👉Although occasional direct connections between cervical sympathetic ganglia and the RLN (sympathetic-inferior laryngeal nerve anastomotic branch or SILAB) have been well described, it is now appreciated that very fine direct anastomoses from the sympathetic ganglia to both the RLN as well as the external branch of the superior laryngeal nerve (EBSLN), and then on to the substance of the thyroid gland, are very common if not universal.
👉It has been reported that up to 2% of SILAB are larger than the RLN and may thus be mistaken for a non-recurrent laryngeal nerve, thus placing the true RLN at risk of division.
👉If there is any doubt about the nature of apparent anastamotic branches they should be traced back laterally.
👉A non- recurrent laryngeal nerve will arise from the vagus whereas a SILAB will usually arise from the middle cervical ganglion, or occasionally from the inferior or superior ganglia.
👉Occasionally a sympathetic branch from the superior cervical ganglion, hitch-hikes along the EBLN and then communicates via a further branch to the RLN along with the ‘nerve of Galen’, although this nerve itself is thought to contain primarily sensory and some motor fibers.
👉Branches also leave the RLN passing directly into the substance of the thyroid gland.
👉While any such branch appearing to pass into the thyroid should be carefully examined in order to avoid dividing a small true anterior branch of the RLN, recognition of the existence of sympathetic anastamoses is vital during thyroid dissection.