The aneurysm of the membranous septum (AVS) is a congenital lesion that is usually associated with other congenital defects . Aneurysm formation in the membranous septum is a common mechanism to reduce interventricular shunting in patients with ventricular septal defects and is believed to be usually benign in nature , and only an occasional finding . This was an unusual case because the AVS caused such a severe obstruction of the RVOT.
An aneurysm of the membranous ventricular septum is a tissue dilatation of this portion, and since it is weak, it bulges to the right ventricle (RV) as a consequence of left ventricle pressure . The most widely accepted theory regarding the etiology of a membranous septum aneurysm is that it forms during the course of spontaneous closure or diminution in the size of a ventricular septal defect (VSD) .
We could not find any previous data on the aneurysm of the membranous septum (AVS) in Syria. It occurs in 0.3% of patients with congenital heart disease . However, one of the reported cases was in a 71-year-old woman with a history of previous myocardial infarction . If aneurysms are rare (0.3% of congenital heart disease), the possibility that they cause obstruction is even rarer . To the best of our knowledge, 11 similar cases have been reported since 1982. Before that, three articles mentioned it [6,7,8]. Only two of those 11 cases [4, 9] were in young children. One of these was in a child with dextrocardia and L-TGA  known as the so-called ‘windsock syndrome’ , which makes our case the second reported case in children in which an aneurysm of the membranous septum dynamically obstructed the RVOT. What makes this case more unique is that no muscular infundibular obstruction was found, although hypertrophied muscle was mentioned to be resected on the anterior wall of the right ventricle in the first reported case . This indicates that the aneurysm was large enough to cause obstruction without any associated hypertrophied muscle.
Although other cases were diagnosed by transesophageal echocardiography  and confirmed by angiography, this was not necessary in our case.
The dyspnoea in this case was an ordinary finding among other cases [2, 11, 12]. However, one of the reported cases presented with chest pain and ventricular tachycardia , but that was the case with previous myocardial infarction. The skull and dental deformities should have warranted a genetics evaluation . However, it could not be carried out due to the difficult circumstances. We could not review some of the previously reported cases thoroughly, as the full article was not available online [1, 14].
In conclusion, the occurrence of RVOT obstruction by a membranous ventricular septal aneurysm is very rare. Further studies are needed to obtain a more comprehensive understanding of aneurysms of the membranous septum (AVS).