FIG 32.3 These images, both showing autopsied specimens sectioned to replicate the four-chamber echocardiographic plane, show the differences in the channels between the ventricles when they are within the substance of the ventricular septum (left) or overridden by the orifice of an arterial valve (right) In the specimens shown, both open to the inlet of the right ventricle, but the channel shown at right is at the margins of the septum and had fibrous continuity between the leaflets of the aortic and tricuspid valves as part of its borders This latter feature makes the defect perimembranous In addition, the perimembranous defect with inlet extension has fibrous continuity between the atrioventricular valves with loss of the normal offset between these two valves Features Requiring Description Appreciation of the borders of the channels between the ventricles as viewed from the right ventricle provides the means of distinguishing between the phenotypes In the categorization to be used in ICD-11, the way in which the defects open to the right ventricle—in other words, their geography—is taken as the initial descriptive feature On this basis, defects are described as being centrally located at the cardiac base, as opening either to the inlet or outlet of the right ventricle, or as found within the substance of the apical muscular septum The defects are distinguished according to the nature of their borders In this last respect, all defects can be described as being muscular, perimembranous, or doubly committed and juxtaarterial (Box 32.2).19 A fourth group had been discussed, namely the allegedly juxtatricuspid and nonperimembranous, or inlet, defect.20 Patients suggested to have such defects, subsequent to echocardiographic interrogation (Fig 32.4), have subsequently been reclassified, either following direct surgical inspection or retrospective echocardiographic assessment, as having perimembranous defects with inlet extension or muscular inlet defects We have never come across a specimen with the alleged fourth pattern in an archive of autopsied specimens Box 32.2 Classification of the Borders of Ventricular Septal Defects Defects abutting on area of continuity between tricuspid and aortic valves (perimembranous) ■ Opening into inlet of right ventricle ■ Opening into outlet of right ventricle ■ Confluent defects Defects encased within musculature of ventricular septum (muscular) ■ Opening to the inlet of the right ventricle ■ Opening between the apical components ■ Opening anterior to the septomarginal trabeculation ■ Opening to the subpulmonary outlet ■ Multiple Defects roofed by arterial valves in fibrous continuity (doubly committed and juxtaarterial) ■ With muscular posteroinferior rim ■ Extending to become perimembranous FIG 32.4 Echocardiographic images demonstrating characteristic features of a perimembranous ventricular septal defect (VSD) with inlet extension (A) The apical four-chamber view demonstrates a large ventricular septal defect below the atrioventricular valves with loss of the normal offset between the tricuspid and mitral valves (red arrow) (B) In the subcostal short axis view, the defect is seen extending from the perimembranous region adjacent to the commissure between the anterosuperior (A) and septal (S) leaflets of the tricuspid valve (asterisk), inferiorly and posteriorly along the septal leaflet of the tricuspid valve into the inlet of the right ventricle This defect was misclassified as an “inlet” ventricular septal defect, or juxtatricuspid defect, but not perimembranous; however, it was confirmed at the time of surgery to be perimembranous, as evident by the extension into the perimembranous region with fibrous continuity between the tricuspid valve and aortic valve (AoV) LA, Left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle Muscular Defects