The Sinuvertebral Nerve Revisited: A Morphological and Immunohistochemical Study

The proven involvement of the sinuvertebral nerve (SVN) in discogenic low-back pain and the demonstration that its blockade has been effective in reducing the intensity and frequency of diffuse low back pain have led to an increase in publications related to the characterization of this nerve. However, there is a huge disparity in the observations resulting from the studies carried out, probably due to the technical difficulty of accessing this structure. In recent years, the number of studies in large samples has increased but some important data in relation to the nature of the sinuvertebral nerve remain unpublished. We studied 100 vertebral column segments between L1 and L5, corresponding to both sides of 10 adult cadavers donated to the Body Donation Centre and Dissection Rooms of the Complutense University of Madrid. All levels were carefully dissected to study sinuvertebral nerve origins and some samples of SVN were selected to be routinely paraffin-embedded and serially sectioned with a Minot-type microtome at a 7 µm thickness. Immediately after dewaxing following the standard histology lab protocols, sections from the selected SVN (well-preserved morphology and histologic condition) were subjected to an immunohistochemical protocol to detect CGRP-IH and VIP-IH. Data analysis was performed using IBM SPSS Statistics version 27 and RStudio. The SVN was observed with a single branch (pattern I) in 82 cases (85.4%) and with two branches (pattern II) at the same level in 14 cases (14.6%). Statistical differences were not found in relation to vertebral levels, side or sex. All sinuvertebral nerve samples that underwent immunohistochemical study were positive for CGRP and VIP, suggesting a mixed autonomic (VIP+) and sensory (CGRP+) fibre composition along the nerve trunk. This study confirms the neurochemistry profile of the SVN due to the realization of the immunochemistry characterization directly in the SVN, not in its innervated structures. This information supports the usage of SVN blocking from a pathophysiological point of view for diagnostic and treatment techniques (e.g., Percutaneous Transforaminal Endoscopic Radiofrequency Ablation of the SVN) in discogenic lumbar pain.