The peri-esophageal connective tissue layers and related compartments: visualization by histology and magnetic resonance imaging

Abstract

An organized layer of connective tissue coursing from aorta to esophagus was recently discovered in the mediastinum. The relations with other peri-esophageal fascias have not been described and it is unclear whether this layer can be visualized by non-invasive imaging. This study aimed to provide a comprehensive description of the peri-esophageal fascias and determine whether the connective tissue layer between aorta and esophagus can be visualized by magnetic resonance imaging (MRI). First, T2-weighted MRI scanning of the thoracic region of a human cadaver was performed, followed by histological examination of transverse sections of the peri-esophageal tissue between the thyroid gland and the diaphragm. Secondly, pretreatment motion-triggered MRI scans were prospectively obtained from 34 patients with esophageal cancer and independently assessed by two radiologists for the presence and location of the connective tissue layer coursing from aorta to esophagus. A layer of connective tissue coursing from the anterior aspect of the descending aorta to the left lateral aspect of the esophagus, with a thin extension coursing to the right pleural reflection, was visualized ex vivo in the cadaver on MR images, macroscopic tissue sections, and after histologic staining, as well as on in vivo MR images. The layer connecting esophagus and aorta was named 'aorto-esophageal ligament' and the layer connecting aorta to the right pleural reflection 'aorto-pleural ligament'. These connective tissue layers divides the posterior mediastinum in an anterior compartment containing the esophagus, (carinal) lymph nodes and vagus nerve, and a posterior compartment, containing the azygos vein, thoracic duct and occasionally lymph nodes. The anterior compartment was named 'peri-esophageal compartment' and the posterior compartment 'para-aortic compartment'. The connective tissue layers superior to the aortic arch and at the diaphragm corresponded with the currently available anatomic descriptions. This study confirms the existence of the previously described connective tissue layer coursing from aorta to esophagus, challenging the long-standing paradigm that no such structure exists. A comprehensive, detailed description of the peri-esophageal fascias is provided and, furthermore, it is shown that the connective tissue layer coursing from aorta to esophagus can be visualized in vivo by MRI.

Keywords: esophageal anatomy; esophageal surgery; magnetic resonance imaging; peri-esophageal fascia.

© 2016 Anatomical Society.

Figures

Figure 1

Figure showing a photograph of an unprocessed transverse tissue section at the level of the thyroid gland (A) with a corresponding MRI image (B), microscopic tissue section (C) and schematic drawing (D). Staining was performed according to Verhoef‐von Gieson, which stains elastin black‐blue and collagen light red‐pink. Black arrows, alar fascia; white arrows, thin visceral fascia enveloping esophagus and trachea. Car, carotid artery; Eso, esophagus; Jug, internal jugular vein; LCM, longus colli muscle; Ln, lymph node; Rln, recurrent laryngeal nerve; SCA, subclavian artery; SCM, sternocleidomastoid muscle; V, vagus nerve; VA, vertebral artery. Blue line, alar fascia and carotid sheaths; green line, visceral fascia; red line, perivertebral fascia.

Figure 2

Figure showing a photograph of an unprocessed transverse tissue section at the level of the tracheal bifurcation (A) with a corresponding MRI image (B), microscopic tissue section (C), and schematic drawing (D). Staining was performed according to Verhoef‐von Gieson, which stains elastin black‐blue and collagen light red‐pink. Black arrows, double layer of connective tissue between esophagus and aorta (proposed name ‘aorto‐esophageal ligament’); blue arrows, a connective tissue layer coursing from aorta to right pleural reflection (proposed name ‘aorto‐pleural ligament’); white arrows, a layer of connective tissue coursing from right to left main bronchus; red arrow, a blood vessel. Av, azygos vein; LMB, left main bronchus; Ln, lymph node; RMB, right main bronchus; TD, thoracic duct. Green line, pleura; purple line, connective tissue layer coursing from left to right main bronchus; black line, connective tissue layer coursing from aorta to esophagus; gray line, connective tissue layer coursing to the right pleural reflection.

Figure 3

Figure showing a photograph of an unprocessed transverse tissue section between tracheal bifurcation and diaphragm (A) with a corresponding MRI image (B), microscopic tissue section (C), and schematic drawing (D). Staining was performed according to Verhoef‐von Gieson, which stains elastin black‐blue and collagen light red‐pink. Black arrows, a layer of connective tissue between esophagus and aorta (proposed name ‘aorto‐esophageal ligament’); blue arrows, a connective tissue layer coursing from aorta to right pleural reflection (proposed name ‘aorto‐pleural ligament’); white arrows, the right and left pleural reflections; red arrows, blood vessels. AV, azygos vein; TD, thoracic duct. Green line, pleura; yellow line, pericardium; black line; connective tissue layer coursing from aorta to esophagus and connective tissue layer coursing from aorta to right pleural reflection.

Figure 4

Figure showing a transverse tissue section at the level of the diaphragm stained according to Verhoef‐von Gieson, which stains elastin black‐blue and collagen light red‐pink (A) and a corresponding schematic drawing (B). White arrows on the stained tissue section, the phrenico‐esophageal ligament; blue arrows, a fascia coursing from aorta to right pleural reflection (proposed name ‘aorto‐pleural ligament’). Eso, esophagus. Green line, pleura or peritoneum; black lines between crura of diaphragm and esophagus, phrenico‐esophageal ligaments; purple line, layer of connective tissue coursing from aorta to right pleural reflection.

Figure 5

T2‐weighted MRI images showing that the layer of connective tissue coursing from aorta to esophagus (proposed name ‘aorto‐esophageal ligament’) can be observed in vivo (A, white arrows). However, if there is insufficient mediastinal fat between aorta and esophagus, the contrast is too low to visualize this connective tissue layer (B).