Lea Alhilali, MD Profile picture
Sep 25, 2022 8 tweets 4 min read Read on X
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 🧵 about how to look at the trigeminal nerve on MRI. #medtwitter #neurotwitter #neurorad #meded #FOAMed #HNrad Image
2/The most important thing to remember is that the nerve is 3D so you have to look for compression in all 3 planes. 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
3/Compression in the axial plane usually will deviate the nerve laterally—making it so that the Alien looks like he is flexing one of his arms. So if you see the Alien trying to show his guns—that’s microvascular compression! Image
4/In the sagittal plane, the nerve looks like an elephant’s trunk coming out of the pons. It should have a smooth curve up and over before it enters Meckel’s cave, just like the way an elephant’s trunk curves. Image
5/If the trunk is flattened, like it’s balancing ball or is curved downwards—that’s microvascular compression in the sagittal plane. If the nerve is pressed downward, you could miss this in the axial plane—bc the movement is parallel to the axial plane. You need a sagittal view Image
6/In the coronal plane, the nerves look like two gun barrels pointed at you, by a very potty bellied cowboy that is the pons. Image
7/If the nerves lose their gun barrel shape, and looks more like a boomerang—in any direction—that is microvascular compression. Coronal is usually the most helpful view, bc you can see movement both up and down and left to right. Image
8/So now you know what the normal trigeminal nerve looks like in all 3 planes—and you can now check for microvascular compression in three dimensions. Remember, images may be 2D, but life—and pathology—are 3D! Image

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More from @teachplaygrub

Dec 23
1/Does trying to figure out cochlear anatomy cause your head to spiral?

Hungry for some help?

Here’s a thread to help you untwist cochlear CT anatomy w/food analogies! Image
2/On axial temporal bone CT, you cannot see the whole cochlea at once. So let’s start at the bottom.

The first thing you come to is the basal turn of the cochlea (makes sense, basal=bottom). On axial images, it looks like a banana. I remember both Basal and Banana start w/B. Image
3/As you move up to the next slice, you start to see the upper turns of the cochlea coming in above the basal turn. They look like a stack of pancakes.

Pancakes are the heart of any breakfast, so they are at the heart or middle of the cochlea on imaging. Image
Read 9 tweets
Dec 19
1/Talk about dangerous liaisons!

Abnormal brain vascular connections like a dural arteriovenous fistula (dural AVF) can be dangerous!

This month’s @theAJNR SCANtastic thread is here to you some durable knowledge about dural AVFs!

ajnr.org/content/45/12/…Image
2/Dural sinuses sit inside dural leaflets.

Arteries that feed the dura also feed the walls of sinuses, like vasa vasorum.

Arteries in the walls of veins are a natural connection between the veins and arteries—but these connections are usually closed in normal pts. Image
3/Whether these connections are open depends on pressure.

Like a hose w/a hole in it, at normal pressures, abnormal connections are not open.

But if pressure is increased w/thrombosis or stenosis, the connections open, like high pressure water squirting out through a hole. Image
Read 18 tweets
Dec 6
1/Time to FESS up! Do you understand functional endoscopic sinus surgery (FESS)?

If you read sinus CTs, you better know what the surgeon is doing or you won’t know what you’re doing!

Here’s a thread to make sure you always make the important findings! Image
2/The first step is to insert the endoscope into the nasal cavity.

The first two structures encountered are the nasal septum and the inferior turbinate. Image
3/So on every sinus CT you read, the first question is whether there is enough room to insert the scope.

Will it go in smoothly or will it be a tight fit? Image
Read 19 tweets
Dec 2
1/Ready for a throw down?

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! Image
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 Image
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. Image
Read 17 tweets
Nov 27
1/Controversy in radiology can get tense!

The Mt Fuji sign for tension pnemocephalus is under scrutiny. When should you call it?

A thread about imaging this important neurosurgery complication Image
2/First, let’s clarify about what the Mt Fuji sign actually is

Most are familiar with the fact that large collections of pneumocephalus can compress the frontal lobes—making them look like the slopes of a mountain

But this isn’t actually enough to call Mt Fuji. Image
3/You also need to see frontal lobe separation

This means subdural air tension > the CSF surface tension between the frontal lobes

Water has one of the highest liquid surface tensions—so means pressure is high

This little V is why it looks like Mt Fuji, not any mountain Image
Read 9 tweets
Nov 25
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

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