Expansion
Phrenic nerve passes in Front of the lung root; the vagus passes behind
Expansion
- Phrenic nerve - in front of the lung root, on the pericardium
- Vagus nerve - behind the lung root, heading for the oesophagus
The alliteration of phrenic and front is the whole trick. The phrenic nerve continues on the fibrous pericardium with the pericardiacophrenic vessels to reach the diaphragm, while the vagus breaks up into the pulmonary and oesophageal plexuses behind the hilum.
This relationship also explains the clinical picture of a hilar tumour: an anterior mass paralyses the hemidiaphragm through the phrenic nerve, while a mass on the left below the arch catches the recurrent laryngeal branch of the vagus and causes hoarseness.