0:00

This was a patient who presented with a clinical

0:04

history of left-sided exophthalmos.

0:08

With patients who have unilateral exophthalmos,

0:11

the most common etiology remains thyroid orbitopathy

0:16

or thyroid eye disease.

0:18

Yes, it's true that thyroid eye disease is generally a

0:21

bilateral process. However, even for unilateral proptosis,

0:25

it is the most common cause.

0:27

The differential diagnosis for unilateral proptosis often

0:31

is extension of sinus inflammation into the orbit,

0:35

which can cause proptosis. In this case,

0:39

the patient is again evaluated with axial and coronal

0:42

CT scan images and one sees the enlargement

0:48

of the extraocular muscles,

0:50

in this case largely the medial rectus muscle.

0:54

We note the sparing of the lateral rectus muscle.

0:57

One of the features of thyroid eye disease

1:01

that distinguishes it from pseudotumor,

1:04

which can also affect the extraocular muscles,

1:08

is the sparing of the tendinous insertions of the muscle.

1:13

So we say that thyroid eye disease

1:16

affects the belly of the muscle,

1:19

but will spare the tendon insertion of the

1:23

muscle to the globe. As we scroll,

1:25

we also see that this is true of the inferior rectus

1:29

muscle as it inserts on the globe as well,

1:32

that it is not as fat anteriorly where it inserts on

1:35

the muscle compared to the muscle belly itself.

1:39

Let's look at the coronal image.

1:41

You see that the superior rectus muscle is

1:44

also quite enlarged in this individual.

1:46

Let's magnify this and demonstrate it better.

1:51

So here is the superior rectus muscle,

1:54

which is quite large on the left side,

1:56

even larger than on the right side.

1:58

We still have a very fat medial rectus muscle and inferior

2:02

rectus muscle. As we course towards the globe.

2:06

You notice that the caliber of these muscles is decreasing

2:11

as the tendinous insertion is not involved.

2:14

This is to be contrasted with idiopathic

2:16

orbital inflammation,

2:18

where sometimes the tendon is most involved

2:21

and the muscle belly less so.

2:23

There is a lipogenic form of thyroid eye disease as well.

2:27

In this case, with lipogenic form,

2:30

one sees prominence of the orbital fat and protrusion of

2:34

the orbital fat out of the natural confines of the orbit,

2:38

and yet the muscles are not enlarged.

2:41

One of the hints that will show you that you're dealing

2:44

with the lipogenic form of thyroid eye disease is when the

2:49

lacrimal gland is displaced out of the lacrimal fossa and

2:53

is anterior to the bony margin of the lateral orbit.

2:57

In this patient, we see the lacrimal gland

3:00

end, which is anteriorly located from the lacrimal fossa

3:05

secondary to the proptosis associated

3:08

with thyroid eye disease.

3:10

So this would be another hint that one is dealing with

3:13

thyroid eye disease, the anterior displacement of the

3:17

lacrimal gland out of the orbit and into the soft

3:20

tissues anterior to the lateral orbital wall.