Continuously dripping from a 10 cc syringe. Drilling will cause some bleeding from the marrow, but the diamond bur can be used to stop the bleeders at a depth of approximately one millimeter.
A faint blue line will become visible. This is the sigmoid sinus. Just stand here.
Your un lateral to the sigmoid sinus. The a perm of the endo lymphatic duct can be found. It is important to define the edges of the sigmoid sinus without penetrating it.
Once the overlying bone has been sufficiently thin, drilling is then stopped and suction is changed to a number 40. Higher magnification is also utilized. A straight pick is used to gently remove the overlying bone.
Sigmoid sinus is gently retracted, medially revealing the operculum, which may not be overtly visible as it will be often be obscured by blood. Now the skeletonized sigmoid sinus is gently retracted, medially revealing the operculom. The groove is now drilled with a smaller 0.5 cutting bit obliterating the endo lymphatic sac, and ultimately leading to the Endo lymphatic duct.
The duct is visible as a dark oval within the whiteness of the surrounding bone. About one Millimeter of the duct is drilled before it is packed with bone wax. Bone wax is pushed into the duct using gel foam.
This occlusion of the endo lymphatic duct will induce endo Lymphatic hydro drops 4.0 poly shorb suture is used to bring the muscle together. Then there's a seamless transition to a subcutaneous suture technique for the skin incision. With this closure, there is no need to remove sutures afterward, and there is no risk that the animal will claw the site or pull a suture or staple out.
Postoperatively, the Guinea pig is put into an incubator to maintain body temperature with 30 minute checks until they're awake. The animal is inspected for respiration rate and body color. This center uses the broad spectrum antibiotic inin and buprenorphine for pain complications.
As with any surgery, there are risks to the subject. So now I'll go over some possible intraoperative complications and how to avoid them. Respiratory depression, the surgeon should always be aware of the animal's respirations if breathing stops or slows.
Discontinue surgery and visually inspect for thoracic movement. If the animal's apneic, check that the mouth and airway are not occluded. Sigmoid sinus penetration use gel foam and compression along with the suction tip until bleeding is stopped.
Dural penetration cover with gel foam vestibular damage do not drill more than one millimeter lateral to the sigmoid sinus or else the posterior semicircular canal can be injured, which would invalidate all data for that particular Guinea pig. Surgical blockage of the endo lymphatic duct in the Guinea pig is a technically demanding surgery, but with proper tools, instruction, and knowledge of the relevant anatomy, it can be performed in a way that is both humane to the animal and useful as a model for human Meniere's disease.
