|Year : 2018 | Volume
| Issue : 2 | Page : 91-95
Review of surgical anatomy of tubercle of Zuckerkandl and its importance in thyroid surgery
Department of Anatomy, Azeezia Institute of Medical Sciences, Kollam, Kerala, India
|Date of Web Publication||9-Apr-2018|
Department of Anatomy, Azeezia Institute of Medical Sciences, Kollam - 691 537, Kerala
Source of Support: None, Conflict of Interest: None
Background and Objectives: Tubercle of Zuckerkandl (TZ) is the posterior or posterolateral extension of thyroid gland. Recurrent laryngeal nerve (RLN) is related to TZ either on its posterior or posteromedial aspect in the deeper fascial plane. The objective of this review is to report separately the prevalence of TZ as noted by anatomists and surgeons. Materials and Methods: An extensive search for articles with TZ either in the title or keywords was done using PubMed, ScienceDirect, Google Scholar, SciELO, EMBASE, and Web of Science databases. The search terms were restricted to TZ, Zuckerkandl tubercle, posterolateral extension of thyroid, RLN, and thyroid surgeries. Results: Out of 39 records, 25 studies, reported total number of sides where TZ was studied with prevalence percentages (n = 4231 sides). This included 6 cadaveric studies and 19 surgical studies. Combined pooled prevalence of TZ was found to be 76.5%. Prevalence in cadaveric and surgical studies was 84% and 69%, respectively. Overall, 15 studies reports RLN is related to posterior or posteromedial to TZ. Conclusions: The prevalence of TZ is 76.5%. When present, it is a useful guide for locating, dissecting, and preserving RLN. Cadaveric studies report a higher prevalence of 84%, while surgical studies report an average of 69% TZ. Most surgical studies report higher right-sided prevalence.
Keywords: Recurrent laryngeal nerve, thyroid surgeries, tubercle of Zuckerkandl
|How to cite this article:|
Viveka S. Review of surgical anatomy of tubercle of Zuckerkandl and its importance in thyroid surgery. CHRISMED J Health Res 2018;5:91-5
|How to cite this URL:|
Viveka S. Review of surgical anatomy of tubercle of Zuckerkandl and its importance in thyroid surgery. CHRISMED J Health Res [serial online] 2018 [cited 2019 Mar 21];5:91-5. Available from: http://www.cjhr.org/text.asp?2018/5/2/91/229578
| Introduction|| |
Posterolateral extension of thyroid lobe is the tubercle of Zuckerkandl (TZ). This is named after eminent anatomist Emil Zuckerkandl (described it in 1902), who is known for his work on neural crest cells (in relation to aorta), temporal bone pneumatization, and fascial covering of kidney. However, Otto Madelung was the first one to describe the posterolateral extension of thyroid gland in 1867. Thyroid parenchyma condenses and forms a small outward posterolateral projection at the level of cricothyroid junction. This is referred as TZ [Figure 1]. While the endodermal outgrowth from the junction of anterior two-third and posterior one-third of tongue descends downward, forming thyroglossal duct, it later divides to the right and left lobes. Adding to these cells, the 4th pharyngeal cleft and ultimobranchial body also contribute to developing thyroid. Such fusion is said to form TZ. Microscopic analysis of component cells of TZ reveals that it has a higher concentration of C cells in addition to thyroid follicles., Superior parathyroid gland being relatively more constant in position is located posterior to TZ.
|Figure 1: Schematic diagram showing posterior extension of thyroid gland - tubercle of Zuckerkandl|
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Nerve injuries are most dreaded complications of thyroid surgeries. Anatomists and surgeons define, delineate, and dissect meticulously the related neck anatomy to denote the nerves in relation to thyroid. External branch of superior laryngeal nerve is related to the superior pole of thyroid gland. To avoid injury to this nerve, superior vascular pedicle of thyroid is ligated very close to the gland. Recurrent laryngeal nerve (RLN) is related to the inferior pole of thyroid gland. The capsular branches of inferior thyroid artery are ligated and transected. The main trunk of inferior thyroid artery is never ligated as it would lead to compromise of blood supply to parathyroid glands. The quality control of thyroidectomies and methods to minimize nerve injury advocates visual identification of the RLN, careful exposure, and preservation of RLN., During thyroidectomy surgeries, before the dorsal mobilization of thyroid lobe, inferior thyroid artery, and RLN are located distal to the artery at the esophagotracheal sulcus and RLN is traced till its entry into the larynx.
Even though the posterolateral projection of thyroid was described in the 18th century, Gilmour reported the relation of TZ with RLN in 1938. It has been underutilized anatomical landmark during thyroid surgeries until 1998 when Pelizzo et al. reported a constant relation of TZ with RLN. Pelizzo et al. have described TZ as an arrow pointing RLN. Since then, the prevalence, relation with RLN, and embryological basis of TZ are being evaluated with much vigor and clarity. Recently, there is surge in interest, both among surgeons and anatomists in identifying TZ and reporting its prevalence. Even though many studies have affirmatively concluded about this posterolateral extension of thyroid, we cannot exclude the possibility of thyroid gland (being soft tissue) occupying a gap at the entry point of RLN into the larynx. The depression created by the entry of RLN into the larynx may be occupied by the posterior or posterolateral extension of thyroid gland and appear as TZ. If such gap-filling posterior extension occurs, there could be differences in prevalence noted in studies carried out during thyroid surgeries and those done with cadaveric (fixed) specimens. Such pressure extension, if present, leads to overestimation of the prevalence of TZ in cadaveric studies. The objective of this review is to report separately the prevalence of TZ as noted by anatomists and surgeons. Studies focusing on differential reporting of fresh cadaveric prevalence and formalin fixed cadavers are also reported.
| Materials and Methods|| |
Study source and duration
During October 2017, an extensive search for articles with TZ either in title or keywords was done using PubMed, ScienceDirect, Google Scholar, SciELO, EMBASE, and Web of Science databases.
To include all relevant studies, a comprehensive search for all articles related to thyroid surgeries was carried out and all articles with reference to TZ were included. The search terms were restricted to TZ, Zuckerkandl tubercle, posterolateral extension of thyroid, RLN, and thyroid surgeries. Only articles in English (both originals and translations) were included in the review.
All articles irrespective of the date of publication were included in the review. Original research and case reports were included in this study.
Data collection and data items
Studies were categorized into two types, surgical studies and cadaveric studies. Data regarding the total number of cases (sides) studied, percentage of cases where TZ was noted, and any special comments either in results section or conclusion section are noted.
Synthesis of results
As this review is about the prevalence of TZ and relation to RLN, only the reported prevalence percentages were taken from the individual studies along with the total number of sides studied. Average of reported mean represented the pooled prevalence of TZ.
| Results|| |
A total of 1550 records were found with keywords used for searching. Out of which, 1511 records are not directly related to TZ and were excluded from the study. A total of 39 records analyzed. Out of which 14 studies were not direct study of TZ in relation to thyroid surgeries and RLN. They were excluded from the study. One review article was excluded from data collection.
Characteristics of included studies
Out of 39 records, 25 studies, reported total number of sides where TZ was studied with prevalence percentages. This included 6 cadaveric studies and 19 surgical studies [Table 1].
Pooled prevalence of tubercle of Zuckerkandl
A total of 514 sides were included from 6 cadaveric studies. The prevalence of TZ ranges from 59% to 100%. Average prevalence is 84% (432 sides). From 19 surgical studies, a total of 3777 sides of thyroid were examined during thyroid surgeries. The prevalence of TZ was 69%. Four studies particularly mention that TZ prevalence was more on the right side.,,, Page et al. have found TZ in only 7% of the sides out of 79 sides studied and all were right sided. Combined pooled prevalence of TZ was 76.5% from 4271 thyroid lobes.
Right sidedness of tubercle of Zuckerkandl
Sheahan and Murphy, Page et al., Yun et al., Mehanna et al., Irawati et al., Gurleyik and Gurleyik, Gil-Carcedo et al., Mehmood et al., and Chintamani  reported that prevalence of TZ is more on the right side. Overall prevalence on the right side is 65% and on the left side is 52%.
Recurrent laryngeal nerve and tubercle of Zuckerkandl
Overall, 15 studies reports RLN is related to posterior or posteromedial to TZ. Gauger  and Mehmood et al. reported RLN is medial to TZ. However, Gurleyik and Gurleyik noted cases where RLN was unusually on the lateral side of TZ.
| Discussion|| |
Intraoperative identification and dissection of thyroid gland capsule are very important in the preservation of RLN. RLN is related just posterior to TZ, and this is the crucial site of RLN injury. Just posterior to TZ, RLN can be found buried deep in the fascial planes of ligament of Berry.,,,, TZ and inferior thyroid artery is located in a superficial plane. RLN enters larynx behind TZ. Therefore, knowledge about RLN anatomy, branching pattern and variations is very essential. Even though, during thyroid surgeries, it is essential to identify, dissect, and preserve the RLN, 0.1%–0.9% results in iatrogenic injury to nerve. Because of higher anatomical variations including extralaryngeal branching, non-RLN and interlacing of inferior thyroid artery and RLN, nerve visualization is essential to preserve it.,,, RLN is particularly injured in cases where there is extra-laryngeal bifurcation. Gurleyik et al. have reported a rare case where non-RLN pointed by a TZ.
Since the prevalence of TZ is bilaterally asymmetrical (with more prevalence on the right), inquisitive enquiry into the concept of posterior extension of thyroid gland under differential pressure effect prevails. Even though the differential formation of thyroid primordia on the right and left side was suggested as reason for higher right-sided prevalence, the definitive evidence of such developmental process influencing thyroid formation is lacking. It may be viewed as differential pressure effects on right side producing a posterior or posterolateral extension of thyroid gland. Since most of the studies reports unilobed TZ, subtle developmental influence or pressure effect may equally be responsible for the formation of TZ. Dhalapathy Sadacharan has reported a giant TZ extending retrosternally. Such extension is more common with lateral aberrant thyroid. Such report (though isolated) strengthens the uncertainty in the nomenclature of extensions of thyroid gland.
Anatomists' perspective of tubercle of Zuckerkandl
Reports from cadaveric studies have stated the prevalence, location, grading, and distance between TZ and RLN. Pelizzo et al. have classified the TZ into 4 Grades according to the size. Grade 0 – unrecognizable, Grade I – lateral edge of thyroid lobe thickening, Grade II – postero-lateral projection of thyroid gland of <1 cm, and Grade III – posterolateral projection >1 cm. Won et al. have studied the TZ in fresh and fixed cadavers and found no difference in morphology, prevalence, and location. This proves that TZ is not mere gap-filling posterior extension of thyroid gland. Similarly, no study considered under this review mention about any other projections from thyroid gland. Therefore, it is concluded from this extensive surgical and cadaveric review, that TZ is a fixed and most often constant anatomical posterior or posterolateral projection of thyroid gland.
Limitations of the review
Only 39 records with TZ details could be retrieved from the search engines. However, many of the articles relating to TZ published in recent journals (not indexed in the above-mentioned databases) could not be traced.
| Conclusions|| |
The prevalence of TZ is 76.5%. When present it is a useful guide for locating, dissecting, and preserving RLN. The prevalence of TZ in cadaveric studies was 84% and from surgical studies was 69%. There is a higher prevalence of TZ in cadaveric studies. Most surgical studies report higher right-sided prevalence.
The author would like to thank the Department of anatomy, Azeezia Institute of Medical Sciences.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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