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A cadaveric study in the coastal population of Andhra Pradesh
Introduction: Thyroid gland is a butterfly shaped endocrine gland, highly vascular, situated infront of the lower part of the neck. Developmental anomalies consist of a diversity of morphological variations of the thyroid gland like hypoplasia, ectopia, hemiagenesis and agenesis. Aims: To study the anatomical differences of thyroid gland and their incidences. Study might helpful for surgeons to know the anatomical variations of the gland and their incidence. So as to plan for proper surgical procedures in thyroid diseases.
Materials & Methods: The present study was done in 50 cadavers (39 male & 11 female) in the coastal region of A.P. Results: There was a variable lobular pattern in 21(42%) cadavers.
Out of these, isthmus was absent in 8 male (20.5%), and 3 female (27.3%) cadavers. Relation of tracheal rings to the isthmus was noted. Pyramidal lobe was present in 17 male (43.5%) and 2 female (18.1%) cadavers. Pyramidal lobe is frequently arising from the Isthmus. Levator glandulae thyroideae (LGT) was present in 16 (41%) male and 2(18.
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1%) female cadavers. The average height and thickness of right lobe is 4.3cm and 1.15 cm respectively, left lobe is 4.2cm and 1.15cm respectively. Conclusion: Morphological variance of the thyroid gland are very common. Hence knowledge of incidence of various congenital anomalies of the thyroid gland is of at most importance to the surgeons.
There are many endocrine glands that maintain homeostasis, but the thyroid is considered as one of the most important endocrine gland, because its secretions will help in the growth differentiation, organisation and maturation of the cells in the body.
Thyroid gland is a bilobed (right and left) connected by a narrow median isthmus. Pyramidal lobe (PL) is a conical part of the gland which extends upwards towards the hyoid bone from the isthmus or either of the lobes. The Levator glandulae thyroideae (a fibrous or fibromuscular band) descends from the hyoid bone or thyroid cartilage to the pyramidal lobe.
Thyroid gland develops mainly from the thyroglossal duct which starts as a diverticulam, immediately behind the tuberculum impar. The diverticulam grows down into the neck and bifurcates to form the two lateral lobes of the thyroid gland. Developing thyroid gland comes in contact with the caudal pharyngeal complex, from which parafollicular cells develop. Developmental anomalies cause various morphological abnormalities in thyroid gland. Thyroid diseases are well documented and require medical and surgical interventions. Clinicians should know about these variations prior to surgical procedures to plan for proper surgeries for better out come. Therefore knowledge of the various congenital anomalies and their incidences is of utmost importance to the clinicians.
The present work was done on 50 well embalmed cadavers in the department of Anatomy, Narayana medical college, Nellore over a period of 3 years, with ages ranging from 40 to 75 years. Among those 50 cadavers, 39 were male and 11 were female.
A vertical midline incision was given from symphysis menti to the jugular notch. Skin and platisma were reflected laterally, deep fascia was removed to expose the infrahyoid muscles. Strapmuscles of the neck were reflected laterally, remaing deep fascia and fat surround the gland was removed.
The thyroid gland was observed for:
A total of 50 cadavers were observed, variations are there in 21(42%) cadavers, remaining 29 cadavers were normal. In 11 cadavers isthmus was absent, among these, 8(20.5%) were male cadavers, 3(27.3%) were female cadavers. Posterior relations of the isthmus was observed and summarised in Table: 1. Mean height of the isthmus was 1.3 cm.
Related structure Frequency Percentage
Pyramidal lobe was found in 19(38%) cadavers, among these 17(43.5%) were male and 2(18%) were female cadavers. There is a case with two pyramidal lobes attached to single levator glandulae thyroideae (Fig 3). Pyramidal lobe was frequently arising from Isthmus. Levator glandulae thyroidea was present in 18(36%) cases. It was extended from the apical end of the pyramidal lobe to the hyoid bone and thyroid cartilage. Outlined all these details in table: 2
Table: 2
Table: 3. Extension of the lobes of the thyroid gland
SUPERIOR EXTENSION LIMIT IN RELATION TO THE MIDPOINT OF THE LAMINA OF THE THYROID CARTILAGE INFERIOR EXTENSION LIMIT IN RELATION TO THE TRACHEAL RING
RIGHT LOBE LEFT LOBE RIGHT LOBE LEFT LOBE
AT BELOW ABOVE AT BELOW ABOVE 5TH 6TH 5TH 6TH
The mean height and thickness of right lobe is 4.3cm and 1.15 cm and left lobe is 4.2cm and 1.15cm respectively. We summarised these details in Table: 4
Table: 4: mean height and thickness of lobes.
The isthmus was found to be absent in 22% (11) of cases. Harjeet et al. [1] described that the two lobes were separated in 7.9% of thyroids. Marshall. C.F. [2] described it as being absent in 10% of cases. Oya [3] observed its absence in 4% of the cases. Most of the anatomical text described the isthmus as being related to 2nd and 3rd tracheal rings, confirmed with 5 cases. In 4 cases, it was related to 1st and 2nd tracheal rings, in 10 cases to the 1st, 2nd and 3rd tracheal rings. In 15 cases it was related to 2nd, 3rd and 4th tracheal rings. In 5 cases it was related to 3rd and 4th tracheal rings. S D Joshi et al [4] found it related to 2nd and 3rd tracheal rings in 19 cases, 1st and 2nd rings in 14 cases, and 1st, 2nd and 3rd tracheal rings in 12 cases.
Pyramidal lobe was present in 38% of cases and maximum number of pyramidal lobes was attached to the isthmus (47%), as compared to the right lobe or the left lobe. In 11.8% and 41.2% of cases, it was attached to the right and left lobes respectively. In a study done by S D Joshi et al [4] PL was present in 37.77%. Marshall [2] described the presence of PL in 43% of cases. Harjeet et al. [1] observed it in 28.9% of specimens. Siraj et al. [5] visualized PL in 41% of patients and they found a greater incidence among females. The presence of two pyramidal lobes attached by a single LGT has been described by some Harjeet et al [1], Marshall C F [2], Oya S A [3] and Joshi S D [4]. In presence study, this was seen in 1 case only. This rare anomaly of double pyramidal process is generally explained by assuming a high bifurcation of the thyroid angle, the growing thyroglossal duct divides at its apex, and each branch give rise to a lobe of the gland Sgalitzer K E [6].
LGT was seen in 18(36%) specimens, which was attached to the hyoid bone in 10(55.6%) cases, upper border of the thyroid cartilage 4(22.2%), and lower border of the thyroid cartilage 4 (22.2%). According to Joshi S D et al [4] they found LGT in 27 (30%) specimens, which was attached to the hyoid in 18 (66.66%), the upper border of thyroid cartilage in 4 (14.81%), and the lower border of the thyroid cartilage in 5 (18.51%) cases. Marshall [2] found LGT attached to the hyoid bone in 17 (28.3%) cases, and in 9 cases it is combined with the fascia covering the thyroid cartilage. Faysal et al. [7] observed an unusual case in which LGT extended from the apex of the mastoid process.
A number of variances in the shape and size of the gland were observed in thyroid studies. The mean length of the lateral lobes is described as 5 cm in the most of the Anatomical texts Duplessies D J [8], Standring S [9], Wood J F [10], Holinshed [11] and Harjeet et al. [1], described it as 4.04 cm for the right lobe and 3.82 cm for the left lobe in the Northwest Indians. S D Joshi et al. [4] conducted a study on the mean length of the right lobe was 4.32 cm and the left lobe was 4.22 cm. The left lobe was comparatively smaller than the right lobe. In the present study, the mean length of right lobe was 4.3 cm and left lobe was 4.2 cm. In India, as the stature of individual is comparatively shorter than that of westerners, this might account for the shortness of lateral lobes.
42% of cases show morphological variations. Good knowledge about these variations is help full for the surgeons to perform successfull thyroid surgeries and to perform proper thyroidectomies in emergencies.
Anomalous development of Thyroid gland. (2019, Nov 15). Retrieved from https://studymoose.com/anomalous-development-of-thyroid-gland-essay
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