Endoscopic ultrasound: imaging techniques and applications in the mediastinum

The esophagus passes through the superior and posterior mediastinum, and provides a window for transesophageal imaging of the mediastinum. The applications of endosonography in the mediastinum can be divided on the basis of location into: (1) periesophageal, and (2) intrinsic to the esophagus. Treatment of non-small cell lung cancer is stage dependent, and endosonography helps sample lymph nodes at levels 4L, 5, 7, 8, 9 as well as the celiac, and the left adrenal nodes. Primary lung tumours in a periesophageal location and those invading the mediastinum can also be safely biopsied. The most common causes of mediastinal lymphadenopathy are tuberculosis, sarcoidosis, metastatic and reactive. Endosonography provides for biopsy of these enlarged nodes easily, safely and with a high diagnostic yield. Endosonography is the most accurate loco-regional staging modality for esophageal cancer with a T-stage and N-stage accuracy of 75%-85%, and 65%-75%, respectively. Dilatation of stenosing esophageal tumours to allow echoendoscope passage for complete staging is controversial. Endosonography can triage patients with esophageal cancer to surgery alone, neoadjuvant therapy, and palliative therapy. Subepithelial lesions of the esophagus include leiomyomas, granular cell tumours, duplication cysts, and inflammatory fibroid polyps. These can usually be diagnosed by endosonography. Application of endosonography in portal hypertension is still experimental, and will not be described in this review. This illustrated review describes the applications of endosonography in the mediastinum, practical tips for optimal imaging, and step-by-step instructions for radial and curved linear array endosonographic imaging, along with relevant applied mediastinal anatomy.