Lea Alhilali, MD Profile picture
Dec 7, 2022 18 tweets 9 min read Read on X
1/Have disagreements between radiologists on the degree of cervical canal stenosis become a pain in the neck?!
Here’s a #tweetorial on cervical stenosis grading that’s easy, reproducible & evidence based
#medtwitter #spine #neurosurgery #radres #neurorad #meded #FOAMed #FOAMrad Image
2/In the lumbar spine, it is all about the degree of canal narrowing & room for nerve roots. In the cervical spine, we have another factor to think about—the cord. Cord integrity is key. No matter the degree of stenosis, if the cord isn’t happy, the patient won’t be either Image
3/Cord flattening, even w/o canal stenosis, can cause myelopathy. No one is quite sure why. Some say it’s b/c mass effect on static imaging may be much worse in dynamic positions, some say it’s repetitive microtrauma, & some say micro-ischemia from compression of perforators Image
4/Let’s start w/canal stenosis. Measurements have been proposed (<10mm), but this is cumbersome & introduces reader variability. Think functionally. Cord swims in CSF, like a fish in water. Like a fish, it needs room to swim. How much room is in the fish bowl determines stenosis Image
5/Mild stenosis is when your fish bowl decorations take up 1 side of the bowl. Not great, but fish can still swim. Moderate means your decorations take up both sides—swimming is really affected. Severe means you went all out w/decorations & there isn’t any more room for the fish Image
6/The sides of the fish bowl are the ventral & dorsal CSF. So mild canal stenosis is when either the ventral or dorsal CSF is effaced, but the other side of the fish bowl is still empty. Not ideal, but the fish can still swim Image
7/For moderate canal stenosis, both sides of the fish bowl have been filled. So both the ventral and dorsal CSF have been effaced. Now the room to swim has been notably limited Image
8/Finally, in severe canal stenosis, the bowl is completely filled and no CSF is seen. There is no room for the fish in this scenario. Similarly, there is no room for the cord and it is compressed. Not only is there no swimming, the fish has been crushed. Image
9/This classification is to all other classifications like a goldfish is to all other pets—super easy & simple. It’s also evidence based. It's the Muhle classification. It has excellent reproducibility. It hasn’t been correlated w/pain, but it's been correlated w/SSEP & outcomes Image
10/But canal stenosis isn’t enough. Cord flattening can cause myelopathy regardless of degree canal stenosis. It’s like being punched in the face—no matter how far away the hit comes from, it still hurts. Cord flattening is like being punched—it hurts even in mild stenosis Image
11/Think of the canal like a parking space. Even if no one encroaches on your space, if someone opens their door & dings your car, your car is still damaged and you are still mad. Your parking space may still be wide open, but you still have a nick in your door. Image
12/Cord flattening has 3 degrees. Either it’s not there, there, or so bad it causes cord damage. Think of it like a fight. Cord deformity w/o signal is like someone pushing you to start a fight---you can still walk away. Cord deformity w/signal is a punch to the face—it’s on! Image
13/Here are examples:

Cord deformity w/o signal (Grade 2, someone pushing and trying to start something)

Deformity w/cord signal (Grade 3, fight has already started & the cord already has a black eye!) Image
14/Remember, this is independent of the degree of canal stenosis. You can have cord deformity and signal even in lesser degrees of canal stenosis. Remember--cord flattening can cause cord damage regardless of the degree of canal stenosis. Image
15/This is the Kang system, and it was created to bring the idea of cord flattening into the rating of cervical spine stenosis, since flattening/deformity contribute to myelopathy regardless of stenosis. Image
16/Why don’t we just use the Kang & forget Muhle? Well, the problem w/Kang is that if there’s no cord signal, many degrees of canal stenosis are equal. Here, both mild stenosis w/flattening & severe stenosis w/flattening are equal in Kang, but clearly one is much more at risk Image
17/So we use both. For every level, we rate the degree of canal stenosis according to Muhle & the degree of cord flattening according to Kang. Remember—there is no perfect classification system. Sometimes you need combine. Image
18/So remember both canal and cord matter in the cervical region! Degree of stenosis is important, but even w/o it, cord flattening can have you swimming w/the fishes. So hopefully, you will take to these rating systems like a fish to water! Image

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More from @teachplaygrub

Mar 10
1/I always say you can tell a bad read on a spine MR if it doesn’t talk about lateral recesses.

What will I think when I see your read? Do you rate lateral recess stenosis?

Here’s a thread on lateral recess anatomy & a grading system for lateral recess stenosis Image
2/First anatomy.

Thecal sac is like a highway, carrying the nerve roots down the lumbar spine.

Lateral recess is part of the lateral lumbar canal, which is essentially the exit for spinal nerve roots to get off the thecal sac highway & head out into the rest of the body Image
3/Exits have 3 main parts.

First is the deceleration lane, where the car slows down as it starts the process of exiting.

Then there is the off ramp itself, and this leads into the service road which takes the car to the roads that it needs to get to its destination Image
Read 21 tweets
Mar 3
1/Does PTERYGOPALATINE FOSSA anatomy feel as confusing as its spelling?

Does it seem to have as many openings as letters in its name?

Are you pterrified of the pterygopalatine fossa (PPF)?

Let this thread on PPF anatomy help you out. Image
2/The PPF is a crossroads between the skullbase & the extracranial head and neck

There are 4 main regions that meet here:

(1) Skullbase itself posteriorly, (2) nasal cavity medially, (3) infratemporal fossa laterally, and (4) orbit anteriorly. Image
3/At its most basic, you can think of the PPF as a room with 4 doors opening to each of these regions: one posteriorly to the skullbase, one medially to the nasal cavity, one laterally to the infratemporal fossa, and one anteriorly to the orbit Image
Read 18 tweets
Feb 28
1/Feel like a fish out of water when it comes to water on the brain?

Read on for this month’s @Radiographics summary of what you need to know about hydrocephalus!!



@cookyscan1 @RadG_editor #RGphx doi.org/10.1148/rg.240…Image
2/To understand hydrocephalus, think of CSF like the flow of traffic

3 main ways traffic backs up:

(1) Obstruction on the road:
For hydrocephalus, this is an obstruction along CSF in the ventricle Image
3/

(2) Obstruction of an off ramp
For hydrocephalus=obstruction at its off ramp into the venous system

(3) Rush hour
For hydrocephalus=over production Image
Read 8 tweets
Feb 27
1/Do scans for dizziness make your head spin?

Need to know what to look for?

Just hear me out!

This month’s @theAJNR SCANtastic will show what to look for:

ajnr.org/content/46/2/3…Image
2/I always remember the rhyme of the big three for dizz-ee!

First, are vestibular schwannomas

These give an ice cream cone shape in the internal auditory canal! So scoop up that finding! Image
3/Next is labyrinthitis

Labyrinthitis can look like night & day, depending on the timing

Late labyrinthitis is dark—loss of bright fluid signal on FIESTA

Early labyrinthitis is bright—enhances on post-contrast Image
Read 12 tweets
Feb 26
1/Time is brain! But what time is it?

If you don’t know the time of stroke onset, are you able to deduce it from imaging?

Here’s a thread to help you date a stroke on MRI! Image
2/Strokes evolve, or grow old, the same way people evolve or grow old

The appearance of stroke on imaging mirrors the life stages of a person—you just have to change days for a stroke into years for a person

So 15 day old stroke has features of a 15 year old person, etc. Image
3/Initially (less than 4-6 hrs), the only finding is restriction (brightness) on diffusion imaging (DWI)

You can remember this bc in the first few months, a baby does nothing but be swaddled or restricted

So early/newly born stroke is like a baby, only restricted Image
Read 10 tweets
Feb 25
1/My hardest thread yet! Are you up for the challenge?

How stroke perfusion imaging works!

Ever wonder why it’s Tmax & not Tmin?

Do you not question & let RAPID read the perfusion for you? Not anymore! Image
2/Perfusion imaging is based on one principle: When you inject CT or MR intravenous contrast, the contrast flows w/blood & so contrast can be a surrogate marker for blood.

This is key, b/c we can track contrast—it changes CT density or MR signal so we can see where it goes. Image
3/So if we can track how contrast gets to the tissue (by changes in CT density or MR signal), then we can approximate how BLOOD is getting to the tissue.

And how much blood is getting to the tissue is what perfusion imaging is all about. Image
Read 18 tweets

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