Mediastinal mass

Mediastinal mass Microchapters
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Overview
Anatomy of Mediastinum
Causes
Differentiating Mediastinal Mass from other Diseases

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Trusha Tank, M.D.[2]

Synonyms and keywords: Mediastinal enlargement; mass in the mediastinum

Overview

The mediastinum is a non-delineated group of structures in the thorax (chest), surrounded by loose connective tissue. It is the central compartment of the thoracic cavity. The mediastinum lies between the right and left pleura in and near the median sagittal plane of the chest. It extends from the sternum in front to the vertebral column behind, and contains all the thoracic viscera except the lungs. On the basis of cross-sectional imaging, mediastinum can be divided into 3 groups: 1) Prevascular compartment: which contains thymus, fat, lymph nodes and left brachiocephalic vein. 2) Visceral compartment, which contains trachea, carina, esophagus, lymph nodes, heart, ascending thoracic aorta, aortic arch, descending thoracic aorta, superior vena cava, intrapericardial pulmonary arteries, and thoracic duct. and 3) Paravertebral compartment: which contains the thoracic spine and paravertebral tissue. A wide variety of diseases involving these organs can present as a mediastinal mass or widening of the mediastinum on imaging studies. Mediastinal widening is diagnosed by the mediastinum measuring greater than 8 cm in width on PA chest x-ray. The mediastinal mass may present with symptoms or even without any symptoms. A mediastinal mass may cause a variety of symptoms by the mass pressing against other mediastinal structures, collectively known as mediastinal syndrome. Mediastinal mass can be differentiated according to the content of the mass such as cystic mass, fatty mass or solid (tumor). Depending on location and composition of the mass further diagnosis is made by specific imaging studies, endoscopic studies, tissue biopsies, histopathological studies and/or growth of microorganism on specific culture medium.

Anatomy of mediastinum

• The mediastinum lies between the right and left pleura in and near the median sagittal plane of the chest.

• It extends from the sternum in front to the vertebral column behind, and contains all the thoracic viscera except the lungs. It may be divided for purposes of description into two parts:
  • Superior mediastinum: Above the upper level of the pericardium, which is named the superior mediastinum with its superior limit at the superior thoracic opening and its inferior limit at the plane from the sternal angle to the disc of T4-T5 (plane of Ludwig)
  • Inferior mediastinum: Below the upper level of the pericardium. This lower portion is again subdivided into three parts:
    • In front of the pericardium, the anterior mediastinum
    • Containing the pericardium and its contents, the middle mediastinum
    • Behind the pericardium, the posterior mediastinum
    • It is surrounded by the chest wall anteriorly, the lungs laterally and the spine posteriorly.
    • It is continuous with the loose connective tissue of the neck, and extends inferiorly into the diaphragm.

• Note that clinical radiologists and anatomists categorize the mediastinum in slightly different ways.

• The International Thymic Malignancy Interest Group (ITMIG) has developed a new scheme to divide mediastinal cavity on the basis of cross sectional imaging for better diagnostic and therapeutic purposes.
  • Prevascular (anterior)
  • Visceral (middle)
  • Paravertebral (posterior)

International Thymic Malignancy Interest Group (ITMIG) Classification of Mediastinum
Compartments	Boundaries	Components
Prevascular	Superior: Thoracic inlet Inferior: Diaphragm Anterior: Sternum Posterior: Anterior aspect of the pericardium Lateral: Parietal mediastinal pleura	Thymus Fat Lymph nodes Left brachiocephalic vein
Visceral	Superior: Thoracic inlet Inferior: Diaphragm Anterior: Posterior boundaries of the prevascular compartment Posterior: Vertical line connecting a point on each thoracic vertebral body 1 cm posterior to its origin	Non vascular: Trachea Carina Esophagus Lymph nodes Vascular: Heart Ascending thoracic aorta Aortic arch Descending thoracic aorta Superior vena cava Intrapericardial pulmonary arteries Thoracic duct
Paravertebral	Superior: Thoracic inlet Inferior: Diaphragm Anterior: Posterior boundaries of the visceral compartment Posterolateral: Vertical line against the posterior margin of the chest wall at the lateral margin of the transverse process of the thoracic spine	Thoracic spine Paravertebral soft tissues
Adapted from Radiographics