Imaging of thyroid eye disease (and other extra-ocular muscle diseases)
Summary
TLDRThis 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
👁 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.
🔍 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.
📏 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.
🔎 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.
🏥 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.
🏥 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.
Mindmap
Keywords
💡Extraocular Muscles
💡Anatomy
💡Pathology
💡Thyroid Eye Disease
💡Orbital Pseudotumor
💡Lymphoma
💡Proptosis
💡Apical Crowding
💡Barret Index
💡Diffusion Weighted Images (DWI)
💡Idiopathic 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
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