Ventricular septum anatomy
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Normal Ventricular Septum Anatomy
The ventricular septum can be divided into four components-
- Inlet septum
- Trabecular septum
- Outlet or Infundibular septum
The image below shows the different parts of the ventricular septum : 1) Membranous 2) Outflow 3) Trabecular septum 4) Inflow 5) Subarterial/supracristal
In the normal heart, the ventricular septum (VS) is mostly muscular. The fibrous component is the so-called membranous septum, and is only a small part of the VS. It is integrated into the aortic root, and is made of fibrous tissue. It is located inferiorly to the inter-leaflet triangle that fills the space between the ascending hinges of the non-coronary and right coronary leaflets of the aortic valve 
When transilluminated from the right atrioventricular aspect, it can be seen, in most cases, to be crossed by the hinge of the tricuspid valve, thus dividing it into atrioventricular and interventricular components. It is then the position of the hinge which determines the proportions which are atrioventricular as opposed to interventricular 
The atrioventricular component of the septum is itself pierced by the atrioventricular conduction axis as it passes from the apex of the triangle of Koch to reach the crest of the muscular septum
Locations of VSD
The disease occurs either due to defective growth or failure to alignment of one of these components. There are two basic different locations of VSD to be distinguished:
a. VSD located over the Crista Supraventricularis (less frequent, 4 -5 % of all VSD), are also called SUPRACRISTAL VSD or subaortic. Defect located in the outflow tract of the right ventricle.
Both the right and posterior coronary aortic valves are directly over the defect. Many times there is aortic insufficiency and rarely the aortic orifice can override the septal defect.
b. VSD located below the Crista Supraventricularis (more frequent). Also known as infracristal or subpulmonar. The defects located in front of the Conus Papillary muscle and behind the Crista are the most common variety.
There are defects behind the Conus Papilary muscle which are the posterior and basal VSD. Usually in this variety the defect size is larger than in the previous type.
There is a third variety located in the muscular interventricular septum (single or multiple orifices) (Roger disease). When the muscular VSD is multiple, resemble Swiss cheese.
Muscular VSD are bounded by muscles and not immediately related to the valves. They can be located in the apical, central, or outlet region of the ventricular septum.
- Anderson RH, Ho SY, Becker AE. Anatomy of the human atrioventricular junctions revisited. Anatomical Record 2000;260:81-91
- Allwork SP, Anderson RH. Developmental anatomy of the membranous part of the ventricular septum in the human heart. Br Heart J 1979; 41:275-280