Title & Abstract

International Journal of Anatomy and Research

Ostium Secundum Atrial Septal Defect: A Case Report with Review of Literature

DOI: 10.16965/ijar.2026.161

Jagadeesan, Saravanan ¹

Vishnumukkala, Thirupathirao ²

Krishnasamy, Narendiran ³

Koshy, Shajan ¹

Moklas, Mohamad Aris Bin Mohd ⁴

Yahaya, Ahmad Yusuf Bin ¹

¹ Department of Anatomy, School of Medicine, Lakeside Campus, Taylor's University, Subang Jaya 47500, Selangor, Malaysia.

² Anatomy Discipline, Human Biology Department, School of Medicine, IMU University, Bukit Jalil, Kuala Lumpur 57000, Malaysia.

³ Clinical Skills Center, School of Medicine, Lakeside Campus, Taylor's University, Subang Jaya 47500, Selangor, Malaysia.

⁴ Department of Human Anatomy, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia.

ABSTRACT

Background.

Atrial septal defect (ASD) is a congenital cardiac abnormality, representing roughly 10% of all congenital heart problems. The ostium secundum type is the truly familiar form, characterised by a deficit in the fossa ovalis. A significant proportion of instances, sometimes diagnosed in childhood, remain asymptomatic and undiscovered for the whole of a patient's life.

Case Presentation.

An incidental discovery of a multi-fenestrated ostium secundum-type atrial septal defect was made during routine cadaveric dissection of a 60-year-old male cadaver. Five distinct fenestrations were observed within and around the fossa ovalis area of the interatrial septum, located in its superior, central, and inferior segments a configuration characteristic of the 'swiss-cheese' septal variety. The fossa ovalis boundary was discernible as a fibrous ring, however the floor and adjacent septum secundum tissue were significantly perforated. This individual has no recorded history of congenital heart disease.

Conclusion.

This case highlights the clinical and anatomical importance of multi-fenestrated ostium secundum atrial septal defect, a morphological variety characterised by numerous distinct perforations instead of the anticipated singular central opening. The observed 'swiss-cheese' pattern has significant implications during surgical intervention, since it frequently prevents conventional single-device transcatheter closure and may require surgical patch repair. This case underscores the significance of cadaveric dissection in revealing intricate congenital abnormalities that may remain asymptomatic during a affected population life.

Keywords: Atrial septal defect; Ostium secundum; multi-fenestrated atrial septal defect; Cadaveric dissection

INTRODUCTION

Congenital heart disorders (CHDs) constitute a diverse array of anatomical defects of the heart and major arteries resulting from defective embryogenesis which occurs during the initial eight weeks of intrauterine development [1]. Atrial septal defect (ASD) is one of the most common CHDs, with an incidence of roughly 1.6 per 1,000 live births, accounting for about 10% of all congenital cardiac malformations [2]. ASD is characterised by abnormal communication between the two atria, allowing oxygenated blood to flow from the left atrium to the right atrium, resulting in right-sided volume overload and, ultimately, pulmonary hypertension and right heart failure [3].

ASDs are categorised into four primary subtypes according to their anatomical position: (1) ostium secundum type, situated in the central area of the interatrial septum at the fossa ovalis; (2) ostium primum type, located in the inferior segment of the atrial septum contiguous to the atrioventricular valves; (3) sinus venosus type, sited near the entrance of the superior or inferior vena cava; and (4) coronary sinus type, the most uncommon variant. The ostium secundum ASD is the most familiar type, representing 75-80% of all ASDs [4,5].

A distinctive and clinically significant characteristic of ostium secundum ASD is its propensity to remain asymptomatic for decades, and in certain instances, throughout the patient's life [6]. This is especially observed in the older demographic, where undetected ASDs may be discovered incidentally either during echocardiographic assessments for unrelated ailments, cardiac catheterisation, or, as in the current instance, after post-mortem cadaveric dissection [7].

The embryological origin of this defect has been thoroughly documented: during cardiac development, the foramen ovale formed by the communication of septum primum and septum secundum fails to close entirely, or the septum secundum develops with excessive fenestration or insufficient tissue mass, resulting in a persistent interatrial communication [8]. We document an inadvertent finding of a substantial ostium secundum-type ASD in a sixty-year-old male cadaver during anatomical dissection. This paper offers an exhaustive examination of the literature related to the morphology, embryology, epidemiology, clinical manifestations, complications, and therapy of this illness.

CASE PRESENTATION

In the normal dissection session held in the Department of Anatomy, a male cadaver approximately 60 years old was examined as part of the standard instructional program. The cadaver was preserved utilising conventional embalming techniques with a 10% formalin solution. No notable medical history or cause of death was provided in the documents accompanying the cadaver.

Upon accessing the thoracic cavity and conducting a systematic dissection of the pericardium, the heart was in situ and subsequently excised according to established anatomical technique. The external inspection of the heart showed no apparent gross abnormalities, including normal size and weight.

Following a meticulous incision of the right atrium along the sulcus terminalis, the inside of the right atrium was revealed. The examination of the interatrial septum revealed numerous distinct perforations concentrated within fossa ovalis and next to the limbus fossa ovalis, indicative of a multi-fenestrated ostium secundum-type ASD (Figure 1). Five distinct fenestrations were identified: (1) a superior-left perforation in the upper-left quadrant of the fossa ovalis; (2) a superior-central fenestration situated just above the center of the fossa ovalis; (3) a smaller superior-right fenestration; (4) a mid-level left-margin perforation along the left border of the septum secundum; and (5) an inferior-left fenestration in the lower-left area of the fossa ovalis. The edges of each defect were smooth, hard, and fibrous, indicative of chronic organised perforations. No other structural anomalies were detected. The tricuspid and mitral valves appeared macroscopically normal.

Figure 1

The findings were consistent with a multi-fenestrated ostium secundum-type ASD, a morphological variant characterised by excessive and spatially distributed resorption of the septum secundum, resulting in multiple discrete communications instead of a single large defect.

DISCUSSION

Ostium secundum ASDs are classified by size (small <10 mm, moderate 10-20 mm, large >20 mm), shape, rim features, and multiplicity [14]. The multi-fenestrated 'swiss-cheese' variant features several discrete perforations across quadrants of the fossa ovalis [15-17]. Rim adequacy (aortic, SVC, IVC, posterior, AV, and coronary sinus rims) is critical for device closure planning. The multi-fenestrated form frequently lacks sufficient rim tissue between individual fenestrations, which renders transcatheter closure with a single device technically difficult or unfeasible, necessitating open surgical patch repair [18,19].

Embryological Basis of Ostium Secundum Atrial Septal Defect

Cardiac septation commences approximately in the fourth week of embryonic development [9]. The septum primum extends downward from the ceiling of the primitive atrium toward the endocardial cushions, forming the transient ostium primum [10]. Programmed caspase-mediated cell death in the upper segment of the septum primum generates the ostium secundum. Subsequently, the muscular septum secundum develops to the right of the septum primum, creating the valve-like foramen ovale [11,12]. In roughly 75% of people, functional closure at birth is followed by anatomical fusion within the initial two years of life [13]. Ostium secundum ASD occurs due to excessive apoptosis of the septum primum, inadequate growth of the septum secundum, or abnormal fenestrations that fail to fuse [11].

Morphological Classification and the Multi-Fenestrated Variant

Haemodynamic Implications and Clinical Manifestations in Adults

Substantial left-to-right shunting causes volume overload in the right atrium and ventricle, resulting in right heart dilation, hypertrophy, elevated pulmonary flow, and potential pulmonary arterial hypertension (PAH) [20]. A pulmonary-to-systemic shunt ratio (Qp:Qs) >= 1.5:1 is considered haemodynamically significant [21]. While many patients remain asymptomatic until the third or fourth decade, adults over 40 years of age experience higher risks of exertional dyspnoea, fatigue, atrial fibrillation, paradoxical embolism/stroke, and right heart failure [22,23].

Diagnostic Techniques, Management, and Educational Value

Transthoracic (TTE) and transoesophageal echocardiography (TEE) provide essential anatomical and rim assessment for closure planning, complemented by cardiac MRI and catheterisation [22,24,25]. ACC/AHA and ESC guidelines recommend closure for significant shunts (Qp:Qs >= 1.5:1) or right heart volume overload [26]. Transcatheter device occlusion is standard for simple defects, whereas complex multi-fenestrated lesions require surgical patch repair [26,27]. Unexpected cadaveric discoveries provide crucial three-dimensional educational insights into congenital cardiac variations that persist undetected throughout life [28-30].

CONCLUSION

We report an uncommon incidental discovery of a multi-fenestrated ostium secundum-type ASD in a 60-year-old male cadaver identified during standard anatomical dissection. Five distinct openings were observed within and surrounding the fossa ovalis, located across the superior, central, and inferior regions of the interatrial septum. This case highlights that multi-fenestrated ostium secundum ASD can remain asymptomatic into advanced age and emphasizes that the 'swiss-cheese' morphology poses unique challenges that often necessitate surgical patch repair rather than single-device transcatheter closure.

Abbreviations & Declarations

ACKNOWLEDGMENTS

The authors like to express gratitude to the cadaver donors and their families, whose altruistic donation to medical science facilitates anatomical instruction and research of this kind.

DECLARATIONS

Funding: This research did not receive any specific support from agencies.

Conflicts of Interest: The authors assert the absence of any conflicts of interest with the publishing of this manuscript.

Author Contributions: Saravanan Jagadeesan: Conceptualization of the cadaveric case report, performed cadaveric dissection, and drafted the manuscript. Thirupathirao Vishnumukkala: Interpreted anatomical findings, literature findings, and critically revised the manuscript. Narendiran Krishnasamy: Participated in specimen examination, literature review, and manuscript editing. Shajan Koshy: Supervised the anatomical study and dissection procedures and reviewed the manuscript. Mohamad Aris Bin Mohd Moklas: Interpretation of anatomical findings, literature review and reviewed the manuscript. Ahmad Yusuf Bin Yahaya: Performed dissection, provided overall supervision, contributed to study design and critical manuscript revision, and approved the final manuscript for publication.

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