Imaging of thyroid eye disease (and other extra-ocular muscle diseases)

Summary

This video delves into the conal space and extraocular muscles, crucial for eye movement. It covers their anatomy, pathology, and disorders like thyroid eye disease, orbital pseudotumor, and lymphoma. The video explains muscle involvement, symptoms, and diagnostic techniques, including the use of the Barret index for assessing optic nerve compression risk.

Takeaways

• 👁️ The conal space in the eye orbits is primarily composed of the extraocular muscles, which are responsible for eye movement.
• 💪 There are six extraocular muscles: superior rectus, inferior rectus, medial rectus, lateral rectus, inferior oblique, and superior oblique.
• 🔄 The superior oblique muscle makes a 90° turn in a small ring of cartilage tissue known as the trar apparatus.
• 📍 The levator palpebrae muscle is not responsible for eye movement but for elevating the upper eyelid.
• 🤔 The anatomy of extraocular muscles can be visualized on coronal T2-weighted images of the orbit.
• 🚨 Three key pathologies affecting the extraocular muscles are thyroid eye disease, orbital pseudotumor (idiopathic orbital inflammation), and lymphoma.
• 🌐 Thyroid eye disease is the most frequent cause of proptosis in adults, often characterized by bilateral and symmetrical enlargement of extraocular muscles.
• 🥤 The 'Coca-Cola bottle' sign refers to the thickening of extraocular muscle bellies with relative sparing of the tendons in thyroid eye disease.
• 📏 The Barret index is a quantitative method to estimate the degree of apical crowding and the risk for compressive optic neuropathy in thyroid eye disease.
• 🔎 Idiopathic orbital inflammation often presents unilaterally with acute symptoms and can involve various orbital structures, including the extraocular muscles.
• 🏥 Orbital lymphoma is the most common primary orbital tumor in older patients, often involving the extraocular muscles and characterized by diffusion restriction on MRI.

Q & A

What is the conal space in the eye orbit?

The conal space in the eye orbit refers to the area where the extraocular muscles are located, which are responsible for eye movement.

How many extraocular muscles are there, and what are their names?

There are six extraocular muscles: superior rectus, inferior rectus, medial rectus, lateral rectus, inferior oblique, and superior oblique.

What is the trar apparatus, and which muscle uses it?

The trar apparatus is a small ring of cartilage tissue where the superior oblique muscle makes a 90° turn.

What is the levator palpebrae muscle responsible for?

The levator palpebrae muscle is responsible for the elevation of the upper eyelid.

What is the annulus of Zinn, and where is it located?

The annulus of Zinn is a small ring of fibrous tissue located deep within the orbit at the orbital apex, surrounding part of the superior orbital fissure and the optic canal.

What is the significance of the annulus of Zinn in the context of extraocular muscles?

The annulus of Zinn is significant because all extraocular muscles, except the inferior oblique muscle, either insert or originate from it.

What are the three important entities of pathology that affect the extraocular muscles?

The three important entities of pathology affecting the extraocular muscles are thyroid eye disease, orbital pseudotumor (idiopathic orbital inflammation), and lymphoma of the extraocular muscles.

What is the most common cause of proptosis in adult patients?

The most common cause of proptosis in adult patients is thyroid eye disease.

How can the Barret index be used to evaluate patients with thyroid eye disease?

The Barret index is a quantitative measure used to estimate the risk of compressive optic neuropathy in patients with thyroid eye disease by measuring the degree of apical crowding.

What is the significance of the 'Coca-Cola bottle' sign in thyroid eye disease?

The 'Coca-Cola bottle' sign refers to the appearance of the extraocular muscles in thyroid eye disease, where the muscle bellies are enlarged and the tendons are spared, resembling the shape of a Coca-Cola bottle.

What distinguishes orbital lymphoma from other pathologies on MRI?

Orbital lymphoma is distinguished by the presence of diffusion restriction on MRI, indicating a hypercellular tumor.

Outlines

00:00

👁 Anatomy of the Extraocular Muscles

The paragraph introduces the anatomy of the eye orbits, focusing on the extraocular muscles which are crucial for eye movement. It explains the location and function of six main muscles: superior rectus, inferior rectus, medial rectus, lateral rectus, inferior oblique, and superior oblique. It also mentions the levator palpebrae muscle responsible for elevating the upper eyelid. The text describes these muscles on a coronal T2-weighted image and their common origin at the annulus of Zinn. It further explains the important neural structures located at the level of the annulus of Zinn, including the optic nerve and the oculomotor nerve.

05:00

🔍 Pathology of Extraocular Muscles

This section delves into the pathology of extraocular muscles, highlighting three key conditions: thyroid eye disease (Graves orbitopathy), orbital pseudotumor (idiopathic orbital inflammation), and lymphoma of the extraocular muscles. It discusses a case of thyroid eye disease presenting with chronic, painless proptosis and diffuse enlargement of the muscles, which is the most frequent cause of proptosis in adults. The paragraph also touches on the association of thyroid eye disease with autoimmune hyperthyroidism and the role of antibodies in its development. It describes the 'Coca-Cola bottle' sign, which refers to the appearance of enlarged muscle bellies with relatively spared tendons. The concept of apical crowding, a potential complication leading to compressive neuropathy of the optic nerve, is also explained, along with the use of the Baret index for its quantification.

10:02

📏 Evaluating Apical Crowding

The focus of this paragraph is on the evaluation of apical crowding in thyroid eye disease, a condition where the extraocular muscles at the orbital apex compress the optic nerve. It discusses how the degree of apical crowding can be estimated using the Baret index, which measures the width of the medial and lateral rectus muscles and compares it to the orbital width at the level of the optic nerve. A Baret index of 60% or higher is indicative of a high risk for optic neuropathy, while an index below 50% suggests a low risk. The paragraph also addresses the variability in the presentation of thyroid eye disease, noting that it is typically bilateral and symmetrical but can also be unilateral and asymmetrical.

15:03

🔎 Advanced Imaging of Thyroid Eye Disease

This section provides an in-depth look at the MRI findings in thyroid eye disease. It describes the characteristic muscle enlargement, particularly affecting the inferior, medial, and superior rectus muscles. The text explains the muscle edema visible on T2-weighted images and the enhancement of muscles and orbital fat on post-contrast images. The paragraph contrasts the acute and chronic phases of the disease, with chronic thyroid eye disease showing fatty infiltration and streaks of fat within the muscle bellies. It summarizes the key imaging features of thyroid eye disease, including muscle enlargement, tendon sparing, and the use of the Baret index to assess apical crowding.

20:04

🏥 Idiopathic Orbital Inflammation

The paragraph discusses idiopathic orbital inflammation, also known as orbital pseudotumor, which can involve various orbital structures, most commonly the extraocular muscles. It highlights the unilateral nature of the disease and its acute and painful presentation. The text describes the imaging findings, including muscle enlargement and enhancement, and the hypointensity of muscle bellies on T2-weighted images due to fibrosis. A specific type of orbital inflammation, IgG4-related disease, is mentioned for its characteristic fibrosis and hypointense appearance on imaging. The paragraph also covers the diverse manifestations of idiopathic orbital inflammation, such as lacrimal gland involvement and optic nerve sheath inflammation.

25:05

🏥 Orbital Lymphoma

This section discusses orbital lymphoma, the most common primary orbital tumor in older patients, which often involves the extraocular muscles. It explains that lymphoma can present as a primary orbital tumor or be part of a systemic lymphoma. The paragraph emphasizes the characteristic imaging feature of lymphoma, which is diffusion restriction due to the hypercellular nature of the tumor. This results in a lower signal on T2-weighted images and high signal on diffusion-weighted images with a corresponding low signal on the ADC map. The text contrasts this appearance with that of IgG4-related disease, noting that the signal intensity is generally not as low as in the latter.

Keywords

💡Extraocular Muscles

Extraocular muscles are the muscles outside the eye that control its movement. There are six such muscles in each eye, including the superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, and inferior oblique. These muscles are crucial for the video's theme as they are the primary focus of the discussion on anatomy and pathology within the orbit.

💡Anatomy

Anatomy, in the context of this video, refers to the study of the structure and parts of the eye orbits and extraocular muscles. The video script provides a detailed description of the location and function of each extraocular muscle, which is essential for understanding the pathological conditions discussed later.

💡Pathology

Pathology is the study of diseases and their causes, processes, and effects on the body. In the video, pathology is used to describe various diseases affecting the extraocular muscles, such as thyroid eye disease, orbital pseudotumor, and lymphoma of the extraocular muscles.

💡Thyroid Eye Disease

Thyroid eye disease, also known as Graves orbitopathy, is an autoimmune disorder that leads to inflammation and enlargement of the extraocular muscles. It is a key concept in the video as it is the most common cause of proptosis (bulging of the eye) in adults. The video describes its symptoms, such as painless proptosis, and its typical appearance on CT scans.

💡Orbital Pseudotumor

Orbital pseudotumor, also referred to as idiopathic orbital inflammation, is a condition that causes inflammation in the orbit, often leading to painful proptosis. The video explains that it is usually unilateral and can involve various orbital structures, including the extraocular muscles, and is differentiated from thyroid eye disease by its acute and painful nature.

💡Lymphoma

Lymphoma is a type of cancer that originates in the lymphatic system. In the context of the video, orbital lymphoma is discussed as a primary orbital tumor that often involves the extraocular muscles. The video highlights the characteristic MRI finding of diffusion restriction in lymphoma, which is indicative of its hypercellular nature.

💡Proptosis

Proptosis refers to the bulging of the eye forward from its socket. It is a symptom discussed in the video in relation to various pathologies, including thyroid eye disease and orbital pseudotumor. The video uses proptosis to illustrate the effects of muscle enlargement and orbital fat volume increase.

💡Apical Crowding

Apical crowding is a term used in the video to describe the compression of the optic nerve due to the swelling of extraocular muscles at the orbital apex. It is a critical concept as it can lead to compressive neuropathy of the optic nerve and potential visual loss, emphasizing the importance of evaluating orbital pathology.

💡Barret Index

The Barret index is a quantitative measure used to estimate the degree of apical crowding in thyroid eye disease. The video explains how to calculate the Barret index by measuring the width of the muscle bellies relative to the orbital width, which helps in assessing the risk for compressive optic neuropathy.

💡Diffusion Weighted Images (DWI)

Diffusion weighted images are a type of MRI sequence that is sensitive to the movement of water molecules. The video mentions DWI in the context of orbital lymphoma, where restricted diffusion is seen due to the hypercellular nature of the tumor, resulting in a high signal on diffusion-weighted images and a low signal on the apparent diffusion coefficient (ADC) map.

💡Idiopathic Inflammation

Idiopathic inflammation refers to inflammation with no known cause. The video discusses idiopathic orbital inflammation, which can involve various orbital structures and presents with acute and painful symptoms. The term is used to differentiate orbital pseudotumor from other causes of orbital inflammation.

Highlights

Introduction to the conal space and extraocular muscles

Description of the anatomy of the extraocular muscles

Explanation of the role of the extraocular muscles in eye movement

Identification of the superior and inferior rectus muscles

Identification of the medial and lateral rectus muscles

Identification of the inferior and superior oblique muscles

Description of the trochlear apparatus and the superior oblique muscle

Introduction of the levator palpebrae muscle and its function

Visualization of extraocular muscles on coronal T2-weighted images

Challenge of visualizing the inferior oblique muscle on standard images

Explanation of the annulus of Zinn and its relation to extraocular muscles

Importance of the annulus of Zinn for the origin of extraocular muscles

Description of the optic nerve and oculomotor nerve at the annulus of Zinn

Introduction to the pathology of the extraocular muscles

Discussion of thyroid eye disease as a cause of proptosis

Description of the chronic and painless nature of thyroid eye disease

Marty Feldman's experience with thyroid eye disease

Explanation of the autoimmune cause of thyroid eye disease

Identification of muscle enlargement and sparing of tendons in thyroid eye disease

Introduction of the apical crowding phenomenon

Explanation of the Barret index for quantifying apical crowding

Discussion of the variability in thyroid eye disease presentation

Description of acute thyroid eye disease on MRI

Identification of chronic thyroid eye disease features on MRI

Differentiation between thyroid eye disease and orbital pseudotumor

Characteristics of idiopathic orbital inflammation

Description of orbital lymphoma and its MRI characteristics

Summary of the pathology of the conal space and extraocular muscles

Anticipation of the next video focusing on the intraconal space

Transcripts

hello and welcome to this third video on

Imaging of the eye orbits and visual

threats in this video I'm going to talk

about the conal space and the conal

space is basically basically boils down

to the extraocular muscles so we're

going to talk about anatomy and

pathology of the extraocular muscles now

with this is the eye self-evidently this

here is the medial side of the eyee this

is the lateral side of the eye and we

have a total of six extra ular muscles

responsible for eye movement we have the

superior rectus muscle on top of the

eyeball the inferior rectus muscle

underneath the eyeball the medial rectus

muscle and the lateral rectus muscle so

that's quite easy to remember I believe

then we have two oblique muscles so

muscles that do not run straight

but make a curve or a turn like the

inferior oblique muscle underneath the

eyeball and the superior oblique muscle

on top and on the medial side of the

eyeball now the superior oblique muscle

makes a 90° turn and this turn is made

in a small ring of cartilage tissue

called the trar apparatus a final muscle

not responsible for eye movement but for

the elevation of the upper eyelid as the

levator palp bra muscle which is located

on top of the superior erectus muscle

here are the muscles Illustrated on

coronal T two- weighted image of the

orbit here we have the superior rectus

muscle inferior rectus muscle the medial

and the lateral rectus muscles the

inferior oblique muscle is very very

hard to see on standard images and is

not visible on the image I provided here

then we have the superior oblique muscle

which is located super laterally in the

orbital space and as said makes a 90°

turn in the trar apparatus and finally

we have the levator palpi muscle on top

of the superior rectus muscle the

extraocular muscles can also be seen on

axal images of course and here we have

the medial and the lateral oh this is

wrong we have

um this is a mistake we just see the

medial and the lateral erectus muscle on

this image and we see that they insert

on the Scara of the globe oh I know what

I mean what I mean is that the several

Rus muscles and the superior oblique

muscle all insert on the Scara of the

globe uh and here we just see the medial

and the lateral rectus muscle of course

and what's more they also have a common

origin namely the analy of Zin located

at the orbital Apex and what is the

analy of Zin the analy of Zin is

basically a small ring of a fibrous

tissue located deep within the orbit at

the level of the orbital Apex and

surrounding part of the superior orbital

fissure the inferior part and also the

optic Canal it's also so called the

common tendonous ring because basically

all extraocular muscles with the

exception of the inferior oblique muscle

insert here or originate here and it's

also called the analyst order ring of a

Zin and we can suspect it on this

three-dimensional reconstruction of the

orbit located over here here we see the

superior orbital fissure and it involves

the inferior part of the superior

orbital fissure and the optic canal now

there are several uh important neuronal

structures which are located uh at the

level of the analyst of sin namely the

optic nerve which runs through the optic

Canal we have the okom motor nerve which

has two branches intraorbitally a

superior branch which innervates the

superior rectus muscle and an inferior

Branch

inating um the uh

I can't find it uh the other extraocular

muscles well not all of them uh but the

medial the inferior uh rectus muscle as

well as the inferior oblique muscle and

finally we have here the abdon nerve

elating the lateral rectus muscle so

it's ring of fibrous tissue origin of

dor muscles and the superior oblique

muscle and surrounding the optic canal

and the inferior part of the Fior

orbital fissure and that concludes this

short introduction on Anatomy let's talk

about pathology and when it comes to

pathology of the extraocular muscles

there are three important entities you

should know namely thyroid uh eye

disease also called Graves orbitopathy

orbital pseudotumor or also called and

that's probably a more correct term

idiopathic orbital inflammation and

finally lymphoma of the extraocular

muscles and other humorous but I'm just

going to talk about lymphoma here

because it's uh the most frequent now

this is a patient with a chronic slowly

Progressive painless proptosis and what

do we see both on these axial and

coronal CT images of the orbits we see

diffuse enlargement of basically all

visible extraocular muscles here is a

line indicating the enomatic line and we

see that this is a severe great Tre

proptosis with the eyeball extending in

front of the inter zygomatic line and

the first thing you should think about

when you see this also taking into

account uh the painless and chronic

aspect of the development of the

symptoms as thyroid ey disease because

it is the most frequent Co cause of

proptosis in adult patients and the

proptosis is called by enlargement of

the extraocular muscles but also by an

increase in the volume of orbital fat

which leads to a decreased orbital

volume and

proptosis thyroid eye disease is mostly

bilateral in about 90% of cases and

mostly symmetrical in about 70% of cases

which is also important in the

differential diagnosis with idopathic

orbital inflammation but more about that

later this is Marty feltman a famous uh

comedic actor uh who played Igor and Mel

Brooks The Young friend Frankenstein and

well he is well known for his let's say

facial appearance he has this very large

bulging eyes and this is because Marty

Felman suffered from thyroid eye disease

and he made this his strong point

because his facial features were an

important part of his uh appearance and

well it's hard to say that um he made

his his strength but well that's what he

did he made it to one of his strengths

uh as a comedic actor um well thyroid

eye disease is associated with

autoimmune hyperthyroidism especially

Graves uh

hyperthyroidism and the development of

thyroid ey disease has nothing to do

with the thyroid function so you can see

it in patients who have uh who are

hyperthyroid but also after

normalization of the thyroid function

patients can have uh the CL

manifestations of thyroid eye disease

and why is that because the disease is

not caused by the increased levels of

thyroid hormones no it is caused by the

antibodies that are formed in this

autoimmune disease more specifically the

presence of anti-open receptor

antibodies and these probably this

Theory probably activate uh thyrotropin

receptors in orbital cells the orbital

fibroblasts and this cause these

fibroblast to change into adipocytes so

fatty cells leading to an increase in

the volume of orbital fat and

furthermore these fibro blasts produce

collagen and um H

uhon oh my God I can't pronounce it in

English so I'm going to do it in Dutch

Huron and extraocular muscles and fat

leading to edema in the extraocular

muscles and fat and develop Vel M of

muscle enlargement orbital fat increase

and

proptosis this is another patient with

thyroid eye disease we see axial and

coronal CT images and we see theuse

enlargement of basically all extraocular

muscles and two things are also very

apparent on this image on the actual

image we see that it are mainly the

extraocular muscle bellies that are

ticken and enlarged and the tendons are

less involved this appearance sometimes

also referred to as the cocacola bottle

sign and I will show you Coca-Cola

bottle in a minute so that you can see

where this sign comes from and another

thing that is apparent so we have

thickening of extraocular muscle bellies

and less or sparing of the extraocular

muscle tendons and another thing that is

apparent on the coronal images is that

we see the optic nerve uh running

towards the orbital Apex and we see that

is completely surrounded by these

swollen extraocular muscles as

especially on the left side where we can

hardly see any orbital fat

surrounding uh the uh optic nerve and

this phenomenon or this appearance is

called apical crowding crowding of the

extraocular muscles at the level of the

orbital Apex causing compression of the

optic nerve and apical Crow crowding can

lead to compressive neuropathy of the

optic nerve and visual loss so it's an

important thing to evaluate on the CT

scans of patients with thyroid eye

disease due to the risk of compressive

optic neuropathy this is another patient

with thyroid eye disease and we see once

again mainly enlargement of the

extraocular muscle bellies but relative

sparing of the tendons giving the

muscles the appearance of a Coca-Cola

bottle and hence the cocaa bottle sign

let's move on and return to apical

crowding here is another patient well

it's the same as the previous one with

um a less orbital fat surrounding the

optic nerve at the level of the orbital

Apex so this is apical Crow

crowding if the fat in the orbital Apex

has disappeared there's a great chance

of optic nerve compression but and this

is something uh I also frequently ask

myself in Daily radiological practice

you always see less orbital fat in a

patient with thyroid eye disease when do

you need to start calling it apical

crowding when do you really have to

point out that there's a risk for

compressive optic neuropathy because in

some patients you see some fat and

another patient n at all when should you

call apical crowding luckily there is

also a quantitative way to give an

estimate on the degree of apical

crowding and that is the baret index or

the baret index I do not know how to

pronounce it exactly doesn't really

matter how do you do it well you look in

the coron

image uh at the extraocular muscles and

the orbit and you do that somewhere at

the level halfway between the posterior

aspect of the globe and the orbital Apex

and at that level you measure the width

of the muscle bellies of the medial and

the lateral rectus muscle and

you um make the sum of that width so uh

and you divide that by the width of the

orbit

um at the level of the optic nerve so

you do a plus b and divide it by C so

you take the width of the medial and the

lateral rectus muscles and you divide it

by the width of the uh orbit uh at the

level of the optic nerve so a line

running through the optic nerve and then

you multiply that with 100 then you get

a percentage and that is basically the

baret index and Studies have shown that

the baret index of 60% and higher is

very sensitive and specific for optic

neurop while a boret index lower than

50% practically rules out um thyroid eye

disease related optic neuropathy so this

is a more quantitative way to estimate

the risk uh for optic neuropa and give a

more quantitative estimate of the degree

of apical crowding and you can also do

that in the vertical plane what do I I

mean this is the horizontal Beret index

but you can also calculate the Beret

index by measuring the width of the

muscle bellies of the superior and the

inferior rectus muscles and divided by

the uh width of the orbit and the

vertical plane so you can measure a

horizontal baret index and a vertical

baret index then you get maybe two

different numbers the highest number is

the one you have to work with that gives

you an idea of the severity of epical

crowding here's once more how to measure

the Barret index because I believe that

the previous image might have been a bit

unclear so you take the width of the

medial rectus and the width of the

lateral rectus muscle um you make the

sum of the width of both muscles and you

divide it by the orbital width at the

level of the optic nerve and multiply

that with 100 this is the horizontal

Beret index you can do the same and the

vertical uh plane uh by using the

superior and the inferior rectus muscles

here is another patient with thyroid eye

disease and we see that there is

proptosis especially of the right eye

and we see enlargement of the right

medial rectus muscle but not so much of

the left well thyroid eye disease is

bilateral 90% of cases and symmetrical

and 70% that means it doesn't always

have to be that that way so I always

teach my residents there are always

exceptions and you have to keep that in

mind so just because this isn't

symmetrical just because this is

unilateral doesn't mean it can't be

thyroid eye disease furthermore if you

look at coronal image you see that two

muscles are involved on the right side

the medial and the inferior rectus

muscle well I first showed you the

inferior than the medial and that's also

no coincidence because in thyroid eye

disease it has been shown that the

disease typically tends to start at a

level of the inferior rectus muscle

followed by the medial rectus muscle and

then it has the following uh appearance

of frequency uh mostly involved is the

inferior rectus muscle followed by the

medial rectus muscle and then the

superior rectus muscle the lateral

rectus muscle and the oblique muscles

and if you look at the first letter of

each of those muscles you get I'm slow

and I'm slow as a pneumonic to memorize

or help you memorize the order in which

extraocular muscles tend to enlarge or

the frequency in which they are enlarged

in thyroid eye disease this is what

thyroid eye disease an acute thyroid eye

disease looks like on MRI images these

are fat supressed two- weighted images

and we see if you enlarge them that the

muscles are bilaterally enlarged I'm

slow

we especially see enlargement of the

inferior medial and superior rectus

muscle but not so much of the lateral

one and we see muscle edema hypertense

signal and on T rated images with

galenium we also see well the muscles

are enhancing but normal muscles also

enhance uh but we also see infiltration

and edema of the intraorbital fat and as

set thyroid eye disease not only

involves the extraocular muscles but can

also involve the inra orbital fat this

is a patient with chronic thyroid eye

disease and in chronic thyroid eye

disease what you see is that you get

fatty infiltration of the extraocular

muscles they tend to become less swollen

might even become atrophic and we see

streaks of fat located in the muscle

bellies and fat is hyper intense on the1

weed images so we see these fatty

streaks indicating chronic thyroid eye

disease

so let's summarize thyroid eye disease

is mainly characterized by enlargement

of the extraocular muscles mostly

bilateral and symmetrical but that

doesn't mean it has to be it mostly

involves the muscle bellies and the

tendons tend to be spared and the

pneumonic IM slow can help you memorize

the order of frequency in which the

various extraocular muscles are involved

in the acute phase the muscle bellies

will be uh show udema on T2 weighted

images and at The Chronic phase fatty

infiltration on T1 weighted images and

something you always have to evaluate as

the presence of apical crowding and you

can use the Barret index to give a more

quantitative estimate of the risk for

the optic nerve and let's look at

something that looks a bit similar but

is not thyroid eye disease this is a

patient with a proptosis of the left eye

uh so it's a great uh one proptosis so

the posterior cleara is still located

underneath the entatic line and we see

that there is enhancement and thickening

of these two muscle bellies namely the

medial and the lateral rectus muscle as

you can see here this is not what we

expect in thyroid eye disease even if it

would be a unilateral asymmetrical

thyroid eye disease then you would

expect it to be the inferior and the

medial Rector muscle furthermore the

this patient had a relatively acute

development of the proptosis while the

enti eye disease proptosis develops

slowly and chronically and is painless

this patient had pain this was a painful

proptosis with painful

diplopia uh on MRI images we see

enlargement and enhancement of the

superior know of the lateral and the

medial rectus muscles and this was a

case of IOP patic orbital inflammation

an entity also known as orbital

pseudotumor although this terminology

often still used is um gradually being

abandoned acid it is idiopathic

inflammation it can be seen in a variety

of autoimmune disorders or it's uh

related with various autoimmune

disorders uh like rheumatoid arthritis

suar what have you not uh but if no

cause is found it is called idiopathic

inflammation and despite the fact that

I'm showing you enlargement of the

extraocular muscles it's also important

to keep in mind that this disease can

involve all orbital structures not just

the extraocular muscles but the

extraocular muscle involvement is the

most frequent form of idiopatic orbital

inflammation and if extraorbital muscles

are involved that are mainly the lateral

and medial erectus muscles

this disease is mostly unilateral

contrary to um thyroid eye disease and

has acute symptomatology and can be

painful steroid treatment however

generally leads to Rapid Improvement of

both symptoms this is another patient

with uh idopathic orbital inflammation

and we see on these unenhanced one weed

images enlargement of the medial no of

the inferior and the lateral Reus

muscles on the left side we see that

they are enhancing and more strongly

enhancing than the contralateral normal

muscles we see that on both coronal and

axial T1 weed images with gadolinium and

this is very conspicuous on T two-

weighted images we would expect udema

right because we associate udema with

acute pathology but in this case the

muscle bellies are very very hypointense

on the two- weighted images they are so

hypointense because this is a disease

associated with the formation of

fibrosis and fibrosis is hypointense or

black on2 what kind of disease causes

this well there's one thing that should

jump to your mind immediately and that

is igg4 related orbital disease igg4

related disease as a disease process

that can be multisystemic it can involve

basically any part of the body but

frequently in involves the orbital

compartment and very characteristic for

this autoimmune disorder is that it

leads to fibrosis in the involved

structure and in the case of the

extraocular muscles these will appear

dark or be

hypointense idopathic orbital

inflammation as said already several

times can involve all aspects of the

orbits not just the extraocular muscles

it can be found in the laal gland

causing a laal gland pseudotumor it can

be found in the orbital fat both in the

anterior orbital fat and then we call it

anterior pseudotumor as well as in the

uh orbital fat at the level of the

orbital Apex it can be found in the

extraocular muscles causing Myositis and

this is the most frequent manifestation

but can also involve the optic nerve

sheet causing an optic

perintis so all in all several

manifestations are possible and these

can be seen in the same and several of

these can be seen in the same patient

causing diffuse idiopathic orbital

inflammation for instance in this

patient we clearly have involvement of

one of the extraocular muscles the

medial rectus muscle but we also see

involvement of the optic nerve sheet

with intense enhancement surrounding the

optic nerve sheet as well as

infiltration and enhancement of the

orbital fat so this is definitely

diffuse idopathic orbital

inflammation uh and a diffuse orbital

pseudotumor here are some images of

various manifestations of idopathic

orbital inflammation this is a patient

with orbital uh cellulitis or

infiltration of the retr buber orbital

fat and also enhancement surrounding the

optic nerve sheet this is a patient with

involvement of the elal gland as well as

the muscle bellies of the superior

rectus and the levator palpi

muscle and this is the same patient we

see that there is thickening and

enhancement of the superior rectus

muscle and on top of that the levator

palp muscle here we have a patient with

mainly involvement bilaterally of the

optic nerve sheet so this is the partic

type of idopathic orbital inflammation I

believe it is probably best seen here on

these sagittal T1 weighted

images so this is another patient with

something different we see in this

patient let's ify these images a bit we

see a proptosis but it looks bilaterally

so maybe the patient does really have a

proptosis just has these kinds of eyes

because the pathology is unilateral

located on the right side and we see

thickening of the muscle Belly of the

right medial rectus muscle this is

enhancing on T1 weed images with cinium

and on diffusion weed images we see and

it's a bit difficult of course because

the other structures are difficult to

see but this here is the muscle belly

has a high signal on the fusion weighted

images and a low signal on the ADC map

why is that because this is a lymphoma

and a lymphoma is a hyper cellular tumor

and hypercellular tumors are often

associated with diffusion restriction

because they have very narrow

intercellular spaces due to the presence

of a lot of very small cells causing

limited room for water molecules to

diffuse between the cells orbital lyoma

is the most common primary orbital tumor

in older patients once again it can

basically involve any part of the orbit

but is often found in the extraocular

muscles it can be seen as a primary

orbital lymphoma but can also be part of

a systemic

lymphoma can involve any part of the

orbit as set and onri is characterized

by the presence of diffusion restriction

it will also have a lower signal on the

two- weighted images but generally not

so low as we see in uh igg4 related uh

orbital disease so that's summarize or

pathology of the konal space and the

extraocular muscles we have seen thyroid

eye disease generally a chronic and

painlessly developing disease in which

extraocular muscles are in the majority

of cases bilaterally swollen and this is

often symmetrical and you can use I'm

slow to see if the order of the involved

muscles as corresponding with what we

expect in thyroid eye disease in orbital

Pudo tumor or idopathic orbital

inflammation the disease tends to be

acute and painful is unilateral in the

majority of cases and mostly involved or

the lateral and medial erectus muscles

and orbital lymphoma then again is

generally a painless disorder mostly

unilateral and the most distinguishing

characteristic on MRI for orbital

lymphoma would be the presence of

diffusion restriction this concludes

this part of orbital Imaging

concentrating on the conal space and the

extraocular muscles the next video will

deal with pathology located inside the

kernal space the intraconal space stay

tuned