0:00

Continuing the theme of extraconal lesions of the orbit,

0:04

we find this patient presented with right-sided

0:09

exophthalmos. On the coronal T1-weighted scan,

0:13

as we scroll through the lesions,

0:15

we notice that the patient has a previous medial

0:19

orbital wall lamina papyracea fracture with some

0:23

herniation of fat as well as the medial

0:27

rectus muscle that is incidental.

0:30

Continuing further posterior,

0:32

we come into a lesion which is displacing the

0:37

medial rectus muscle medially and the superior

0:40

rectus muscle medially and inferiorly.

0:44

So here's our medial rectus muscle and our superior

0:48

rectus muscle displaced by the mass.

0:51

So this identifies this as an extraconal.

0:54

It's outside the muscle cone and actually

0:56

displacing the muscles medially. The mass is.

1:00

Quite large and displaces the optic nerve as well medially,

1:07

it continues further posterior in the orbit

1:11

to the orbital apex. And as you can see,

1:14

there is replacement of the high signal intensity

1:18

of the anterior clinoid process, bone marrow by the mass.

1:22

So here is the bone marrow of the anterior process on

1:26

the left side and this mass actually emanates

1:29

from the anterior clinoid process.

1:32

So this is a bony mass that is infiltrating

1:35

anteriorly into the orbit in the extraconal space.

1:39

Let's look at its characteristics on the T2-weighted imaging.

1:44

The lesion is seen as being very dark in signal

1:48

intensity on the T2-weighted scans.

1:52

So here we see the mass on the T2-weighted

1:56

scan, low in signal intensity.

1:58

This may suggest it can either be bone or it can be fibrous tissue,

2:04

which also is going to be dark in signal intensity

2:07

and seems as if it may even simulate the signal intensity of muscle.

2:12

This is the temporalis muscle.

2:17

The next thing to look at is its characteristic

2:20

on post-contrast imaging.

2:23

If it's a purely bony lesion,

2:26

that's dark in signal intensity on T2-weighted imaging,

2:30

we would not expect it to show contrast enhancement.

2:36

As we scroll through the post-contrast images,

2:39

however, we see that this lesion shows avid contrast enhancement.

2:45

It's going from the orbital apex anteriorly and

2:49

displacing the muscles as well as

2:52

the optic nerve sheath complex.

3:00

The very dark signal intensity on T2-weighted

3:03

scan and yet showing avid contrast enhancement

3:07

suggests a specific diagnosis of solitary fibrous tumor.

3:12

Solitary fibrous tumor is the term that is

3:14

now used for this lesion in the orbit.

3:17

Previously, it was termed hemangiopericytoma or fibrous

3:23

histiocytoma or giant cell angiofibroma.

3:29

Its characteristic feature is that it is CD34 positive on staining,

3:36

and that identifies it as a solitary fibrous tumor.

3:39

Solitary fibrous tumors may be benign or malignant,

3:44

and they can have infiltrative growth within the orbit.