Thread by @teachplaygrub

1/Time to go with the flow!

Hoping no one notices you don’t know the anatomy of internal carotid (ICA)?

Do you say “carotid siphon” & hope no one asks for more detail?

Here’s a thread to help you siphon off some information about ICA anatomy!

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 b/c 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”!!