Two important points are highlighted in these cases. First, anterior leaflet perforation and commissure leaflet prolapse presented similar images in specific 2-D views. Second, to differentiate between these conditions, confirmation from multiple 2-D and 3-D views, as well as assessment of the regurgitation orifice, is crucial.

In the 2-D view, cardiac structures in the same plane are visualized. However, if cardiac structures not on the same plane are redundant or exhibit significant motion, they may appear. Based on this principles, normal commissure leaflets are typically small and not always identified on echocardiography. However, if they become redundant or exhibit substantial motion, such as in cases of prolapse and flail, they may be visualized, even if they are not on same plane (Fig. 3).

Schematic illustration of the commissure leaflet prolapse (black triangles), regurgitation orifice (blue circles), and mitral regurgitation jet (red ellipses). Case 1: Imaging plane with the probe advanced from the mid-esophageal 4-chamber view. In this image, anterior (A3), posterior (P3), and posterior commissure (PC) (black triangle c) are observed. The redundant PC (black triangle c) was superimposed on the A3. Mitral regurgitation jets due to both A3 (red ellipse b) and PC (red ellipse c) are shown, but the regurgitation orifice (blue circles b) was only shown on A3. Case 2: Imaging plane with the probe with a counterclockwise rotation from the mid-esophageal long-axis view. In this image, A1 and anterior commissure (AC) (black triangle a) are shown. Prolapse of the AC (black triangle a) is superimposed on the anterior leaflet (A1). Mitral regurgitation jet (red ellipse a) due to AC is shown with regurgitation orifice (blue circle a) due to AC prolapse

In case 1, the prolapse of the redundant PC overlapped with the anterior leaflet, leading to the appearance of A3 and the redundant PC in the same plane. The mitral regurgitation originating from the PC appeared as a perforation of the anterior leaflet (Fig. 1, white arrows). The presence of two regurgitant jets, known as the “crossed sword sign,” suggests the presence of complex lesions [4, 5]. Additionally, In ME-4-chamber view, only one regurgitation orifice was observed on the left ventricular side, originating from the regurgitation jet of A3 (Fig. 3). The regurgitation jet in the middle of the anterior leaflet did not have a regurgitation orifice on the left ventricular side, representing the regurgitation jet caused by PC (Fig. 3).

In case 2, due to the impingement of the aortic regurgitant jet on the mitral anterior leaflet and the presence of IE, expansion of the infection to the mitral valve was suspected. The ME-LAX view with the probe rotated counterclockwise indicated regurgitant jet with regurgitation orifice at the center of the anterior leaflet, involving A1 and P1 segments. In this case, the AC exhibited slight redundancy, and the leaflet motion was intense, suggesting flail motion. Although a regurgitation orifice was observed, no anterior leaflet perforations were noted. The regurgitation jet caused by AC prolapse was visualized as a perforation of the anterior leaflet because, in the counterclockwise rotated image from the LAX, the anterior leaflet (A1) was superimposed on the intense motion of the AC prolapse (Fig. 3). Therefore, in this case, obtaining not only the regurgitation orifice but also multiple 2-D and 3-D images is essential for confirming the diagnosis.

The use of 3-D imaging plays a significant role in the diagnosis of mitral valve morphology and in identifying the prolapse of the main mitral valve. This can be achieved by examining not only the en face view 3-D images but also by rotating the 3-D images from the en face view to different angles, which facilitates the diagnosis of the lesion [1].

However, the volume rate of 3-D TEE color images usually can be low, depending on the equipment model, thereby limiting the diagnostic capabilities of mitral valve lesions solely based on 3-D TEE color images. In case 1, the use of a Philips CX50 system with a 3-D TEE color Doppler image at a very low volume rate did not contribute to the diagnosis of mitral valve regurgitation. In case 2, with a high-volume rate model such as the Philips Epic 7C, the 3-D color Doppler image might not have been able to reveal small regurgitant orifices (Fig. 2).

In conclusion, mitral regurgitation resulting from commissure leaflet prolapse can mimic an anterior leaflet perforation in 2-D images. To ensure accurate diagnosis, it is crucial to rely not only on comprehensive multisectional 2-D and 3-D images but also to emphasize the left ventricular side of the regurgitant orifice. This approach enhances the accuracy of diagnosing mitral valve lesions.