Intramuscular distribution of the phrenic nerve in human diaphragm as shown by Sihler staining

Introduction: Intramuscular innervation of the human diaphragm has not been well described. The goal of this study was to elucidate the detailed intramuscular distribution of the phrenic nerve in the human diaphragm. Methods: Fifteen human diaphragms were visualized using modified Sihler staining, and the detailed intramuscular phrenic nerve distribution was photographed and recorded. Results: Three types of primary phrenic nerve branches were noted. Each type of primary branch innervated a confined muscular subvolume of the diaphragm, and the intramuscular branches in each subvolume anastomosed largely with one another and formed a characteristic "net" of nerve branches. A few small nerve filaments were seen entering the peripheral diaphragm. The directions and locations of nerve branches innervating the hiatal diaphragm were not symmetrical between sides. Conclusion: These findings may offer useful information for anatomists, physiologists, and clinicians.