Location Dependent Nerve Shielding by Peri-Arterial Blood Vessels and Lymph Nodes

ackground: Periarterial lymph nodes and blood vessels have been implicated in shielding nerves from radiofrequency heating but the spatial distribution shielded nerves surrounding renal arteries is unknown.

Methods: Eighteen swine were collected, fixed, processed for H&E and sectioned. Nerve, lymph node and vessel distances from the lumen were measured in a total of 106 sections and nerves categorized as shielded or not by vessels or lymph nodes. Radial nerve distributions were evaluated per artery and axial segments (Fig 1A) and per circumferential quadrants (Fig 1B).

Results: Per artery, mean nerve distance was 3.3mm and only 16% (180/1141) were shielded. Mean nerve distance was highest in proximal sections (4.8mm, P<0.001) and in the posterior/dorsal direction (4.5mm, P<0.001) and lowest in middle/distal sections (2.2mm) and anterior/ventral direction (1.5mm). The number/percentage of shielded nerves increased superlinearly with mean nerve distance from the lumen (spearman r=0.93, P=0.007). Segment, shielded nerves peaked proximally (110/464) and dipped in the middle segment (22/349). Circumferentially, shielded nerves peaked in the superior quadrant (88/514) and dipped ventrally (6/179).

Conclusion: The data imply that nerve shielding from heat by veins and lymph nodes correlates with mean nerve distance from the lumen. In porcine renal arteries, shielding was maximal in proximal segments and the superior direction. These data are relevant to interventional procedures, as RDN treatment protocols are able to focus on distal segments but cannot yet controllably focus on particular quadrants and do not account for presence of heat shielding structures.