THE MEMBRANOUS PORTION OF THE INTERVENTRICULAR SEPTUM IN NEONATES - AN ANATOMIC STUDY IN NEONATAL CADAVERS

The membranous portion of the interventricular septum (MPIS) has been described as a small, oval portion of the cardiac septum that lies imm ediately below the aortic valve. Its location and relationship with th e aortic valve are very important in surgical interventions. Several s tudies have been reported in adults but few in neonates. For this reas on, studies of the MPIS were made in the hearts of 26 (12 male, 14 fem ale) fullterm neonates. The left side of the MPIS was photographed wit h transillumination from the right ventricle. The shapes of the septum were assessed from the photographic images. In addition, in accordanc e with the ruler in the photographs a millimetric scale was prepared o n the tracing paper and the surface area of the MPIS and its distance from the superior border of the aortic valve were measured. In these 2 6 cases, the following shapes of MPIS were found: semilunar, 7 (26.92% ); triangular, 6 (23.07%); quadrangular, 5 (19.23%); oval, 4 (15.38%); circular, 2 (7.69%); irregular, 2 (7.69%). Its surface area varied fr om 2-21 mm(2) (mean 5.84 mm(2)). The superior border of MPIS was in cl ose relationship with the aortic valve. In 10 cases (38.46%) the MPIS was in direct continuity with the attachments of both the right and po sterior aortic cusps, in 8 (30.76%) only with the posterior aortic cus p, in 5 (19.23%) only with the right aortic cusp, while in 3 (11.53%) the superior border of MPIS was below the attached portion of both cus ps. The distance between the superior border of the MPIS and the attac hment of the right or posterior aortic cusps did not exceed 3.5 mm. Th ere were no statistically significant sex-related differences in shape , surface area and relationship with the aortic valve.