A study on the variants of phrenic nerve roots with histological correlation

Introduction: The Phrenic nerve primarily supplies the diaphragm and hence is important for breathing. As per the standard text books, its root value is C3, C4 and C5. However, a few studies have shown that, it is primarily formed by the C4 with contributions from C3 and C5. Therefore, this study aimed at identifying the roots of the phrenic nerve and subject it to histological procedure to identify the maximum contribution in its formation. Materials and methods: 20 formalin-fixed adult cadavers of both sexes were used for the study. The necks were dissected bilaterally and the roots of the phrenic nerve were identified, colored and photographed. The transverse section of the phrenic nerve immediately after its formation was taken and subjected for the histological procedures. The sections were stained with osmic acid and photographs were taken. Results: 20% of the dissected necks showed that the phrenic nerve had root value C3, C4, C5 and 55% of the dissected necks had root value C4, C5. Osmic acid stained histological sections confirmed that C4 gives a major contribution to phrenic nerve. Conclusion: The results of the present study are in support of the fact that C4 gives major contribution for the phrenic nerve. This fact helps the surgeons in finding out the exact cause of paralysis of the diaphragm and also help in sectioning the phrenic nerve for the nerve graft in the repair of post cricoarytenoid muscle.