Perimembranous central ventricular septal defect
Definition
This is a generic term that, if possible, should not be used in preference to more specific terms regarding the geographical site of the defect's extension: central and basally, to the right ventricular inlet, or to the right ventricular outlet. This code is used by some as synonymous with the conoventricular VSD, or the paramembranous VSD. It is also known as the type II VSD. It should not be used to code an inlet VSD, or the so-called atrioventricular canal VSD. More specific terms exist for coding these entities. It is used by some to describe an isolated perimembranous VSD without extension, although it is unlikely that perimembranous defects exist in the absence of deficiency of their muscular perimeter. The conoventricular VSD with malalignment should be coded as an outlet defect, as should the perimembranous defect opening to the outlet of the right ventricle. All perimembranous defects, nonetheless, have part of their margins made up of fibrous continuity either between the leaflets of an atrioventricular and an arterial valve or, in the setting of double outlet right ventricle or overriding of the tricuspid valve, by fibrous continuity between the leaflets of the mitral and tricuspid valves. Such defects can also extend to become doubly committed and juxta-arterial (conal septal hypoplasia) when there is also fibrous continuity between the leaflets of the arterial valve or when there is a common arterial valve.
Coding note
Although best used to describe the perimembranous defect that opens centrally at the base of the right ventricle, this term might be used to code perimembranous defects with inlet or outlet extension. It is recommended, however, that the more precise terms be used whenever possible for coding the latter lesions. This code is used by some as synonymous with the perimembranous, conoventricular, Type II, or the paramembranous defects. It should not be used to code an inlet VSD, or the so-called atrioventricular canal VSD. More specific terms exist for coding these entities. It is used by some to describe an isolated perimembranous VSD without extension, although it is unlikely that perimembranous defects exist in the absence of deficiency of their muscular perimeter. The conoventricular VSD with malalignment should be coded as an outlet defect, as should the perimembranous defect opening to the outlet of the right ventricle. All perimembranous defects, nonetheless, have part of their margins made up of fibrous continuity either between the leaflets of an atrioventricular and an arterial valve or, in the setting of double outlet right ventricle or overriding of the tricuspid valve, by fibrous continuity between the leaflets of the mitral and tricuspid valves. Such defects can also extend to become doubly committed and juxta-arterial (conal septal hypoplasia) when there is also fibrous continuity between the leaflets of the arterial valves or when there is a common arterial valve. Specific codes exist for these variants, which ideally should not be coded using this term.