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
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
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
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
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
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
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
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
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”!!
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@TheAJNR 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
@TheAJNR 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
1/Do radiologists sound like they are speaking a different language when they talk about MRI?
T1 shortening what? T2 prolongation who?
Here’s a translation w/an introductory thread to MRI.
2/Let’s start w/T1—it is #1 after all! T1 is for anatomy
Since it’s anatomic, brain structures will reflect the same color as real life
So gray matter is gray on T1 & white matter is white on T1
So if you see an image where gray is gray & white is white—you know it’s a T1
3/T1 is also for contrast
Contrast material helps us to see masses
Contrast can’t get into normal brain & spine bc of the blood brain barrier—but masses don’t have a blood brain barrier, so when you give contrast, masses will take it up & light up, making them easier to see.
1/Asking “How old are you?” can be dicey—both in real life & on MRI! Do you know how to tell the age of blood on MRI?
Here’s a thread on how to date blood on MRI so that the next time you see a hemorrhage, your guess on when it happened will always be in the right vein!
2/If you ask someone how to date blood on MRI, they’ll spit out a crazy mnemonic about babies that tells you what signal blood should be on T1 & T2 imaging by age.
But mnemonics are crutch—they help you memorize, but not understand. If you understand, you don’t need to memorize
3/If you look at the mnemonic, you will notice one thing—the T1 signal is all you need to tell if blood is acute, subacute or chronic.
T2 signal will tell if it is early or late in each of those time periods—but that type of detail isn’t needed in real life
Here's a little help on how to do it yourself w/a thread on how to read a head CT!
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!
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
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!
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
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.