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Ultrasound Evaluation of Normal Thyroid Size

Journal of College of Medical Sciences-Nepal, Vol-18, No 4, Oct-Dec 2022
ISSN: 2091-0657 (Print); 2091-0673 (Online) Open Access 

DOI: 10.3126/jcmsn.v18i4.50275

Prabhat Basnet,1 Ashutosh Kumar Singh,2 Hari Prasad Upadhyay,3 Rajib Chaulagain4

1Department of Radiology, College of Medical Sciences, Bharatpur, Nepal, 2Department of Oral and Maxillofacial 
Surgery, Institute of Medicine, Kathmandu, Nepal, 3Department of Statistics, Birendra Multiple Campus, Chitwan, Nepal, 
4Department of Oral Pathology, Chitwan Medical College, Chitwan, Nepal.

Original Research Article

Correspondence: Dr. Prabhat Basnet, Department of Radiology, College of Medical Sciences, Bharatpur, Chitwan, Nepal. 
Email: pbasnet99@gmail.com. Phone: +977-9848023405.

ABSTRACT

Introduction

Normal thyroid size determination is very important for the accurate diagnosis of various 
thyroid disease. There are different thyroid pathologies which lead to increase in size of the 
thyroid gland, therefore it is essential to know the accurate dimension of the thyroid gland. 
This study was aimed to evaluate the normal range of thyroid gland dimensions.

Methods

The study was a descriptive cross-sectional study conducted on 115 patients, in Department 
of Radiology and Imaging, College of medical sciences, Bharatpur, Nepal. All ultrasound 
examinations were performed using Toshiba Aplio 500 superficial probe. The data was 
analyzed using Statistical Package for the Social Sciences (SPSS) version 16 (SPSS, Inc., an IBM 
Company, Chicago, IL). Descriptive statistics was used to analyze the data. 

Results

Among the 115 patients who participated in the study, 24 (20.9%) were male and 91 (79.1%) 
were female. The mean length of the right lobe was more (3.67±0.338 mm) than in the left 
lobe (3.45±.423 mm). The overall mean volume of thyroid gland was 6.71±2.05 ml. The mean 
volume of thyroid gland in males was 7.91±2.91 ml and in females was 6.40±1.63 ml.

Conclusions 

The present study estimated the normal dimension of thyroid gland. The normal dimension 
of thyroid gland volume was found to be more in male than in female. The mean total volume 
was found to be similar to the earlier published study from Nepal. 

Keywords: measurement; thyroid gland; ultrasound; volume.



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INTRODUCTION 

The thyroid gland is an endocrine gland located 
within the lower neck, draped anteriorly around 
the trachea. The two thyroid gland lobes, right 
and left lobes are connected together by a thin 
structure known as isthmus. The major role of 
thyroid gland is production, storage and release 
of thyroid hormones which are very vital in 
development and growth of humans.1-3

The thyroid gland’s shape, size and volume 
varies remarkably among individuals. Many 
physiological as well as pathological factors 
affect the thyroid gland dimensions. Studies 
have reported that thyroid glands are affected 
by age, gender and race.3,4 Spatiotemporal 
variation in the size and volume of thyroid 
gland have also been reported. Studies have 
shown it to be larger and heavier in females.5 
In pathological conditions such as goiter, 
thyroiditis, the alterations in dimensions 
of thyroid gland have been reported.6 The 
standard size, shape and weight of thyroid 
gland and associated variations is necessary for 
the head neck surgeons. Often the estimation 
of thyroid volume is helpful in monitoring 
the efficacy of medicine in goiter, thyroiditis 
and thyrotoxicosis. Moreover, the baseline 
dimensions are important for personnel 
exposed to radiations in order to provide the 
protection against the radiation hazards.1,6,7 

There is paucity of literatures determining the 
normal thyroid gland dimensions in Nepalese. 
Till date published literatures have determined 
the volume of thyroid gland6 and the thickness 
of thyroid isthmus among Nepalese8, there is 
no consensus on the length, breath and width 
of the thyroid gland among Nepalese and no 
studies have been reported from Chitwan. This 
study was aimed to determine the dimensions of 
thyroid gland by ultrasound.

METHODS

This was a hospital-based descriptive cross-
sectional study done in the Department of 
Radiology and Imaging of College of Medical 
Sciences, Bharatpur, Chitwan, for the period of 
three months (March, 2021 to May 2021). In this 
study using a convenience sampling method, 
altogether 115 patients were included. Ethical 
approval was obtained from Ethical Committee 
of College of Medical Sciences, Bharatpur, Nepal 
(COMSTH-IRC/2021-54). The objectives of the 
study and the procedure was well explained to 
the patients and written consent was obtained 
from the patients who participated in the study. 

The patients who were referred to the department 
for ultrasonography examination for reasons 
other than thyroid ultrasound scan and who 
consented to participate in the study were 
included in the study while female patients who 
were during menstruation, pregnancy or who 
have delivered within the last twelve months 
were excluded. Patients with swelling in the 
anterior region of the neck and clinical evidence 
of thyroid disease and those who had history of 
previous thyroid surgery were also excluded.

A single consultant radiologist performed the 
thyroid measurement, with an ultrasound 
machine, Aplio 500 Toshiba Machine with 
superficial probe of frequency 7-10MHZ. Before 
doing ultrasound, the patients were instructed 
to remove jewelry and tie towel across the 
chest. Then they were asked to lie in the supine 
position and a pillow was placed under the 
patient’s shoulder. This was done to aid in 
the extension of the neck. A coupling gel was 
applied over the anterior region of the neck and 
the transducer was placed over the thyroid gland 
region. The images were taken in transverse 
and longitudinal planes. The measurements of 
craniocaudal (L) and sagittal (D) dimensions 
were carried out on the longitudinal image while 

Basnet et al. Ultrasound Evaluation of Normal Thyroid Size.



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Basnet et al. Ultrasound Evaluation of Normal Thyroid Size.

the mediolateral diameter (W) was obtained 
from the transverse image. The measurement 
of right and left lobes was taken and analyzed 
separately. All measurements were carried 
out by single radiography consultant to avoid 
individual variation. 

The thyroid gland volume was calculated using 
the rotation ellipsoid method:

Volume = L × D × W × 0.52 (correction factor)

Where: l  = craniocaudal dimension 

W  = mediolateral dimension 

D  = sagittal dimension

The isthmus volume was calculated as:

Volume of isthmus = L × D × W × 0.479.

In addition, the volume of the right and left lobes 
was summed to obtain the total thyroid volume. 
The isthmus was not included in the sum. 

Statistical analyses were performed using 
Statistical Package for the Social Sciences 
(SPSS) version 16 (SPSS, Inc., an IBM Company, 
Chicago, IL). Descriptive statistics was used to 
analyze the data and the results was presented 
using frequency, percentage, mean, and standard 
deviation (SD). The results were presented in 
form of tables.

RESULTS 

Total 115 patients were enrolled in our study. 
Male patients were 24 (20.9%) and female 
patients were 91 (79.1%) (Table 1). 

Table 1. Characteristics of participants.

Variables Frequency (%)

Mean Age (years) ± SD 30.57±11.611

Gender
Male 24 (20.9)

Female 91 (79.1)

Table 2 showed the descriptive statistics of 
length, breadth, depth and volume of each lobe 
and isthmus. Mean length of thyroid lobe was 
higher in right lobe (3.67±0.338 mm) than in the 

left lobe (3.45±.423 mm) while the breadth was 
slightly higher in left lobe (1.52±0.224 mm). The 
mean volume of right lobe was higher (3.42±1.197 
ml).

Table 2. Dimensions and volume of right lobe, left 
lobe and isthmus.

 Variables
Right lobe
Mean ± SD

Left lobe
Mean ± SD

Isthmus
Mean ± SD

Length (cm) 3.67±0.338 3.45±.423 1.45±0.403

Breadth (cm) 1.50±0.256 1.52±0.224 0.29±0.090

Depth (cm) 1.16±0.200 1.17±0.192 0.25±0.084

Volume (ml) 3.42±1.197 3.30±1.065 0.06±0.063

The overall mean volume of thyroid gland 
was 6.71±2.05 ml. The mean volume of thyroid 
gland for both lobes in males and females were 
7.91±2.91 ml and 6.40±1.63 ml respectively (Table 
3).

Table 3. Total volume of thyroid gland.

Volume (ml) Mean ± SD

Male (ml) 7.91±2.91

Female (ml) 6.40±1.63

Total volume (ml) 6.71±2.05

DISCUSSION 

The thyroid gland, a vital endocrine gland, 
plays a critical role in regulating metabolic 
functions including heart rate and cardiac 
output, lipid metabolism, heat regulation, and 
skeletal growth. It is due to the release of thyroid 
hormones triiodothyronine and thyroxine (T3 
and T4). Apart from this thyroid gland also 
consists of parafollicular cells that synthesize 
calcitonin.9 

The thyroid gland examination is a routine 
clinical examination done. This may be due 
to the increase in the prevalence of thyroid 
disorders. The thyroid disorders are more 
common in females than in males.10 It is said that 
the thyroid nodules often missed do not show 
obvious symptoms. Thus, careful preoperative 



JCMS | Vol-18 | No 4 | Oct-Dec 2022318

assessment is necessary for diagnosis and 
treatment planning.1,10,11 In addition to this, 
studies have also shown morphometric 
variations of thyroid gland. The variations have 
been observed in relation to age, gender, race 
and ethnicity.2,3,7,12-14 Apart from this seasonal 
variation in the release of thyroid hormone have 
been reported.15-17 This study also focused on the 
dimension of the thyroid gland.

The thyroid gland has been studied using 
various modalities such as CT, MRI, ultrasound. 
Anatomist have also observed the thyroid gland 
dimension based on cadaver.5,18,19 The present 
study used ultrasound to measure the dimension 
of thyroid gland. This is method is widely used 
due to its non-invasive, less expensive and lack 
of release of any harmful ionizing radiation.1,4,20,21 
Due to this nature it is also used for diagnostic 
and therapeutic interventional procedures 
related to thyroid gland.10

This study found the length of the right lobe was 
higher than the left lobe. Only slight discrepancy 
between the right and left lobe in relation to the 
breadth and depth was observed. In contrast to 
the present study, Lee et al reported longer length 
of thyroid gland. However, they also reported 
the right lobe length to be longer than left lobe.22 
In their study the mean width of right lobe and 
left lobe was 15.7±2.6 mm and 15.2±3.1 mm 
while the mean thickness was 20.9±3.4 mm and 
18.9±3.4 mm.22 This measurement was greater 
than the present study. The difference in the 
measurement may be associated with variation 
of body size, study location and sample size.

In the present study the right thyroid lobe volume 
was greater than the left thyroid lobe volume. 
The mean volume of right lobe was 3.42±1.197 
ml while the left lobe was 3.30±1.065 ml. The 
mean total volume of the thyroid gland was 
6.71±2.05 ml. This finding is similar to the study 
conducted by Yousef et al,23 Turcios et al24 and 

Kayastha et al.6 In a similar study done among 
Nepalese patients, Kayastha et al reported the 
mean volume of thyroid gland as 6.629 ± 2.5025 
ml.6  Yousef et al observed the total mean thyroid 
volume as 6.44 ± 2.44.23 Turcios et al reported the 
total volume as 6.6 ± 0.26 ml. This value was 
slightly lower than the present study. This may 
be due to the variation of geographical location, 
sample size, the supplementation of iodine. 
Hegedus et al measured the thyroid gland of 111 
health people and found the mean total volume 
of thyroid glands slightly higher than the present 
study.17 In contrast to the present study, another 
study done in Nigeria reported the total mean 
thyroid gland volume to be 6.03±2.49 ml.25 The 
reduction in volume may be attributed to the 
geographical location. 

Studies have also reported variation in gender 
stating the thyroid gland to be larger and heavier 
in females. Apart from this the size also varies 
during menstruation and pregnancy in female.5 
The thyroid gland also undergoes physiological 
changes during pregnancy and menstruation in 
females.26 This study also observed variations 
among the gender. It was 7.91±2.91 ml in males 
and 6.40±1.63 ml in females. In agreement with 
the present study, Salaam et al also reported the 
thyroid volume higher in male than in female.25 
Hegedus et al in their study observed the thyroid 
volume to be slightly greater in females.17 

In the present study the volume of isthmus was 
0.06±0.063 ml. This volume was not incorporated 
in the mean total volume of thyroid gland 
as its mean thickness in the present study 
was 0.29±0.090 cm. This was below three mm 
thickness.27 The mean thickness was slightly 
lesser than reported by Kayastha et al.8

There are limitations of present study. There 
was non-uniform distribution of gender which 
have also caused slight increase in variation in 
the total volume in male. This study was based 

Basnet et al. Ultrasound Evaluation of Normal Thyroid Size



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on patients coming to single tertiary care centre 
of Nepal so the results cannot be generalized. 
The study did not observe other physiological 
factors that might have impact on the dimension 
of thyroid gland.

CONCLUSIONS 

The present study evaluated the dimension 
of thyroid gland using ultrasound. The mean 
thyroid volume was found to be more in male 

Basnet et al. Ultrasound Evaluation of Normal Thyroid Size.

than in female. The mean total volume was 
found to be similar to the earlier published study 
from Nepal.

ACKNOWLEDGEMENTS

The authors would like to acknowledge all the 
participating patients in this study.

Conflict of Interest: None 

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