Table of Contents
- Case Overview
- Step-by-Step Technique
Semicircular canal dehiscence is associated with conductive hearing loss, autophony, and pressure/sound induced vertigo. Patients who are symptomatic may elect to undergo surgical intervention. The transmastoid approach affords the opportunity for an outpatient procedure to expose and plug the canal around the defect.
Patients with superior semicircular canal dehiscence (SSCD) can present with a variety of symptoms. Several symptoms overlap with other otologic and vascular syndromes, and should be distinguished from SSCD by a detailed history and physical exam. Since the first description of its manifestations by Minor,1 diagnostic methods and treatments have evolved significantly.
Symptoms often include autophony, aural pressure, vestibular symptoms induced by noise or pressure changes, pulsatile tinnitus, and hearing loss.
On physical exam, the patient’s tympanic membrane and middle ear space may appear normal. Upon the induction of loud sounds or pressure changes (pneumatic otoscopy), patients may experience a vertical and torsional nystagmus aligned with the superior canal.2 In cases with conductive hearing loss, a tuning fork will demonstrate bone conduction greater than air conduction in the affected ear, and lateralization to the affected ear on Weber exam.
Additional studies are critical in the diagnosis of SSCD. Autophony is present in patients with patulous eustachian tube, and numerous middle ear conditions cause conductive hearing loss. A high resolution computed tomography (CT) scan of the temporal bone should be obtained to determine the amount of bone overlying the superior canal. When ordering these tests, it is important to specify the orientation of the reconstructions in the plane of the canal as well as perpendicular to that plane. Vestibular evoked myogenic potentials (VEMP) can also aid in the diagnosis. Thresholds for eliciting a response in cervical VEMP testing are lower in the affected ear compared to a normal ear.
An audiogram may demonstrate a conductive hearing loss. An important distinction is the presence of suprathreshold bone conduction lines.
Diagnosis of SSCD may be an incidental finding of a CT obtained for an unrelated purpose. Patients may be asymptomatic or have any of the previously mentioned symptoms in combination. For patients who are asymptomatic or not bothered by symptoms, observation may be appropriate. For those with more troublesome or debilitating symptoms, several surgical options exist.
If the primary symptoms are pressure-induced (Tullio phenomenon), placement of a tympanostomy tube may be useful. For others, canal resurfacing via a middle fossa craniotomy or plugging via the same approach or by mastoidectomy may be required.
The patient in this case was significantly bothered by her autophony given the necessity for her to talk frequently at work. She also had dizziness that was induced by straining (Valsalva against a closed glottis). When the diagnosis was confirmed, options of observation, vestibular therapy, and surgical intervention were discussed. The middle cranial fossa approach and transmastoid approach were discussed with the advantages and disadvantages of each. Given the outpatient nature of the transmastoid procedure, and the significant detriment to quality of life by her symptoms, the patient elected to proceed.
In older patients, a middle fossa craniotomy with retraction of the temporal lobe may have greater risk than in younger patients. Additionally, patients undergoing middle fossa craniotomy often require a lumbar drain and inpatient admission. Conversely, the transmastoid approach affords the opportunity for an outpatient procedure. Patients should be counseled regarding the specific risks of the procedure, which include facial nerve injury and transient or permanent hearing loss.
General anesthesia, endotracheal intubation, and avoidance of any long-acting muscle relaxants due to the need for facial nerve monitoring throughout the procedure.
The patient is placed supine with the head turned away from the operative side. The arms are tucked, and the blood pressure cuff should be placed on the arm opposite of the surgical side. The bed is rotated 180 degrees away from anesthesia.
Bi-channel facial nerve monitoring is utilized.
Standard Betadine scrub and solution is used.
A standard postauricular incision is performed approximately 5–10 mm posterior to the postauricular sulcus. After dividing the skin and subcutaneous tissue, the temporoparietal fascia is encountered. Deep to this, an avascular plane superficial to the temporalis fascia is opened and carried to the level of the external auditory canal. Superiorly, the dissection is opened more anteriorly over the root of the zygoma. Temporalis fascia may be harvested, pressed, and set aside to dry. A periosteal incision is then made along the temporal line. Either a “T-shaped” or “7-shaped” incision is made by bisecting the mastoid tip. The periosteum is elevated superiorly, posteriorly, and then anteriorly to expose the spine of Henle. Next, a mastoidectomy should be performed, delineated by the tegmen superiorly, the sigmoid sinus posteriorly, and the ear canal anteriorly. During the drilling, the surgeon may collect the bone dust to use as pâté for occluding the canal later in the procedure. When the antrum is opened, the lateral semicircular canal and the short process of the incus should be identified. Next, the facial nerve can be exposed distal to the second genu and along the descending segment. It does not need to be decompressed or exposed to the stylomastoid foramen. With the tegmen and the lateral semicircular canal exposed, the superior canal at the common crus is located. It is traced superiorly and anteriorly to uncover its entire course. It is important to understand the anatomy of the superior canal relative to the other semicircular canals and the petrous ridge. “Blue-lining” of the canal is then performed. The lateral surface of the canal is carefully thinned until the endosteum is exposed. It is critical to perform this step carefully, as violation of the membranous labyrinth can result in profound sensorineural hearing loss. Some surgeons will blue line small areas anteriorly (just proximal to the ampullated end) and posteriorly (just distal to the common crus) for plugging. Others will expose the entire canal, thus ensuring that the occlusion occurs around the defect in the tegmen. Next, bone pâté is carefully packed anterior and posterior to the defect (if limited exposure) or along the course of the canal. Bone wax can be gently pressed over these areas using a moistened cottonoid. Alternatively, previously harvested fascia can be cut and tucked over the bone pâté. A small piece of Gelfoam can then be laid over the canal.
The periosteum is closed in interrupted fashion using 3-0 Vicryl suture. The first stitch is typically thrown to approximate the Palva flap with the most posterosuperior aspect of the periosteal incision. After closing the periosteum, the deep dermal layer is also closed in interrupted fashion using a 4-0 Monocryl suture.
The wound is dressed with Steri-Strips after applying benzoin or Mastisol, followed by either a Glasscock dressing or a mastoid pressure dressing.
Patients are advised of the following
- Keep the head of the bed elevated to 30 degrees for 48–72 hours after surgery.
- No nose blowing.
- Do not try to stifle coughing or sneezing, do so with the mouth open.
- Do not shower for 48 hours. At this point, the patient may shower but should only let soap and water run over the incision, without scrubbing. It should be dried by gently patting the area.
- The Steri-Strips may begin to peel and fall off, but they should be left in place until removed by the surgeon.
- Postoperative pain is managed with ibuprofen, 600 mg tablets every 6 hours as needed, provided that the patient does not have any adverse reactions or history of gastric ulcer.
- If narcotics are provided, patients should take a stool softener to avoid any straining during bowel movements.
- Do not lift greater than 10–15 pounds for 2 weeks after surgery.
Standard postoperative instructions regarding fevers, pain management, and warning signs are provided with phone numbers to the office and hospital to reach a physician at any time.
Follow up for a wound check should occur 1–2 weeks following surgery.
An audiogram is performed 3 months following surgery.
- Standard microscopic ear tray
- Drill system with cutting and diamond burrs
- Facial nerve monitoring system
Author C. Scott Brown also works as editor of the Otolaryngology section of the Journal of Medical Insight.
The patient referred to in this video article has given their informed consent to be filmed and is aware that information and images will be published online.
- Minor LB. Superior canal dehiscence syndrome. Am J Otol. 2000;21(1):9-19.
- Cremer PD, Minor LB, Carey JP, Della Santina CC. Eye movements in patients with superior canal dehiscence syndrome align with the abnormal canal. Neurology. 2000;55(12):1833-41. doi:10.1212/wnl.55.12.1833.
Cite this article
Brown CS, Kaylie DM. Transmastoid repair of superior semicircular canal dehiscence. J Med Insight. 2023;2023(248). doi:10.24296/jomi/248.
Table of Contents
- Posterior Limb
- Anterior Limb
All right, this patient - we're doing a left superior - transmastoid superior canal dehiscence repair, and he has a confirmed superior canal dehiscence on this side with symptoms of autophony, ear fullness, which is actually his major complaint, and dizziness. So, this is how we repair it. So, 15 blade. And we get down into the layer of the temporal parietal fascia down below it - through that into the loose areolar tissue, which gives us next bloodless plane. Get through the fascia. There we go - pops open. Okay, getting closer to the ear canal. Lift this up a little bit more here, and as you get closer to the ear canal, you start to see some blood vessels running right in front of the ear canal. It tells you you're about as close as you need to get. And that's right about here. So that's as far - close as we need to get there, and now we have it exposed. Can you hold the ear, please? You have a bipolar? Dry it up a little bit. And get all this dry so it doesn't bleed on us during the case. Okay. Can I have the bed towards me a little bit, please? I'll take the ear. All right, I'll take a Bovie. So, now we'll make our T-incision. And that gets up there close to the - hold ear, please - and I'll take a bipolar - to the deep temporal artery. And we have suction? And bipolar cautery usually works better up here than monopolar, so you can really grab the tissue and get both ends of the artery. All right, and I'll take the Bovie back. I'll take the ear. Okay, hold the ear, and I'll take a Lempert. Bovie the periosteum. Take that. Okay. Up to the ear canal, right there. This is as close as we need to get, and I'll take a Weity. So this gives us - all the way up to - suction - all the way up to the zygomatic root, so we can get really anterior - so we have enough room. All right, Bovie. And I'll just remove these attachments off of the - of the sternocleidomastoid - off of the mastoid tip. These don't come off very easily with the Lempert elevator. They're pretty adherent, so I always Bovie these off of - get the whole mastoid exposed. Now I have ear canal, tegmen, mastoid tip - got the whole thing exposed. So now we can switch to the microscope.
All right, so I'll start with 5 cutter. So the thing to be aware of with this is the tegmen is often very thin and with multiple - multiple dehiscences, so you got to be really careful when you're drilling not to injure the dura. All right, water on. We'll start at the linea - linea temporalis, which is a good approximation for where the middle fossa is. Make sure you've got air cells there. See how that drill can get stuck in little holes and skip. So you always want to - you never want to plunge, and if there are holes, you always want to smooth them out. All right, so now I'm going to come along the ear canal, and then take the cortex off. So that's pretty much the cortical mastoidectomy, and let me have irrigation. It's real important to keep the bone dust off the field and keep it really clean, because it can dull the blade, it can dull the burr, and it'll also obscure your view. So... Okay, water down just a hair. Up. Very small difference between too little and too much. All right, so, now what we do is we follow the tegmen and making room, All these air cells need to go. So there we see the first glimpse of the tegmen, right through there. You just hold here. Gimmick. So we see as we lose the air cells, this is a very thin bone, and that's - we're seeing the the dura. You get a little better focus. We're seeing all the epidural blood vessels right here through this very thin bone here. That's what you go to be real careful of. Drill. So the idea is you find the tegmen, and then you catch up inferiorly and posteriorly. So I move deeper here and then open it up superiorly and remove all these air cells. You can see all the little - in a well-aerated mastoids, these little bone chips break off very - pretty easily. All right, so let me have an irrigation again. All right, drill. So I'm just opening it up widely posteriorly and inferiorly, making sure it's nice and saucerized. And by saucerized, I mean it's widest at the tip - out on the outside. Bipolar. So no overhanging ledges. Drill. Good. Saucerizing the ear canal there - back to the ear canal, and we're starting to get into the antrum. And now we're exposing the antrum. You see the lateral canal pretty nicely there, and I'm going to change my angle, so I can look into the - this direction more, and we're going to start seeing the incus. By pinning the ear canal, I can now - get closer into the antrum. We don't need to do much posteriorly there. So we do need to get all the way into the antrum. So it's always good to use as big a drill bit as you can. Let me have a 4 cutter - a 4 diamond, I mean. Water off. And a Gimmick. So I'm just starting to see the incus here. There's the incus. And this is the lateral semicircular canal. So this gives me my landmarks for how I'm going to be able to find the other canals. So here we have - this isn't actually an exposed area of dura. There's a natural dehiscence in the bone there, which can happen, so you just want to be real careful of the dura there. Don't want to injure it. So I'm going to polish this up. A little water on. Get some of the bleeding. The diamond is very good for polishing bone. It doesn't tear dura. Water off. Here's another area of exposed natural dehiscence right there. Let me see the bipolar. So these are just things you have to be super careful of, because these people have very thin tegmen, and if they didn't have a thin tegmen, they wouldn't have superior canal dehiscence. So it just kind of goes with the territory. Can I have bone wax on the back of a Freer? Which reminds me, I want to collect... What I want to do now is get some bone pâté. Can you put a 4 cutter on? I want to use some bone pâté to - to help plug the hole that I'm going to make in the lateral canal. 4 cutter. So I'm going to take some of this cortex. So I'm using not much water here - just keep it dry. All right, now I'll take a Freer. So I'll collect all this stuff. May I have a Petri dish? Dry. And I'll just collect this. And I'm going to mix this with bone dust - with - this bone dust with some bone wax to make a little paste that'll be really good for plugging the tiny little holes I'm going to make. And that should be plenty. All right, let me have irrigation. All right.
So, now what I need to do is skeletonize the labyrinth a little bit more so I can get - start looking for my superior canal. And I know that my lateral canal is right here, so the superior canal is going to be coming above it - and posterior canal is going to be running 90 degrees here. Water on. And that tells me that I know the posterior canal and the superior canal will join together to form the common crus. Getting a little more working room here. Great, can I have a 3 cutter? So I'm starting to see here through this bone - water off. Let me have a Gimmick. So again, the lateral canal - so the posterior canal is going to be running orthogonal, 90 degrees to it, so right here's where the common crus is going to be. Superior canal is going to run like this. So when I clear these air cells out, I'm going to see the - the limbs of the posterior canal and superior canal coming together. Water on. All right, let me have a 3 diamond. Water off. We're getting near some dura. Don't want to mess with that. Water on. All right, water off. Let me see a Freer. Make sure we're in good focus here. All right, why don't you put a 2 diamond on. So what I'm looking for is a lot - water on. So right here - this is going to be posterior crus, and this is going - this is going to be superior canal, and this going to be posterior canal. This is where they're going to form the common crus. So superior canal is going to be going like this. And so what I'm going to want to do is make a hole in the anterior limb and a hole in the posterior limb here, and plug those with bone wax to keep - water off. Bipolar. So before I start doing that, I'm going to want to check the ABR. Make sure we're doing okay with that. So - and ABR is still real good, so what I'll do is make the bone wax pâté. So let me - let me see that - that stuff. Here we have our bone pâté. Let me have a ball of wax. Just a big ball. Get it kind of soft. And then kind of mix it all together here into one thing. You just - we'll just leave it up like that for now.
And so, we'll start with the superior canal - the superior limb - or the anterior-most limb. Let me put on a 1 diamond. Well, I'll start with a 2, and I'll go in the back here. Okay.
So, the limbs are going to be coming like this together, so this will be the posterior canal, and this will be superior canal. So I'm going to start looking right in here, and I'll just go real carefully. Water on. Just back-and-forth real carefully until I start seeing a blue-line. Zoom in just a little bit more. Can I get the bed away, please? All right. So I think I'm starting to get a sense right here. All right, let me have a 1 diamond. Drill carefully - a layer at a time. And... there we go. Water off. Right there's where I see it. Can you guys - does that show up? Yeah. All right, so I'm going to make that just a little bigger. Water on. All right, good. Water off. Let me have a Gimmick. So it's st- that's it right there. All right, so I'll check the ABR again. And the ABR is running. Do we have neuro-patties? How are we doing Holly? ABR is good. ABR is good, okay. So, let me have the drill one more time. I'm just going to real carefully thin eggshell this just a little more. Water on. All right, water off. Good. Now let me have the - put the blue suction on - blue suction tip. And there's a - and let me have a Rosen. So here we have a small hole. All right, let me have - let me have a dissector. Or a Gimmick. A Gimmick will work. And let me see the paste. Okay, now I'm going to put this over the hole. And let me have a bipolar and a neuro-pattie. And use that to pack it in. Not quite so wet. Can I have a - clean that? So we try to avoid suctioning over the open hole, but then we have it nice and plugged. Can I have another neuro-pattie? This shouldn't be drip - yeah, there we go. And we'll just - mash that in. All right, so that - Gimmick. So that was the hole right there, and now it's plugged. So that puts that all in there. And we'll check the ABR one more time. ABR is good.
All right, so now, dura - so you see how close it is. All right, why don't you put a smaller suction irrigator on? So the key is not to suction when you make the hole into the - into the canal, because that will cause deafness. All right, let's get the water on. All right, down. Down, down, down - keep going. Up - up a little. All right, I'll take a 1 diamond. And there's the blue-line, right there. Water off. Is that showing up okay? All right, let me have the blue suction and a Gimmick - I mean, a Rosen. All right. All right - oops - grab another little piece here. Good. All right, let me have a bipolar. And a neuro-pattie. And, push that in there. Let's check on ABR. ABR is still good. Excellent. Okay, so hearing's still good, and it looks like there might be just a tiny little bit of CSF coming out of there, so let me see a Freer. And let me have a 5 suction. Let me see the rest of the bone pâté. I'll pack this up here. And... call that good. And that's how you - that's how you do a transmastoid, two-holed approach for isolating a superior canal dehiscence.