0:00

It's the CT scan of the head

0:03

in an eleven-month old child being performed

0:05

for delayed milestones.

0:08

So, we can see the lateral ventricles

0:12

and third ventricle.

0:13

They're upper normal in caliber,

0:14

but this can be normal at this age.

0:17

The rest of the head CT is

0:19

looking fairly normal.

0:20

We can see the anterior fontanelle

0:21

remains partially open,

0:23

which is appropriate for this age.

0:26

As we go posteriorly or inferiorly

0:30

into the posterior fossa,

0:31

we can see the cerebellar tonsils extending

0:34

into the level of the foramen magnum,

0:36

and even caudal to the level

0:37

of the foramen magnum.

0:39

This is suggestive of a Chiari Type I malformation,

0:43

and an MRI scan is helpful

0:46

to further characterize.

0:49

Again,

0:50

the landmarks that we look for are the basion

0:54

and the opisthion to represent the

0:58

level of the foramen magnum.

1:01

If we draw a line between the

1:03

basion and the opisthion,

1:05

we can measure the extent of

1:07

cerebellar tonsil ectopia,

1:09

and the cerebellar tonsils, in this case,

1:12

extend approximately 16 mm below the plane

1:14

of the foramen magnum.

1:16

But it's important to recognize that

1:20

the most important features

1:23

for evaluating a Chiari malformation

1:25

include things like clinical symptoms

1:29

and physiologic parameters.

1:31

Physiologic parameters such as CSF flow study,

1:34

and possibly the presence of syringohydromyelia,

1:39

which is an indication of a clinically

1:42

abnormal CSF flow study.

1:46

Just the extent of cerebellar tonsillar ectopia

1:49

alone is insufficient to fully characterize and

1:53

understand a Chiari Type I malformation.

1:58

This patient on a CSF flow study,

2:00

actually has slight narrowing of the CSF space

2:04

ventral to the brain stem at the

2:05

level of the foramen magnum.

2:07

But there's bidirectional flow

2:08

of cerebral spinal fluid.

2:10

Most importantly,

2:12

upon a detailed neurologic exam by a

2:15

neurosurgeon, this patient was asymptomatic.

2:18

There was no syringohydromyelia.

2:21

There was patent CSF flow dynamics at

2:24

the level of the foramen magnum.

2:25

And so, this patient was just observed.

2:28

And for four years,

2:30

upon repeat imaging,

2:32

there was no further development of an abnormality.

2:36

And over the course of four years,

2:39

they decided to not pursue surgery.

2:43

So, this is an example that just the level of

2:47

cerebellar tonsillar ectopia alone,

2:49

in this case, 16 mm,

2:51

which sounds like a lot,

2:52

is not uniquely sufficient to determine whether

2:56

or not a patient needs to get

2:58

a surgical decompression.