The thoracic esophagus: sectional anatomy and radiosurgical applications

The relationships of a tumor of the thoracic esophagus to the adjacent mediastinal structures are currently studied by means of computed tomography (CT), magnetic resonance imaging (MRI) and, more recently, by echoendoscopy. However, the assessment of axial mediastinal CT and of MRI in the coronal and sagittal planes calls for some degree of experience. To further this training a sectional anatomy is proposed in correlation with imaging of the thoracic esophagus and the posterior mediastinum. Ten fresh subjects whose vascular networks had been previously injected with colored resin were sectioned along the three planes of space after positioning under CT monitoring. The axial sections were compared with the CT images made with a GE 9800 Quick scanner. Three frontal and sagittal sections were compared with the MRI images made with a GE Signa apparatus using a high magnetic field. The relations of the esophagus were studied at three levels: the supra-azygo-aortic segment, where it is related to the left subclavian artery; the inter-azygo-aortic segment, where access to the esophagus is barred on the left by the aortic arch and on the right by the arch of the azygos vein, section of which provides ample access; and the sub-azygo-aortic segment, where the esophagus passes behind the left main bronchus and to the right of the descending aorta, two organs whose invasion contraindicates excision of a tumor of the esophagus but is difficult to assess by current thoracic imaging techniques. The esophagus then descends behind the left atrium; the investigation of the kinetics of the heart cavities by transesophageal echocardiography is an application of this anatomic relationship. These anatomic sections should form useful teaching aids for the study of CT and MR images by radiologists and should help surgeons to assess the possibilities of tumor excision.