Transesophageal ultrasonography of the normal canine mediastinum

The mediastinum of eight normal research dogs was examined by transesophageal ultrasonography with a 5 MHz frequency transducer to establish a baseline for future use of this new imaging modality as a diagnostic tool. Each examination consisted of 360 degree scans in both transverse and sagittal planes from the thoracic inlet to the esophageal hiatus. Dissections of four of these research dogs were then performed to confirm transesophageal ultrasonography findings. Transesophageal ultrasonography of the mediastinum was a good imaging modality for the evaluation of the heartbase, the major cranial mediastinal vessels, the descending aorta, and occasionally part of the azygos vein. Anatomic orientation was best obtained by beginning the examination at the heart base. Lymph nodes and smaller caliber vessels could not be distinguished from surrounding tissues; however, Doppler ultrasound was useful for identifying the smaller vessels. Although a 5 MHz frequency transducer is preferred for transesophageal echocardiography, a higher frequency transducer would improve the resolution of the images of small near-field structures and may be more appropriate for mediastinal imaging.