Lea Alhilali, MD Profile picture
Mar 27 22 tweets 10 min read Twitter logo Read on Twitter
1/Feeling unarmed when it comes to evaluating cervical radiculopathy & foraminal narrowing on MR?

Here’s a #tweetorial that’ll take that weight off your shoulder & show you how to rate cervical foraminal stenosis!
#medtwitter #meded #FOAMed #radtwitter #neurorad #spine #radres
2/First, the anatomy. Nerve rootlets arise from the anterior & posterior horns, merging to form anterior (motor) & dorsal (sensory) nerves roots in the thecal sac.

These come together & the dorsal root has its dorsal root ganglion before the spinal nerve extends extravertebral
3/Think of it like a road system but carrying information/impulses instead of cars. Small roads (rootlets) merging to make larger roads (roots), before these finally merge together onto the big highway, which is the dorsal root ganglion and spinal nerve
4/This highway of impulses & information must travel from the spinal cord inside the dura, to the rest of the body/arms in the extravertebral space.

The neural foramen is the doorway to pass from intradural to extra vertebral.
5/Neural foramen is narrower than the intradural space/thecal sac or extravertebral region

It’s like our information highway must pass through a tollbooth—where the 8 lane highway narrows to 4. This can cause a bottleneck if there’s too much traffic before the road widens again
6/Impingement may occur anywhere on the highway (medial/intradural, intermediate/foraminal, lateral/extravertebral). Medially, it’s mostly from uncovertebral joint/disc which sit in front of the anterior root. Weakness may occur; amyotrophy will not w/o cord flattening also
7/At the other end (extravertebral), the nerve sits in the neural sulcus of the transverse process. It’s like an emergency exit slide from a plane—except it’s a nerve exiting a foramen not a plane. Posterior wall is the facet & hypertrophy here will hit the nerve in its slide
8/Impingement medially & laterally are rare compared to foraminal impingement, as foramen is the bottleneck (tollbooth) of our road from spinal cord to arm

Neural foramen is made of disc/uncovertebral joint anteriorly & facet posteriorly. Hypertrophy of either will narrow it
9/How do we image the foramen to detect stenosis/impingement?

Unlike the L-spine, we can’t do straight sagittals bc the foramina come at a 45 degree angle anteriorly—like when someone is reaching anteriorly to hug you

So true sagittals don’t show the foramen in cross-section
10/Maybe oblique sagittals perpendicular to the foramen?

Sounds great, but if there’s curve/kyphosis/rotation, position of the foramen changes w/respect to the oblique sagittal, so it may not be perpendicular anymore. Neck is susceptible to imperfect positioning in the scanner
11/How about axials?

Unlike the lumbar, where foramina take off at sharp angles like a Xmas tree—cervical foramina are much more flat, like a totem pole, so they are almost entirely in the axial plane.

Axial plane is 90 degrees & cervical foramina angles are very close to that
12/Axial images are actually good at evaluating cervical foramina.

Axial stenosis ratings have very good concordance w/oblique sagittal ratings (for experienced readers, not residents)--& using axials saves you 2 extra oblique sagittal acquisitions!
13/So how do we rate foraminal narrowing in the axial plane?

Think of the nerve root like a hot dog, sitting between the two buns of the disc/uncovertebral joint & facet. The more you put in your hot dog, the more the hot dog itself is squished. Same w/the nerve root.
14/Spurring & degenerative change are like the extra topping that push on the hot dog inside the buns. A small amount of toppings/degenerative change, leaves the hot dog space. But if you pile on fixings, then the hot dog is taken over.

Ask yourself--how is my hot dog doing?
15/So how much is too much?

Take inspiration from the carotid. W/carotid stenosis, narrowing the lumen >50% of the normal downstream lumen results in hemodynamic effects.

Same w/the foramen—narrowing it >50% of the downstream nerve causes significant symptoms
16/So mild stenosis is like when there’s calficied plaque in the carotid wall that doesn’t narrow it at all.

Moderate stenosis is when the plaque narrows the lumen, but not >50%.

And finally, severe stenosis is when you narrow it >50% of the normal downstream lumen
17/But there isn’t a downstream foramen like there’s a downstream lumen for the carotid. So you use the diameter of the normal extravertebral nerve instead—b/c it’s rarely compressed.

Mild stenosis is like just a little ketchup & mustard on the bun but hot dog still has space.
18/Moderate stenosis is when you aren’t just putting on sauce, you are adding things that take up space, like relish. But there’s only so much relish one can put on, so it doesn’t take up more than half the bun.
19/Severe stenosis is like a chili cheese dog, where the hot dog is smothered & it has no room in the bun away from the chili or cheese. Here the narrowing is greater than 50%
20/This is the Kim classification & has strong correlation w/symptoms

I like it bc it doesn’t require calipers to estimate a >50% narrowing

It’s technically for axial T2 images, but it’s been applied to gradient images & even CT, although there’s not yet confirmatory evidence
21/You might say, 50% stenosis may be hemodynamically significant, but it’s not severe. Why is it severe in the foramen?

It’s bc hemodynamics is linear, where more stenosis = more effect. But pain is kind of binary—once there’s pain, it’s there, whether narrowing is 55% or 95%
22/So now you know how to both image and assess stenosis in the cervical neural foramen.

Now hopefully rating cervical foraminal narrowing won’t be a pain in the neck!

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Mar 20
1/Does the work up for dizziness make your head spin?

Wondering what you should look for on an MRI for dizziness?

Here’s a #tweetorial on what you can (and can’t) see on MRI in #dizziness

#medtwitter #meded #neurotwitter #neurorad #radres #HNrad #neurotwitter #stroke #FOAMed Image
2/The etiology for dizziness depends both on how you define dizziness (i.e., vertigo, imbalance) & where you see the patient

For imaging, subtle distinctions in symptoms usually aren’t provided & many common diagnoses are without imaging findings (BPPV, vestibular migraine) Image
3/The most important finding on imaging for dizziness is a stroke from vertebrobasilar insufficiency (VBI)

It's a relatively uncommon etiology of dizziness, but its prevalence increases in emergent/acute dizziness populations

Missed VBI can have profound consequences/morbidity. Image
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Mar 15
1/I call the skullbase “homebase” bc you can’t make an anatomy homerun without it!

Most know the arteries of the skullbase, but few know the veins. Do you?

Here’s a🧵to help you remember #skullbase venous #anatomy!
#medtwitter #meded #neurorad #radtwitter #neurosurgery #radres Image
2/When I look at the skullbase veins, I see an angry Santa yelling at me. His eyebrows are raised, his mouth is open, & he has a mustache w/a big beard hanging down.

Each I look at the skullbase, I look for this Santa—bc each part of him is an important venous structure. Image
3/So let’s start w/Santa’s eyes. The eyes are actually not a venous structure, but an important landmark—foramen ovale, where the V3 trigeminal nerve exit.

I remember ovale is Santa's eyes bc eyes are OVAL, so his eyes are OVALE Image
Read 8 tweets
Mar 11
1/To call it or not to call it? That is the question!

Do you feel a bit wacky & wobbly when it comes to calling normal pressure hydrocephalus on imaging?

Here’s a #tweetorial about imaging NPH!

#medtwitter #meded #neurotwitter #neurorad #radres #dementia #neurosurgery #FOAMed
2/First, you must understand the pathophysiology of “idiopathic” or iNPH. It was first described in 1965—but, of the original six in the 1965 cohort, 4 were found to have underlying causes for hydrocephalus.

This begs the question—when do you stop looking & call it idiopathic?
3/Thus, some don’t believe true idiopathic NPH exists. After all, it’s a syndrome defined essentially only by response to a treatment w/o ever a placebo-controlled trial.

However, most believe iNPH does exist--but its underlying etiology is controversial. Several theories exist
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Mar 6
1/I always say you can tell a bad read on a spine MR if it doesn’t talk about the lateral recess

What will I think when I see your read? What do you say about lateral recesses?

Here’s a #tweetorial on lateral recess #anatomy & grading stenosis
#medtwitter #neurorad #spine
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
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.

The off ramp leads into the service road, which takes the car to the roads that it needs to get to its destination
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Feb 28
1/Does trying to remember inferior frontal gyrus anatomy leave you speechless?

Do you get a Broca’s aphasia trying to name the parts?

Here’s a #tweetorial to help you remember the #anatomy of this important region

#medtwitter #meded #neurotwitter #neurorad #radtwitter #radres
2/Anatomy of the inferior frontal gyrus (IFG) is best seen on the sagittal images, where it looks like the McDonald’s arches.

To find the IFG on MR, I open the sagittal images & scroll until I see the arches. When it comes to this method of finding the IFG, "i’m lovin it."
3/Inferior frontal gyrus also looks like a sideways 3 on sagittal images, if you prefer.

This 3 is helpful bc the inferior frontal gyrus has 3 parts—or "pars"
Read 13 tweets
Feb 22
1/Having trouble remembering how to differentiate dementias on imaging?

Here’s a #tweetorial to show you how to remember the imaging findings in dementia & never forget!

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2/The most common functional imaging used in dementia is FDG PET. And the most common dementia is Alzheimer’s disease (AD).

On PET, AD demonstrates a typical Nike swoosh pattern—with decreased metabolism in the parietal & temporal regions
3/The swoosh rapidly tapers anteriorly—& so does hypometabolism in AD in the temporal lobe. It usually spares the anterior temporal poles.

So in AD look for a rapidly tapering Nike swoosh, w/hypometabolism in the parietal/temporal regions—sparing the anterior temporal pole
Read 16 tweets

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