Interatrial septal aneurysm

Interatrial septal aneurysm or atrial septal aneurysm (ASA) is defined as an abnormal protrusion of the interatrial septum. The exact length of the protrusion that defines an interatrial septal aneurysm varies in the literature, ranging from >11 mm to >15 mm beyond normal excursion in adults and 5 mm in children.

It can be limited to the fossa ovale or involve the entire inter-atrial septum.

Epidemiology

It is encountered in approximately 1% of the pediatric population.

Pathology

Associations

Interatrial septal aneurysm is associated with an increased incidence of peripheral arterial embolism and increased stroke risk.

It is known to be associated with the following:

• atrial septal defect
• patent foramen ovale

Classification

Several classification systems have been proposed, on system is as :

• type 1R: bulging is in the right atrium only
• type 2L: bulging is in the left atrium only
• type 3RL: major excursion bulges to the right atrium and the lesser excursion bulges toward the left
• type 4LR: maximal excursion of the atrial septal aneurysm is toward the left atrium with a lesser excursion toward the right atrium
• type 5: atrial septal aneurysm movement is bidirectional and equidistant to both atria during the cardiorespiratory cycle

Complications

• cryptogenic stroke
  • some consider an aneurysm of more than 10 mm excursion to be associated with markedly increased risk (odds ratio 8)
  • the concurrent presence of a patent foramen ovale is thought to have a synergistic effect on stroke

Differential diagnosis

On imaging consider:

• accessory left atrial appendage