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Lea Alhilali, MD

@teachplaygrub

May 16, 2022 • 7 tweets • 4 min read • Read on X

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1/
Why is cranial nerve 6 uniquely affected by⬆️ intracranial pressure? Why is it special? A common question after the CN6 tweetorial.
Here is a maybe #tweetorial, but maybe a🧵about why CN6 is alone affected by ⬆️ pressure. #FOAMed #medtwitter #Medstudenttwitter #neurotwitter

2/
Think of the intracranial CSF space like a balloon, distended by CSF instead of air. Cranial nerves begin inside the balloon, and then they exit as they begin their extradural portion

3/
Most cranial nerves move immediately away from the CSF space after they exit—usually going out through their respective foramina. However, CN6 uniquely runs along the outside of the “balloon” in Dorello canal

4/
Increased intracranial pressure is like expanding the balloon. Most cranial nerves are not affected by the expanded balloon because they move away from the surface of the balloon right after they exit

5/
However, because of the unique course of CN6 along the surface of the “balloon” in Dorello canal, the increased intracranial pressure or expanding “balloon” pushes against the extradural portion of CN6

6/
Unfortunately, CN6 has nowhere to go to escape this increased pressure, as on the other side of it is the clivus. So in the increased pressure pushes it against the clivus in Dorello canal

7/
This makes a “CN6 sandwich”! CN6 gets sandwiched between clivus & dura. It's this compression that uniquely gives you an isolated CN6 palsy w/⬆️pressure!
So when you see an isolated CN6 palsy in intracranial hypertension, think of balloons & sandwiches & you’ll remember why!

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More from @teachplaygrub

Lea Alhilali, MD

@teachplaygrub

Mar 16

1/Remembering spinal fracture classifications is back breaking work!

A thread to review the scoring system for thoracic & lumbar fractures—“TLICS” to the cool kids!

2/TLICS scores a fx on (1) morphology & (2) posterior ligamentous complex injury

Let's start w/morphology

TLICS scores severity like the steps to make & eat a pizza:

Mild compression (kneading), strong compression (rolling), rotation (tossing), & distraction (tearing in)

3/At the most mild, w/only mild axial loading, you get the simplest fx, a compression fx—like a simple long bone fx--worth 1 pt.

This is like when you just start to kneading the dough. There's pressure, but not as much as with a rolling pin!

Read 13 tweets

Lea Alhilali, MD

@teachplaygrub

Mar 14

1/The 90s called & wants its carotid imaging back!

It’s been 30 years--why are you still just quoting NASCET?

Do you feel vulnerable when it comes to identifying plaque vulnerability?

Here’s a thread to help you identify high risk plaques with carotid plaque imaging

2/Everyone knows the NASCET criteria:

If the patient is symptomatic & the greatest stenosis from the plaque is >70% of the diameter of normal distal lumen, patient will likely benefit from carotid endarterectomy.

But that doesn’t mean the remaining patients are just fine!

3/Yes, carotid plaques resulting in high grade stenosis are high risk.

But assuming that stenosis is the only mechanism by which a carotid plaque is high risk is like assuming that the only way to kill someone is by strangulation.

Read 25 tweets

Lea Alhilali, MD

@teachplaygrub

Mar 12

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!

https://x.com/teachplaygrub/status/1587472264764657664

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:

https://x.com/teachplaygrub/status/1587472264764657664

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 pts

Read 12 tweets

Lea Alhilali, MD

@teachplaygrub

Mar 10

1/I always say you can tell a bad read on a spine MR if it doesn’t talk about lateral recesses.

What will I think when I see your read? Do you rate lateral recess stenosis?

Here’s a thread on lateral recess anatomy & a grading system for lateral recess stenosis

2/First anatomy.

Thecal sac is like a highway, carrying the nerve roots down the lumbar spine.

Lateral recess is part of the lateral lumbar canal, which is essentially the exit for spinal nerve roots to get off the thecal sac highway & head out into the rest of the body

3/Exits have 3 main parts.

First is the deceleration lane, where the car slows down as it starts the process of exiting.

Then there is the off ramp itself, and this leads into the service road which takes the car to the roads that it needs to get to its destination

Read 21 tweets

Lea Alhilali, MD

@teachplaygrub

Mar 3

1/Does PTERYGOPALATINE FOSSA anatomy feel as confusing as its spelling?

Does it seem to have as many openings as letters in its name?

Are you pterrified of the pterygopalatine fossa (PPF)?

Let this thread on PPF anatomy help you out.

2/The PPF is a crossroads between the skullbase & the extracranial head and neck

There are 4 main regions that meet here:

(1) Skullbase itself posteriorly, (2) nasal cavity medially, (3) infratemporal fossa laterally, and (4) orbit anteriorly.

3/At its most basic, you can think of the PPF as a room with 4 doors opening to each of these regions: one posteriorly to the skullbase, one medially to the nasal cavity, one laterally to the infratemporal fossa, and one anteriorly to the orbit

Read 18 tweets

Lea Alhilali, MD

@teachplaygrub

Feb 28

1/Feel like a fish out of water when it comes to water on the brain?

Read on for this month’s @Radiographics summary of what you need to know about hydrocephalus!!

@cookyscan1 @RadG_editor #RGphx doi.org/10.1148/rg.240…

2/To understand hydrocephalus, think of CSF like the flow of traffic

3 main ways traffic backs up:

(1) Obstruction on the road:
For hydrocephalus, this is an obstruction along CSF in the ventricle

3/

(2) Obstruction of an off ramp
For hydrocephalus=obstruction at its off ramp into the venous system

(3) Rush hour
For hydrocephalus=over production

Read 8 tweets

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