Lea Alhilali, MD Profile picture
Jun 17, 2022 20 tweets 10 min read Read on X
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 #tweetorial on how to read a head CT!
#medtwitter #FOAMed #FOAMrad #medstudenttwitter #medstudent #neurorad #radres @MedTweetorials #neurosurgery 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 and denser things are brighter on CT Image
4/Once you see blood, the next question is—where is it? To know this, we need to know meningeal layers. Outer most layer is the dura mater. I remember it bc dura mater is DURAble. It is thick like a winter coat. Like a winter coat, it doesn’t hug the curves & hides rolls of fat. Image
5/Inner most layer is the pia mater. It is thin and hugs the curves of the brain like an adult onsie. I remember it bc pee-ah mater is just a few letters away from pee-jay mater—so it sounds like adult onsie PJs Image
6/In between these two layers is the arachnoid. It is called that because it contains web like septations like a spider’s web (ARACHnoid like ARACHnophobia). So now you know the meningeal layers. I remember the order bc the meninges “P-A-D” the brain—Pia/Arachnoid/Dura Image
7/Blood can be anywhere in these layers. EPIdural is beside the dura, or outside all layers. SUBdural is below the dura, but still outside pia & arachnoid. SUBarachnoid is below both dura & arachnoid. I’m skipping intraparenchymal hemorrhage here bc that is relatively obvious. Image
8/Each of these types of hemorrhage has a unique look on CT. Epidural hemorrhage is called “lentiform” bc it is convex out like a lens or a pregnant belly. Subdural hemorrhage wraps around the brain like a crescent. Subarachnoid hemorrhage is curvy between gyri like a snake Image
9/So why is intracranial hemorrhage so dangerous? You won’t exsanguinate from intracranial hemorrhage like a retroperitoneal bleed. The reason intracranial hemorrhage is so dangerous is bc the calvarium is a closed space with no give for anything extra. Image
10/So when you add something extra like blood, the calvarium won’t give, and something else has to—and that’s the brain. Blood will push on the brain causing damage from the associated mass effect. Image
11/Let’s talk about mass effect. Symmetry is beautiful—that’s why Denzel Washington is such the epitome of beauty bc he is perfectly symmetry. The brain on a CT should be symmetric. A CT tech once told me he could make all the findings on CTs bc all he did was look for asymmetry. Image
12/So on every CT you should look for symmetry—and things that are asymmetric are BAD. If you can’t draw a line down the middle have each side be a mirror image—something is wrong. Image
13/This asymmetry was from an subdural hemorrhage that was the same density as brain—making it difficult to visualize, but you could tell it was there from the asymmetry it caused. Mass effect causes asymmetry Image
14/Mass effect can cause brain to herniate into wrong compartments. There are 2 main herniation types. Subfalcine herniation is where one side slides under the falx to the other side. On CT, we call this midline shift—how much one side shifts under the midline to the other side Image
15/Next is transtentorial herniation—where the supratentorial compartment herniates through the tentorium that separates the cerebral hemispheres from the cerebellum. We see this on CT by effacement of the basilar cisterns—which are CSF spaces at the base of the brain. Image
16/The two most important cisterns for herniation are the suprasellar cistern—which looks like a pentagon—and the ambient/quadrigeminal cistern that look like the mouth of a semi-evil smiley face with the lateral and third ventricles as the eyes and nose. Image
17/With transtentorial herniation, we are looking for that pentagon to become a triangle or that smiley to get a Bell’s palsy—with part of it missing. If you see either of those, there is transtentorial herniation. Image
18/The final thing to look for on a head CT is a stroke. We see this as loss of gray-white differentiation. Normally, the interface between gray and white matter is crisp and looks like long octopus arms of white matter reaching out into the gray matter. Image
19/With a stroke, this interface gets blurred. It is like some took a painting that had a clear line between the white and gray matter and just smeared the white matter into the gray matter. If I see anywhere where the white matter looks smeared into the gray, I call an infarct Image
20/So now you know the basics of head CTs! Hopefully now your reads of the bread of neuroimaging will go smoothly like butter! Image

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Sep 13
1/Hate it when one radiologist called the stenosis mild, the next one said moderate--but it was unchanged?!

How do you grade it?

Do you estimate? Measure? Guess???

Here’s a thread about a lumbar grading system that’s easy, reproducible & evidence-based! Image
2/Lumbar stenosis has always been controversial.

In 2012, they tried to survey spine experts to get a consensus as to what are the most important criteria for canal & foraminal stenosis.  

And the consensus was…that there was no consensus

So what should you use to call it? Image
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Sep 9
1/Nothing is more CENTRAL to reading an MRI than finding the CENTRAL sulcus?

How do YOU find it?

Are you just using gestalt when you say “frontal” or “parietal”? 

Time to recenter your search pattern with this thread on how to find the central sulcus on a brain MRI! Image
2/On axial images, at the very top of the brain, the superior frontal gyrus & precentral gyrus combine to look like a bent knee

You can remember that bc precentral is the motor strip & you move by bending your knee! Image
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You can remember this bc superior frontal gyrus & precentral gyrus together look like a letter L.

And you make the L loser L sign w/your hand! Image
Read 12 tweets
Sep 3
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 thread about how to look at the trigeminal nerve on MRI! Image
2/The most important thing to remember is that the nerve is 3D so you have to look at it in all three planes.

So what is the normal and abnormal appearance of the trigeminal nerve in each plane? Image
3/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
Read 13 tweets
Aug 28
1/Feeling mad every time they ask you if it’s safe to give gad?

Do you know which gadolinium contrast material is safe to give?

At an impasse about the contrast class?

Read on as this month’s @theAJNR SCANtastic answers the question: Is Gad Bad?

ajnr.org/content/45/8/1…
Image
2/Whether or not to give gadolinium is a common question, as almost 1/2 of all MRI studies use gadolinium contrast.

Contrast-enhanced imaging can help elucidate many different pathologies, including tumors, demyelinating disease, & infection Image
3/What is gadolinium, that we're injecting into so many people?

It’s actually a metal, like iron or calcium. Pure gadolinium looks just like a shiny rock that you would find in a mine

But what makes gadolinium special for MRI is that it has 3 unpaired electrons Image
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Aug 19
1/Do questions about brainstem anatomy cause you to suddenly get a case of locked in syndrome?!

Do you try to localize the lesion or just wait for the MR?

Wait no more!

Here’s a thread about the brainstem Rule of Four to help you localize brainstem lesions! Image
2/The hallmark of a brainstem lesion/syndrome is:

(1) Ipsilateral cranial nerve deficit

(2) Contralateral body deficit (be it weakness, sensory loss, or ataxia) Image
3/You can remember this because often your head has certain feelings that opposite the feelings in your heart/body.

Similarly, the cranial nerve deficit can be the opposite of the body deficit

This split between head and body is key for recognizing brainstem syndromes Image
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Aug 16
1/Is your understanding of medial temporal anatomy, well, temporary?

If only there was a way to make hippocampal anatomy memorable!

Here is a thread of the basics of hippocampal anatomy that will hopefully stay in your hippocampus! Image
2/Its name “hippocampus” comes from its shape on gross anatomy.

Early anatomists thought it looked like an upside down seahorse—w/its curved tail resembling the tail of a seahorse.

Hippocampus literally means seahorse. Image
3/In cross section, it has a spiral appearance, leading to its other name, Cornu Ammonis, translated Ammon’s Horn.

Ammon was an Egyptian god w/spiraling rams horns.

The hippocampal subfields are abbreviated CA-1, CA-2, etc, w/CA standing for “Cornu Ammonis” Image
Read 17 tweets

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