The appearance of many normal anatomic structures can be quite variable and may lead to pitfalls in diagnosis, resulting in unnecessary alarm and inappropriate intervention. These structures are distinct from artifacts, which, although similarly misleading, are the result of an interaction between the tissues and the physical properties of ultrasound (see Chapters 1 and 2 ). A mass is an abnormal structure within any part of the heart or immediately adjacent tissue.
When an unusual cardiac mass is seen on transesophageal echocardiography (TEE), normal anatomic variants must be differentiated from pathologic entities such as thromboses, vegetations, or tumors. When an echo-free space is identified, normal structures must be differentiated from pericardial cysts, aneurysms, or abscesses.
To help differentiate a mass from an artifact, it is useful to identify the structure throughout the cardiac cycle in at least two imaging planes and to alter the transducer frequency, image depth, and focal zone to optimize image quality.
This chapter is divided into two sections. In the first section, the sources of common diagnostic pitfalls are discussed, classified according to their location. In the second section, pathologic masses that may be identified by TEE are considered. In most instances, these normal variants and pathologic structures are highly characteristic and can be positively identified. However, histologic diagnoses are not provided by TEE, and differentiation between a normal variant and a pathologic mass may not be possible by TEE alone.
Common diagnostic pitfalls
Normal structures that may cause diagnostic pitfalls with TEE are listed in Table 6-1 . Readers seeking additional information are referred to the reviews by Blanchard and colleagues and Seward and colleagues.
Right Atrium
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Left Atrium
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Atrial Septum
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Right Ventricle
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Left Ventricle
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Valves
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Pericardial Space
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Great Vessels
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Extracardiac Structures
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Right atrium
Embryologic development of the atria gives rise to many potentially misleading anatomic structures.
Crista terminalis
The crista terminalis is a vertical ridge of muscle projecting into the cavity of the right atrium from the angle between the anterior SVC and the right atrium and running toward the inferior vena cava (IVC). It separates the smooth- from the rough-walled (pectinate muscles) areas of the right atrium. It is best seen in the midesophageal bicaval view, in the region of the (RA-SVC) junction ( Figure 6-1 ). During transverse imaging (at 0 degrees) of the superior region of the right atrium, it may appear as a bright, sometimes rounded, echo density on the lateral wall. Slight withdrawal of the probe identifies it as being in the region of the RA-SVC junction.
Eustachian valve
The eustachian valve is a commonly seen embryologic remnant whose function in utero was to direct oxygenated blood flow from the IVC, through the foramen ovale, to the left atrium. It is seen at the junction of the IVC and right atrium and is best visualized in the midesophageal bicaval view ( Figure 6-2 ). It is an elongated, undulating, usually membranous structure. Occasionally, it may be large enough to cause obstruction of blood flow or make placement of venous bypass cannulae difficult. Rarely, it may be the site of infected vegetations.
Thebesian valve
The thebesian valve is formed by fibrous bands at the opening of the coronary sinus. Rarely, a thebesian valve may make coronary sinus catheterization difficult.
Chiari network
The Chiari network is a thin, highly mobile, filamentous structure arising from the eustachian valve, the thebesian valve, or both that is found in 1.3% to 4% of normal hearts at autopsy. At surgery, it presents as a fine network of delicate strands whose broad base has a variable attachment to the lateral and superior walls of the right atrium and the atrial septum. It is the attachment to other parts of the right atrium that differentiates a Chiari network from a large fenestrated eustachian valve. On TEE, the motion of the filaments appears to be random and unrelated to the opening and closing of the valves. It is sometimes difficult to differentiate a Chiari network from the leaflets of the (TV). A useful technique is to attempt to visualize both structures simultaneously, which is usually possible in a modified midesophageal (RV) inflow–outflow view by slowly rotating the transducer back (toward 0 degrees) from the standard position.
The presence of a Chiari network has occasionally been associated with thrombus formation, embolus entrapment, arrhythmias, and catheter entrapment. However, it is not usually considered an indication for any specific intervention.
Right atrial appendage
The right atrial (RA) appendage may appear as an echo-free space anterior to the ascending aorta (i.e., in the far field, beyond the aorta) and near the (RVOT), in the midesophageal (AV) long-axis view. It is more usually seen in the midesophageal bicaval view (see Figure 3-9 ).
Enlarged coronary sinus
The coronary sinus is considered enlarged if its diameter is greater than 1 cm. It may be confused with a cyst, a mitral annular abscess, or an aneurysmal circumflex artery. Enlargement of the coronary sinus is often associated with a persistent left-sided SVC ( p. 92 ). It can also be due to elevated RA pressure or anomalous pulmonary venous drainage into the coronary sinus. The coronary sinus is best seen in short axis in the midesophageal two-chamber view and in long axis by advancing or retroflexing the probe from the midesophageal four-chamber view (see Figures 3-11 and 6-3 ).
Pectinate muscles
Pectinate muscles are prominent muscular ridges that give the anterior walls of the atria a roughened, irregular appearance. They may look like pearls on a string. They are more prominent in the right atrium, atrial appendages, and hypertrophied atria.
Catheters and wires
Central venous catheters, (PA) catheters, and pacing wires are often seen but are usually easy to differentiate from native structures. They are imaged in the right-heart views (midesophageal four-chamber, RV inflow–outflow, and bicaval).
In the RV inflow–outflow view, a PA catheter is typically seen “wrapping around” the AV, sequentially in the right atrium, RVOT, and PA. It may be useful to confirm that the origin of the catheter is in the SVC by withdrawing the probe into the midesophageal ascending aortic short-axis view. The tip of a PA catheter can often be visualized in the distal main PA or proximal right PA in this view ( Figure 6-4 ). Occasionally, thrombi may form on a catheter or pacing wire.
Left atrium
Warfarin or Coumadin ridge
Warfarin ridge or Coumadin ridge is a term referring to the atrial tissue between the (LA) appendage and the left upper pulmonary vein ( Figure 6-5 ). This tissue may accumulate fat, creating a masslike appearance, usually with a thin, proximal part and a thicker, more bulbous, distal part.
Left atrial membrane
The LA membrane is seen in partial cor triatriatum (forme fruste of cor triatriatum). It is a thin membrane, which extends from the common wall between the LA appendage and the left upper pulmonary vein to the superior limbus (posterior margin) of the fossa ovalis. It is usually incomplete and nonrestrictive to blood flow. The first sign of this abnormality is usually the appearance of a greatly elongated warfarin ridge in the midesophageal two-chamber view.
Native left atrium following heart transplantation
In patients who have undergone heart transplantation, a variable amount of native left atrium is left behind, creating the appearance of a fluid-filled mass behind the transplanted atrium. It is usually posterior and superior to the transplanted atrium and may show spontaneous echo contrast. In some cases, the space is much larger than the transplanted left atrium. Close inspection usually reveals the site of connection between the native left atrium and the transplanted left atrium (see Figure 15-1 ).
Left atrial appendage
The LA appendage is a small, complex, blind-ended structure with several anatomic pitfalls that can make interpretation of echo images difficult. It is of variable size and shape and, unlike the left atrium, is not smooth walled.
Multilobed left atrial appendage
The normal LA appendage is often multilobed and may send an accessory lobe into the transverse pericardial sinus ( Figure 6-6 ). This may appear as a confusing echo-free space in the area of the transverse sinus ( p. 92 ).
Pectinate muscles in the left atrial appendage
The normal LA appendage is lined with ridges of pectinate muscle ( Figure 6-7 ); these must be differentiated from thrombi, which may be difficult in the case of small thrombi. Pectinate muscles may appear strand-like and may span the appendage; a thrombus is generally rounded and may fill the appendage. A thrombus may be adherent to the wall but, unlike pectinate muscles, it may be pedunculated and mobile. LA appendage thrombi are discussed further on p. 94 .
The LA appendage is usually well seen in the midesophageal two-chamber view, but the angle at which it is best visualized varies between 0 and 90 degrees. 3-D imaging significantly facilitates a thorough examination of the LA appendage, especially by allowing visualization of orthogonal planes simultaneously.
Stapled-off left atrial appendage
An incompletely stapled-off LA appendage may appear as a cavity where the appendage would normally be seen. Color flow Doppler may demonstrate a small connection with the rest of the left atrium if the appendage has not been completely isolated.
Inverted left atrial appendage
Inversion of the LA appendage is a rare complication of cardiac surgery that presents as a new LA mass during deairing or after separation from CPB ( Figure 6-8 ); it usually occurs as a result of surgical deairing maneuvers. The apparent mass is located just superior to the MV and inferior to the pulmonary veins. It is homogenous, is usually freely mobile, and may prolapse into the MV (usually with no hemodynamic effects). Visualization of the appendage is no longer possible in any view.
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