The crista terminalis is a smooth muscular ridge in the superior aspect of the right atrium, formed following resorption of the right valve of the sinus venosus. It represents the junction between the sinus venarum, the "smooth" portion of the right atrium derived from the embryologic sinus venosus, and the heavily trabeculated right atrial appendage.
Coursing between the caval orifices, it divides the pectinate muscle origin and the right atrial appendages in the right atrium. Its identification is significant in the determination of atrial situs.
The crista terminalis is found closely associated with the posterolateral right atrial wall. It divides the right atrium into smooth posteromedial and trabeculated anterolateral portions.
A prominent crista terminalis may be incidentally discovered on transthoracic echocardiography, typically best visualized in the apical four chamber view. When a mass is visualized in the right atrium, features suggestive of a prominent crista terminalis include :
- rounded margins, closely apposing the posterolateral wall of the right atrium
- isoechoic to adjoining myocardium
- dynamic increase in size during atrial contraction
If transesophageal echocardiography is performed the bicaval view in the midesophageal position allows simultaneous visualization of the venae cavae, atria, and interatrial septum .
While its presence is of no pathologic significance, unusual prominence of the crista terminalis has been associated with:
- atrial fibrillation and/or flutter
- implicated as the ectopic focus of arrythmogenesis
- inappropriate sinus tachycardia (IST)