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Orbit Anatomy on CT

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On this axial CT scan,

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we can review some of the anatomy.

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The most superficial thing that we

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are seeing is the skin surface of the eyelids.

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The next thing that is outlined is the cornea.

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And as you can see,

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this is continuous with the sclera.

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We do not resolve the retina choroid and

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sclera on CT scanning or MRI scanning.

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They are called the ocular membranes.

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You notice that this patient has had a lens implant

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as this little waferlike structure here,

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replacing the normal lens.

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But it does allow us to see the anterior

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chamber of the globe very well.

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You recall that we are not able

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to see the posterior chamber,

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but that area behind the lens in

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the globe is the vitreous

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or the posterior segment.

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When we shift from ocular anatomy

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to the orbital anatomy,

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one can see the fat of the intraconal space.

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As one scrolls,

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you can see the extraocular muscles, as well as the

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optic nerve inserting into the back of the globe.

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Within the muscles, one finds the dark density fat

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and we also see outside the muscle

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we have dark density fat.

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So this is the difference between the intraconal fat

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versus the extraconal fat of the extraconal space.

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Here we are seeing a portion of the superior oblique

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muscles attachment to the globe,

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but we also see the medial rectus and lateral rectus

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muscle, as well as more inferiorly, the inferior

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rectus muscle as it inserts on the globe.

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In the coronal plane,

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one can see this anatomy quite nicely.

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One has the superior rectus muscle,

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medial rectus muscle,

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inferior rectus muscle and lateral rectus muscles.

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In this particular patient,

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they are enlarged because of thyroid

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eye disease or thyroid orbitopathy.

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Within that space, within the cone,

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or the intraconal space, one has intraconal fat.

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But you also see that there is fat outside

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the muscles in the extraconal space.

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You also note the close proximity of the ethmoid

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sinus to the medial aspect of the orbit,

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which is why one can have sinus inflammatory

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complications that affect the orbit.

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Here is the superior oblique muscle,

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again, innervated by the trochlear nerve,

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cranial nerve four.

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And again, the lateral rectus muscle innervated

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by cranial nerve six, the abducens nerve.

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As you can see, below the orbit,

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one has the maxillary sinus, and above the orbit,

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the brain.

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This small area here,

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which can be seen bilaterally in the floor of the

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orbit is the opening for the infraorbital nerve.

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This is a nerve that is a branch of the second

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division of the fifth cranial nerve,

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the trigeminal nerve of the maxillary nerve.

Report

Description

Faculty

David M Yousem, MD, MBA

Professor of Radiology, Vice Chairman and Associate Dean

Johns Hopkins University

Tags

Orbit

Non-infectious Inflammatory

Neuroradiology

Neuro

Metabolic

Head and Neck

CT

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