a thyroid surgeon must have intimate knowledge about all anatomic variations of the gland affecting the safety of surgical operations . emil zuckerkandl ( 18491910 ) , an austrian anatomist has described many anatomical structures in the body [ 1 , 2 ] . zuckerkandl 's tubercle ( zt ) is defined as posterior extension of the lateral lobes composing of thyroid tissue only . it should be included in the nomina anatomica as the  processus posterior glandulae thyroideae  described by zuckerkandl . the surgical importance of zt can be summarized as ( 1 ) dissection and excision of zt for total thyroidectomy and ( 2 ) close relationship between zt and recurrent laryngeal nerve ( rln ) . the completeness of thyroidectomy requires removal of enlarged zt which is posterolateral extension of thyroid lobes adjacent to rln . close relation of two structures urges careful , fine , and very close dissection around the nerve . due to posterior location of an enlarged zt , thyroid surgeon must be focused on its relations with inferior laryngeal nerve for safe identification of the nerve and resection of the tubercle . the presence of zt and close association of rln to an enlarged tubercle has been documented in many patients [ 710 ] . we aim to study the presence of zt , its relations with rln , and variations of this relationship during surgical dissection of lateral lobes of the thyroid gland . a prospective study about surgical anatomy of the thyroid was conducted on 100 thyroidectomy patients between may 2009 and august 2011 . total thyroidectomy and hemithyroidectomy ( unilateral total lobectomy - isthmusectomy ) are our procedures for the treatment of surgical diseases of the thyroid . all operations were performed by a single surgeon in order to provide a standard dissection . main subjects of this study are the presence and incidence of zt and its relations with rln . after freeing and medially mobilizing lateral lobes of the thyroid gland at both sides with classical surgical approach , the inferior thyroid arteries were identified , isolated and a loop of silk suture was placed around arteries for traction . during surgical dissection of posterior plan if clearly delineated tubercle was identified at posterolateral aspect of the thyroid lobes , we studied its relations with rln . the operation was total thyroidectomy in 60 ( 60% ) and unilateral total lobectomy ( 27 right and 13 left lobes ) in 40 ( 40% ) patients . therefore , this study was performed on 87 right and 73 left lobes of the thyroid . larger zts were identified in 66 ( 66% ) patients , and 81 of 160 ( 51% ) excised lobes . the presence of prominent zt was observed in 53 of 87 ( 61% ) right and 28 of 73 ( 38% ) left lobes . zts were present bilaterally in 15 ( 25% ) of 60 total thyroidectomy cases ( table 1 ) . bilateral enlarged tubercles are easily observed on the pathologic specimen of the thyroid gland of the same patient ( figures 1(a ) , 1(b ) , and 1(c ) ) . a large zt sometimes constitutes significant part of the thyroid lobe ( figure 1(d ) ) . after gentile lateral traction of inferior thyroid artery , rlns have been successfully identified in all cases . results of the relationship between the tubercle and the recurrent nerve are important observations of this study . the smaller zt was pointing like an arrow - head the neurovascular ( recurrent nerve and inferior artery ) crossing point in many patients . we observed common relationship between rln and zt in 76 ( 94% ) of 81 tubercles ; the nerve usually passes medial to the tubercle , by other words rln is placed between the tubercle and the trachea . the nerve was located posterior to zt ( figure 2 ) . on the other hand , the tubercle was placed between the nerve and the trachea , pushing the recurrent nerve laterally in 5 ( 6% ) instances . the thyroidal tissue was totally excised ( unilaterally or bilaterally ) including zt and pyramidal lobe when present without nerve injury in all patients . [ 1 , 10 ] . emile zuckerkandl has been reported in 1902  processus posterior glandulae thyroideae  [ 1 , 2 ] . the zt is posterior extension of the gland composed of thyroidal tissue . in case of goiter formation first surgical importance of zt emerges from indication of total resection of the gland that the completeness of thyroidectomy requires total removal of enlarged tubercle . completeness of resection requires an awareness of thyroid development including attention to pyramidal remnants , to abnormalities associated with zt . the resection of enlarged tubercle at posterior site of the thyroid requires delicate and careful dissection adjacent to the nerve . identification of zt and an understanding of the relationship between the zt and rln are essential for safety of thyroid operations [ 7 , 9 , 10 ] . although zt is classified into four grades according to size , this grading is mainly important for cadaveric anatomical studies . surgeons generally perform thyroid operations on voluminous goiter that when present larger tubercles are observed on surgical specimens . therefore , by surgical point of view an enlarged zt parallel to goiter formation merits more interest than smaller one . it makes surgical dissection challenging at posterior site of the lateral lobes around rln and inferior artery . when present , mobilization of a prominent zt has surgical importance by completeness of thyroidectomy and identification and isolation of the rln . the presence of larger tubercles in 66% of our patients confirms that it is a common anatomical part of the gland . many authors have recently reported the incidence of zt as more than 50% of their patients ; kaisha et al . 59% , hisham and lukman   55% , and gauger el al .   63% ( grade 3 as 45% ) . on the other hand , page et al . our results of the incidence of enlarged zt as 51% in excised lateral lobes indicate importance of the tubercle for completeness of thyroidectomy . [ 13 , 14 ] have reported an incidence of grade 2 and 3 tubercles as 64% and 65% in lateral lobes . yun et al .   have found grade 2 and 3 zt in 68% ( right side 72% and left side 64% ) of lateral lobes . bilateral occurrence of zt is a less common observation as 25% in our series of total thyroidectomy cases . we can comment that enlarged zt is a common anatomical structure situated at posterolateral site of thyroidal lobes of goiter cases . therefore , in the majority of patients the tubercle can affect completeness of thyroidectomy especially for less - experienced hands . some brief knowledge about embryogenesis of the thyroid gland may help understanding surgical importance of zt . the thyroid gland develops from two anlages ; the larger median anlage and paired smaller lateral anlages which become attached to the posterior surface of the thyroid . it is estimated that the lateral thyroid anlage contributes perhaps 1% to 30% to the thyroid weight . residual posterolateral projection from the lateral thyroid component is known as the zt . in the last 20 years , hemithyroidectomy and total thyroidectomy are the procedures of choice for the management of patients with goiter . in this period delbridge   has stated that the completeness of resection has been assured by moving from an anatomically based approach to an embryologically based approach . rln injury may be prevented by its full isolation based on intimate knowledge of the anatomy including all its variations . zt appears as an indicative arrow for the nerve and neurovascular crossing point in some patients . we can comment that after medial mobilization of the lobes , when present , zt may be used as a landmark facilitating identification of the nerve . many authors have previously stated that the zt is a reliable and constant anatomical landmark as an arrow pointing the rln [ 4 , 5 , 1214 ] . the site of greatest risk during thyroidectomy to the rln is in the last 2 - 3  cm extralaryngeal course of the nerve before its laryngeal entry above the trunk of the inferior thyroid artery . based on our findings zt pointing , like an arrow head , neurovascular crossing point promotes surgeon 's challenge to identify rln . on the other hand , mobilization of the tubercle medially allows easy identification of the nerve at this dangerous site . understanding the relationship between the nerve and the tubercle leads to perform safer thyroid surgery . the resection of zt for total thyroidectomy requires refined and meticulous dissection adjacent to the nerve . thyroidectomy technique is improved because of the constant relationship between these two structures at a level where the risk of injury is greatest . our findings in the great majority ( 94% ) of lateral lobes with documented larger zt confirm this statement . an enlarged tubercle usually covers a segment of the distal part of the nerve passing in the tracheo - esophageal groove . on the other hand , we also observed unusual position of zt and rln at both sides ; rlns are anterior ( or lateral ) to zt in 6% of occurrences . all thyroid surgeons must be aware of this uncommon variation in order to prevent injury to the nerve during total resection of the gland . hisham and lukman   have previously reported that in 6% of dissection , the rln was on the anterior surface of the tubercle . have also reported that in 93% of patients with enlarged zt , the rln lays medial to the tubercle , and the nerve was found lateral to it in the remaining 7% of their cases . the surgeon must be aware of the tubercle , and he must face the zt without fear but with care . identification of zt , an understanding of the relationship between the zt and rln , and isolation of the nerve before dissection of zt are essential for performing safer thyroid surgery .    in conclusion , zuckerkandl 's tubercle which is defined as posterior extension of lateral lobes of the thyroid gland , is a common anatomical structure found in the majority of cases . excision of the tubercle requires fine and meticulous dissection with great care because of close relationship between zt and rln . based on the occurrence of unusual variations , we propose to identify the rln before attempting dissection of adjacent structures . fine and delicate dissection with care around the zt is also mandatory after identification and isolation of the rln for preventing nerve injury .
background . variations of recurrent laryngeal nerve ( rln ) and zuckerkandl 's tubercle ( zt ) , which is posterior extension of lateral lobes , may affect safety of thyroidectomy . 
 methods . 
 total and hemithyroidectomy were surgical procedures in 60 and 40 patients , respectively . surgical anatomy was studied in 87 right and 73 left lobes . 
 presence of zt was noted and its incidence was determined . 
 rlns were identified and fully isolated . 
 relationship between zt and rln was established . 
 results . 
 zts were identified in 66 ( 66% ) patients and in 81 ( 51% ) lobes . 
 zt was present in 53 ( 61% ) right and in 28 ( 38% ) left lobes . 
 zts were bilateral in 15 ( 25% ) of 60 total thyroidectomy cases . 
 smaller tubercles show the neurovascular crossing point . 
 rln was posterior ( medial ) to zt in 76 ( 94% ) occurrences . 
 rln was laying on anterior surface of zt only in 5 ( 6% ) instances . 
 conclusions . 
 rln is unusually laying lateral to zt which is common structure in the thyroid . 
 lateral rln may be more vulnerable to injury . 
 total thyroidectomy requires dissection of zt adjacent to rln . 
 based on unusual relations and variations , rln should be fully isolated before excision of adjacent structures .