Lea Alhilali, MD Profile picture
Feb 1, 2023 15 tweets 8 min read Read on X
1/If all you know is: To Zanzibar By Motor Car—then you don’t even know half of facial nerve anatomy—literally!

Here’s a #tweetorial on the facial nerve anatomy you don’t know!

#medtwitter #neurotwitter #neurorad #radres #meded #FOAMed #neurosurgery #neurology #radtwitter
2/On coronal MRI sequences, the brainstem in the region of the facial nerve looks like a bodybuilder.

But it looks like one of those body builders who concentrates only on upper body workouts, so they are huge up top (the pons) & but have chicken legs (the medulla)
3/Facial nerve comes out in this region from between the pons & medulla.

It looks like a weightlifting belt, coming out from the waist between the giant pons upper body & the medulla chicken legs
4/Intracranial segments of the facial nerve follow the stages of life.

To begin, you are born. So is the facial nerve.

It leaves the pons at the root exit point—just as you exit your mother’s womb at birth
5/Next is the attached segment. This is the next stage of life

Just like after birth, you are very attached to your mother in childhood, so too is the facial nerve “attached” to the pons after its birth, like a little kid

It runs closely along the pons undersurface at first
6/Next stage of life is when you must finally leave the safety of clinging to your parents

So too must the facial nerve leave the undersurface of the pons. This is called the root detachment point

You can remember this b/c most teenagers are very cool & “detached” at this age
7/Next is stage of life is transitional.

After leaving for college, you’re not quite independent—you still go home & do your laundry & beg for money! So it’s a “transitional zone” for you

Same for facial nerve—initially it’s “transitional” between central & peripheral myelin
8/Finally is the cisternal segment. This is the stage of life when you’re finally mature & go out on your own

Same for the facial nerve. It’s left the central myelin of its pontine mama behind & is now fully peripheral myelin. It’s ready to go out & meet CN VIII in the IAC
9/The full course of the facial nerve is best seen on coronal images

On the axial images, you can see the portions after it has left the pons (root detachment point, transitional zone & cisternal segment)

You can’t see more proximally b/c this is covered by the pons on axials
10/It’s important to know this anatomy so you can look for compression of the facial nerve in this region.

Most often it’s compression from a vessel (microvascular compression).

Microvascular compression can lead to hemifacial spasm
11/This is most common in the transitional zone b/c central myelin is vulnerable & here central myelin is out in the cistern

It’s like how kids are most likely to get into trouble in the college years—b/c you’re still a kid, but now exposed to more temptations/real world danger
12/You can see compression of the transitional zone on the axial images b/c the transitional zone is after the nerve has left from under the pons

So always look for vessels compressing the nerve right next to pons—like bad influences bringing you trouble during the college years
13/Besides the college years, the next most common time to get into trouble is your childhood. Same w/the facial nerve

Next most common place for microvascular compression is the attached segment. Even though its under the roof of its pontine mama, it can still get punched
14/But you can’t see this area on axial images b/c it’s hidden under the pons!

Most common cause of a failed decompression is that transitional zone compression is relieved but attached segment compression is missed

So always check coronals for attached segment compression!
15/So now you know the intracranial facial nerve by remembering how its segments follow the stages of life—& you know where to look for compression by remembering which stages of life are vulnerable to trouble

Hopefully this will keep you out of trouble w/facial nerve anatomy!

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More from @teachplaygrub

Apr 25
1/Radiologist not answering the phone?

Just want a quick read on that stat head CT?

Here's a little help on how to do it yourself w/a thread on how to read a head CT! Image
2/In bread & butter neuroimaging—CT is the bread—maybe a little bland, not super exciting—but necessary & you can get a lot of nutrition out of it

MRI is like the butter—everyone loves it, it makes everything better, & it packs a lot of calories. Today, we start w/the bread! Image
3/The most important thing to look for on a head CT is blood.

Blood is Bright on a head CT—both start w/B.

Blood is bright bc for all it’s Nobel prizes, all CT is is a density measurement—and blood is denser (thicker) than water & denser things are brighter on CT Image
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Apr 23
1/Time to FESS up! Do you understand functional endoscopic sinus surgery (FESS)?

If you read sinus CTs, you better know what the surgeon is doing or you won’t know what you’re doing!

Here’s a thread to make sure you always make the important findings! Image
2/The first step is to insert the endoscope into the nasal cavity.

The first two structures encountered are the nasal septum and the inferior turbinate. Image
3/So on every sinus CT you read, the first question is whether there is enough room to insert the scope.

Will it go in smoothly or will it be a tight fit? Image
Read 19 tweets
Apr 21
1/Ready for a throw down?

MMA fights get a lot of attention, but MMA (middle meningeal art) & dural blood supply doesn’t get the attention it deserves.

A thread on dural vascular anatomy! Image
2/Everyone knows about the blood supply to the brain.

Circle of Willis anatomy is king and loved by everyone, while the vascular anatomy of the blood supply to the dura is the poor, wicked step child of vascular anatomy that is often forgotten Image
3/But dural vascular anatomy & supply are important, especially now that MMA embolizations are commonly for chronic recurrent subdurals.

It also important for understanding dural arteriovenous fistulas as well. Image
Read 17 tweets
Apr 16
1/ Need a global perspective on dementia?

Do you know the global cortical atrophy (GCA) score for evaluating dementia patients—or are you still gestalting volume loss???

Don’t estimate when you can calculate!

Here’s a thread of what you need to know about the GCA score! Image
2/The global cortical atrophy score calculates cortical volume loss on a scale of 0-3 in 13 different regions & ventricular dilatation

Gyri shrink down w/atrophy, the same way your cheeks shrink down with aging! Image
3/Gyri look like lips with around a mouth of sulcal space.

Without volume loss, the gyri look like big fat pursed model lips

But w/volume loss they open up like the scream w/thinning of the lips Image
Read 9 tweets
Apr 14
1/Wish that your knowledge of autoimmune encephalitis was automatic?

Do you feel in limbo about limbic encephalitis?

Do you know the patterns?

Read on for what you need to know in this month's @RadioGraphics review!



@cookyscan1 @RadG_Editor doi.org/10.1148/rg.240…Image
@RadioGraphics @cookyscan1 @RadG_Editor 2/Two pearls:
(1) Most common pattern is limbic encephalitis
(2) Small cell can cause any autoimmune pattern.

You can remember the causes by the demographic:
Young man: testicular
Older: Small cell
Woman with psychiatric symptoms (limbic): breast Image
@RadioGraphics @cookyscan1 @RadG_Editor 3/Limbic encephalitis is the most common pattern

But it has many, many different causes

Remember--limbic involvement is shaped like a question mark!

So for limbic encephalitis, the cause remains a question bc differential is so broad

Must question & clinically correlate! Image
Read 8 tweets
Apr 2
1/One important aspect to stroke care is well, ASPECTS.

It’s a simple score system—but it’s important to understand all aspects!

Read on for the latest research on ASPECTS in this month’s @theAJNR SCANtastic!

ajnr.org/content/46/3/5…Image
2/ASPECTS stands for “Alberta Stroke Program Early CT Score.”

It’s meant to replace gestalt-ing what percent of the MCA territory is infarcted.

Instead, it uses a 10-pt score to semi-quantitate the infarcted tissue in the MCA territory on non-contrast head CT Image
3/You can think of it as a score card for the MCA.

For each region of MCA territory NOT infarcted, the pt gets one point—for a highest score of 10, and lowest score of 0 Image
Read 18 tweets

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