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2010-07-13-10 Isolated atrial septal aneurysm © Cerekja www.TheFetus.net

Isolated atrial septal aneurysm

Albana Cerekja MD. PhD.*, Flavia Ventriglia MD.**, Juan Piazze MD. PhD.***

 
*   Ultrasound Division, ASL Roma B, Rome, Italy.
** Pediatric Cardiology. Policlinico Umberto I. University “La Sapienza” Rome, Italy.
***Ultrasound Division, Ceprano Hospital, Ceprano, Italy.


Synonyms

Redundant septum primum flap, Foramen Ovale Aneurysm, Atrial Septal Aneurysm (ASA), Aneurysm of Septum Primum

Anatomy

The thin membranous septum primum divides the fetal atria early in embryonic development. The thicker septum secundum grows along the septum primum, and contains an opening that occupies the middle third and is referred to as the foramen ovale. This one is guarded by a thin membrane, the foraminal flap which flickers into the body of the left atrium (1). The foramen ovale allows normal right-to-left atrial shunting during fetal life. Earlier in the gestation, closure of the foramen has been associated with severe hypoplasia of the left ventricle whereas later closure has been associated with right heart failure and rarely with the formation of an aneurysm of the atrial septum. The foramen ovale is defined as restrictive if its maximal diameter measures less than 3 mm (2).

Flow across the foramen ovale displaces the septum primum into the left atrium. The septum primum is relatively pocket-shaped and is not intact along the entire extent of the inter-atrial septal wall, allowing blood to pass from right to left atrium. The opening of the septum primum is not directly over with the foramen ovale, so the septum primum will effectively close the foramen ovale in early neonatal life as left atrial pressure exceeds right atrial pressure and the septum primum adheres to the septum secundum (3).

During development, if there is overabundant or weakened septal tissue, the septum becomes very mobile. This can be visualized at echocardiography and the degree of deviation can be measured.

In the adult life, maximal deviation of the interatrial septum more than 15 mm, is called an atrial septal aneurysm. If the amount of septal excursion is less than 15 mm, it is referred to as a redundant atrial septum (4).
Prenatally, an abnormally redundant septum primum flap is considered in case it extends at least halfway across the left atrium (5).
This finding has been reported in around 1.2% of fetuses referred for echocardiographic examination (6).

There is a strong association between atrial septal aneurysm and fetal atrial arrhythmias which are usually benign and do not require any treatment. In absence of associated anomalies, it doesn't require any special prenatal management (7).

Echocardiography

Transverse views better represent the structure of the atrial septum because it is oriented at 90 degree angle relative to the ultrasound beam. The pattern of motion of the foramen ovale flap can be observed on M-mode. On the two dimensional scan it could be seen to move throughout the cardiac cycle but when recorded in M-mode this motion could be seen to be organized. The flap approaches or closes the atrial septum twice during each cardiac cycle (8). This movement pattern is consistently recordable in every normal fetal heart. Allan et al (9) studied flap’s excursion by echocardiography. They found out that when this motion is timed with the fetal electrocardiogram and left atrial wall motion, there appears to be an abrupt closure of the foramen ovale flap during atrial systole. It then opens more gradually and then drifts closed during ventricular systole. Closure during ventricular systole may be the result of the effect of the pulmonary venous return to the left atrium meeting a closed mitral valve. Once ventricular systole ends the foramen ovale flap opens again. This suggests a biphasic pattern of flow from the right to the left atrium related to atrial systole but also being determined by the relative systemic and pulmonary venous returns.


Case 1

This is a case of a 39-year-old woman G3 P2 with non-contributive personal history. Her second baby boy, underwent a left nephrectomy due to severe hydronephrosis.

Fetal anomalies scan at 21 weeks of gestation did not reveal any anomaly.  Echocardiogram performed at 28 weeks revealed an aneurysm of the foramen ovale flap and no other cardiac anomalies.
Following scan at 31 weeks showed atrial septal aneurysm without any signs or heart arrhythmia.
The foramen ovale flap is reaching more than halfway across the left atrium.There was a small uterine septum at the uterine fundus.

Images 1-6: Arrow indicates the foramen ovale reaching almost the free left atrium wall.







Images 7,8: Doppler imaging showing flow via foramen ovale.



Images 9,10: M-mode



Image 11: Arrow shows the uterine septum.



Video 1,2: Videos showing atrial septal aneurysm, note that the tissue of foramen ovale is extended more than halfway across the left atrium.



Video 3,4: Doppler imaging showing flow via foramen ovale.

 

Case 2

Case of the atrial septal aneurysm diagnosed at 37 weeks of gestation. Foramen ovale flap is reaching far left towards the left atrial wall. The width of the foramen ovale is around 6 mm.
A 28-year-old G2 P1 with non-contributive personal and familial history. First trimester scan did not show any anomalies. Second trimester scan was normal except for a small subaortic ventricular septal defect. Echocardiography performed at 23 weeks confirmed the finding and did not evidence any other anomalies.

At 33 weeks, the atrial septal aneurym was evidenced. Images and videos show the foramen ovale flap reaching
far left towards the left atrial wall. The width of the foramen ovale is around 6 mm.

Images 1,2: 4-chamber view with the foramen ovale flap bulging into left atrium. Image 2 shows M-mode showing the foramen ovale flap deviation.



Images 3,4: Arrow indicates the foramen ovale flap.



Images 5,6: Doppler imaging on image 5 shows a slight deviation of the mitral flow caused by foramen ovale flap.
Image 6 shows the flow via foramen ovale (6 mm).



References:

1. Chiappa EM, Cook AC, Botta G, Silverman NH. Echocardiographic Anatomy in the Fetus Springer 2008; pg 62.
2. Lev M, Arcilla R, Rimoldi HJA, Licata RH, Gasul BM. Premature narrowing or closure of the foramen ovale. Am Heart J. 1963;65:638–647.
3. Necas M. Redundant Septum Primum Flap in Fetus with Premature Atrial Contractions. OBGYN.net. April 2000.
4. Griffin BP, Topol EJ. Manual of Cardiovascular Medicine 3° edition. Lippincott Williams and Wilkins 2008 pg 444.
5. Kachalia P, Bowie JD, Adams DM, Caroll BA: In Utero Sonographic Appearance of the Atrial Septum Primum and Septum Secundum. J Ultrasound Med 1991;10:423-6.
6. Katayama H, Mitamura H, Mitani K, Nakagawa S, Ui S, Kimura M. Incidence of atrial septal aneurysm: echocardiographic and pathologic analysis Cardiol. 1990;20(2):411-21.
7. Rice MJ, McDonald RW, Reller MD. Fetal atrial septal aneurysm: a cause of fetal atrial arrhythmias. J Am Coll Cardiol 1988;12:1292-97 .
8. Eric H. Dellinger. Atrial septal aneurysm. TheFetus.net 1993.
9. Allan LD, Joseph MC, Boyd EGCA, Campbell S, Tynan M. M-mode echocardiography in the developing human fetus Br Heart J 1982;47:573-83.



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