The interatrial septum is a complex structure derived from multiple embryonic components. Central to its anatomy is the fossa ovalis (FO), a depression representing the closed foramen ovale. This region is pivotal in fetal circulation, allowing right-to-left atrial shunting of oxygenated blood. After birth, functional closure occurs due to rising left atrial pressures, but anatomic closure may be incomplete in some individuals, leading to patent foramen ovale (PFO)(1). Anatomical variations of the FO are clinically relevant during transseptal catheterisation, device closure procedures, and electrophysiological mapping.

The embryologic development of the interatrial septum involves coordinated formation of the septum primum, the septum secundum, and their fusion with the endocardial cushions. Alterations in this process can result in structural diversity. Previous studies have described different morphologies and dimensions of the FO, but data from large samples remain limited (2, 3).

This study aims to provide a comprehensive analysis of FO morphology and morphometry in 50 cadaveric human hearts, discuss embryological correlates, and highlight clinical implications.

Study Design and Sample Collection This descriptive cross-sectional study was conducted in the Department of Anatomy at University College of Medical Sciences, Delhi, on fifty adult human cadaveric hearts (age range 30–80 years) already present in the dissection hall. Hearts with gross pathological abnormalities or significant trauma, or previous surgeries, were excluded. Preparation and Dissection The adult human cadaveric hearts, after removal from the cadavers, were stored in 10%. Formalin. Each heart was subjected to a vertical incision along the superior and inferior vena cava. The heart was opened, and the interatrial septum was examined for the fossa ovalis. The fossa ovalis was identified as a depressed area on the septal surface. Morphological Assessment FO shapes were categorised as: • Oval • Circular • Irregular Additional variables recorded: • Position (central, superior, inferior, leftward) • Border (Annulus Fossa Ovalis) characteristics (thick/prominent, thin/smooth) • Presence of atrial septal aneurysm • Patent foramen ovale (based on probe patency) Morphometric Measurements Digital callipers (precision ±0.01 mm) measured: • Maximum anteroposterior diameter (APD) • Maximum vertical diameter (VD) • Perimeter • Border thickness Measurements were taken by two independent investigators; mean values were used. Statistical Analysis Data were entered into SPSS v23 (IBM Corp.). Mean ± SD, frequencies, and percentages were computed. Fig.1: Shapes of fossa ovalis (FO). (A) Oval and (B) circular. Fig.2: A. Redundant Fossa Ovalis (FO) with Annulus Fossa Ovalis (AFO) raised along its superior aspect. B. Aneurysmal Fossa Ovalis with flat Annulus Fossa Ovalis. Fig. 3: Image showing different arrangements of fibrous strands around the Fossa Ovalis (FO). (A). Along Posteroinferior margin, (B). Inferior margin, (C). Antero & Posteroinferior margin, (D). A fibrous band present horizontally along the inferior margin, separate from the margin. Fig. 4: (A) Patent Foramen Ovale (PFo), (B) & (C) Probe Patency Test: A metallic probe negotiated through the right atrium (RA), seen coming out through the left atrium (LA)

A total of 50 hearts were examined. Morphological and morphometric findings.

Table 1: Distribution of FO Shapes and Positions

Key Findings: The oval shape predominated. Most fossae were centrally located (48%).

Table 2: Morphometric Dimensions (Overall)

Observations: AP diameter exceeded vertical diameter. Border thickness exhibited broad variation.

Table 4: Additional Anatomical Variants

Clinical Insight: PFO and aneurysmal septa are important for interventional planning. Patent foramen ovale (PFO) has been implicated in the aetiology of several different pathologies, including cryptogenic stroke, decompression sickness in divers, etc. The patent foramen can act as a route for paradoxical embolism. PFO is not an uncommon condition, with a probe-patency in 15–35% population (1)

Morphological Variability

The fossa ovalis morphology displayed considerable variation. The oval shape was most common (55%), consistent with Bhatnagar et al., who reported similar dominance of oval forms in their series (50–60%) (2). Circular and irregular shapes represented 20% and 25%, respectively, which may influence the approach to transseptal puncture. An irregular FO, with non-uniform borders, presents a challenge for imaging and catheter orientation.

Embryological Correlation

The FO is a vestige of the fetal foramen ovale, formed by the overlapping of the septum secundum over the septum primum. Failure of complete fusion results in residual patency (PFO) or aneurysmal bulging. In this study, PFO prevalence was 12%, aligning with autopsy studies reporting PFO in 10–25% of adults (3,4). Embryologically, variations in cushion fusion and septal tissue proliferation may account for morphological differences.

Clinical Implications

Understanding FO anatomy is critical for several procedures:

• Transseptal Catheterisation: Optimal puncture site is typically the thin-walled fossa. Irregular shapes or thick borders increase the risk of misplacement and complications (5).
• Closure of PFO/ASD: Morphometry dictates device selection and sizing. Smaller or irregular defects may require specialised devices (6,7).
• Electrophysiological Mapping: Atrial fibrillation ablation and left atrial access often utilise the FO route. Awareness of anatomical variants enhances procedural success (8).
• Echocardiography Interpretation: Accurate imaging depends on recognition of normal versus pathological FO appearances (9).

Comparisons with Imaging Studies

Echocardiographic studies have evaluated FO dimensions in vivo. Chhabra and Jones reported mean diameters slightly smaller than cadaveric data, likely due to dynamic cardiac cycle effects (10). Cadaveric measurements may overestimate dimensions due to formalin fixation and lack of in vivo pressure. The understanding of morphological and topographical variations of the fossa ovalis is essential to clinicians during cardiac interventional procedures and device implantation in congenital heart anomalies (11).

Limitations

This study’s limitations include:

• Lack of age stratification due to incomplete donor demographics.
• Potential fixation artefacts altering septal pliability.
• Absence of clinical histories to correlate with pathology.

Future research should integrate imaging-pathology correlations and examine genetic influences on septal morphology.

The fossa ovalis shows distinct morphological and morphometric patterns with clinical relevance for interventional cardiology. Accurate knowledge of its anatomy, rooted in embryologic understanding, enhances procedural safety and diagnostic accuracy. Sex-based differences underscore the necessity for individualised assessments during cardiac interventions.

1. Joshi SD, Chawre HK, Joshi SS. Morphological study of fossa ovalis and its clinical relevance. Indian Heart J. 2016 Mar-Apr;68(2):147-52. doi: 10.1016/j.ihj.2015.08.001. Epub 2016 Jan 18. PMID: 27133322; PMCID: PMC4867950.
2. Bhatnagar A, Bahl A, Nayar PG, Kulshreshtha D. Morphological variations in fossa ovalis region: An autopsy study. J Anat Soc India. 2022;71(2):145–52.
3. Hagen PT, Scholz DG, Edwards WD. Incidence and size of patent foramen ovale during the first 10 decades of life: An autopsy study of 965 normal hearts. Mayo Clin Proc. 1984;59(1):17–20.
4. Lechat P, Mas JL, Lascault G, et al. Prevalence of patent foramen ovale in patients with stroke. N Engl J Med. 1988;318(18):1148–52.
5. Gloekler S, Wenaweser P, Buser P, et al. Transseptal puncture complications in the real world: A 12-year single-centre experience. EuroIntervention. 2012;8(7):876–83.
6. Berger F, Vogel M, Kramer-Plachky P, et al. PFO and ASD device closure: Long-term results of double-umbrella devices. Heart. 2000;83(4):455–60.
7. Butera G, Carminati M. Interventional closure of atrial septal defects and patent foramen ovale in adults. J Interv Cardiol. 2004;17(5):339–49.
8. Santangeli P, Di Biase L, Burkhardt JD, et al. Transseptal puncture in electrophysiologic procedures: Techniques and pitfalls. J Cardiovasc Electrophysiol. 2013;24(6):702–12.
9. Lang RM, Badano LP, Mor-Avi V, et al. Recommendations for cardiac chamber quantification by echocardiography. Eur Heart J Cardiovasc Imaging. 2015;16(3):233–70.
10. Chhabra L, Jones PG. Echocardiographic assessment of interatrial septum: Clinical and research perspectives. J Ultrasound Med. 2019;38(10):2701–15.

Prabhu, Latha V.; Murlimanju, B. V.; Yadav, Shubhangi1; Rao, Yelluru Lakshmisha; Vadgaonkar, Rajanigandha; Pai, Mangala M.; Marathe, Aradhana2; Padubidri, Jagadish Rao3. Morphology and Topography of Fossa Ovalis, Limbus Fossa Ovalis, and Probe Patency of Foramen Ovale in Formalin-fixed Hearts. Journal of the Anatomical Society of India 74(4): p 332-337, Oct–Dec 2025. | DOI: 10.4103/jasi.jasi_170_25