Superior mediastinum above the sternal angle; anterior, middle and posterior below it
Mnemonic
Divide at the sternal angle (of Louis), the plane of T4/T5:
- Superior mediastinum, above the plane
- Inferior, below, subdivided into anterior, middle and posterior
“ITM” for the anterior mediastinal masses, the four Ts: Thymoma, Teratoma and germ cell tumours, Thyroid (retrosternal goitre), Terrible lymphoma.
The middle mediastinum is essentially the pericardium and its contents, so a mass there is usually a cyst, a node or a vascular abnormality; the posterior compartment carries the oesophagus, descending aorta, thoracic duct and sympathetic chain, so masses there are typically neurogenic.
Expansion
The mediastinum is everything between the two pleural sacs. The plane of the sternal angle (T4/T5) splits it into:
- Superior mediastinum - above the plane
- Inferior mediastinum - below the plane, subdivided into:
- Anterior - in front of the pericardium
- Middle - the pericardium and its contents
- Posterior - behind the pericardium
A quick way to hold it: anterior is thymus and fat, middle is heart, posterior is the structures passing from thorax to abdomen.