Mediastinum Anatomy

The mediastinum is the central partition of the thoracic cavity, lying between the two pleural sacs and extending from the thoracic inlet above to the diaphragm below, and from the sternum in front to the vertebral column behind. It contains the heart and pericardium, the great vessels, the trachea and oesophagus, the thymus, and numerous nerves and lymphatics. Because so many structures are packed into this central column, anatomists and radiologists divide it into compartments to organise description and localisation.

Definition

The mediastinum is the median region of the thoracic cavity between the two pleural cavities, bounded by the thoracic inlet, the diaphragm, the sternum, and the vertebral column, and containing the heart, great vessels, trachea, oesophagus, thymus, and associated nerves and lymphatics.

Scope

This topic covers the boundaries of the mediastinum, its classical anatomical subdivisions and the modern cross-sectional (CT-based) compartmental schemes, and the principal structures within each compartment. It is a reference-educational account of normal mediastinal anatomy and the conventions used to describe it, not clinical guidance.

Core questions

• What are the boundaries of the mediastinum?
• How is the mediastinum divided in classical anatomy versus cross-sectional imaging schemes?
• Which major structures lie in each compartment?
• Why do anatomical and radiological compartment definitions differ?

Key concepts

• Superior and inferior mediastinum
• Anterior, middle, and posterior mediastinum
• ITMIG cross-sectional compartments (prevascular, visceral, paravertebral)
• Heart and pericardium
• Great vessels
• Trachea and oesophagus
• Thymus

Mechanisms

The classical anatomical scheme first divides the mediastinum by a transverse plane at the sternal angle (the plane of the manubriosternal joint and the T4-T5 disc) into a superior mediastinum above and an inferior mediastinum below; the inferior part is then subdivided into anterior, middle (containing the heart and pericardium), and posterior compartments. Because these subdivisions are defined relative to the pericardium and are difficult to apply on axial images, the ITMIG cross-sectional classification instead defines prevascular, visceral, and paravertebral compartments using boundaries reproducible on CT, which improves communication between clinicians and radiologists (Liu 2011; Carter 2017; Lee 2021; Standring 2020).

Clinical relevance

Localising a lesion to a mediastinal compartment narrows the range of structures it may arise from and shapes how findings are described on imaging. This entry explains the compartmental conventions and the structures within each; it describes anatomy and reporting frameworks and does not offer diagnostic or treatment recommendations.

Evidence & guidelines

The classical superior/anterior/middle/posterior subdivision is described in standard reference anatomy (Standring 2020; Moore 2018; Liu 2011). For cross-sectional imaging, the ITMIG classification provides a widely adopted CT-based three-compartment scheme (prevascular, visceral, paravertebral) intended to standardise mediastinal description (Carter 2017; Lee 2021).

Debates

Which mediastinal compartment scheme should be used?

Classical anatomy partitions the mediastinum relative to the pericardium, but these planes are hard to apply to axial CT; the ITMIG cross-sectional model redefines compartments using imaging-reproducible boundaries, and the two schemes coexist in anatomical teaching and radiological practice.

Seminal works

• carter-2017
• liu-2011
• standring-2020

Frequently asked questions

How is the mediastinum classically divided?

A plane at the sternal angle separates a superior mediastinum from an inferior mediastinum, and the inferior part is further divided into anterior, middle (heart and pericardium), and posterior compartments (Liu 2011; Standring 2020).

Why does imaging use a different compartment scheme?

The classical planes are defined relative to the pericardium and are awkward on axial images, so the ITMIG cross-sectional model defines prevascular, visceral, and paravertebral compartments with boundaries that are reproducible on CT (Carter 2017).