Lea Alhilali, MD Profile picture
Oct 4, 2022 18 tweets 10 min read Read on X
1/Ready for some heavy lifting? My second #tweetorial on the BRACHIAL PLEXUS! This time we cover how the #brachialplexus looks on #MRI.

#medtwitter #meded #neurosurgery #orthotwitter #orthopedics #neurorad #radres #medstudent #FOAMed #FOAMrad #spine #radiology #neurotwitter Image
2/Brachial plexus is how the cervical nerves reach the arm. In the coronal plane, it looks like a slide, guiding nerves downward. Bc nerves are traveling laterally, sagittal MRI plane is our plane of choice to cut the nerves in cross section & see down the barrel of the nerves Image
3/But it’s more than a slide, it’s a complex highway, w/nerves joining & dividing—like highway off ramps & on ramps. If you want to know more about this intrinsic anatomy, see my first brachial plexus tweetorial here: Image
4/The most medial sagittal cut, right after the neural foramina, shows us the roots (Remember Rad Techs Drink Cold Beer). In the sagittal plane, the roots look like the rungs of a ladder. This makes sense, bc we are climbing up the ladder of the slide to go down to the arm Image
5/The anatomic landmark for the roots is the 1st rib head. I remember this bc the roots are closest to the CNS or HEAD, so they are by the rib HEAD. The roots together w/the rib head make the ladder look like a folding ladder, w/the rib head supporting the ladder root rungs Image
6/Here are the roots on a sagittal MRI—ladder rungs are the roots, supported like a folding ladder by the first rib head. Image
7/Next are the trunks. Trunks on sagittal MRI are easy—they are arranged like, wait for it…a tree TRUNK. They are right behind the subclavian artery, which looks like a little shrub in front of the tree trunk. Image
8/There are 2 anatomic landmarks for the trunks. Trunks are at the posterior 1st rib & in between the scalene muscles. The rib & the scalene look like an A-frame house, one that people often have for cabins in the woods. So you have trees & bushes in front of a A-frame cabin. Image
9/Here are the trunks on a sagittal MRI, with the trunks looking like, well, trunks & the scalene muscles making the A-frame cabin in the woods in the background. Image
10/Next is the divisions. I remember what these look like on sagittal images by remembering that DIVISIONS are DIVINE /DRESSY—all w/the letter D. They look like a fancy hair updo on top of the subclavian artery head. Image
11/The anatomic landmark for the divisions is the clavicle. The divisions sit BEHIND the clavicle. I remember this bc Victorian ladies with fancy updos will have fans that they hide their face behind. Similarly, the divisions hide behind the clavicle. Image
12/Here are the divisions on a sagittal MRI, they are clumped together like a fancy bun above the head of the subclavian. The clavicle is in front of them, allowing them to keep their Victorian modesty from the prying eyes of men Image
13/Next are the cords. The subclavian artery and the cords are organized so they look like a paw print. I remember this bc both Cord and Cat start w/C. So cords make a cat claw print. Image
14/Anatomic landmark for the cords is the coracoid. Cords are underneath the coracoid. I remember this bc Cats who make the paw prints are always hiding under something like a couch. So the cords hide under the coracoid. I remember it’s the CORacoid bc cats hide when CORnered Image
15/Here are the cords on a sagittal MRI, with the paw print hiding underneath the coracoid process above it. Image
16/Last are the branches. In the sagittal plane, the subclavian artery together w/the branches looks like a fat beetle with four legs. I remember this bc Branches and Beetle, or Bug, all start w/B. Image
17/Here are the branches on sagittal MRI, w/the subclavian artery as fat body of the beetle and the branches as the beetle’s arms. Image
18/You can remember this w/an old fashioned fairy tale--about a house in the woods, home to a divine but shy princess. She had a cat that hid under things & ate all bugs in the home, bc no princess wants bugs! Now you know the imaging anatomy. Next tweetorial will be pathology! Image

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More from @teachplaygrub

Jul 29
1/Talk about bad blood!

Do you know when a hematoma is going to expand?

Read on for month’s @theAJNR SCANtastic on all you need to know about imaging intracranial hemorrhage!

ajnr.org/content/46/7/1…Image
@TheAJNR 2/Everyone knows about the spot sign for intracranial hemorrhage

It’s when arterial contrast is seen within a hematoma on CTA, indicating active
extravasation of contrast into the hematoma.

But what if you want to know before the CTA? Image
@TheAJNR 3/Turns out there are non-contrast head CT signs that a hematoma may expand that perform similarly to the spot sign—and together can be very accurate.

How can you remember what they are? Image
Read 9 tweets
Jul 25
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 thread to help you siphon off some information about ICA anatomy! 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
Read 10 tweets
Jul 23
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
Jul 21
1/Do you know all the aspects of, well, ASPECTS?

Many know the anterior circulation stroke scoring system—but posterior circulation (pc) ASPECTS is often left behind

25% of infarcts are posterior circulation

Do you know pc-ASPECTS?!

Here’s how to remember pc-ASPECTS! Image
2/Many know anterior circulation ASPECTS.

It uses a 10-point scoring system to semi-quantitation the amount of the MCA territory infarcted on non-contrast head CT

If you need a review: here’s my thread on ASPECTS: Image
3/But it’s only useful for the anterior circulation.

Posterior circulation accounts for ~25% of infarcts.

Even w/recanalization, many of these pts do poorly bc of the extent of already infarcted tissue.

So there’s a need to quantitate the amount of infarcted tissue in these ptsImage
Read 12 tweets
Jul 2
1/The medulla is anything but DULL!

Does seeing an infarct in the medulla cause your heart to skip a beat?

Does medullary anatomy send you into respiratory arrest?

Never fear, here is a thread on the major medullary syndromes! Image
2/The medulla is like a toll road.

Everything going down into the cord must pass through the medulla & everything from the cord going back up to the brain must too.

That’s a lot of tracts for a very small territory. Luckily you don’t need to know every tract Image
3/Medulla has 4 main vascular territories, spread out like a fan: anteromedial, anterolateral, lateral, and posterior.

You don’t need to remember their names, just the territory they cover—and I’ll show you how Image
Read 18 tweets
Jun 30
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

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