• The left atrium (LA) (especially the left atrial appendage [LAA] [Fig. 15-1]) is a common area of thrombus formation when associated with atrial arrhythmias or mitral stenosis.

• The left ventricle (LV) is a common area of thrombus formation when associated with left ventricular dysfunction (global or regional) (Fig. 15-2), aneurysm, or pseudoaneurysm (Fig. 15-3). The apex is a common area for thrombus formation.

• Thrombus formation within the right heart may occur in cases of severe right atrial enlargement (i.e., atriopulmonary Fontan) or right ventricular dysfunction. More commonly, thrombus formation occurs within veins and embolizes to the right heart. Thrombus may become trapped in the right atrium (RA) (Chiari network or Eustachian valve), in the right ventricle (RV) (tricuspid valve apparatus or right ventricular trabeculations), or pulmonary arteries (PAs) as it embolizes (Fig. 15-4).

• Noninfectious vegetations may also occur and are commonly referred to as marantic or nonbacterial thrombotic endocarditis (NBTE). NBTE usually occurs in the context of a malignancy or autoimmune disease (Fig. 15-5). A metastatic malignancy does not necessarily have to be present. Although blood cultures and an accurate determination of whether the patient was exposed to antibiotics at the time of blood sampling for culture are essential in identifying vegetations as infectious or noninfectious, there are some imaging characteristics of NBTE: vegetations tend to be less mobile, more sessile, and located toward the base of the leaflets. Because the base of the valve leaflets is more commonly affected, less severe valve regurgitation is noted. Anticoagulation should be considered in patients with NBTE.

• Mobility and location are important distinguishing features of a vegetation. Vegetations have motion independent of a valve leaflet and are most commonly associated with the upstream surface of a valve leaflet (e.g., the right atrial side of the tricuspid valve [Fig. 15-6]) but have also been reported on the Eustachian valve, residual Chiari network, subvalvular apparatus, and chamber wall. Commonly, the vegetations are not rounded in appearance. Vegetations usually have low reflectance of ultrasound waves but over time may become more calcified (high reflectance). Visualization of vegetations in more than one ultrasound window decreases the likelihood of an ultrasound artifact.

• Vegetations can occur on intracardiac devices such as pacing/defibrillator leads and central venous catheters (Fig. 15-7).

• Infections of bioprosthetic or prosthetic valves are more typically an annular disease, which can result in valve dehiscence or annular abscess (Fig. 15-8).