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 ?
- 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