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The petrous apex is considered a portion of the

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temporal bone that is usually joined.

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with the inner ear phenomenon.

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Although it has nothing to do with

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the labyrinthine structure.

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So, I'm just going to make a slight introduction to

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petrous apex lesions and then show a

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couple of examples of pathology.

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So, Petrous apicitis is inflammation of the petrous

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apex. It's very much like sinusitis.

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However, because of its proximity to the 6th cranial

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nerve and the fifth cranial nerve,

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you do have this entity known

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as Gradenigo's syndrome,

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where you have otorrhea fluid coming out of the

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ear as well as pain in the fifth

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cranial nerve distribution,

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as well as potentially a 6th nerve palsy.

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So, this usually is secondary to bacterial

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petrositis and not viral petrositis.

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Just as in the paranasal sinuses,

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you can have obstruction of the drainage of an

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air cell, and that can lead to a mucocoele.

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Mucocoeles can occur in the petrous apex.

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The petrous apex is also in close proximity

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to the petrosal sinuses,

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as well as the transverse and sigmoid sinuses.

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And therefore, inflammation at the petrous apex

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can lead to sinus thrombosis.

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Again, these are usually bacterial infections like

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the type that one would see in sinusitis.

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In addition to inflammatory lesions

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of the petrous apex,

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you can have masses that occur in the petrous apex

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and these include bony lesions such as metastases,

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or you can have a phenomenon called

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the cholesterol granuloma.

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Cholesterol granulomas occur secondary to weeping

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of blood products into the petrous apex air cells.

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It's initially thought that maybe this occurs

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secondary to barometric pressure differences

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leading to the hemorrhage that occurs in the

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petrous apex. But from that point on,

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you have a foreign body reaction that grows and grows

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and expands the petrous apex and leads to this

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entity known as cholesterol granuloma.

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As I mentioned previously,

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mucocoeles can occur in the petrous

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apex and simulate a mass.

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You may also see epidermoid lesions of bone

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as well as chondroid lesions of bone.

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Because of the proximity of cranial

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nerve five to the petrous apex,

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with the trigeminal impression occurring

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on the petrous apex,

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you may have neurogenic tumors such as schwannomas,

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which may undercut the petrous apex.

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The petrous apex is also in close proximity to the

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dura of the middle cranial fossa, and that can

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lead to tumors of the dura, such as meningioma.

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The petrous internal carotid artery also courses

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along the petrous apex, and therefore, aneurysms of

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the internal carotid artery in its petrous

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portion may also act as a petrous apex mass.

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This is the classic region of the petrous apex.

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You notice that this is a pre-gadolinium

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enhanced T1-weighted scan.

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And you see a bright lesion that is

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expanding the right petrous apex.

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So, the lesion here is bright on T1.

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But not only that,

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when you compare the caliber of the petrous apex on

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the left side to the width of the petrous apex

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on the right side, it is enlarged.

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And this lesion is associated with kind of a mixed

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signal intensity on this ugly

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looking T2-weighted scan.

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And the entity here is the cholesterol granuloma.

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That is a foreign body reaction

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started by blood products.

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And the high signal intensity on the T1

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weighted scan is likely predominantly met

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hemoglobin rather than true cholesterol.

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And you have the foreign body reaction that will

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account for mixed signal intensity

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on the T2-weighted image.

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Here is another lesion of the petrous apex.

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You notice that on the CT scan, you have bilateral

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lytic lesions affecting the petrous apex.

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Here is our petrous apex.

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And on the right side,

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you see this expansion and irregular margin to the

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petrous apex. Here is our internal carotid artery.

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And you have bilateral lesions here of the petrous

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apex. On the MRI post-gadolinium coronal scan,

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we see that in point of fact,

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these lesions have the same

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signal intensity as CSF.

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they are secondary to herniation of the meninges

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into the petrous apex and from

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there an expansile process.

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While these can occur de novo,

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they may also occur in association with the entity

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of idiopathic intracranial hypertension (IIH),

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also known as pseudotumor cerebri.

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So, with pseudotumor cerebri,

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the imaging findings tend to be enlargement of

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the sella with an empty sella appearance,

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enlargement of the optic nerve sheath complex,

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as well as enlargement of Meckel's cave,

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which can lead to, if eroded,

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a meningocele at the

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meninges of Meckel's cave.

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These are bilateral in 30%.

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They may lead to CSF leakage.

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Here is another example of a patient who has a

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petrous apex lesion that is associated with

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herniation of brain tissue and

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CSF into the petrous apex.

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This is a true meningoencephalocele.

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So, we have the meninges and the

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Meckel's cave meningocele.

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But here we have both the meninges as well

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as brain tissue herniating down.

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Into a true encephalocele. As I mentioned,

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there are numerous potential neoplasms that can

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affect the petrous apex. In this example,

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on the right-hand side,

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we see a post-gadolinium axial scan,

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and most of us are savvy enough to recognize the

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dural tail of a meningioma that is

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affecting the apex. In this case,

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the petrous apex may be showing some

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hyperostosis with a little

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new bone formation associated with the meningioma.

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And you can also see the expansion of the bone

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with hyperostosis on the coronal scan.

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One thing to note with this axial and coronal scan

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is the lumen of the internal carotid artery.

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Here is the normal internal carotid artery

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in the cavernous carotid artery.

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Here is the narrowed internal carotid

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artery caused by the meningioma.

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This is also identified here on the coronal scan

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by the narrowed lumen of the

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internal carotid artery.

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This is a phenomenon that we often see in patients

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who have meningiomas, narrowing of the internal

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carotid artery in the cavernous sinus.