Thyroid surgery carries risks of complications, particularly injury to the parathyroid glands and laryngeal nerves. Proper identification and preservation of these structures improve surgical outcomes [1]. Recurrent laryngeal nerve (RLN) injury is a significant concern, with permanent palsy occurring in 0.3–3% of cases and transient palsy in 5–8%. Among endocrine surgeons, RLN palsy occurs in 1–2%, but rates can reach up to 14% in some cases [2–4]. The most common mode of injury is nerve edema or stretching rather than severance. Identifying and dissecting the RLN reduces the risk of injury, with rates between 0–2.1%, though higher in revision surgeries (2–12%) or when the nerve is not clearly identified (4–6.6%) [5]. Emil Zuckerkandl (1849–1910) described the Tubercle of Zuckerkandl (ZT), a posterior thyroid extension derived from the 4th branchial cleft [6,7]. Its surgical relevance includes: 1. Close association with the RLN. 2. Necessity of ZT dissection in total thyroidectomy. 3. Its embryological role in medullary carcinoma [8,9]. ZT classification based on size: • Grade 0: Unrecognizable • Grade I: ≤5 mm • Grade II: 6–10 mm • Grade III: >10 mm ZT serves as a landmark for RLN identification and neurovascular crossing points. Its removal improves surgical safety, as failure to do so may cause persistent symptoms or recurrence [10]. Typically, the RLN runs medial to ZT, facilitating safer dissection. However, in rare high-risk cases, an enlarged ZT may position the RLN laterally, increasing the risk of injury. The superior parathyroid gland, also derived from the 4th branchial cleft, is frequently located near ZT [11]. Understanding ZT anatomy enhances surgical precision and minimizes complications. However, there is limited Indian data from studies analyzing in situ thyroid specimens, particularly in cancer cases. This study aims to assess ZT presence and its relationship with RLN during thyroid gland dissection.

The study was conducted in the Department of Surgical oncology., State Cancer Institute from February 2024 to February 2025 on 110 patients of thyroidectomy including 83 female patients and 27male patients. Out of these 22 were cases of hemithyroidectomies, 88 cases were of total thyroidectomy. Intraoperatively Zuckerkandl tubercle was identified, size of thyroid lobe and of Zuckerkandl tubercle were measured. Grading of tubercle as per its size has been done. Direction of tubercle towards the entry of recurrent laryngeal nerve and its relation with recurrent laryngeal nerve were observed. The position of superior parathyroid gland and inferior thyroid artery with respect to Zuckerkandl tubercle were observed. Following observations were made: 1. Presence of Zuckerkandl tubercle. 2. Grading in relation to lobe. 3. Direction of Zuckerkandl tubercle towards RLN. 4. Relation of RLN with parathyroid gland and Inferior thyroid artery.

In our study ZT was identified in 87.86% (179 out of 206) of the cases. For 42 thyroid lobes ZT could not identified. A total of 206 cases among which 93 were of right side surgery, 62 of left side surgery and 51 were bilateral. Amongst the 179 cases in whom ZT could be identified, ZT was found on the right side [85.41% i.e. 123 out of 144(93 of 51)], 81.41% [92 out of 113(62 ? 51)] to the left side and 15.68% (8 out of 51) were B/L (Tables 1, 2, 3). Other observations of present study. 1. The relationship between recurrent laryngeal nerve and ITA was studied. It revealed that mostly the ITA is anterior to RLN (in 70.89%) and posterior to RLN in 29.10% (Table 4) Table 1 ZT (Zuckerkandl tubercle) ZT No of patients % Identified 95 86% Not identifiable 15 14% Table 2 Position of Zuckerkandl tubercle Relation No of patients % posterior 105 95.45% anterior 2 1.8% lateral 3 2.7% Table 3 Grading of zuckerkandl tubercle Grade No of patients % zero 13 11.8% I 49 44.5% II 42 38.1% III 6 5.4%

ZT was first described by Otto Wilhelm Madelung in 1867 as a posterior horn of thyroid [12], but it was Emil Zuckerkandl who popularized it in 1902 and mentioned it as processus posterior glandula thyroidea^ [13]. Gilmour in 1938 described its relationship with RLN and superior parathyroid [14]. Having been described over a century it is frequently underutilized. In 1998 Pelizzo‘re-discovered’ this structure as a constant anatomical surgical landmark for identifying the RLN and graded it according to the size [10]. The RLN generally courses deep to this structure and superficial to the lateral border of the trachea. However, this relationship can vary due to the enlargement of the tuberculum placing the RLN at risk of injury during exploration. During thyroid surgery, identification and preservation of the recurrent laryngeal nerve and all of its divisions is essential to decrease the morbidity of the procedure. The thyroid gland develops embryologically through the fusion of the median anlage, which descends from the foramen caecum, with the smaller paired lateral anlages that originate from the ultimobranchial body. By the end of the third week, the median anlage has formed the primary structure of the thyroid. During the fifth week, the lateral anlage attaches to the back of the thyroid and gives rise to parafollicular C cells, which are derived from neural crest cells and produce calcitonin. The reasons for the fusion of the median and lateral anlages remain unclear, and ZT may be related to these lateral anlages.15 The reported incidence of ZT in the literature ranges from 7.04% to over 80%.[9,16,17,18,19] . This wide variation in incidence may be attributed to geographical, genetic, or ethnic differences. Nonetheless, our findings indicate that ZT remains a consistent feature. In 1998, Pelizzo et al. [10] reported the presence of ZT in 104 Italian patients during lobectomy and found grade 0 in 24 (23 %), grade I in 9 (8.6 %), grade II in 56 (53.8 %), and grade III in 15 (14.4 %) sides. Majority of the studies have documented grade I and grade II ZT with highest occurrence with incidence ranging from 18 to 90 % as summarised in Table 2 [20, 10,18, 21–24]. In a study of 104 lobectomies by Pelizzo et al. [10] the tubercle of Zukerkandl was identified in 78.2% of the lobectomies on the right and 75.5% of the cases on the left. The authors concluded that identifying this tubercle faciliatates RLN identification. Gil Carcedo [25] stated that the Zuckerkandl tubercle is a residue from the embryological development of the thyroid gland and highlighted its importance as a reliable reference point for locating the superior parathyroid, the inferior thyroid artery, and the RLN. In total, 195 thyroid lobes which he analyzed the Zuckerkandl tubercle was certainly detected in 155 thyroid lobes (79.48%). Gravante et al. [26] found an incidence of Zuckerkandl tubercle 63–80% in his series of studies. Gravante et al. stated, ‘‘Although not always present, the Zuckerkandl tubercle is an easy and simple way to localize the recurrent laryngeal nerve. Multiple other studies across the globe have also reported the incidence to be higher on the right side [18,19,21]. Even though the incidence is higher on the right side it is commonly present bilaterally. Therefore it can be used as landmark to identify RLN bilaterally. ZT is like an eloquent arrow pointing to the nerve. Similar description is provided by Pelizzo in literature[10]. If mobilized medially ZT would allow easy identification of the nerve before it turns below the inferior cricothyroid articulation. No branches were identified above the ZT. Thus, the ZT is a useful guide to locate and protect the RLN as it enters the cricothyroid muscular interval. Using tubercle of Zuckerkandl as an anatomical landmark to dissect thyroid gland, none of the patients had RLN damage as documented by postoperative assessment of cord mobility.

The unusual lateral or anterior course may increase the risk of injury. During resection of the tubercle, the recurrent laryngeal nerve can be dissected and protected by continuation of the capsular dissection technique. • The study was aimed to emphasise the importance of zuckerkandle tubercle as an important landmark to trace recurrent laryngeal nerve in thyroid surgery. • The ZT was identifiable in significant percentage (p value 0.01) (87.86%) of the studied cases. • The ZT was seen to point towards the entry of recurrent laryngeal nerve and the nerve was medial to the ZT in majority of them.

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