0:00

We're about to proceed from the neoplastic

0:05

category and demyelination category,

0:09

to the congenital category

0:11

in looking at lesions of the intradural

0:14

intramedullary spinal cord. Far and away,

0:17

the most common is going to be syringohydromyelia

0:22

associated with a Chiari I malformation.

0:25

As we look at this T1, T2, and STIR image.

0:30

what we see is the cerebellar tonsils are

0:33

descended through the foramen magnum.

0:36

We can measure this by drawing a line across the

0:40

foramen magnum and then the depth of the

0:48

cerebellar tonsils,

0:50

and this measures 9 mm down here in yellow.

0:55

9 mm is above the threshold, we usually set at

1:00

5 mm below the level of the foramen magnum

1:02

for cerebellar tonsillar descent.

1:05

Over the course of the past several years,

1:08

we've discovered a number of cases of.

1:11

intracranial hypotension, secondary

1:14

to CSF leakage in the spine,

1:17

which has led to acquired cerebellar tonsillar

1:22

descent through the foramen magnum.

1:24

So this is now a differential diagnosis,

1:27

not just a willy-nilly diagnosis of Chiari I malformation.

1:31

Now we have to look for other manifestations,

1:34

potentially of intracranial hypotension.

1:37

Whenever you have cerebellar tonsils extending

1:39

through the foramen magnum,

1:41

you have the potential for alteration

1:43

of the CSF flow mechanics.

1:46

And that can lead to the presence of syringohydromyelia .

1:52

The purists would say that hydromyelia

1:56

is dilatation of the central canal

2:00

of the spinal cord, whereas a syrinx is a cavity

2:07

or fluid collection eccentric from the

2:11

central canal of the spinal cord.

2:14

Because in many instances, we can't tell whether

2:17

it's actually eccentric or centrally

2:19

located within the spinal cord.

2:21

We will combine the two terms and use

2:25

syringohydromyelia. Classically with Chiari I

2:28

malformations, tonsillar herniation

2:31

through the foramen magnum,

2:32

it is classically a hydromyelic cavity.

2:37

And the etiology for this appears to be that

2:39

with the obstruction of normal CSF flow, the

2:43

pressure builds in the spine and is transmitted

2:47

along the perivascular spaces of the spinal cord

2:51

into the central canal where it decompresses

2:55

in the spinal cord.

2:57

So this is the explanation for why one gets

3:00

hydromyelia associated with a Chiari one malformation.

3:05

The treatment for the Chiari I malformation

3:08

is a suboccipital decompression procedure,

3:11

often taking the posterior arch of C1 because

3:14

this also contributes to the narrowing.

3:17

And then there is a duraplasty procedure to

3:20

expand the CSF cavity, so that way the tonsils.

3:24

freely move in the CSF space and there is good pulsation.

3:30

This patient has superimposed degenerative disc disease.

3:33

You notice a herniation at C4-5

3:35

and again at C6-7, and also has one of the characteristic

3:39

features of syringohydromyelia.

3:43

and that is that there appear to be webs or

3:47

multiple cavities to this collection that you're

3:50

seeing on the T1 and T2-weighted scans.

3:55

So,

3:57

Chiari I malformation associated

4:00

with hydromyelia or syringohydromyelia.

4:04

Remember that we use the term Chiari I

4:07

malformation in those cases that do not have

4:11

congenital myelomeningoceles. For that,

4:15

we will use the term Arnold Chiari malformation.