Lea Alhilali, MD Profile picture
Jan 23, 2023 10 tweets 6 min read Read on X
1/Time to go with the flow!

Hoping no one notices you don’t know the anatomy of internal carotid (ICA)?

Do you say “carotid siphon” & hope no one asks for more detail?

Here’s a #tweetorial to help you w/ICA #anatomy!

#medtwitter #meded #neurotwitter #neurorad #radres #FOAMed Image
2/ICA is like a staircase—winding up through important anatomic regions like a staircase winding up to each floor

Lobby is the neck. First floor is skullbase/carotid canal. Next it stops at the cavernous sinus, before finally reaching the rooftop balcony of the intradural space Image
3/ICA is divided into numbered segments based on landmarks that denote transitions on its way up the floors.

C1 is in the lobby or neck.

You can remember this b/c the number 1 looks elongated & straight like a neck Image
4/C2 is the petrous or horizontal segment. This is where the ICA gets to the next floor, the skullbase

I remember this b/c the ICA makes a curve forward here, like a swan’s neck--and number 2 has a forward, swan like curve that looks just like the curve of the petrous segment Image
5/C3 is the lacerum segment—from above foramen lacerum to petrolingual ligament.

It’s easy to remember b/c lacerum comes from the latin word for torn (b/c foramen lacerum is irregular like a tear or laceration)

Number 3 zig zags like a laceration or torn edge, so C3 = lacerum Image
6/C4 is the cavernous segment

Cavernous segment has the anterior genu. Here, the ICA makes a curve back, so it looks like a knee (genu is latin for knee)

You can remember C4 is cavernous bc the number 4 has a curve back like the anterior genu of the cavernous ICA, like a knee Image
7/C5 is the clinoid segment—at the ant. clinoid process

Clinoid process gets its name from its sloped shape. It’s from the same latin root as recline (CLIN)

And we all take a break (take five some might say😉) by sitting back or reclining

Take FIVE & reCLINE. C5 is CLINoid Image
8/C6 is the ophthalmic segment.

I remember this b/c the circle of the number 6 looks like eyes and its curve looks like eyebrows.

So 6 is an eye = ophthalmic Image
9/C7 is the communicating or terminal segment

You can remember this bc the number 7 looks like the ICA ending & giving off the PCOMM

The number 7 has the shape of a turn off right before the road ends—& the ICA gives off the PCOMM in its C7 segment right before terminating Image
10/Now you can remember all the segments of the ICA!

Hopefully this will help you to be precise in your localization and siphon away the term “carotid siphon”!! Image

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More from @teachplaygrub

Sep 15
1/Time is brain!

So you don’t have time to struggle w/that stroke alert head CT.

Here’s a thread to help you with the CT findings in acute stroke! Image
2/CT in acute stroke has 2 main purposes

(1) exclude hemorrhage (a contraindication to thrombolysis)

(2) exclude other pathologies mimicking acute stroke. But you can also see other findings to help diagnosis a stroke. Image
3/Infarct appearance depends on timing.

In first 12 hrs, the most common imaging finding is…a normal head CT

However, you may see a hyperdense artery or basal ganglia obscuration. Later, you see loss of gray white differentiation & sulcal effacement Image
Read 13 tweets
Sep 12
1/Do you feel there’s a back-log of findings in a spine MRI report?

Everyone talks about discs & facets, but not everyone talks about the endplates

Do you?

Do you need to talk about degenerative changes (Modic changes) of the endplates?

Here’s thread w/all you need to know! Image
2/Over 30 years ago, Modic et al. found there were 3 types of degenerative endplate changes:

(1) T2 bright changes (indicating edema, Modic 1)
(2) T1 bright changes (indicating fat, Modic 2)
(3) T1 & T2 dark changes (indicating sclerosis, Modic 3)

But what do they mean? Image
3/Let’s start w/Modic 1.

These are bright on T2, indicating edema

On pathology, it’s what you’d expect w/edema: inflammation, vascular granulation tissue, & high cellular turnover

Vascular granulation tissue means these can enhance on post contrast images—mimicking discitis! Image
Read 18 tweets
Sep 10
1/Are you FISHING for a way to better evaluate subarachnoid hemorrhage?

Are you hungry for a way to classify these patients?

Donut you worry!

Here’s a short thread to help you remember the modified Fisher scale for classifying subarachnoid hemorrhage. Image
2/Just think of the brain as a donut. Like a donut, it’s a bunch of stuff around a hole in the middle.

Ventricles are the hole in the middle of the brain just like there’s a hole in the middle of the dough in a donut.

Just don’t quote me to your neuroanatomy professor…. Image
3/Subarachnoid hemorrhage (SAH) added to the brain makes it less healthy, the same way adding toppings to a donut makes it less healthy.

Increasing severity of SAH is like increasingly unhealthy donut toppings. Fisher scale quantifies the vasospasm risk for increasing SAH Image
Read 8 tweets
Sep 8
1/Talk about twisting your back!

Do spine vascular lesions make your brain feel as tangled as the dilated vessels you see?

Want some more information on malformations?

Here’s a thread on spine vascular anatomy to give you durable knowledge on dural arteriovenous fistulas (dAVF)Image
2/To understand spinal dural AVFs, you need to understand basic spinal vascular anatomy.

The spine is LONG—to get blood from the top to the bottom is like going through the length of a marathon course Image
3/So we will need to tackle it like you tackle running a marathon.

When you run a marathon, you replenish yourself at aid/water stations along the way so you can make it all the way through.

Same w/spinal arterial vasculature—it needs to be replenished on the way down. Image
Read 19 tweets
Sep 3
1/Does the work up for dizziness make your head spin?

Wondering what to look for on an MR for dizziness

This month’s @theAJNR SCANtastic will tell you all you need about imaging Meniere’s disease!

ajnr.org/content/46/8/1…Image
@TheAJNR 2/The etiology for dizziness can have very diverse causes—each with very different treatments.

So it is important to try to differentiate

Meniere’s is a common cause & we can help diagnose it w/imaging! Image
@TheAJNR 3/To understand Meniere’s disease, you must know labyrinth anatomy

It has layers, like Russian nesting dolls. Outer doll is the bony labyrinth, holding perilymph & a second doll—membranous labyrinth.

Inside the membranous labyrinth is endolymph Image
Read 13 tweets
Aug 1
1/They say form follows function!

Brain MRI anatomy is best understood in terms of both form & function.

Here’s a short thread to help you to remember important functional brain anatomy--so you truly can clinically correlate! Image
2/Let’s start at the top. At the vertex is the superior frontal gyrus. This is easy to remember, bc it’s at the top—and being at the top is superior. It’s like the superior king at the top of the vertex. Image
3/It is also easy to recognize on imaging. It looks like a big thumb pointing straight up out of the brain. I always look for that thumbs up when I am looking for the superior frontal gyrus (SFG) Image
Read 12 tweets

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