0:01

This is a head CT on a four-year-old boy

0:03

with a headache.

0:04

The head CT, at first glance,

0:07

looks fairly normal.

0:08

We're looking through it.

0:09

We're not seeing any sign of hydrocephalus,

0:12

any mass, or anything like that.

0:14

But as we go down lower,

0:16

we can see at the level of the foramen magnum,

0:18

there's fullness,

0:19

there's soft tissue-like material

0:21

posterior to the brain stem.

0:23

With modern CT scans,

0:25

we have the ability to have

0:26

multiplanar reformats.

0:28

And this sagittal reformat shows us cerebellar

0:31

tonsils protrude caudal to the level

0:33

of the foramen magnum.

0:35

This can be approximated on CT,

0:38

but the best characterization for this is on MR.

0:43

MR, if we zoom in,

0:46

allows us to see several landmarks.

0:49

There is the basion,

0:51

which is the inferior aspect of the clivus,

0:55

in particular,

0:56

the basioccipital portion of the clivus.

0:59

And then we have the opisthion.

1:01

The basion and opisthion represent the anterior

1:05

and posterior margins of the foramen magnum.

1:08

We can use that to draw a line

1:11

between the basion and the opisthion to

1:13

approximate the plane of the foramen magnum.

1:16

And then, we can make a measurement perpendicular

1:18

to that line to see how far caudal to that

1:22

plane the cerebellar tonsils extend.

1:25

And here, they extend approximately nine and a

1:27

half millimeters below the plane

1:28

of the foramen magnum.

1:30

And that is typically considered to

1:32

be a Chiari Type I malformation.

1:34

But how do we determine how significant this is?

1:37

Well, the extent of tonsillar descent

1:39

is one mechanism,

1:41

but another tool we have is CSF flow studies.

1:47

This is a dynamically acquired cardiac

1:51

gated phase-contrast image.

1:54

This is acquired sagittally at the

1:56

level of the foramen magnum.

1:58

We can see the basic anatomic details

2:01

that we see in the structural image.

2:03

And as we

2:06

scroll through the cine,

2:08

we can see different phases of CSF pulsations.

2:13

And we can see here the brainstem,

2:18

the upper cervical cord.

2:21

And so this is the cervical medullary junction.

2:24

And we can see that ventral to the brainstem

2:27

and cervical medullary junction,

2:29

we have patent bi-directional flow

2:32

of cerebrospinal fluid.

2:33

We can see it going from dark

2:36

to bright.

2:38

So that is showing two different

2:41

directions of flow.

2:42

We're also seeing flow posterior to the brainstem

2:46

at the level of the foramen magnum.

2:48

So this is a sign that,

2:51

at the time the study is performed,

2:54

there's not a significant alteration

2:57

in CSF flow dynamics

2:59

at the level the foramen magnum.

3:01

Now,

3:02

one of the other things that's a part of a

3:05

Chiari Type I malformation imaging workup

3:08

is imaging of the cervical spine.

3:11

And we can see here the cerebellar tonsillar

3:14

ectopia extending below the plane

3:16

of the foramen magnum.

3:17

And what we see of the cervical

3:19

cord looks normal.

3:20

We do not see any signs of a fluid collection

3:23

within, either hydromyelia or syringohydromyelia.

3:27

So, this case is an example

3:30

of a mild Chiari Type I malformation

3:33

without appreciable

3:34

alteration in CSF flow dynamics

3:36

and without evidence of syringohydromyelia.