Morphological variations of the thyroid gland and its relationship to the recurrent laryngeal nerve: A cadaveric study

Abstract

The thyroid gland is prone to variations due to its embryological origin and descent. These variations can cause distortion of its morphology and have been associated with thyroid disorders. This study aimed to provide evidence-based data on the morphological variations of the thyroid gland. In this study, the morphological variations of the thyroid gland pertained to the presence or absence of pyramidal lobe (PL), levator glandulae thyroidae (LGT) and isthmus. The main objective of this study was to assess the morphological variations of the thyroid gland and its relationship to the recurrent laryngeal nerve in cadavers. This was a cross-sectional descriptive study, conducted at the Pathology Department of the University Teaching Hospitals (UTH) in Lusaka, Zambia. In the study there were 46 cadavers; 36 males and 10 females aged between 20-64. The study involved dissection and removal of the hyoid bone, larynx, trachea, oesophagus, and thyroid gland en bloc. The thyroid gland was observed for the presence of the PL and LGT, and absence of isthmus. If present, the length, width and height were measured using a Vernier caliper. Location of the isthmus as well as the relationship of the thyroid gland to the recurrent laryngeal nerves (RLNs) were also observed. The most common variation was presence of PL, 32.61% (36% of males and 20% of females). The most common origin of the PL was both the isthmus (40%) and left lobe (40%). Levator glandulae thyroideae were commonly attached to the hyoid bone (72.7%). Statistically significant differences (<0.0001) were found in the mean length of LGT between males and females. Thickness of the PL was more in females than males and this difference was significant (< 0.015). The majority of the isthmi were found located on tracheal rings 1 and 2 (32.6%). The RLNs were mostly medial to the thyroid gland; LRLN (93.5%) and RRLN (91.3%). There was a high incidence of RLNs traversing the larynx posterior to the cricothyroid joint, 89.1% of LRLN and 93.5% of the RRLN. Knowledge of these variations, their measurements and the relationship of the thyroid gland to the RLNs may be of help to surgeons to perform safe and effective thyroid surgeries with reduced complications.