Atrial septal pouch: a comprehensive morphologic and morphometric evaluation with clinical relevance

Purpose: The septal pouch is an anatomical variant resulting from incomplete fusion between the septum primum and the septum secundum at the interatrial septum. This partial fusion creates a conical pouch, which is potentially predisposed to thrombus formation, increasing the degree of thromboembolic risk. This cadaveric study aimed to evaluate the prevalence, morphology, and morphometry of septal pouches and their associations with other septal defects. Methodology: The interatrial septa of 60 human hearts were examined for septal pouches. Characteristics such as pouch type, apex and base orientation, base width, depth, and morphological variants were documented. Results: Atrial septal pouches (ASPs) were identified in 22/60 (37%) specimens. Right atrial septal pouches (RSPs) were predominant (30%), whereas left atrial septal pouches (LSPs) were found in 7% of the patients. Most RSPs exhibited a thin, membranous, flattened morphology, although some were thick and muscular. All LSPs were thin and flattened, with a superiorly directed ostium and an inferiorly directed apex. Histologically, the pouches demonstrated a trilaminar arrangement, comprising the myocardium sandwiched between two endocardial layers, with collagen-rich connective tissue beneath. Conclusion: This study highlights important anatomical insights regarding septal pouches, emphasizing the higher prevalence and varied morphometry of RSPs. Given their potential clinical significance in thromboembolic phenomena, further investigation into septal pouch involvement in cardiovascular diseases is warranted.