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Cystic lung nodules were first introduced into the Lung

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Reds interpretation schema in the December, 2022 update.

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This is an area for which less is known scientifically.

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While there are some series in the literature

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of cystic lung nodules, they are relatively small.

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We've pulled together a multidisciplinary group

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through the Lung Rads committee to make an assessment

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of cancer risk based on different cystic nodule features

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and to put them into the lung RADS interpretation schema.

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We expect that the development

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of the schema will be applied in practice by researchers

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around the country to be able to

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evaluate if the cystic nodule schema is working

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and predicts the risk of cancer

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as we've laid it out in lung rads.

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So we're gonna talk about cystic lung nodules.

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We're not talking about your simple lung cysts.

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I'll show some examples of what those are.

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Simple benign lung cyst not included the lung rad schema.

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They're just normal lung findings.

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We'll talk about some microcystic

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and macrocystic lesions, nodules

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that have tiny little soap bubbles of nodules

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and nodules that have bigger areas of cyst formation.

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Many would define walls.

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One important characteristic is the overall size of the

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cystic nodule might grow

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or the cystic nodule might stay the same size,

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but the cysts within them are getting bigger.

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So it's important to not only look at the overall size,

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but to look at the size of the cysts,

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just like in a part solid lung nodule we'd like at the total

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size, but we also look to see what's happening

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with the solid component

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and measure that we'll also talk about cystic nodules

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that have a dominant solid nodule component with them

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and how those should be managed.

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And all of these across the lung rats interpretation schema.

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So here I've laid out the different types

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of pulmonary S system

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where they fit in the lung rats three four A

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and four B categories as well as some caveats.

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And I will say there are a number of caveats

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and things to keep in mind with a number of footnotes

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that were included in Lung RADS 2022 that we'll talk about

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to apply to cystic nodules.

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The first category three is an atypical pulmonary cyst

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that's thick walled and may have a growing cystic component.

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Category four, a atypical pulmonary cysts are thick walled

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cysts or multilocular baseline

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or a thinner thick walled cyst

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that becomes multilocular over time.

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Started out un becomes multilocular.

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Category four B. The highest uh, level

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of risk are thick wall cysts with growing wall thickness

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or growing nodularity in the wall of the cyst.

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It could be a growing multilocular cyst,

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meaning the cyst is getting bigger.

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It could be a multilocular cyst

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where there's more loculation within it

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or there's newer increased opacity be

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that nodular opacity round glass opacity

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or consolidation related cyst. So these are

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Much more complex cysts

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and they have the same three four A four B recommendation

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schema of six months, three months

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and referral for diagnostic assessment

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and management as we use in all the other nodule types.

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A couple of things, cavitary nodules, you know,

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where does a thick walled cyst and

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and a cavitary nodule begin?

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Hard to know exactly for sure.

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That's an area of uncertainty.

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If something is predominantly cavitary,

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more thick walled than it is cystic, we recommend

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that those be managed the same way

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as we do solid nodules in the lung rad scheme.

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So if you have a cavitary nodule

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where the soft tissue is the largest component

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and the cavitary or cystic component is the smallest

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component, follow that solid nodule recommendation schema.

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When you're looking at nodules within cystic lesions,

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they can be nodules that are endophytic, they're

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inside the cyst, they can be mural,

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they can be centered on the wall of the cyst

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or they can be exophytic outside the cyst.

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The nodules associated with cyst can be solid,

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but they can also be nonsolid or ground glass or part solid.

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Now to some of the footnotes in lung RADS 2022,

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a thin walled cyst is a unilateral cyst

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with uniform wall thickness that's under two millimeters.

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These thin walled cysts can be considered benign

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and are not even included in the lung Rad schema,

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thin walled benign cyst unilateral under two millimeter wall

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thickness benign don't get included in long rads.

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When we move to thick wall cysts, they can be unilateral

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with uniform wall thickness.

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They can have asymmetric wall thickening

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or even nodular wall thickening.

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That's two millimeters or greater.

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And for these, we consider these atypical pulmonary cysts.

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These cysts can be multilocular cysts.

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We still manage them as thick wild cysts.

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And then that transition to cavitary nodule, as I mentioned,

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is when the thickening

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of the wall becomes the dominant feature

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and the cystic lucid component becomes the minority.

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We consider these more like solid nodules

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and should manage them like solid nodules.

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We have a cyst that could be associated with the nodule.

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Maybe you have a cyst with a discreet exophytic nodule.

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We're gonna manage it by the nodule component.

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If there's a dominant nodule, we apply the same types

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of growth parameters for the nodule size one

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and a half millimeter increase in diameter.

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But we also include increased wall thickness

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or increased nodularity within the wall

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as indicating growth.

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If you see air fluid levels

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or fluid containing cysts, this is most likely

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to be an infectious process

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and there are not classified in Lung-RADS under the

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category three four nomenclature.

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If you think these are infection,

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it would be either an S finding or we consider it

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Uh, long rat zero finding where it obscures enough

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of the lung parenchyma

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that we can't really clear the lung for screening.

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And the long rat's classification

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for atypical pulmonary cyst is not intended to be applied

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for cystic lung disease.

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People who smoke cigarettes are increased risk

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of developing, for example,

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laying her hand cell histiocytosis

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with nodules in cyst in an upper lobe predominant pattern.

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Those type of cysts are evidence

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of a diffuse lung disease process

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and not a focal process that we're looking for with respect

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to lung cancer screening.

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So let's look at a few examples since this is a relatively

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new nomenclature that's been rolled out.

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These are examples of thin walled cysts on the left thin

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round under two millimeter wall thickness, no nodularity,

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no ground glass associated with it.

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And here we have in the middle another thin

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walled cysts in some place.

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The wall is so thin you can't even see it.

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These are not classified at all in lung rats.

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They're simply simple, benign random lung cysts.

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One thing to be careful about is when a vessel

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is along the wall of a cyst,

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it can make it look like excentric wall thickening.

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So as you're scrolling through what looks like a simple cyst

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and you see something along it that is very transient,

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trace it back to the nearest vessel,

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make sure it's just not an area related to a vessel

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and it is not wall thickening.

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So that's just an interpretation pitfall to avoid.

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Let's look at a couple of the cystic nodules.

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This is a category four A cyst. It's a cystic nodule.

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There's more lucency than solid components,

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so we're not treating it like a cavitary nodule.

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And it has an excentric focal area of wall thickening

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as you can see here by the arrow.

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So we've got an atypical pulmonary cyst thick wall

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with focal asymmetric wall thickening

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and it measures seven millimeters.

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This makes us a category four, a long rad cyst.

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We recommend the three month followup

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and it was not changed.

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This patient then gets downgraded

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to a category three using the new step

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to management approach that would make them come back

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for a followup CT in six months.

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From that time point, again, stable, they would step down

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to a lung rats two.

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Here's another cyst also Category four A.

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We see several loculation, several areas of focal lucency

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and an area of thickening, a septation that's asymmetric.

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On one side of it, this is a category four A cyst.

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The patient undergoes the followup low dose ct

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and now there's a true exophytic solid component.

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This increases the likelihood of this being cancer.

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And so this patient moves into the four B category,

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the highest category for management

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and diagnostic assessment.

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This turned out to be a squamous cell carcinoma.

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So new solid components associated

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with an atypical cyst are very important to recognize.

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You have an example of a four B lesion.

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There is clearly a large septated cyst here within thin

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walls, but right next

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to it is a large exophytic 16 millimeter nodule.

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It's not the dominant component

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'cause there's more cyst than there is solid.

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This is a category four B atypical cyst

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and this patient will be recommended

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for diagnostic assessment

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and this proved to be an invasive lung adenocarcinoma.

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A couple things about multilocular cysts

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and these are examples of multilocular cysts

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that were identified on baseline screening exams.

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They're very heterogeneous.

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They can be cyst with a single septation.

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They can be assist with large, medium,

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and small sized areas of internal septation.

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They can be multicystic like this one

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and they can be cystic with a little bit

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of ground glass interspersed within them.

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So these are complex.

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It's a heterogeneous group of cysts with varying types

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of septation cyst size as well

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as internal opacities and ground glass.

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But all of these would be considered category four a lesions

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on baseline screening ct.

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When we follow up some

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of these multilocular cysts, let's take a look.

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One of these is a case that I showed you on the last

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where we have a multilocular cyst here in the right upper

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lobe on the baseline screen

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and it's become bigger on the next annual screen.

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This takes it from a four A to a four B

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to go undergo diagnostic assessment.

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If we look at this other example on the right,

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we have a complex multilocular cyst with an area

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of thin mildly nodular septation.

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On the baseline screen at annual ct, we see

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that not only there is there a new irregular nodule within

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it, but the cyst itself outside the nodule has increased.

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The cysts peripheral

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to the solid component have increased in size and number.

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So we have a new solid component

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and an overall increase in size of this multilocular cyst.

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Taking this also to category four B lesion.

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So that's some description of the lung RADS 2022, inclusion

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of cystic lung nodules in the

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interpretation schema for the first time.

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Some of the tenets that are important, identification of

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benign cysts as not being important.

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Simple cysts versus cysts with septations,

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thickening nodularity,

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or a growing nodular component as well as growing

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cystic components in terms of size and number of cysts.

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That should be taken into consideration when looking at

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cystic lung nodules.