Aneurysm dissecting into the myocardium.

When the SVA dissects into the interatrial septum, interventricular septum, or ventricular free wall, an echolucent space is visualized that is encapsulated by the separated myocardium, bulging into both sides and even forming a "third chamber" between the atria and the ventricles (Fig 3D). A flow signal filling it from the aortic root can be demonstrated with 2D and color Doppler echocardiography. The dark space is thought to be the aneurysmal body if the aneurysm is unruptured and undergoes inconspicuous morphological change during the cardiac cycle. CDFI generally detects the internal flow that is directly continuous with the aortic root. An aneurysmal thrombosis may occur in this condition. If the aneurysm ruptures, it is thought that the encapsulated blood resides in the muscular portion connecting the aneurysm. The morphological characteristics of the fluid area usually change, displaying a characteristic collapse during systole and expansion during diastole. The perforation of the aneurysm may not be easily detected at times and should be carefully evaluated from multiple planes. CDFI shows a to-and-fro signal at the site of perforation of the aneurysm, filling the dissected space from the aneurysm during diastole but reversing direction during systole.

Some complications should be given special attention, including obstruction of the left or right ventricular outflow tract due to the space-occupying effect of the myocardial dissection, thrombosis in the dissection lumen, calcification or fibrillation of the dissection intima, conduction disturbances (especially conduction block), and segmental ventricular wall motion abnormalities. In our cases, the only patient with an aneurysm dissecting into the interventricular septum suffered both left and right ventricular outflow tract obstructions, left bundle branch block, and severe aortic regurgitation.

The unruptured SVA protruding into the myocardium should be differentiated from a myocardial cyst. The echolucent cavity in a patient with SVA is filled with flow signals and is continuous with the aortic root. Its area is somewhat changeable during every cardiac cycle, though this is not obvious. The morphological characteristics of the fluid cavity of the myocardial cyst are stable: no communication to the aortic root and no blood flow. These qualities make them easy to differentiate. However, it should be noted that when the SVA dissection is small and has a thrombus, the morphological characteristics of the echolucent cavity might also be stable with no flow signal within it, similar to the myocardial cyst [7].

Aneurysm extending into LV.

On the echocardiogram, a thin-walled saccular lesion arises at a low site between the sinus base and the aortic annulus and extends into the left ventricular outflow tract. The aneurysm usually goes back and forth between the aortic root and the left ventricular cavity with diastolic dilation and systolic compression [8]. This pattern is the only one of the ruptured SVA patterns that represents a single diastolic shunt (other patterns represent a continuous or dual-phase shunt). It is worth noting that of our 4 cases extending into the LV, the aneurysm went back and forth between the LV and RV via a huge ventricular septal defect in just one case. To our knowledge, this is the first report of this special representation in patients with SVA.

Compared with other patterns, the aneurysm originating from a low site of the sinus can more easily lead to aortic regurgitation. In addition to dilation of the annulus and valvular prolapse, secondary contributing factors may be hypoplasty of the adjacent cusp or prolapse of both cusps and annulus due to decreased support. Therefore, the morphology of the cusps and the motion of the annulus should be scrutinized to guide clinical decisions. Prolapse of the cusp and annulus was observed in all of our 4 cases with LV involvement and an adjacent cusp was found to be hypoplastic in 1 case. Complications in this pattern also include obstruction of the left ventricular outflow tract, thrombosis in the aneurysmal body, and myocardial ischemia. Myocardial ischemia may result from intermittent coronary ostial obstruction when the aneurysm moves into the aortic root during systole or coronary insufficiency by massive aortic regurgitation [9].

An aneurysm rupturing into the LV should also be differentiated from an aorto-left ventricular tunnel, an avulsed inner membrane of the aorta protruding into the left ventricular outflow tract during dissection of the aortic root, a ruptured perivalvular abscess, and severe prolapse of aortic valve. An aorto-left ventricular tunnel arises above the level of the ostia of the coronary arteries and consists of a tunnel or ampullar-like pattern without significant morphological change and movement [10]. In a patient with aortic dissection, in the presence of hypertension, the inner membrane protrudes into the LV not through the perivalvular location but through the valvular orifice without displacing the aortic annulus. A ruptured perivalvular abscess of the aortic valve is associated with typical echocardiographic findings of infective endocarditis such as vegetations. The abscess has a smaller area and a partially thin or thick wall. Its morphology and location are relatively stable. Severe prolapse of the aortic valve displays a flail-pattern movement of the involved cusp and stagger of the valvular tips without displacement of the aortic annulus.

Aneurysm extending into LA or pulmonary artery.

In addition to their special extending positions, the echocardiographic features of these two patterns are similar to those extending into the right heart chambers. It should be noted that a huge aneurysmal body might obstruct the mitral valve [11] or pulmonary trunk.

A SVA extending into the LA should be differentiated from an annular subaortic aneurysm extending into the LA [12]. The SVA originates above the aortic annulus with communication to the aortic root and is dilated during diastole and compressed during systole. On the contrary, the annular subaortic aneurysm originates beneath the aortic annulus with communication to the left ventricular outflow tract and is dilated during systole and compressed during diastole.

Extracardiac SVA.

An extracardiac SVA either protrudes from a higher region of the sinus of Valsalva than an intracardiac SVA or it diffusely involves the whole sinus, usually reported to be larger than the intracardiac sinuses because the limitations of pressure and volume are relatively smaller [13]. Echocardiography can detect the diffuse expansion of a thin-walled involved aortic sinus. The linear or shell-like enhanced and thickened wall can be visualized if it is calcified. The morphological changes and the mobility of the extracardiac aneurysms are not apparent during each cardiac cycle. In this pattern, a thrombus in the aneurysmal body is likely to occur and should be carefully evaluated. The huge aneurysm may distort the aortic annulus and root resulting in both aortic regurgitation and rotation of the aortic root. Therefore, the aneurysmal origin must be identified using only the short-axis view of the aortic root and not the long-axis view of the LV.

A huge extracardiac aneurysm can compress the adjacent cardiac structures (mainly the atrium or the affiliated venous structures) causing anatomical deformation and even obstruction, as seen in 2 of our cases. It may occasionally cause myocardial ischemia due to severe distortion of the coronary ostia or compression of the coronary trunk. The most acute and fatal complication of extracardiac SVA is spontaneous rupture into the pericardial or pleural cavity [14].

An extracardiac SVA involving all sinuses should be differentiated from an aneurysm of the ascending aorta involving the aortic sinuses. In patients with a SVA, the dilation of the aortic sinuses occurs prior to that of the ascending aorta and can compress the adjacent cardiac structures. Nevertheless, an aneurysm of the ascending aorta involving aortic sinuses might be a complication associated with Marfan's syndrome, atherosclerosis, or other diseases. Dilation of the aorta preferentially localizes in the ascending aorta and rarely causes the compression.

In our group, one extracardiac case from the LCS was misdiagnosed as a diverticulum of the LCS because it looked like a saccular bulge. However, an aortic root diverticulum is extremely rare. Our literature search uncovered only one report in a Chinese document that described a cecal tube-like structure with a small opening and a deep cavity arising from the aortic root at the valve commissure [15]. Except for reports describing a Kommerell diverticulum of the aortic arch, there are no other similar cases with which to compare experiences. We suggest that the sac structure should be diagnosed as a SVA if its opening is confined to an aortic sinus. An aortic root diverticulum should be considered if it appears at the sinus commissure with a “narrow neck and deep belly.”

Aneurysm extending into multiple chambers.

In this pattern, the aneurysm usually originates near or at the tricuspid annulus and extends into both the RA and RV, as reported by our group. The sac may be observed fusing with the tricuspid valve to varying degrees, especially when associated with the vegetation. The fusion makes it difficult to judge the extending position, which led to a misdiagnosis because, in our cases, it only protruded into the RA. TEE may be helpful to precisely display the relationship between the aneurysm and the adjacent structures. Tricuspid insufficiency is the most common complication caused by the compression and displacement of the tricuspid valve.

Aneurysm arising from the LCS.

Clinically, an aneurysm arising from the LCS can be found extending into the pulmonary artery or left atrium when arising from the base; into the left ventricle when arising from the portion between the sinus wall and the annulus; into the extracardiac position when arising from the higher region; and occasionally dissecting the interventricular septum or the interatrial septum [6,16]. In our group, the aneurysms arising from the LCS had an extracardiac protrusion in 1 case and ruptured into the LV in the other.

Determination of the origin of the SVA plays a key role in diagnosis. One can accurately assess its origin from the short-axis echocardiographic view of the aortic root; echocardiography is the diagnostic method of choice. Distinct echocardiographic features of different pathological patterns originating in the LCS have been discussed in the preceding sections according to the positions of their protrusions.

Aneurysm with tortuous course.

A SVA usually extends directly into the adjacent cardiac chamber or vessel. In a few reports, the elongated aneurysmal body forms a tunnel and goes through several cardiac structures. The pathological anatomy and hemodynamic changes of these cases are extremely complex, especially when they occur concomitantly with other cardiovascular malformations. Choudhary et al. [4] reported one aneurysm from the LCS that formed a long tunnel and finally ruptured in the connection between the superior vena cava and the RA via the interatrial septum. Yildirim et al. [17] reported an aneurysm arising from the LCS and dissecting into the interatrial septum, forming a long tunnel and finally rupturing into the RA. In our cases, one aneurysm from the RCS extended into the RA, went through the tricuspid valve, and finally ruptured into the RV.

The complex and variable aneurysmal course combined with the possibility of multiple openings into several extending positions make echocardiographic diagnosis extremely challenging. Our case of a complex course was simply diagnosed as a SVA rupturing into the RV, and we did not detect the tortuous course because of lack of experience; the tortuous course was later identified during the operation. We suggest that once a long aneurysm forms a tunnel, this special pattern should be routinely investigated and excluded. The operator must carefully evaluate its origin and course using multiple views, including the non-standard planes.