4.3 Thoracic Cavity

The loose connective tissue of the mediastinum communicates freely with the neck.

Divisions of mediastinum

All mediastinal topography relatable to plane passing through Angle of Louis (manubriosternal joint & 2^nd cc anteriorly ® lower border T4 posteriorly).

Above = superior mediastinum, below = inferior mediastinum.

Fibrous pericardium divides latter into 3 parts: 1 in front (anterior), 1 behind (posterior) and middle in between (pericardium & heart). Anterior & posterior mediastina communicate directly with superior mediastinum.

In plane between superior & inferior mediastina (at Angle of Louis) Pl195

(1) Tracheal bifurcation

(2) Concavity of aortic arch, ligamentum arteriosum

(3) Bifurcation of pulmonary trunk

(4) Azygos vein enters SVC

(5) Thoracic duct reaches L side of oesophagus

(6) Attachment of prevertebral fascia

Spread of Neck Infections

Prevertebral and pretracheal fascia extend from neck into superior mediastinum.

- prevertebral fuses with anterior longitudinal ligament over T4

- pretracheal fuses with pericardium over front of heart.

Hence neck infections in front of pretracheal fascia à anterior mediastinum

Else they tend to à posterior mediastinum.