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Is it a thickened interatrial septum . . . or . . . a double atrial septum ?

Posted Sep 03 2011 11:13am

 Inter atrial septum(IAS)  is a delicate structure , formed by a  “curious IAS  embryological process”  , when  two septums ,  two ostiums  cross each  other .They  fold  and unfold  like  curtains  in different times ,  ultimately result in a  single membrane separating LA and RA  with a  central physiological   hollowness called foramen  ovale .

All along this process ,  blood has to shunt  from  RA to LA  untill the baby comes out ,  when the direction reverses that  result in the flap  of foramen ovale locking  against the septum secundum with raising LA pressure . So , basically the genesis of  IAS is all  about growing,   resorbing  and  sticking of two septums . This starts in utero and continues well after birth. One can imagine  complexity of  the factors that determine the thickness of IAS.

The IAS thickness varies between 2mm to 4  mm . With increasing use of trans esophageal echocardiography and also the need for cardiologists to puncture the IAS , it is becoming important to study the anatomy of IAS in detail.

A new  cause of  thickened IAS  is reported recently .

 This is refered to as Double Inter atrial septum,  fused like a sandwich  with a  potential space  in between  .

The embryological basis is not clear. (A septum primum and secundum fusion ?)

The PFO   is an  oblique orifice in many .It is some times refered to as tubular PFO . A large tubular PFO can mimic a double IAS.

An  aneurysm of IAS  may get  fused to appear like a double septum

or Is it  IAS dissection which  give an appearance like double IAS ?

Personal perspective

  • It is very difficult to embryologically  explain the concept of double IAS .  I would think  , it is  double layer  of single embryological  septum   with a  potential  space  in between .
  • It is possible an intra mural hematoma (Spontaneous or acquired ) may cleave the septal plane and mimic a double IAS   when the   thrombus gets dissolved later.

Other causes of thick IAS

Septal thickness an issue during transeptal puncture . During PTMC and left heart catheterization a thick septum may be a hurdle.

Infiltrative  myopathies especially amyloidosis is known for a very thick non -puncturable IAS  

Reference

1. http://ejechocard.oxfordjournals.org/content/9/5/707.full

2. http://www.ncbi.nlm.nih.gov/pubmed/16950474?dopt=Abstract


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