Atrioventricular septal defect with an absent or tiny ostium primum defect: a case series of three surgical cases.

Although atrioventricular septal defects are categorized according to the anatomical atrioventricular orifice, the location of the intracardiac shunt in atrioventricular septal defects is important from a surgical perspective. Herein, we report three cases of atrioventricular septal defects with a small or no ostium primum defect. Case 1 (3-month-old girl) was diagnosed preoperatively with a ventricular septal defect, secundum atrial septal defect, and mitral valve cleft. After the operation, the diagnosis was corrected to an atrioventricular septal defect and was repaired completely. Case 2 (9-year-old girl) underwent pulmonary artery banding for a ventricular septal defect with a straddling mitral valve. After the experience with Case 1, we realized similarities between Cases 1 and 2. Therefore, we corrected the diagnosis to atrioventricular septal defect and achieved definitive repair. Based on these experiences, we accurately diagnosed Case 3 (3-month-old boy) with an atrioventricular septal defect. This variant is poorly known; however, proper morphological understanding is necessary to facilitate anatomical repair and prevent postoperative atrioventricular blocks. Some cases of this variant may be diagnosed as a ventricular septal defect with straddling mitral valve and are unable to receive definitive repair. The direction of the cleft, absence of atrioventricular valve offsetting, and trileaflet of the left atrioventricular valve all seem useful for making a diagnosis, and these can be easily confirmed by echocardiography.