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Dr. Laser,

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this is a 76-year-old woman with an extra-axial lesion,

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namely a meningioma in the olfactory groove.

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We've got an axial FLAIR and axial T2,

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with a nice cleft sign around the periphery of the lesion,

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and then a coronal T1 C+ showing an enhancing lesion.

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So, where do you get these meningiomas

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that arise from arachnoid capsules?

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Where can they occur and where do they occur?

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So typically, what I like to do is I like to break it

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down into supratentorial versus infratentorial.

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In your supratentorial compartment,

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which comprises the majority of the lesions of 80% to 90%,

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50% of them are along the falx.

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Then you have your convexities, which is another 20%-30%.

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Additional areas where you have them

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is this olfactory groove meningioma,

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which we have here.

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You have a planum sphenoidale meningioma,

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which is another 5% to 10% of the time.

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Sphenoid wing is another typical location,

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and then you have your infratentorial,

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which is about 10% of the time.

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So, let's save the infratentorial

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breakdown for another vignette.

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But here's our lesion in the sagittal projection.

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You can see it's almost bowing

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the olfactory groove right here.

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And you would have the...

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this is the carotid artery right there.

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There's the pituitary glands.

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You'd have the anterior clinoids right off to the side.

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Then you get right into the planum and limbus sphenoidalis

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the planum sphenoidale and limbus,

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and then into the olfactory groove,

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which is where our lesion is.

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You can see the gray and white matter displaced.

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There's a little cleft sign right there,

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even on the T1-weighted image,

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and the lesion goes right up to the bone.

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So, it's in a very typical location.

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Now, what are some other potential mimics that

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may involve the extra-axial space?

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You've already said the most common location for somebody

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taking boards is going to be the supratentorial space,

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and where typically along the falx.

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Typically along the falx.

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And a lot of times

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you see them a little more commonly anteriorly.

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So that might be a potential board question.

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And then for mimics of extra-axial lesions that are

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meningiomas, you've got dural lesions like dural sarcomas.

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In my experience,

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dural melanoma or melanosis is a great mimicker

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of meningioma, fortunately not common.

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And then you've got dural lymphoma,

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which may cross into the bone,

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although you'll see later on that aggressive meningiomas

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may involve the bone metastases, granulomas,

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and then primary bone lesions,

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including hemangiopericytoma,

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which used to be categorized as a meningioma and is now

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reclassified as a fibrous or fibrohistiocytic lesion.

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Let's move on, shall we?