0:00

Let's take an axial midbrain specimen

0:03

in our discussion of classic PD.

0:05

We'll start on the viewer's left

0:08

where we have the red nucleus.

0:11

And actually, the red nucleus is right

0:15

up against the substantia nigra.

0:17

So, these have already started to bleed together.

0:20

But we do see a linear area of

0:25

iron staining that is brown,

0:27

that has a relatively delicate appearance to it,

0:30

something like this.

0:31

Sometimes you'll see more than one,

0:33

very reminiscent of the tail of a swallow.

0:37

Now,

0:38

this particular example was not completely normal

0:42

as we don't have a nice stripe between our red

0:44

nucleus and our substantia nigra

0:47

over here on the right,

0:49

we've lost the normal definition of the red nucleus,

0:52

which is a more advanced example

0:55

or case of Parkinson's disease.

0:57

And then look at the attenuated appearance or loss

1:01

of staining along the lateral aspect of the

1:04

substantia nigra.

1:05

There,

1:06

and also peripherally there.

1:08

We've lost our little linear delicate area

1:11

of staining along the margin free edge.

1:13

And a lot of times, in Parkinson's disease,

1:16

what you'll see is the substantia nigra very

1:19

intense and low signal here,

1:23

variable in the middle and then fades away on the

1:26

outside and then comes to a blunt end

1:29

as opposed to having this wispy,

1:31

fading away, swallow tail side.

1:34

Let's look at an MRI example with some

1:37

diagrams of the swallow tail.

1:40

There it is seen diagrammatically.

1:42

There's the swallow with the tail.

1:44

There's the magnified view of the substantia

1:48

nigra with the lateral swallow tail appearance

1:52

as opposed to the fat, short,

1:54

blunt-ended appearance of the substantia nigra

1:58

with hyper-concentration medially that

2:01

you'll see in Parkinson's disease.

2:03

The other sign of Parkinson's disease,

2:06

neither of which is specific, by the way,

2:08

loss of the swallow tail sign or bleeding of the

2:12

red nucleus into the substantia nigra

2:15

so that the two become inseparable.

2:18

Neither of those signs are specific

2:21

for Parkinson's disease.

2:23

But in mid to late-stage Parkinson's disease,

2:25

the absence of both of them would mitigate strongly

2:28

against the diagnosis of classic PD.