Lea Alhilali, MD Profile picture
Sep 25, 2022 8 tweets 4 min read Read on X
1/Sometimes the tiniest thing can be the biggest pain—that’s microvascular compression of the trigeminal nerve! But seeing such a tiny finding can be hard!

Here’s a 🧵 about how to look at the trigeminal nerve on MRI. #medtwitter #neurotwitter #neurorad #meded #FOAMed #HNrad Image
2/The most important thing to remember is that the nerve is 3D so you have to look for compression in all 3 planes. Let’s start w/the axial plane. On a normal axial, the trigeminal nerves should look like the arms of an alien sticking out of the pons. Image
3/Compression in the axial plane usually will deviate the nerve laterally—making it so that the Alien looks like he is flexing one of his arms. So if you see the Alien trying to show his guns—that’s microvascular compression! Image
4/In the sagittal plane, the nerve looks like an elephant’s trunk coming out of the pons. It should have a smooth curve up and over before it enters Meckel’s cave, just like the way an elephant’s trunk curves. Image
5/If the trunk is flattened, like it’s balancing ball or is curved downwards—that’s microvascular compression in the sagittal plane. If the nerve is pressed downward, you could miss this in the axial plane—bc the movement is parallel to the axial plane. You need a sagittal view Image
6/In the coronal plane, the nerves look like two gun barrels pointed at you, by a very potty bellied cowboy that is the pons. Image
7/If the nerves lose their gun barrel shape, and looks more like a boomerang—in any direction—that is microvascular compression. Coronal is usually the most helpful view, bc you can see movement both up and down and left to right. Image
8/So now you know what the normal trigeminal nerve looks like in all 3 planes—and you can now check for microvascular compression in three dimensions. Remember, images may be 2D, but life—and pathology—are 3D! Image

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More from @teachplaygrub

May 21
1/Having trouble remembering what you should look for in vascular dementia on imaging?

Almost everyone worked up for dementia has infarcts. Which ones are important?

Here’s a thread on the key findings in vascular dementia! Image
2/Vascular cognitive impairment, or its most serious form, vascular dementia, used to be called multi-infarct dementia.

It was thought dementia directly resulted from brain volume loss from infarcts, w/the thought that 50-100cc of infarcted related volume loss caused dementia Image
3/But that’s now outdated. We now know vascular dementia results from diverse pathologies that all share a common vascular origin.

It’s possible to lose little volume from infarct & still result in dementia.

So if infarcts are common—which contribute to vascular dementia? Image
Read 21 tweets
May 20
1/Correlate clinically!

It’s harder than you think in THALAMUS—where its size is small & but the clinical symptoms are large.

Here’s a thread to help you remember the main thalamic syndromes & their locations! Image
2/Thalamus is a dense network of nuclei & tracts connected to almost everything in the brain. So almost any symptom can be correlated to it.

So saying “thalamus” as the answer when asked where a lesion is located is always reasonable—even w/o knowing what the symptoms are! Image
3/Think of the thalamus like the internet service provider or ISP for the brain.

Like an ISP, everywhere is connected through it. And like an ISP, things go bad when it goes down.

But just like an ISP, the problems created depend on where in the network the outage is located. Image
Read 23 tweets
May 17
1/ I always say, "Anyone can see the bright spot on diffusion images—what sets you apart is if you can tell them why it’s there!”

If you don't why a stroke happened, you can't prevent the next one!

Can YOU tell a stroke’s etiology from an MRI?

Here’s a thread to show you how! Image
2/First a review of the vascular territories.

I think the vascular territories look a butterfly—w/the ACA as the head/body, PCA as the butt/tail, and MCA territories spreading out like a butterfly wings. Image
3/Of course, it’s more complicated than that.

Medially, there are also small vessel territories—the lenticulostriates & anterior choroidal.

I think they look like little legs, coming out from between the ACA body & PCA tail. Image
Read 25 tweets
May 14
1/Got the diagnosis when it comes to vessel stenosis?

Or is your knowledge narrow when it comes to vessel narrowing?

When it comes to vasospasm, do you know why it happens or what to look for?

Here is the thread you NEED to unravel why vessels twist up! Image
2/Vasospasm results from subarachnoid hemorrhage (SAH) & a buildup of multiple factors

It’s like how you can handle 1 nag from your boss on Monday—but after nagging all week, you break down on Friday!

Same w/vasospasm—it doesn’t happen until the end of the week after SAH! Image
3/So what is nagging that causes the vessel to shut down?

When the body breaks down blood from SAH, it releases free heme

And this free heme causes a cascade of negative consequences, call heme-related inflammation

So free heme is the annoying boss! Image
Read 21 tweets
May 13
1/ “Now listen carefully!”

Everyone has so much fear about the anatomy where they hear!

Do you dread temporal bone anatomy?

Do find the understanding ossicles impossible?

Do you know the ice cream cone sign on CT & then nada?

Then you need this thread on ossicular anatomy! Image
2/For the middle ear, I have a rule of 3s.

Middle ear is divided into 3 parts & it contains 3 ossicles.

Today we will focus on the ossicles—each of which has 3 parts! Image
3/First ossicle you meet when you enter the middle ear is the malleus.

It’s called the malleus because it acts like a mallet that hits a drum—literally—the ear drum!

I think it looks like Dr. Evil’s mini me, with its short body and round bald head Image
Read 19 tweets
May 10
1/Have disagreements between radiologists on the degree of cervical canal stenosis become a pain in the neck?!

Worried about sticking your neck out and calling severe cervical stenosis?

Here’s a thread on cervical stenosis grading that’s easy, reproducible & evidence based! 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 dynamically, some say repetitive microtrauma, & some say micro-ischemia from compression of perforators Image
Read 18 tweets

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