Right atrial pseudotumor due to crista terminalis

Imaging description The crista terminalis is a smooth, vertically oriented, muscular ridge within the posterior wall of the right atrium (Figure 1.1). It is located at the site of embryonic fusion of the trabeculated and smooth-walled portions of the right atrium. The smooth-walled portion is also known as the sinus venosus. The crista terminalis is a critical structure for the cardiac conduction system, containing the sinoatrial node superiorly, and a frequent location of atrial tachyarrhythmias. Most often the crista terminalis has low attenuation on computed tomography (CT) and is isointense to the right atrial wall on magnetic resonance imaging (MRI) (Figure 1.1). In patients with lipomatous hypertrophy of the interatrial septum, the crista terminalis may also be enlarged and will include fat, which will be low attenuation on CT (Figure 1.2) and high signal on bright blood and T1-weighted MRI images. In these cases, an etching artifact may also be recognized on bright blood steady-state free precession images, due to the interface of crista terminalis fat and the right atrial wall (Figure 1.3). The fat within an enlarged crista terminalis is contiguous with periatrial fat. Importance A prominent crista terminalis can be mistaken for a right atrial mass. This could lead to inappropriate therapy and the associated risks of that therapy; for example, increased bleeding risk if anticoagulation is used in cases of suspected thrombus, or unnecessary open heart surgery if mistaken for myxoma. Typical clinical scenario The size of the crista terminalis has an average thickness of 4.5 mm; however, it is highly variable in size and can range from almost imperceptible to prominent and polypoid, projecting into the lumen of the right atrium. It is often enlarged in patients with increased periatrial fat and lipomatous hypertrophy of the interatrial septum. Differential diagnosis A prominent crista terminalis should be distinguished from right atrial masses. In particular, right atrial thrombus or right atrial myxoma should be considered when an intraluminal polypoid mass is visualized attached to the right atrial wall.