The membranous septum of the heart: an anatomical review

The aim of the review is to explore and clarify the degree of consistency of different researchers’ views on the terminology and nomenclature of the membranous septum (MS), to discover the blank spaces of the theme and the most controversial areas, and to outline promising directions of anatomical studies of this structure. The review exhibits developmental historical insight and current concepts for the MS. There is no doubt that both tubercles of the atrioventricular cushions and dorsal mesenchymal protrusion are involved in the development of the MS. The roles of the mesenchymal cap and the neural crest are even more understudied. The review includes comprehensive analysis of the height, length, width, and thickness of the MS. The literature under review amply describes variability of shape, so it is attempted to clarify whether it is the real anatomical diversity or terminological discrepancies. The prevalence, adjacent anatomy, gross- and microanatomical features of the components are explored. The MS is reviewed as a constituent part of the fibrous skeleton of the heart neighboring to the atrioventricular conduction axis. The publications on the microscopic anatomy of the MS are discovered to be extremely scarce. To describe intracardiac topography, one should use the same landmarks suitable for clinical practice in an attitudinal approach fashion, no matter what kind of heart is described, whether fetal or postnatal.