Abstract
Communicating fibres between the phrenic nerve and sympathetic nervous system may exist, but have not been characterized histologically and immunohistochemically, even though increased sympathetic activity due to phrenic nerve stimulation for central sleep apnoea may entail morbidity and mortality. We, therefore, conducted a histological study of the phrenic nerve to establish the presence of catecholaminergic fibres throughout their course. The entire phrenic nerves of 35 formalin-fixed human cadavers were analysed morphometrically and immunohistochemically. Furthermore, the right abdominal phrenic nerve was serially sectioned and reconstructed. The phrenic nerve contained 3 ± 2 fascicles in the neck that merged to form a single fascicle in the thorax and split again into 3 ± 3 fascicles above the diaphragm. All phrenic nerves contained catecholaminergic fibres, which were distributed homogenously or present as distinct areas within a fascicle or as separate fascicles. The phrenicoabdominal branch of the right phrenic nerve is a branch of the celiac plexus and, therefore, better termed the “phrenic branch of the celiac plexus”. The wall of the inferior caval vein in the diaphragm contained longitudinal strands of myocardium and atrial natriuretic peptide-positive paraganglia (“caval bodies”) that where innervated by the right phrenic nerve.
Highlights
The phrenic nerve arises from the anterior roots of the third to fifth cervical nerves and is known to innervate the diaphragm[1,2]
Since phrenic nerve stimulation can be performed on both sides and at different levels of the nerve, we looked at morphological differences along the course of the phrenic nerve and compared left and right phrenic nerves at different levels
In the wall of the inferior caval vein of the 4 cadavers studied, we identified a total of eight tangled structures (Fig. 4C, lower left inset and 5) that contained an extensive venous plexus surrounding large cell bodies with granular inclusions (Fig. 5 inset) and a network of nerve fibres (Figs 5 and 6A,B) originating from the right phrenic nerve on the opposite side (Fig. 4C)
Summary
The phrenic nerve arises from the anterior roots of the third to fifth cervical nerves and is known to innervate the diaphragm[1,2]. A continuation of the right phrenic nerve towards the aortic autonomic plexus in the abdomen, the so-called phrenicoabdominal branch, is often reported[7,9,10]. This branch contains one or several ganglia that stain positive for tyrosine hydroxylase (TH)[11], indicating catecholaminergic signal transmission. We conducted a detailed histological study to establish the presence of catecholaminergic fibres in the phrenic nerve throughout its course from its cervical roots to its connection with the celiac plexus. Since phrenic nerve stimulation can be performed on both sides and at different levels of the nerve, we looked at morphological differences along the course of the phrenic nerve and compared left and right phrenic nerves at different levels
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