The anterior recurrent laryngeal nerve : an uncommon topographical variation observed during thyroid surgery

Safeguarding the recurrent laryngeal nerve (RLN) is crucial during thyroid surgery. Nerve paralysis due to accidental injury of the RLN, can occur in 1-2% of cases, even by experienced surgeons [1]. Common variations of the RLN include the non-recurrent laryngeal nerve and extra-laryngeal bifurcation. A rare but well documented entity is the anterior recurrent laryngeal nerve (ARLN). We present this unusual variation of the position of the right RLN, in a 57 year old female who underwent thyroidectomy for a benign multinodular goitre.


Introduction
Safeguarding the recurrent laryngeal nerve (RLN) is crucial during thyroid surgery.Nerve paralysis due to accidental injury of the RLN, can occur in 1-2% of cases, even by experienced surgeons [1].Common variations of the RLN include the non-recurrent laryngeal nerve and extra-laryngeal bifurcation.A rare but well documented entity is the anterior recurrent laryngeal nerve (ARLN).We present this unusual variation of the position of the right RLN, in a 57 year old female who underwent thyroidectomy for a benign multinodular goitre.

Case Report
A 57 year old euthyroid female presented with a benign multinodular goitre of 10x8x4cm in maximum dimensions, of 15 years duration.Indirect laryngoscopy revealed normal bilateral vocal cords.
During thyroidectomy, the left recurrent laryngeal nerve and parathyroid glands were identified and preserved.On lifting the right lobe medially an unusual occurrence was identified.The right RLN was found running superficially and anteriorly over the lower part of the thyroid lobe (Figure 1).The Zuckerkandl's tubercle (ZT) served as an important landmark to confirm the position of the RLN.The nerve had to be lifted off the gland and meticulously dissected away to deliver the lobe.The nerve was traced down into the root of the neck confirming that it was not a non-recurrent laryngeal nerve.Its position was superficial to the inferior thyroid artery and behind the inferior parathyroid gland.Post-operatively the patient developed hoarseness of voice due to paralysis of the right vocal cord, as confirmed by indirect laryngoscopy.This probably occurred due to traction when the nerve was being lifted off the gland.Her voice returned to normal after 5 weeks.

Discussion
The RLN usually runs behind the thyroid gland in the tracheo-oesophageal groove.Dissections of human cadavers have shown that the paths of the recurrent laryngeal nerves were occasionally different from that shown in the standard literature [2].In a recent study, Shen et al [3] demonstrated that the RLN lies in positions away from the tracheooesophageal groove in 43 patients.
Hunt el [4] have shown that in rare situations the RLN ascends anterolateral to the trachea away from the tracheaoesophageal groove and consequently remains widely exposed and vulnerable to injury during surgery.Distortion from large nodules can cause the RLN to lie anteriorly over the thyroid gland [5].Gurleyik [6] reported two cases wherein the RLN was pushed laterally by an enlarged ZT.
In our centre we routinely identify and trace the course of the RLN for all thyroidectomies.The RLN usually appears like a white ribbon with a thread of fine blood vessels running over its surface.We were able to identify the nerve by its characteristic appearance although it was in a totally unexpected position.The nerve could have otherwise been easily overlooked and seriously injured.

Figure 1 .
Figure 1.The right recurrent laryngeal nerve (white arrows) can be seen running anteriorly and superficially over the thyroid gland.Normally the RLN should be in a plane behind the lobe in the trachea-oesphageal groove.The Zuckerkandl's tubercle (ZT) serves as a pointer to the RLN.The black arrow denotes position of the inferior thyroid artery.