An unusal conversation with a flamboyant student fellow,
May I know , What is the normal Pericardial thickness, ?
Which pericardium you mean sir ? ,Parietal or visceral?
Would like to know both .
It is variable sheet of tissue .You want the thinnest part or thickest part ?
Don’t beat around the bush .Tell some answer.
You want, autopsy thickness, or real life thickness as surgeon sees it ?
I want it in practical Imaging modality
Do you want Echo, CT or MRI thickness ?
I should say , its too much for a first-year fellow in reverse questioning!
Ok relax sir, shall I tell the systolic or diastolic thickness?
So, you decided to spoil my day.
Ok, one final clarification sir,, you want thickenss over anterior RV aspect or over posterior atria ?
You are getting on my nerves. Thankyou, will you please leave the class .
Yes, pericardial anatomy ,can indeed make us crazy. Let us try to get some answer .
Whenever some one is asking about pericardial thickness, it generally mean the parietal,thicker fibrous outer layer. It’s about 1 to 4 mm*, never more than 3 -4 mm .As we can see, it is a highly variable sheet of folded tissue with different adherent surfaces. The visceral pericardium is very much less than 1 mm, in fact,it need to be measured in microns. It is called the epicardium and adheres seamlessly to the myocardium with intervening fat. (Sub epicardial fat)
Ref: Normal pericardium measures 0.4–1.0 mm thick in autopsy studies but normal pericardium measures 1.2 mm in diastole and 1.7 mm in systole on MRI studies [1].It is sort of surprising finding, to note pericardium also thickens in systole.
Mind you, echo over estimate the thickness, and its crudest form of measurement and should not be relied upon.Even CT over estimates.MRI is currently closer to true thickness.
In constrictive pericarditis, which pericardium compresses the heart?
In effusive constrictive pericarditis, organized fluid makes the two layers stick together and makes it thick, making it difficult to differentiate the two layers in any imaging modality. Hence, the answer is that both layers together compress the heart, but the fibrous layer is primarily responsible and exerts more pressure per inch.
Can epicardium per-se thicken with normal thickness of parietal pericardium?
We are not clear about it. The rarity of constriction in viral myo-pericardiits comparred to tuberculous suggest isolated epiicardial constriction is rare as epicardium is sngle sheet of cell .In wonder inflitrative pericarits might occur arsoing pure feom epeicardium following myo or epimyo caritis. . I dont know , may occur in some myopericardits.We need to ask Dr Renu virmani.
(*Answer to this question might alos explain why rheumtic pericardiits doesnt cause constriction as it doesnt involve fibrous pericardium )
Does sub-epicardial fat make epicardium appear thick ? How to differntiate it ?
This is a tough one to diffferentiate . There have been cases of constrictive physiology due to epicardial fat (Effusive-constrictive pericarditis with massive epicardial fat A Goto, M Lancet September 01, 2001)
One final question: Is it the thickness or the elastance /resistance of the pericardium that determines the likelihood of constriction?
Pericardial histology and elastance are more important. We know, that transient constriction with normal pericardial thickness is a very well recognized entity. (Haley JH,JACC 2004)
Final message
Never under-estimate the importance of pericardial anatomy. It can go as deep as its recesses and the tortuous sinuses. Try reading this wonderful review by Rodriguez.(Ref 1) I guess it might have taken tons of time to write such a great article. Don’t excuse yourself to waste 20 minutes in between your angioplasty times.
Reference
Dr.S.Venkatesan MD 