An atrial septal aneurysm is a localized bulging or ballooning of the thin wall that separates the heart’s two upper chambers. Most people who have one never know it, because the aneurysm itself rarely causes symptoms and is typically discovered by accident during a heart ultrasound ordered for something else. The clinical significance of an atrial septal aneurysm depends almost entirely on what it travels with: when it coexists with a small hole between the atria called a patent foramen ovale, stroke risk rises meaningfully, and there are established links to certain arrhythmias and migraine with aura.
What Counts as an Atrial Septal Aneurysm
The wall between the left and right atria, called the interatrial septum, is normally a flat or gently curved membrane. In some people, part of that membrane is abnormally mobile and billows into one atrium or the other, or swings back and forth with each heartbeat. Exactly how much bulging qualifies as an aneurysm depends on who is measuring. A widely used criterion from a large multicenter study defines it as a protrusion greater than 10 mm beyond the plane of the septum, measured by transesophageal echocardiography (a probe placed in the esophagus to image the heart from behind).1PubMed. Atrial septal aneurysm in adult patients. A multicenter study using transthoracic and transesophageal echocardiography Other researchers set the bar higher, requiring at least 15 mm of protrusion or 15 mm of side-to-side excursion during breathing, with a base diameter of at least 15 mm.2PubMed Central. Echocardiographic Findings in Patients with Atrial Septal Aneurysm: A Prospective Case-Control Study This lack of a universal definition is one reason prevalence estimates vary so widely in the medical literature.
On imaging, the aneurysm can involve the entire septum or just the thin, central area known as the fossa ovalis. In the multicenter study, those two patterns split almost evenly: roughly half of the 195 patients had aneurysms spanning the whole septum, while the other half had aneurysms confined to the fossa ovalis.3PubMed. Atrial septal aneurysm in adult patients. A multicenter study using transthoracic and transesophageal echocardiography The distinction matters because the fossa ovalis is the same area where a patent foramen ovale sits, which helps explain why the two findings so often appear together.
How Cardiologists Classify the Bulge
Not all atrial septal aneurysms move the same way. A classification system based on imaging of over 200 adults sorts them into five types depending on which direction the membrane bows:4PubMed. Atrial septal aneurysm: a new classification in two hundred five adults
- Type 1R: bulging only into the right atrium
- Type 2L: bulging only into the left atrium
- Type 3RL: major excursion toward the right, with a smaller swing toward the left
- Type 4LR: major excursion toward the left, with a smaller swing toward the right
- Type 5: bidirectional, swinging equally into both chambers during the breathing cycle
The direction of bulging can influence what conditions the aneurysm is associated with. Bidirectional types (3RL, 4LR, and 5) tend to be the most mobile, and some research suggests they carry a higher risk of complications because the constant swinging may promote blood clot formation along the aneurysm surface or stretch the tissue enough to keep a patent foramen ovale open.
The Stroke Connection
The most studied clinical risk associated with atrial septal aneurysms is stroke, specifically the kind known as cryptogenic stroke, where no obvious cause like atrial fibrillation or carotid artery disease can be found. When investigators have compared young adults with unexplained strokes to matched controls, both atrial septal aneurysm and patent foramen ovale show up more frequently in the stroke group. One study of patients under 55 found that each abnormality alone roughly quadrupled the odds of cryptogenic stroke, but having both together raised the odds more than 30-fold compared to having neither.5PubMed. Atrial septal aneurysm and patent foramen ovale as risk factors for cryptogenic stroke in patients less than 55 years of age
A landmark four-year follow-up study reinforced that the pairing is what matters most. Patients who had a patent foramen ovale alone saw about the same rate of recurrent stroke as patients who had neither abnormality. But patients who had both a patent foramen ovale and an atrial septal aneurysm had a recurrent stroke rate of about 15% over four years, roughly four times higher than the group with neither defect.6PubMed. Recurrent cerebrovascular events associated with patent foramen ovale, atrial septal aneurysm, or both There were actually no recurrences among the patients who had an atrial septal aneurysm alone without a patent foramen ovale, which highlights that the combination is far more dangerous than either alone.
A pooled analysis of multiple studies confirmed that the aneurysm itself was an independent predictor of recurrent stroke even after adjusting for other risk factors, with an adjusted hazard ratio of about 3.3, while patent foramen ovale size alone was not a significant predictor.7PubMed. Atrial septal aneurysm contribution to the risk of cryptogenic stroke in patients with patent foramen ovale: A brief updated systematic review and meta-analysis In that analysis, roughly a quarter of enrolled patients with patent foramen ovale also had an atrial septal aneurysm, illustrating how commonly the two overlap.
Why the Aneurysm Promotes Clots
The prevailing theory for how an atrial septal aneurysm contributes to stroke involves two pathways. When a patent foramen ovale is present, a blood clot that forms in a leg vein can travel through the hole to the left side of the heart and from there to the brain. The aneurysm may help keep the foramen ovale open or create a funnel that guides clots through it. The second pathway does not require a hole at all: the repetitive billowing motion of the aneurysm can encourage fibrin-platelet deposits to form on its left atrial surface, and those deposits can break free and travel to the brain.8Medical Reports. The silent bulge: Stroke from an isolated atrial septal aneurysm without patent foramen ovale, a rare case report Isolated strokes from aneurysms without a patent foramen ovale are rare but documented, which is why the condition is not dismissed as completely harmless even when it appears alone.
Atrial Septal Aneurysm and Migraine with Aura
A link between cardiac septal abnormalities and migraine has been explored for decades, and the evidence consistently points to migraine with aura as the relevant subtype. One echocardiographic study found isolated atrial septal aneurysm in about 29% of migraine-with-aura patients compared to fewer than 4% of migraine-without-aura patients and about 2% of controls.9PubMed. Prevalence of atrial septal aneurysm in patients with migraine: an echocardiographic study A larger observational study found that the combination of patent foramen ovale with atrial septal aneurysm was nearly four times more common in migraine-with-aura patients than in people without migraine, whereas a patent foramen ovale without an aneurysm did not reach statistical significance.10PubMed Central. Patent Foramen Ovale With Atrial Septal Aneurysm Is Strongly Associated With Migraine With Aura: A Large Observational Study
Migraine with aura was also more prevalent in a study comparing patients who had both a patent foramen ovale and an atrial septal aneurysm to those with a patent foramen ovale alone, with rates of about 33% versus 21%.11PubMed Central. Clinical relevance of atrial septal aneurysm and patent foramen ovale with migraine The same group with both defects also had a higher frequency of small ischemic brain lesions on imaging. The leading hypothesis is that micro-emboli or vasoactive substances bypass the lung filter via the patent foramen ovale and reach the cerebral circulation, triggering the spreading cortical depression that produces the visual aura. The aneurysm’s role may be to increase the amount of right-to-left shunting by keeping the foramen ovale more widely patent. It is worth stressing that this remains an association, not a proven causal chain, and closing the foramen ovale has not consistently cured migraine in clinical trials.
Arrhythmias and Electrical Effects
A floppy, mobile segment of septum can stretch the surrounding atrial tissue and alter the way electrical signals travel through the heart. Studies using 24-hour heart monitoring have found higher rates of premature atrial beats, premature ventricular beats, runs of supraventricular tachycardia, and paroxysmal atrial fibrillation in people with atrial septal aneurysms compared to matched controls without them.12PubMed. Association between atrial septal aneurysm and arrhythmias These arrhythmias were independently associated with the presence of the aneurysm after accounting for other variables.
The mechanism appears to involve delays in the electrical activation of different parts of the atria. Research using tissue Doppler imaging found that patients with atrial septal aneurysms had significantly longer electromechanical delays within the left atrium and between the two atria. Among those patients, the ones who also had arrhythmias had even greater delays. A specific measurement of intra-left atrial delay above roughly 40 milliseconds identified patients at risk for supraventricular arrhythmias with good sensitivity and specificity.13PubMed. Atrial Septal Aneurysms and Supraventricular Arrhythmias: The Role of Atrial Electromechanical Delay This finding suggests that the mechanical distortion of the septum creates small zones of slow conduction that act as substrates for abnormal heart rhythms.
Most of these arrhythmias are nuisances rather than emergencies, producing palpitations or a sense that the heart is skipping. But persistent atrial fibrillation is a different matter because it independently raises stroke risk, creating an additional pathway through which an atrial septal aneurysm could contribute to cerebrovascular events beyond the embolic mechanisms described earlier. When an aneurysm is very large, above about 30 mm, and accompanied by symptomatic arrhythmias, surgical intervention becomes a serious consideration.14International Journal of Surgery Case Reports. A large atrial septal aneurysm presenting with severe arrhythmias: A case report
Atrial Septal Aneurysm in Infants and Children
Atrial septal aneurysms are not limited to adults. They can appear in infancy, often in the setting of an atrial septal defect or other congenital heart condition that places extra pressure on the thin, immature septum. One early pediatric study found that the neonatal septum may be especially vulnerable to aneurysm formation because of inherent structural weaknesses. Encouragingly, in infants whose underlying heart defect was repaired surgically or closed spontaneously, the aneurysms shrank or disappeared during follow-up. In contrast, aneurysms became more prominent when hemodynamic stress persisted.15PubMed. Atrial septal aneurysms in infants and children
A separate follow-up study of children confirmed this pattern: no clinical complications were attributed to the aneurysms themselves, and among children whose associated atrial septal defects closed, the aneurysms often vanished as well. The investigators suggested that the aneurysm may even play a role in the spontaneous closure of small atrial septal defects, with the redundant tissue acting as a natural patch.16PubMed. Natural course of atrial septal aneurysm in children and the potential for spontaneous closure of associated septal defect For pediatricians and parents, the practical message is that an atrial septal aneurysm discovered in a baby during a routine echocardiogram is usually not a cause for alarm and will often resolve as the child grows, provided no significant underlying defect is driving it.
Connective Tissue Disorders and Underlying Causes
Why do some people develop a floppy septum while others do not? The full answer is not settled, but there is strong circumstantial evidence that the quality of the connective tissue matters. Early case reports linked atrial septal aneurysms to Marfan syndrome, noting that the same kind of tissue weakness that causes aortic root dilation and mitral valve prolapse could also affect the interatrial septum.17The American Journal of Cardiology. Atrial septal aneurysm, ectasia of a sinus of valsalva and mitral valve prolapse in Marfan’s syndrome
Broader screening studies have found that young people with features of a marfanoid body type, meaning tall stature, long limbs, and joint hypermobility, even without a formal Marfan diagnosis, carry a higher burden of minor heart anomalies including atrial septal aneurysm, tricuspid valve prolapse, and aortic valve asymmetry. In one such study, the average number of these small heart anomalies was more than twice as high in the marfanoid group as in controls.18Pediatrician (St. Petersburg). Small heart anomalies as cardiac manifestations of hereditary connective tissue disorders This does not mean that everyone with an atrial septal aneurysm has a connective tissue disorder, but it does suggest that heritable variation in tissue elasticity contributes to who develops the condition and who does not.
Treatment and When Intervention Is Considered
Most isolated atrial septal aneurysms require no treatment at all. A long-term follow-up study that monitored patients with incidentally discovered aneurysms for an average of nearly six years found no strokes or systemic embolic events during the entire observation period.19American Heart Journal. Low incidence of embolic strokes with atrial septal aneurysms: A prospective, long-term study For the majority of people, periodic echocardiographic monitoring is sufficient.
The picture changes when a patent foramen ovale coexists and the patient has had a cryptogenic stroke. In those cases, closure of the patent foramen ovale using a catheter-based device is an established treatment. One series using a septal occluder device in patients with challenging anatomies, including those with large atrial septal aneurysms, achieved a complete closure rate of about 95% at six months with no major procedural complications. Later complications occurred in a small percentage of patients, including new-onset atrial fibrillation and one case of device-related clot.20PubMed. Using the GORE® Septal Occluder (GSO) in challenging patent foramen ovale (PFO) anatomies Several large randomized trials (CLOSE, RESPECT, DEFENSE-PFO) have shown that device closure reduces recurrent stroke compared to medication alone in patients with a patent foramen ovale and an atrial septal aneurysm, and the presence of the aneurysm is now considered a factor that strengthens the case for closure.
Open surgical repair is reserved for unusual situations. Very large aneurysms, particularly those above 30 mm, that produce symptomatic arrhythmias resistant to medication may warrant surgical resection or plication of the redundant tissue.21International Journal of Surgery Case Reports. A large atrial septal aneurysm presenting with severe arrhythmias: A case report This is rare enough that the literature consists mainly of individual case reports rather than large series.
Pregnancy and Atrial Septal Aneurysm
Pregnancy increases blood volume by roughly 40% to 50%, which raises filling pressures in the heart and can make a pre-existing atrial septal aneurysm more prominent or change its behavior. Case reports describe pregnant patients with atrial septal aneurysms developing arrhythmias and, in theory, an aneurysm under increased hemodynamic stress could dilate enough to compress nearby cardiac structures. Conservative management with monitoring is generally preferred during pregnancy, especially when there is no associated atrial septal defect or history of blood clots. Medications like beta-blockers, aspirin, or anticoagulants can be used for mild symptoms, though each carries its own pregnancy-specific risks that require careful balancing.22Austin Journal of Obstetrics and Gynecology. Atrial Septal Aneurysm during Pregnancy: A Case Report Cardiac surgery during pregnancy is feasible but carries significant risks for both mother and fetus, so it is reserved for situations where the aneurysm is causing serious hemodynamic compromise.
If you already know you have an atrial septal aneurysm and are planning a pregnancy, it is worth discussing the finding with both your cardiologist and your obstetrician ahead of time. The vast majority of pregnancies in women with incidental atrial septal aneurysms proceed without complications, but having a monitoring plan in place is sensible given the hemodynamic changes pregnancy demands.
What Imaging Can and Cannot Tell You
Standard transthoracic echocardiography, the non-invasive ultrasound where a probe is placed on the chest, can detect many atrial septal aneurysms, but it is not as reliable as transesophageal echocardiography, where the ultrasound probe sits in the esophagus just behind the heart. The interatrial septum is a thin, deep structure, and image quality from the chest depends heavily on body size and lung interference. In the multicenter study referenced earlier, transesophageal imaging was the standard for both detecting and measuring the aneurysm.23PubMed. Atrial septal aneurysm in adult patients. A multicenter study using transthoracic and transesophageal echocardiography
Cardiac MRI and CT scanning can also visualize atrial septal aneurysms and are sometimes used when echocardiographic images are suboptimal or when the clinical question involves the relationship between the aneurysm and surrounding structures. Cardiac MRI has the advantage of showing dynamic motion over the cardiac cycle without radiation. In practice, though, echocardiography remains the first-line imaging tool because it is widely available, inexpensive, and provides real-time assessment of how the aneurysm moves. Bubble studies, in which agitated saline is injected intravenously during echocardiography, help determine whether a patent foramen ovale is also present by showing whether microbubbles cross from the right atrium to the left.
When an Incidental Finding Should Prompt Further Workup
If a routine echocardiogram turns up an atrial septal aneurysm and you have never had a stroke, transient ischemic attack, or unexplained neurological symptoms, the discovery is rarely a reason for aggressive intervention. However, it does warrant a few considerations. Your doctor may order a bubble study to check for a coexisting patent foramen ovale, especially if you are young and the aneurysm is mobile. If you experience migraine with aura, palpitations, or episodes of feeling lightheaded, mentioning the aneurysm finding to the specialist evaluating those symptoms can help contextualize the workup.
The situation is different if you have already had a cryptogenic stroke. In that case, the combination of atrial septal aneurysm and patent foramen ovale is a strong indication for closure, and current guidelines from multiple cardiology and neurology societies reflect this. The aneurysm itself is increasingly seen not as a bystander but as an independent marker of higher recurrence risk that tips the decision in favor of intervention.24PubMed. Atrial septal aneurysm contribution to the risk of cryptogenic stroke in patients with patent foramen ovale: A brief updated systematic review and meta-analysis If you had a stroke and were told you have a patent foramen ovale but not told whether an atrial septal aneurysm was also present, it is worth asking, because the answer could change whether closure is recommended.