Lea Alhilali, MD Profile picture
Feb 22, 2023 16 tweets 8 min read Read on X
1/Having trouble remembering how to differentiate dementias on imaging?

Here’s a #tweetorial to show you how to remember the imaging findings in dementia & never forget!

#medtwitter #meded #neurorad #radres #dementia #alzheimers #neurotwitter #neurology #FOAMed #FOAMrad #PET
2/The most common functional imaging used in dementia is FDG PET. And the most common dementia is Alzheimer’s disease (AD).

On PET, AD demonstrates a typical Nike swoosh pattern—with decreased metabolism in the parietal & temporal regions
3/The swoosh rapidly tapers anteriorly—& so does hypometabolism in AD in the temporal lobe. It usually spares the anterior temporal poles.

So in AD look for a rapidly tapering Nike swoosh, w/hypometabolism in the parietal/temporal regions—sparing the anterior temporal pole
4/Medially, in AD, there’s involvement of the precuneus & posterior cingulate. In fact, the earliest AD findings may be in the precuneus

So medially, instead of a Nike swoosh, you see an Adidas logo—w/a wedge in the region of the precuneus widening anteriorly to the cingulate
5/So in AD, look for the sneaker signs:

—Adidas logo medially in the region of the precuneus

—Nike swoosh along the parietal & temporal regions, sparing the anterior temporal pole.

So if you see sneaker logos—it’s AD. Just call it!
6/Dementia w/Lewy Bodies (DLB) also has temporoparietal hypometabolism—but it also involves the occipital cortex—a very specific finding for DLB. DLB also extends to the ant. temporal cortex.

Together, these regions of hypometabolism look more like an L. And Lewy starts w/an L
7/Next is frontotemporal dementia. As one might expect, it has hypometabolism in…wait for it…the frontal & temporal regions. This is one for Captain Obvious. However, it is a little more complicated than that.
8/Medially, frontotemporal dementia involves the anterior cingulate gyrus. I remember this bc the involvement of the anterior cingulate gyrus makes a hook—so it looks like a lowercase letter f—and frontotemporal starts with f
9/There are also variants of frontotemporal dementia that will not show the classic frontal & temporal involvement.

First, is the frontal variant. This only involves the frontal lobe. It presents w/disinhibition as one would expect to see with frontal lobe involvement
10/Temporal variant involves temporal lobe only. Language processing is here (Wernicke’s anyone?). So this presents w/language difficulties (semantic dementia)

So you DON’T have to have BOTH frontal & temporal involvement to have frontotemporal dementia bc there are variants
11/Corticobasilar degeneration involves the sensorimotor cortex & basal ganglia.

I remember this bc CORTICObasilar goes along the CORTICOspinal tract—so it has hypometabolism at the home of the corticospinal tract, the sensorimotor cortex
12/You also see basal ganglia & thalamus hypometabolism in corticobasilar degeneration. This makes sense bc corticobasilar contains “BASilar” referring to the BASal ganglia

So the 2 regions of hypometabolism in corticobasilar degeneration are in the name—cortex & basal ganglia
13/A rare dementia is posterior cerebral atrophy (PCA). As its name implies, hypometabolism is POSTERIOR—occipital cortex & post temporal lobe

I like to call it posterior CAPE atrophy bc the distribution looks a cape—w/arms (ant temporal lobes) sticking out from under the cape
14/You might say PCA looks like Lewy Body dementia—but PCA doesn’t usuallly involve the ant temporal lobes

So the ant temp lobe involvement that gave Lewy body its L shape is cut short—making the PCA distribution look more like a c than an L

Remember C is PCA & L is Lewy body
15/Finally, vascular dementia has a variable distribution, depending on the regions infarcted (V is both for Vascular & Variable)

These patients may have wedged shaped regions of hypometabolism corresponding to cortical infarcts—remember this bc a wedge is just an inverted V.
16/So now you know the patterns of hypometabolism on PET for the major dementias

This list isn’t all inclusive & there can be variations or even mixed dementias

But hopefully this gives you a starting point you won’t soon forget!

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More from @teachplaygrub

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
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

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