Anat Sci Int (2012) 87:45–49 DOI 10.1007/s12565-011-0115-9
ORIGINAL ARTICLE
Variations in the anatomy of the thyroid gland: clinical implications of a cadaver study Prakash • Thimmiah Rajini • Archana Ramachandran • Geethanjali Basavraj Savalgi • Sivacharan Panchagnula Venkata Varsha Mokhasi
•
Received: 12 May 2011 / Accepted: 31 August 2011 / Published online: 29 September 2011 Ó Japanese Association of Anatomists 2011
Abstract Surgical removal of the thyroid gland is associated with risk of damage to the parathyroid glands, external branch of superior laryngeal nerves, inferior laryngeal nerves, and haematoma due to vascular damage and the chance of residual thyroid tissue being left in case of cancer and Graves’ disease. The present study was designed to report the prevalence of anatomical variations and developmental anomalies of the thyroid gland that will hopefully help to minimise the aforementioned complications related to thyroid surgery. A total of 52 male and 18 female properly embalmed cadavers were dissected. The thyroid gland was examined for the presence of the pyramidal lobe, levator glandulae thyroideae and partial or complete absence of isthmus. Length, greatest transverse and anteroposterior extent of both the right and left lobe of the gland was recorded. A pyramidal lobe was present in 43.9% male and 22.2% female cadavers and was more prevalent on the left side of the median plane. Levator glandulae thyroideae was present in 34.6% male and 27.8% female cadavers. Isthmus was absent in 9.6% male and 5.6% female cadavers. The average length, greatest transverse and anteroposterior extent of right lobe was 4.43, 2.54 and 1.69 cm, respectively, whereas for the left lobe it was 4.21, 2.63 and 1.7 cm, respectively. The nature of the specimens studied, and the region where the study is carried out, affect the different goitre zones, age, sex, and race of population studied, all of which can contribute to the
Prakash (&) T. Rajini A. Ramachandran G. B. Savalgi S. P. Venkata V. Mokhasi Department of Anatomy, Vydehi Institute of Medical Sciences and Research Centre, 82 EPIP Area, Whitefield, Bangalore 560066, Karnataka, India e-mail:
[email protected]
anatomical variations of the thyroid gland found in different reports by various authors. Keywords Anatomy Cadaver Development Thyroid Gland Dissection
Introduction Thyroid gland surgery is one of the more common surgical interventions in the head and neck region. Accurate knowledge of anatomical variations of the thyroid gland is important as it is relevant in different types of thyroidectomy and tracheostomy. Risk of damage to the parathyroid glands, external branch of the superior laryngeal nerves, inferior laryngeal nerves and haematoma due to vascular damage can be minimised by keeping in mind all the anatomical variations and developmental anomalies of the thyroid gland. Bliss et al. (2000) concluded that one of the cornerstones of safe and effective thyroid surgery is to understand and remember the surgical anatomy of the thyroid gland and its possible variations. Ranade et al. (2008) reported various developmental anomalies of the thyroid gland and suggested that it is of paramount importance to accurate clinical interpretation that such variations are not overlooked in differential diagnosis. Various authors have time and again reported their observations regarding the anatomy of the thyroid gland through their study on cadavers, operated patients and different imaging techniques [1–26]. Geraci et al. (2008) studied the intraoperative incidence of the pyramidal lobe and reported that only about 50% were identified preoperatively with Tc-99m pertechnetate scintigraphy (8% false positive) or ultrasonography (4% false positive). Preoperative diagnoses on scintigraphic images are not reliable as the frequency of
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pyramidal lobe presence could be a source of pitfalls in thyroidectomy (Braun et al. 2007). Cadavers are still the best means to study all the domains of anatomy. Hence, the present cadaver study was undertaken to report the prevalence of anatomical variations and developmental anomalies of the thyroid gland that will hopefully help to minimise the aforementioned complications related to thyroid surgery.
Materials and methods Seventy properly embalmed and formalin fixed cadavers were selected for the present study. The anatomy of the thyroid gland in cadavers remains intact and is not affected after embalming with formalin. A total of 52 male and 18 female cadavers with an age range between 20 and 70 years were dissected in the head and neck region. Blocks dissected from cadavers was used as specimens. Healthy specimens free from thyroid disease were selected for the present study. Dissection started with skin incision followed by removal of the infrahyoid muscles to expose the thyroid gland enclosed with false and true capsules. The thyroid gland was examined for presence of anatomical variations and developmental anomalies like agenesis of the thyroid gland, partial or complete absence of isthmus, accessory thyroid tissue, ectopic thyroid tissue, pyramidal lobe, levator glandulae thyroideae. The variations were classified broadly into four categories (no pyramidal lobe, pyramidal lobe, levator glandulae thyroideae and absence of isthmus). The pyramidal lobe was formed of glandular tissue whereas the levator glandulae thyroideae contained muscle and fibrous tissues. Several parameters, including the length, greatest transverse and anteroposterior extent of both the right and left lobe of gland, were recorded.
Results The following gross observations were recorded. Pyramidal lobe was present in 21 out of 52 (43.9%) male cadavers and in 4 out of 18 (22.2%) female cadavers (Table 1; Figs. 1, 2). Pyramidal lobe was more prevalent on the left side of the median plane (Figs. 1, 2). The Zuckerkandl part of the thyroid gland was not observed in the lateral aspect of the gland. Levator glandulae thyroideae was present in 18 out of 52 (34.6%) male cadavers and 5 of 18 (27.8%) female cadavers (Table 1; Figs. 3, 4, 5). Absence of the isthmus was apparent in 5 out of 52 (9.6%) male cadavers and 1 out of 18 (5.6%) female cadavers (Table 1; Figs. 5, 6). The average length of the right lobe was 4.43 cm and that of the left lobe was 4.21 cm. The average greatest
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transverse and anteroposterior extent of the right lobe was 2.54 and 1.69 cm, respectively. On the other hand, the greatest transverse and anteroposterior extent of left lobe was 2.63 and 1.7 cm, respectively, on average.
Discussion Approximately 70% of the congenital lesions in the neck region result from variable persistence of the thyroglossal duct (Ignjatovic´ 2000). An embryological basis should be considered for all such developmental anomalies. Of all the endocrine glands, thyroid development starts at earliest during embryonic development of human beings (Devi et al. 2009). Any deviation from the normal development of the thyroid gland, including descent of median thyroid diverticulum from foramen caecum at the tongue to its adult position between fifth cervical and first thoracic vertebra and partial persistence of the thyroglossal duct or tract, result in formation of various structures such as a pyramidal lobe, levator glandulae thyroideae, agenesis of thyroid gland, partial or complete absence of isthmus, accessory thyroid tissue and ectopic thyroid tissue. Knowledge of the variant anatomy of the thyroid gland, including its vasculature and innervations, is very important in the surgical treatment of different tumours of the thyroid gland and thyrotoxicosis. Total, subtotal and partial thyroidectomy performed for the treatment of different stages of carcinoma thyroid require precise and accurate knowledge of the variations associated with the thyroid gland. During thyroidectomy, the pyramidal lobe—also called Lalouette’s lobe—should be looked for and removed as failure in its identification can result in incomplete resection of the thyroid gland (Geraci et al. 2008). All thyroid diseases are described in the pyramidal lobe, which is formed from normal thyroid tissue (Ignjatovic´ 2000). Residual thyroid tissue in the pyramidal lobe can lead to serious complications in diseases like cancer and Graves’ disease, where complete removal of the thyroid gland is indicated (Wahl et al. 1997). Dysorganogenesis related to developmental anomalies of the thyroid gland can result in agenesis of isthmus and the presence of ectopic thyroid tissue (Pastor et al. 2008; Devi et al. 2009). In most tetrapod species, there are two paired thyroid glands—that is, the right and left lobes are not joined together (Romer and Parsons 1977). The thyroid glands of birds, amphibians and many mammals are paired organs lacking an isthmus (Breit et al. 1998; Devi et al. 2009). The thyroid glands are normally in position without an isthmus in rhesus monkeys (Macacus rhesus) (Pastor et al. 2008; Devi et al. 2009). A comparative study anatomy suggests that the isthmus connecting the two lobes appeared during the course of evolution. Ha´jovska´ (2002) studied the embryonic thyroid gland in 18 fetuses of
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Table 1 Comparison of the results of the present study with similar reports in the literature Sample no.
Authors (year of study)
Nature of specimens studied
Prevalence of pyramidal lobe (%)
Prevalence of levator glandulae thyroideae (%)
Prevalence of partial or complete absence of isthmus (%)
Prevalence of accessory thyroid gland (%)
1.
Ranade et al. (2008)
Adult cadaver
Male 58; female 0
Male 56.8; female 11.8
Male 30.9; female 47.1
Male 1.1; female 0
6.9
1.7
2.
Cicekcibasi et al. (2007)
Aborted fetuses
18.3
3.
Braun et al. (2007)
Adult cadaver
55
4.
Sturniolo et al. (2008)
Operated patients
25.5
5.
Sultana et al. (2008)
Adult cadaver
Male 52.1; female 41.7
6. 7.
Geraci et al. (2008) Joshi et al. (2010)
Operated patients Adult cadaver
12 37.8
8.
Sultana et al. (2009)
Adult cadaver
9.
Present study (2010)
Adult cadaver
30
16.7
43.3 Male 43.9; female 22.2
Fig. 1 Presence of a centrally placed pyramidal lobe related to the isthmus of the thyroid gland. The right lobe of the thyroid gland is much longer compared to the left lobe. Asterisk Pyramidal lobe, double asterisk right lobe, SMG submandibular gland, HB hyoid bone, VN vagus nerve, ESL external branch of superior laryngeal nerve, STV superior thyroid vessels, TC thyroid cartilage, CT cricothyroid muscle, CCA common carotid artery, IJV internal jugular vein, TG thyroid gland, SH sternohyoid muscle, ST sternothyroid muscle
sheep of the Slovac merino breed by light microscopy and found that, in the majority (10 out of 18) of sheep fetuses, the thyroid gland consists of two separate lobes and their structure remained the same from day 32 to day 36 of development. Ontogeny repeats phylogeny. Formation of an isthmus is an advanced stage in embryogenesis, and developmental arrest before this stage can result in absence of isthmus of the thyroid gland. Table 1 compares the results of the present study with previous reports on thyroid gland anatomy. In our study, the pyramidal lobe was present in 43.9% male cadavers and in 22.2% female cadavers—a greater prevalence than that reported by some authors (Cicekcibasi et al. 2007;
Male 34.6; female 27.8
Male 9.6; female 5.6
0
Fig. 2 Presence of pyramidal lobe on left side of median plane related to the left lobe of the thyroid gland. Asterisk Pyramidal lobe, SMG submandibular gland, HB hyoid bone, OH omohyoid muscle, TC thyroid cartilage, CT cricothyroid muscle, VN vagus nerve, IJV internal jugular vein, CCA common carotid artery, CC cricoid cartilage, TG thyroid gland, SC sternocleidomastoid muscle, SH sternohyoid muscle, ST sternothyroid muscle, TR tracheal ring
Sturniolo et al. 2008; Geraci et al. 2008; Joshi et al. 2010) but lower prevalence than that reported by other authors (Ranade et al. 2008; Braun et al. 2007; Sultana et al. 2008). In the present work, the prevalence of levator glandulae thyroideae was 34.6% in male and 27.8% in female cadavers, which again was greater than reported by Joshi et al. (2010) and less than reported by others (Ranade et al. 2008; Sultana et al. 2009). Isthmus was absent in 9.6% male and 5.6% female cadavers in our study, which was higher in prevalence than work reported by Braun et al. (2007) and lower in prevalence than studies reported by Ranade et al. (2008) and Joshi et al. (2010). The nature of the specimens studied, and the region where the study is carried out, affect the different goitre zones, age, sex, and race of population studied, all of which can contribute to
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Fig. 3 Presence of levator glandulae thyroideae on left side of median plane extending to the hyoid bone. Asterisk Levator glandulae thyroideae, HB hyoid bone, SMG submandibular gland, OH omohyoid muscle, SH sternohyoid muscle, TC thyroid cartilage, CT cricothyroid muscle, CC cricoid cartilage, VN vagus nerve, IJV internal jugular vein, CCA common carotid artery, SYC sympathetic chain, TG thyroid gland, SC sternocleidomastoid muscle, ST sternothyroid muscle, TR tracheal ring
Fig. 4 Presence of centrally placed levator glandulae thyroideae extending to the thyroid cartilage. Asterisk Levator glandulae thyroideae, SMG submandibular gland, OH omohyoid muscle, HB hyoid bone, SC sternocleidomastoid muscle, TC thyroid cartilage, CT cricothyroid muscle, VN vagus nerve, CCA common carotid artery, IJV internal jugular vein, TG thyroid gland, SH sternohyoid muscle, ST sternothyroid muscle
the anatomical variations of the thyroid gland found in different reports by various authors. Conflict of interest
None.
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Fig. 5 Presence of the levator glandulae thyroideae centrally placed and extending to the thyroid cartilage. The isthmus of the thyroid gland is totally absent. Asterisk Levator glandulae thyroideae, double asterisk total absence of the isthmus, SMG submandibular gland, HB hyoid bone, SH sternohyoid muscle, ST sternothyroid muscle, TC thyroid cartilage, CT cricothyroid muscle, VN vagus nerve, CCA common carotid artery, TG thyroid gland, IJV internal jugular vein, TR tracheal ring
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