BACKGROUND AND OBJECTIVE: Most studies related to phrenic nerve are conducted based on an anatomical perspective and there is no histological study associated with this nerve. Since detecting the approximate time of death based on tissue destruction and determining the main branch of phrenic nerve based on the number of nerve fibers is extremely important, the histological examination of phrenic nerve was evaluated in the present study.

METHODS: In this experimental study, the left and right phrenic nerves, obtained from 10 male corpses, were described using Grant's method of dissection after cutting the chest. In order to count the number of nerve fibers in the constituent branches (C3, C4 and C5), Hematoxylin and Eosin staining and Bielschowsky staining were used. In addition, to determine tissue destruction time, phrenic nerve of 8 rabbits were examined one to eight days after their death.

FINDINGS: The results regarding tissue destruction time demonstrated that phrenic nerve starts to degenerate on the sixth day after death and is completely degenerated on the seventh and eighth days. Moreover, mean nerve fibers in C3, C4 and C5 were 41.2% (2224), 44.9% (2428) and 13.9% (749), respectively. The differences between the number of nerve fibers in these branches was statistically significant (p<0.05).

CONCLUSION: The results of this study demonstrated that a significant part of phrenic nerve fibers are originated from C4 branch. In addition, tissue destruction of this nerve starts on the sixth day after death.