0:00

Let's take a look at the pars marginalis

0:02

in the axial projection.

0:05

Now, if I were to localize the pars marginalis,

0:08

in the sagittal projection,

0:10

the continuation of the cingulate sulcus,

0:12

following it on up to the pars marginalis or marginal sulcus,

0:17

that corresponds to these two foci that look a

0:21

little bit like kind of a droopy mustache, if you will,

0:24

perhaps Salvador Dali's mustache.

0:27

Now, if we were to look at how we would acquire CT cuts,

0:31

so we would acquire them obliquely like this,

0:34

that would mean that the marginal sulcus or the pars

0:38

marginalis kind of has the same position as we go from

0:42

caudad to craniad in the axial projection.

0:45

On the other hand, if we are acquiring MR images,

0:50

they're going to be in the orthogonal projection.

0:52

So let's, once again, draw the pars marginalis.

0:57

This time we have orthogonal cuts.

1:00

Let's just change color to make it really clear.

1:02

If we're going this way,

1:06

look at what happens to the pars marginalis.

1:08

As we go up,

1:09

it goes more posterior or sits more posteriorly.

1:14

Now, let's look in the axial projection.

1:17

Here we are down low in the pars marginalis,

1:20

which is this ascending sulcal structure.

1:22

Right here.

1:23

We have our droopy mustache.

1:25

And then as we go up,

1:27

the mustache is a little bit straighter.

1:30

It's also found at the widest biparietal

1:32

diameter at the 9 o'clock, 3 o'clock position,

1:36

typically is where you're going to see

1:38

the pars marginalis.

1:39

And there it is.

1:41

Our mustache is getting a little bit straighter.

1:43

Let's keep going more craniad.

1:46

And now our mustache is kind of flipping up a little bit

1:48

like Salvador Dali's mustache that's no longer drooping.

1:52

And why is this important?

1:54

It's important because just anterior to the

1:57

pars marginalis is the central sulcus.

2:01

And this little notch right here in the precentral gyrus

2:05

is the hand motor area of the left cerebral hemisphere,

2:09

similarly on the right side.

2:11

The central sulcus of Rolando

2:13

sits anterior to this little basket right here,

2:16

so it kind of pokes its way just in

2:18

front of the pars marginalis,

2:20

while directly behind it is the postcentral sulcus.

2:25

You all know from prior vignettes,

2:27

if you've watched them,

2:28

that the postcentral sulcus is the upswing

2:32

of the arcuate-shaped intraparietal sulcus.

2:35

So we've got postcentral sulcus,

2:37

precentral sulcus, precentral gyrus, postcentral gyrus,

2:43

hand motor area,

2:45

pars marginalis.

2:47

And the pars marginalis looks a little bit different

2:50

on MR than CT for reasons previously discussed.

2:54

Pomeranz out.