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Radiol Oncol 2021; 55(3): 317-322. doi: 10.2478/raon-2021-0025
317
research article
Five-year follow-up and clinical outcome in 
euthyroid patients with thyroid nodules 
Katica Bajuk Studen
1,2
, Simona Gaberscek
1,2
, Edvard Pirnat
1,2
, Katja Zaletel
1,2
 
1 
Department of Nuclear Medicine, University Medical Centre Ljubljana, Slovenia
2 
Faculty of Medicine, University of Ljubljana, Slovenia
Radiol Oncol 2021; 55(3): 317-322.
Received 5 December 2020
Accepted 15 April 2021
Correspondence to: Katica Bajuk Studen, Department of Nuclear Medicine, University Medical Centre Ljubljana, Slovenia. 
E-mail: katica.bajuk@kclj.si
Disclosure: No potential conflicts of interest were disclosed. 
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Background. Thyroid nodule diagnosis has become increasingly frequent. Defining optimum surveillance intervals for 
patients with unsuspicious thyroid nodules remains a challenge. This was a single centre cohort study in which patients 
diagnosed with unsuspicious thyroid nodules in whom no treatment was indicated were invited for re-evaluation 5 
years after the diagnosis. The primary end point of the study was to estimate the change in nodule size with thyroid 
ultrasound (US) and the secondary end point was to assess the need for clinical management 5 years after the di-
agnosis.
Patients and methods. Baseline patient parameters and ultrasound characteristics of the nodules were retrospec-
tively collected. At follow-up, thyroid ultrasound was performed. 
Results. A hundred and eighteen (107 women / 11 men, aged 56.8 ± 13.4 years) patients were included in the study 
having 203 nodules at baseline, with mean largest nodule diameter 10.5 ± 7.4 mm. After 5 years, 58 (28.6%) nodules 
significantly increased in size, 27 (13.3%) decreased, and for 104 (51.2%) of nodules, no change in size was noted. 
Fourteen (6.9%) nodules disappeared. Additional 26 new nodules (mean largest diameter 7.7 ± 5.0 mm) in 16 patients 
were identified at follow-up. Regarding the clinical outcome, no new thyroid cancers were found. For 107 (90.7%) 
patients no further management was indicated. Five (4.2%) patients were referred to thyroidectomy because of the 
growth of the nodules. Two (1.7%) patients were treated for hyperthyroidism. Four (3.4%) patients did not complete 
the study. 
Conclusions. We report a single centre experience of the natural history of unsuspicious thyroid nodules. Our results 
showed that 71.4% of such nodules remained stable in size, decreased or even disappeared and that the vast major-
ity of the patients remained clinically stable with no need for treatment 5 years after the diagnosis.
Key words. thyroid, nodule, goiter
Introduction
Thyroid nodules are discrete lesions within the 
thyroid gland that are morphologically distinct 
from the surrounding thyroid parenchyma.
1
 
Currently, thyroid nodule diagnosis has become 
increasingly frequent due to incidental findings 
in different imaging tests performed for reasons 
unrelated to thyroid pathology.
2,3
 The prevalence 
of thyroid nodules detected by thyroid ultrasound 
(US) in unselected populations was reported to be 
of up to 50% in adult females and 30% in adult 
males.
4
The initial evaluation of patients with thyroid 
nodules consists of careful clinical, imaging and 
laboratory assessment, often aided by US-guided 
fine needle aspiration biopsy (FNAB). It should 
identify a small subgroup of nodules that ei-
ther harbour thyroid cancer (approx. 10%), cause 
compressive symptoms (approx. 5%) or progress 

Radiol Oncol 2021; 55(3): 317-322.
Bajuk Studen K et al/ Five-year follow-up of thyroid nodules 318
to functional disease (approx. 5%) and therefore 
need further clinical management.
1,5,6
 The rest of 
the nodules can safely be managed with a surveil-
lance program. However, since the knowledge of 
the natural history of thyroid nodules is incom-
plete, defining optimum surveillance intervals still 
remains a challenge with goals not to miss out a 
clinically significant change of the nodule and not 
to overburden medical facilities and patients with 
unnecessary follow-up examinations. At present, 
long-term follow-up recommendations are mainly 
based on expert opinion consensus since there is 
no reliable method to identify patients likely to 
experience clinically significant nodule growth or 
change to malignancy.
1,6
The purpose of our study was to establish a nat-
ural history of thyroid nodules in a cohort of euthy-
roid patients diagnosed with unsuspicious thyroid 
nodules. The primary end point of the study was 
to estimate the change in nodule size with thyroid 
US and the secondary end point was to assess the 
need for clinical management five years after the 
diagnosis.
Patients and methods
The study was carried out in 2015–2017 as a 5-year 
follow-up of patients diagnosed with thyroid nod-
ules at the Outpatient Thyroid Department of the 
University Medical Centre Ljubljana in the years 
2010–2012. Only patients with unsuspicious nod-
ules in whom at the time of diagnosis no treat-
ment was indicated and who did not have autoim-
mune thyroid disease were included in the study. 
None of the patients was receiving levothyroxine 
therapy. Five years after the initial diagnosis, pa-
tients were invited by mail for clinical and US re-
evaluation. The study was performed in an iodine 
sufficient area.
7
 It was approved by the Republic of 
Slovenia National Medical Ethics Committee (No. 
0120-721/2015-2). A written informed consent was 
obtained by all patients included in the study.
At baseline, a complete thyroid gland examina-
tion was performed, including clinical examina-
tion, thyroid US and measurement of thyrotropin 
(TSH), free thyroxine (fT
4
), free triiodothyronine 
(fT
3
), thyroid peroxidase antibodies (TPOAb), thy-
roglobulin antibodies (TgAb) and thyroglobulin 
(Tg). If the largest diameter of thyroid nodules ex-
ceeded 1 cm, thyroid scintigraphy was performed. 
To rule out malignancy, US-guided FNAB was per-
formed in hypofunctioning thyroid nodules with 
suspicious US features. 
At follow-up, the evaluation included clinical 
examination and thyroid US. If a significant in-
crease of one or more thyroid nodules was con-
firmed or new nodules larger than 5 mm were de-
tected, the patient was advised to proceed to a fur-
ther complete thyroid gland examination that was 
scheduled at a separate visit. The complete thyroid 
gland examination included clinical examination, 
thyroid US, TSH and Tg measurement, FNAB for 
nodules with suspicious ultrasound appearance, 
and re-evaluation of the need for treatment.
All laboratory measurements were performed 
at the biochemical laboratory of the Department 
of Nuclear Medicine of the University Medical 
Centre Ljubljana. Serum concentration of TSH, fT
4
, 
fT
3
, TPOAb and TgAb was measured by ADVIA 
Centaur System (Siemens Medical Solutions 
Diagnostics). Reference values for TSH were 0.35–
5.5 mIU/L, for fT
4
 11.5–22.7 pmol/L, for fT
3
 3.5–6.5 
pmol/L, and for TPOAb and TgAb less than 60 
kIU/L. Thyroglobulin was measured by Kryptor 
platform (Brahms), based on TRACETM (time-re-
solved amplified cryptate emission) method with 
reference values between 0.5–58 μg/L. 
Thyroid US was performed by 1 of 2 experienced 
thyroid specialists using an US machine (SSD-4000; 
Aloka Co, Ltd, Tokyo, Japan) with a 7.5-MHz lin-
ear transducer. The number of the nodules was 
recorded as well as their size in three dimensions. 
Multinodularity was defined as having more than 
1 nodule. The volume of the nodules was calcu-
lated by the formula width x length x thickness x 
π/6. Suspicious ultrasound features were defined 
as at least one of the following: hypoechogenicity, 
irregular margins, taller-than-wide shape, and mi-
crocalcifications. A significant change in the size of 
thyroid nodule was defined as the increase or de-
crease that involved at least 2 nodule dimensions, 
each amounting to at least 2 mm and representing 
at least 20% of the baseline diameter.
1,9
 Thyroid au-
toimmunity was defined as hypoechoic US pattern 
and/or increased level of TPOAb and/or TgAb.
Thyroid scintigraphy was performed using a 
gamma camera equipped with a pinhole collimator 
(Siemens BASICAM) after intravenous administra-
tion of 100 MBq of Tc-99m pertechnetate.
Cytology results of FNAB were reported using 
the Bethesda system.
8
 Only patients with unsuspi-
cious cytology results were included in the study 
(Bethesda category 2 as well as cysts, categorized 
as Bethesda 1). 
The statistical analysis was performed with 
IBM SPSS Statistics Version 25 Software. Values 
are expressed as mean ± standard deviation (SD). 

Radiol Oncol 2021; 55(3): 317-322.
Bajuk Studen K et al/ Five-year follow-up of thyroid nodules 319
For categorical baseline characteristics, differences 
between subgroups of patients were assessed by 
Pearson chi-square test. For continuous baseline 
characteristics, correlations with subgroup classi-
fication were assessed using Spearman’s rho test. 
Correlations of growth indicative variables with 
baseline parameters were calculated by using the 
Pearson correlation test (Pearson correlation coef-
ficient, r). p-value below 0.05 was considered sta-
tistically significant.
Results
The recruitment process is summarized in Figure 1. 
One hundred and eighteen patients were included 
in the study, with 203 thyroid nodules identified 
at baseline. One hundred and seven (90.7%) of the 
included patients were females and 11 (9.3%) were 
males. Basic characteristics of the included patients 
and the two subgroups with or without nodule 
growth are depicted in Table 1. 
Mean baseline largest diameter of the nodules 
was 10.5 ± 7.4 mm and mean baseline volume 1.1 ± 
2.2 mL, with nodule baseline largest diameter dis-
tribution shown in Figure 2. In 55 nodules, FNAB 
was performed. The result of FNAB was Bethesda 
category 2 for 38 nodules and Bethesda category 1 
(cyst) for 17 nodules. 
After 5 years, 58 nodules significantly increased 
in size, 27 nodules significantly decreased in size; 
whereas for 104 of nodules, no significant change 
in size was noted (Figure 3). Furthermore, 14 of 
them disappeared. Twenty-six new nodules (mean 
largest diameter 7.7 ± 5.0 mm, mean volume 0.4 ± 
0.8 mL) in 16 patients were found. The presence of 
multiple nodules was found to be significantly as-
sociated with nodule growth (Table 1).
The parameters of 58 nodules that signifi-
cantly increased in size were further analyzed. 
FIGURE 1. Flowchart explaining the recruitment process and 
the number of included patients and thyroid nodules.
TABLE 1. Basic characteristics of patients included in the study (N = 118) 
Parameter
All patients
(N = 118)
Nodule Growth New nodules detected
Without
(N = 72)
With
(N = 46)
p
Without
(N = 102)
With
(N = 16)
p
Age (years) 51.6 ± 13.4 51.8 ± 13.6 51.2 ± 13.2 0.81 51.2 ± 13.6 53.9 ± 11.9 0.46
TSH (mIU/L) 1.64 ± 0.85 1.73 ± 0.83 1.49 ± 0.85 0.07 1.63 ± 0.83 1.72 ± 1.00 0.80
Tg ( μg/L) 42.4 ± 184.9 51.3 ± 237.2 28.8 ± 33.4 0.08 43.7 ±196.6 33.2 ± 70.5 0.68
Maximum diameter of the largest nodule (mm) 12.2 ± 8.2 11.7 ± 8.4 12.9 ± 7.7 0.11 12.2 ± 8.3 12.2 ± 7.6 0.86
Volume of the largest nodule (mL) 1.4 ± 2.4 1.4 ± 2.6 1.4 ± 2.1 0.17 1.4 ± 2.5 1.2 ± 1.4 0.70
Multinodularity (%) 
55 
(46.6%)
27 
(37.5%)
28 
(60.9%)
0.02 48 (47.1%)
7 
(43.8%)
1.0
Tg = thyroglobulin; TSH = thyrotropin;
FIGURE 2. Nodule largest diameter distribution at baseline 
(N = 203).

Radiol Oncol 2021; 55(3): 317-322.
Bajuk Studen K et al/ Five-year follow-up of thyroid nodules 320
Correlations between baseline parameters (base-
line age, baseline Tg, baseline largest nodule di-
ameter and baseline nodule volume) and changes 
in the largest nodule diameter and nodule volume 
are depicted in Figure 4. Baseline TSH level was 
not found to correlate with changes in the largest 
nodule diameter nor nodule volume, r = – 0.119, 
p = 0.37 and r = – 0.082, p= 0.60, respectively (not 
shown in Figure 4). Baseline Tg level, baseline 
largest nodule diameter as well as baseline nod-
ule volume positively and significantly correlated 
with nodule growth (p=0.03, p=0.011 and p<0.001, 
respectively). 
Clinical outcome after five years
No new thyroid cancers were found. For 107 
(90.7%) patients no further management was in-
dicated. Five (4.2%) patients were referred to thy-
roidectomy because of the growth of the nodules. 
Two (1.7%) patients were treated for hyperthyroid-
ism (one received radioiodine treatment because 
of toxic multinodular goiter, another was treated 
FIGURE 3. Growth status of the nodules after 5 years (N = 203). 
A significant change in the size of a thyroid nodule was defined 
as the increase or decrease that involved at least 2 nodule 
dimensions, each amounting to at least 2 mm and representing 
at least 20% of the baseline diameter.
FIGURE 4. Correlations of baseline parameters with change in the largest nodule diameter and change in the nodule volume in 
nodules that significantly increased in size at the five-year follow-up (N = 58).
A B
C D

Radiol Oncol 2021; 55(3): 317-322.
Bajuk Studen K et al/ Five-year follow-up of thyroid nodules 321
with anti-thyroid drugs because of newly occurred 
Graves’ disease). Four (3.4%) included patients 
who were advised to proceed to a complete thy-
roid gland examination did not decide to do so for 
unknown reasons and were lost to follow-up.
Discussion 
In our study, we report a single center experience 
of the natural history of unsuspicious thyroid 
nodules in euthyroid patients for whom no treat-
ment was indicated at the time of diagnosis. Our 
results show that 71.4% of such nodules remain 
stable in size, decrease or even disappear and that 
the vast majority of the patients remain clinically 
stable with no treatment indication five years af-
ter the diagnosis. The presence of multiple nodules 
in patients is associated with nodule growth. For 
nodules that grow, nodule’s growth positively cor-
relates with the baseline Tg level, baseline largest 
nodule diameter as well as with the baseline nod-
ule volume. 
Previous studies have reported conflicting re-
sults regarding the natural course of thyroid nod-
ules.
10,11,12
 These results could be due to the method-
ological problems – different, often short follow-up 
intervals and different cut-offs of change in nodule 
size were used, which are not easily reproducible. 
In our study, the size change of the nodule was 
considered significant if a change of 20% or more 
was recorded in at least 2 nodule diameters, with 
a minimum increase of 2 mm. This approximates 
a nodule volume change of 50% which represents 
the minimal significant and reproducible change in 
nodule size suggested to be applied in clinical in-
vestigations and practice.
1,6,9
 Our finding that after 
five years, most of the nodules remained stable, de-
creased or even disappeared is in agreement with 
a previously published study applying the same 
strict cut-off measure for a significant change in 
nodule size.
13
Our finding that nodule growth was positively 
associated with the baseline largest nodule diam-
eter and nodule volume as well as with the pres-
ence of multiple nodules is also in agreement with 
a previous report.
13
 As expected, no association of 
baseline TSH level with nodule growth was found 
in our study since only patients with TSH within 
normal limits were included. 
The pathogenesis of thyroid nodules as well as 
their growth are influenced by genetic and envi-
ronmental factors. Among environmental factors, 
iodine supply is probably the most important risk 
factor with nodular goiter being more prevalent in 
iodine deficient areas.
14
 Our study was conduct-
ed in an area that was iodine-sufficient for more 
than ten years before baseline evaluation of the 
patients.
7
 Therefore, the change in size of thyroid 
nodules reported in our study can be attributed to 
genetic and non-iodine related factors.
15
 However, 
firm data of relative contributions and causality of 
those factors is lacking and should be elucidated 
by future research.
Our finding that more than 90% of the patients 
five years after initial diagnosis did not need any 
further management of thyroid nodules supports 
our approach of a thorough first examination, 
which enables identifying a subgroup of patients 
who need treatment (due to malignancy, thyroid 
autonomy or compressive symptoms). It seems 
that such approach is more important than plan-
ning different follow-up strategies. Of note, pa-
tients with autoimmune thyroid disease with 
possible increasing TSH levels over time, patients 
with suspicious US features of thyroid nodules and 
those with inconclusive cytology reports were not 
included in the study. In such patients, follow-up 
is indicated.
1,6
 
Conclusions
In conclusion, our results support the approach 
that after a thorough first examination the major-
ity of patients with unsuspicious thyroid nodules 
do not need frequent follow-up. Further research 
should elucidate the genetic determinants and bio-
logical characteristics of thyroid nodules that grow 
in time.
Acknowledgement
This work was supported by the national project 
funded by Slovenian Research agency (Project 
number J3-1760).
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