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Mediastinum

The mediastinum is the central compartment of the thoracic cavity located between the two pleural cavities. It extends from the thoracic inlet superiorly to the diaphragm inferiorly and from the sternum anteriorly to the vertebral column posteriorly. The mediastinum contains vital thoracic organs, major vessels, nerves, lymphatic structures, and connective tissue.

It is a key anatomical region in thoracic imaging, surgery, oncology, and cardiopulmonary medicine.

Synonyms

  • Mediastinal compartment

  • Central thoracic compartment

Location

  • Situated between the right and left pleural cavities

  • Extends from the thoracic inlet to the diaphragm

  • Anterior boundary: Sternum and costal cartilages

  • Posterior boundary: Thoracic vertebral bodies

  • Lateral boundaries: Mediastinal pleura

  • Superior boundary: Thoracic inlet

  • Inferior boundary: Diaphragm

Subdivision (compartments)

Superior mediastinum:

  • Extends from thoracic inlet to the plane of the sternal angle (T4–T5)

Inferior mediastinum: Divided into

  • Anterior mediastinum

  • Middle mediastinum

  • Posterior mediastinum

Anatomical contents

Superior mediastinum:

  • Thymus (or thymic remnant)

  • Aortic arch and branches

  • Superior vena cava (upper part)

  • Trachea

  • Esophagus

  • Thoracic duct

  • Vagus and phrenic nerves

Anterior mediastinum:

  • Fat and connective tissue

  • Thymus (especially in children)

  • Lymph nodes

Middle mediastinum:

  • Heart and pericardium

  • Ascending aorta

  • Pulmonary arteries and veins

  • Tracheal bifurcation

  • Main bronchi

Posterior mediastinum:

  • Descending thoracic aorta

  • Esophagus

  • Azygos and hemiazygos veins

  • Thoracic duct

  • Sympathetic chains

Relations

Anteriorly:

  • Sternum

  • Anterior chest wall

Posteriorly:

  • Thoracic spine

Laterally:

  • Mediastinal pleura and lungs

Superiorly:

  • Neck structures through thoracic inlet

Inferiorly:

  • Diaphragm

X-ray appearance

Chest radiograph (PA and lateral):

  • Mediastinum: Soft-tissue opacity between lung fields

  • Mediastinal contours: Smooth and symmetric margins

  • Superior mediastinum: Defined by tracheal air column and vascular shadows

  • Silhouette sign: Helps localize mediastinal versus pulmonary pathology

CT appearance

Mediastinal window:

  • Fat: Low attenuation

  • Soft tissues and vessels: Clearly differentiated

  • Organs: Heart, great vessels, trachea, and esophagus well delineated

Lung window:

  • Mediastinal boundaries: Sharp interface between lungs and mediastinum

  • Air-containing structures: Trachea and bronchi well visualized

  • Pleural reflections: Clearly seen at mediastinal margins

  • Helpful for assessing: Lung–mediastinum interface and air leaks

MRI appearance

T1-weighted images:

  • Fat: High signal intensity

  • Vessels and muscles: Intermediate signal

  • Vascular flow: Signal voids depending on sequence

  • Air-filled structures: Signal voids

  • Excellent for identifying fat-containing mediastinal regions

T2-weighted images:

  • Fluid-containing structures: High signal

  • Soft tissues: Intermediate signal

  • Vascular flow: Signal voids depending on sequence

STIR:

  • Fat suppression: Fat appears dark

  • Soft tissues and fluid: High signal

  • Useful for highlighting edema and soft-tissue contrast within the mediastinum

X ray image

Mediastinum Anatomy, Location and Imaging Appearance CT anatomy image -img-00000-00000