ABSTRACT
The phrenic nerves arise from C3 to C5 nerve roots and run in the lower neck obliquely in front of the scalenus anterior muscles where they used to be crushed for the treatment of pulmonary tuberculosis. Where the phrenic nerves lie anterior to the hilum, they are usually too small to be visualised by CT, but as they approach the diaphragm, they may sometimes be seen as small 'nodules' on the pericardium or lines on the surface of the diaphragm, where they elevate a small sleeve of parietal pleura. The right recurrent laryngeal nerve passes around the right subclavian artery, close to the lung apex, where it may sometimes be involved by a rightsided primary or secondary Pancoast tumour, a subclavian artery aneurysm or a tumour arising from the subclavian artery. Bilateral phrenic palsy is an uncommon but well recognised cause of breathlessness, typically presenting with orthopnoea, less commonly breathlessness on exercise or immersion.
