Thoracic Radiology questions...

[FunnyDocMan1234]

Hi all, I'm a pulm fellow and have had some thoracic rads questions accumulate that I haven't been able to get a good answer for. Would appreciate any insight!

- What exactly does the term "reticulation" refer to? Does this just mean irregular interlobular septal thickening or is there a more exact definition?

- If a CT does not show a pericardial effusion is it pretty much ruled out, or does a TTE add sensitivity? Does contrast affect the sensitivity of CT for pericardial effusion?

- What is the basis of calling a pleural effusion an exudate based on CT scan?

- Why is lung parenchyma hyperlucent in mosaic attenuation due to pulmonary vascular disease. I understand the hyperlucensy in mosiac attenuation due to air trapping (simply due to air) but not sure why the parenchyma would appear similar in PVD.

more critical care related:
- Is a CT sinus actually helpful in looking for sinus infection or will a noncon head CT show evidence of this if truly significant infection?


Thanks!

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[Clean7795]

Reticulation -> I do not know of the specific definition but it does usually have a certain net-like look to it and is usually a term used when we want to describe something that is associated with interstitial fibrotic changes for CT. On X-ray it is more of a general term and can refer to interlobular septal thickening as well (if we were to see that on CT, most would directly just call it interlobular septal thickening rather than "reticulations").

CT for pericardial effusion -> While I do not think CT should be ordered to examine a pericardial effusion, in a case without artifact and decent myocardial contrast enhancement, my feeling is that a CT is extremely accurate in determining if there is a pericardial effusion. The caveat is that often there is trace fluid and some rads will call it a trace effusion while most will feel it is physiologic fluid and not mention it. The reason you want a TTE instead is that if there is a pericardial effusion that needs to be acted on, cardiologists feel much more comfortable with a TTE rather than a CT.

Exudative -> Hounsfield attenuation/density. I usually use a more general term over exudative, or I report it as requesting correlation for an exudative effusion, mainly because I don't want them to feel "trapped" by what I report.

Sinusitis in ICU patients -> Unless it is florid, imaging in general is very poor for diagnosing sinusitis in ICU patients. Often intubated patients will get baseline opacification of their paranasal sinuses, which overlaps with what 99% of mild-moderate sinusitis will look like.

Still, if you have no other choice, you are truly clinically suspecting sinusitis, and you're looking for a nasty invasive infection, then both are adequate.
CT sinus advantages is that it gives extra imaging information if an ENT surgeon were to intervene. Most rads will also report these cases with more attention paid to the sinuses.

CT heads on the other hand will usually have at most 1 line talking about the paranasal sinuses. Still if you want to look at the anatomic information yourself, most of the same information is there (though you probably won't have thin slice/high freq reconstructions that ENT would want).

 

[Cognovi]

Reticulations - are inclusive of but generally finer/smaller than interlobular septal thickening, therefore includes intralobular septal thickening, intralobular lines, parenchymal bands. If it is just interlobular septal thickening, like in pulmonary edema, we'd just say that. If there's a finer component, as in pulmonary fibrosis, then we'd go with reticulation.

Pericardial effusion - agree with the above poster and would add that I don't think contrast adds sensitivity for detection of pericardial effusion. On the off chance that a pericardial mass is causing the effusion, contrast is helpful. I have seen a rare case of a myxoid liposarcoma metastasis to the pericardium causing a huge pericardial effusion and the mass would not be discernable on CT aside from a few intratumoral enhancing vessels.

Exudative effusion - I think CT is relatively inaccurate in distinguishing exudate vs transudate, but if an effusion is denser than ~15 HU, there's pleural thickening, and loculation, then I would think it's more likely than not to be exudative.

Mosaic attenuation of vascular etiology: oligemia appears lucent because the vessels are smaller

 

[Cognovi]

more critical care related:
- Is a CT sinus actually helpful in looking for sinus infection or will a noncon head CT show evidence of this if truly significant infection?

Significant sinus infection short of orbital or intracranial complications is a clinical diagnosis, not a radiologic one. CT will show some opacification of paranasal sinuses, which you can interpret as infection or as just backed up secretions because the patient has tubes in their nose and throat.

Orbital or intracranial complications are another story. MRI is preferred, followed by contrast-enhanced CT. Head CT provides a higher dose and soft tissue detail but as the above poster noted, less attention is paid to the sinuses, the bottom part may even be cut off, and the images are probably suboptimal for ENT surgical navigation software.

 

[2brads]

The chest guys in residency defined reticulation as “intervening lines”. Most radiologists use it for “net-like” densities.

CT is very sensitive for pericardial fluid. Although I’m not sure it should be used only to determine if fluid is present.

I don’t use the verbiage “exudate”. If there are septations, enhancement, nodules or increased density I describe it as such and leave it up to the ordering doc if they think it’s blood, pus, protein, etc.

I’m not sure what PVD refers to exactly but mosaic attenuation can occur with chronic occlusive subsegmental PE because of V/Q matching.

CT can show signs of sinusitis but it is not specific. MRI can be more useful (particularly with invasive fungal sinusitis).