Robert Prosek, University of Illinois Cardiology Resident:
I questioned Dr. Buchanan about an 11 week-old Boxer that was referred to our surgery group for suspected persistent right aortic arch. I bet a pizza against that diagnosis because the trachea deviated to the right in the DV radiograph but the surgeons proved me wrong.

Is the rightward tracheal position in this case caused by extreme dilation of the esophagus? I thought leftward tracheal deviation was almost pathognomonic for PRAA because Dr Buchanan reported leftward deviation in 27/27 dogs with PRAA in the section on aortic arch embryogenesis and pseudo-vascular ring anomalies in his Small Animal Cardiac Surgery collection.

Figure 1 DV radiograph of an 11 week old Boxer with PRAA confirmed at surgery showing rightward curvature of the trachea.

Figure 2 Lateral radiograph showing ventral deviation of the trachea and dilation of the esophagus.

Response by Dr. Jim Buchanan:

Robert, I think there was sufficient evidence in the radiographs to bet a deluxe pizza in favor of a PRAA rather than against it:

1. In the Boxer DV film (Figure 3) the descending aorta comes off the midline instead of the usual one o'clock position (black arrow).

2. The ascending aorta silhouette is more prominent and the shadow is wider than normal to the right of the trachea at the 11 o'clock position (white arrow).

3. In the Boxer lateral radiograph (Figure 4) the ventral curvature and obvious narrowing of the trachea cranial to the heart are quite characteristic of PRAA (arrows). Moreover, the degree of ventral curvature is consistent with a coexistent retroesophageal left subclavian artery or even double aortic arch; 33% of 52 dogs with PRAA had retroesophageal LSA and 12% had double aortic arch. The majority of these dogs had marked ventral deviation of the trachea and I hope your surgeon looked carefully for these common coexisting anomalies.

Figure 3 Boxer DV radiograph showing midline descending aorta shadow (black arrow) and wide, rightward ascending aorta shadow (white arrow).

Figure 4 Boxer lateral radiograph showing marked ventral curvature and compression of the trachea cranial to the heart (arrows).

  
4. By tweaking the contrast and brightness to bring out the trachea more in your DV film, a leftward deviation and narrowing of the trachea can be seen in its typical location just cranial to the heart (see dots in Figure 5). I agree that most of the trachea is deviated to the right by the enlarged esophagus. Figure 6 from another dog shows a comparable example of PRAA with an overfilled cranial esophagus pushing most of the trachea to the right but an obvious focal leftward deviation just cranial to the heart similar to your case.

A manuscript in JVIM (in press, July 2004) gives more information on tracheal effects of PRAA along with supportive data. Included in the paper are photomicrographs comparing tracheal position in a normal newborn dog (Figure 7) and a 1-day-old dog with PRAA (Figure 8) that strangled when the ductus arteriosus contracted and the vascular ring compressed the trachea too much. I hope the above comments and the paper answer your questions.

Jim Buchanan
Emeritus Professor of Cardiology
University of Pennsylvania

Figure 5 Boxer DV radiograph after photoshop editing with dotted lines showing leftward curvature of the trachea just cranial to the heart.

Figure 6 DV radiograph of another dog with PRAA showing more obvious leftward deviation of the trachea just cranial to the heart.

Figure 7 Photomicrograph of the trachea and great vessels in a normal newborn dog. The trachea (T) is straight and the aorta (A), ductus arteriosus (D), and pulmonary artery (P) are all situated to the left of the trachea.

Figure 8 Photomicrograph of the trachea and great vessels in a 1 day old dog that was strangled by PRAA. The right sided aorta (A) pushed the trachea (T) leftward. The trachea and esophagus (E) are compressed between the aorta and the contracted ductus arteriosus (D).