Training in VNG

How to Diagnose Lateral Canal BPPV

10 mins
24 February 2022


This video describes the different lateral canal BPPV variants and how to differentiate between them using VNG goggles and the head roll test. You can read the full transcript below.


Equipment needed

Let's now talk about Lateral Canal BPPV. In order to diagnose this, you need the same equipment as you needed to diagnose both anterior and posterior canal BPPV. You need a VNG goggle with a cover, which is going to put the patient in complete darkness.


Which test to use?

The test, however, which we use to diagnose lateral canal BPPV, is different. We do instead of the Dix Hallpike - a Head Roll test, and you will see an example of how this is administered later on.


Where are the crystals inside the canal?

What makes Lateral Canal BPPV a bit more complex than anterior and posterior canal BPPV is that the position of the crystals inside the canal can be in two locations. And this gives different nystagmus characteristics when doing the Head Roll test.

So when diagnosing lateral canal BPPV, the first question which you need to ask is where are the crystals inside the canal?

One position is actually very close or attached to the Cupula. And in this situation, we call this apogeotropic lateral canal BPPV. The other position where the crystals can be is closer to the utricle and that portion of the arm of the canal. In this case, we get something called geotropic variant of BPPV. And again, at different nystagmus characteristic to the apogeotropic form.


Geotropic BPPV

Let's look at this in a little bit more detail to make it a bit clearer. We'll start with a geotropic BPPV patient. So this patient has geotropic BPPV. So we need to do a Head Roll test.

So first of all, we're going to lay the patient supine. And then we're going to roll the head to the left and to the right. And when we do that, it's going to elicit nystagmus.

So let's roll the head to the left first. So we can see that the left ear is pointing towards the ground and on the screen, we can see the patient's eyes and a VNG recording.

What will happen initially when the patient is turned in this position is that the eyes are going to slowly - in the geotropic form - drift to the right. And then there's going to be a corrective movement towards the left ear, or towards the ground. And this is going to be a left beating nystagmus.

And then the eyes are going to drift to the right again, and then correct down for a left beating nystagmus - drifting to the right and beating down to the left. So we get a left beat nystagmus in this patient.

The second part of the Roll test is to bring the patient back to the supine and roll them to the other side. So this time their right ear is facing the ground and note that the eyes are showing that with the right eye now being positioned closest to the ground.

Let's now look at what we'll record using the VNG goggle. So this time in the geotropic form and the patient in this position, the eyes are going to move slowly to the left and then beat to the right. And if you look, the right ear is pointing to the ground.

So again, it's pointing towards the ground geotropic. So eyes slowly moving to the left, beating to the right. Slowly moving to the left and beating to the right. So we have left beating nystagmus when the head is to the left and we have right-beating nystagmus when the head is to the right.

Both of those nystagmuses are beating towards the ground and therefore we call this geotropic BPPV.


Example of lateral canal BPPV

The second question is which ear is affected. The ear which is affected is the side which has the largest nystagmus. So what we'll do is we'll now watch a video and see an example of lateral canal BPPV.

And then you can make a guess at which ear is affected. So in this video, what we'll see is the patient turns their head to the right, so they're laying supine, and when they turn their head to the right, that bar was orange, and it turns green.

So that green is the indicator that lets us know that we're in the correct direction, right? And so as long as the patient has their head turned to the right, we see this right beating horizontal nystagmus, right? And then in a moment, they're going to turn their head to the left.

We're going to see the same thing happen. The bar is going to go from orange to green when they turn to the left, and then after a few seconds, we're going to see the nystagmus is going to change directions.

So now watch just about here. Now we see the nystagmus starting to beat to the left. So when the patient has their head to the right, they have right-beating nystagmus. When they have their head to the left, they have left-beating nystagmus.

This is geotropic nystagmus: It lets me know that those crystals are in that horizontal canal. And then in just a second, when this test stops, you're going to see a bar graph pop up. And that bar graph is our quick glance that lets us know which side is affected.

So you'll see that the head is rolled to the right. Right beating nystagmus of six. Six is the cutoff for normal. So that bar graph is white. So that side is the smaller side or the side with the least amount of nystagmus.

When they turn their head to the left, you see 11 degrees of nystagmus. And so that's great because it's higher than six or seven degrees and higher turns the bar grey.

So with one quick glance, we can see that this patient has stronger nystagmus when their head is rolled to the left. So we know that the left lateral canal is the affected canal right. So really simple but very accurate tool.


Apogeotropic BPPV

Let's now talk about apogeotropic BPPV of the lateral canal. In this variant, the crystals migrate further down the canal than in the geotropic form, and rest close to or adhered to the cupula. This is going to give different nystagmus characteristics when we administer the Head Roll test.

The Head Roll test is administered in the same way as how you would administer it when testing for geotropic BPPV. Whilst the patient is supine, we're now going to move the patient's head to the left. We can see that the left ear is pointing towards the ground, as, of course, is the left eye.

On the nystagmus graph, this is going to generate an eye movement recording, which is going to drift the eyes slowly towards the ground and then beat rightwards for their corrective movement. So eyes drifting slowly to the left and then pointing rightwards towards the sky as the corrective movement.

Slowly to the left, and then a corrective right beating nystagmus. With the head in head left position, we're getting a right beating nystagmus.

Next, we bring the patient back to supine, and then we roll them over so that the right ear is facing the ground. And this is reflected by the left and right eyes now changing position. So you can see that the right eye is also pointing towards the ground.

In the apogeotropic form, this is going to cause the eyes to move slowly towards the right. And then beat to the left, which is towards the sky. So the eyes are going to drift slowly to the right and beat to the left, slowly to the right and beat to the left.

So this means we get with head right a left beating nystagmus, which is opposite to the nystagmus, which we saw on the geotropic form.

The next question, which you need to ask is which side is affected, is it the left ear or is it the right ear? The answer is the side which has the smallest nystagmus.


Leigh Martin
Leigh Martin is a British Audiologist and adjunct lecturer at the University of Cork, Ireland. Clinically, he has worked in the National Health Service specializing in paediatric audiology as well as vestibular diagnostics and rehabilitation. Leigh has also sat on the board of directors for the British Academy of Audiology. Since 2013, Leigh has supported the growth and development of the Interacoustics Academy and holds the position of Director of the Academy. Leigh has presented at numerous scientific conferences and meetings across a diverse range of audiological topics as well as having published papers in both video head impulse testing (vHIT) and wideband tympanometry.

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