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 a thyroid colloid cyst ( tcc ) is a nonneoplastic thyroid nodule with a histology showing marked follicular dilatation and epithelial flattening .
a tcc contains a dense viscous material comprised of a concentrated solution of thyroglobulin ; the cause of a tcc may be related to a defect in intraluminal thyroglobulin reabsorption .
a tcc is commonly detected by an ultrasound ( us ) examination of the neck or thyroid ; however , its clinical significance is low because a tcc is not associated with a thyroid malignancy and is easily diagnosed by us examination because of its typical sonographic features [ 2 , 3 ] .
many researchers and guidelines do not recommend us - guided fine - needle aspiration for tccs because tccs have inadequate cytology and typical sonographic features [ 28 ] .
however , tccs can result in an acute onset of symptoms , such as a palpable mass or pain , if they become larger than 2  cm at their largest diameter and if they develop an intralesional hemorrhage [ 2 , 9 ]
. nevertheless , no data exists regarding the long - term interval changes of tccs . to the best of my knowledge ,
no previous study has employed a sonographic follow - up for tccs by using a long - term follow - up interval of over 5 years .
this study assessed the prevalence and interval changes of tccs  3  mm at their largest diameter in postlobectomy patients who received treatment for papillary thyroid microcarcinoma ( ptmc ) .
from january 2007 to december 2008 , 437 patients ( 374 women and 63 men ; range 1872 years ; mean age 45.5 years ) underwent lobectomy for the treatment of papillary thyroid microcarcinoma ( ptmc ) in our hospital .
all the patients underwent thyroxine - replacement therapy after lobectomy . among them , 268 patients ( 227 women and 41 men ; range 1870 years ; mean age 45.5 years ) were included in this study that had 4 or more postoperative follow - up us examinations after lobectomy .
the institutional review board approved this study ( irb 13 - 158 ) , and informed consent was waived for this retrospective study .
an experienced radiologist performed the thyroid us examinations using a high - resolution ultrasound instrument ( hdi 5000 or iu 22 ; philips medical systems , bothell , wa , usa ) equipped with a 515  mhz linear probe .
a tcc was defined as a pure thyroid cyst with intracystic comet - tail artifact(s ) . to clarify the sonographic detection and to facilitate the evaluation of an interval change for the tccs , only tccs  3  mm at their largest diameter were included in this study . in the case of multiple tccs , only the dominant tcc ( i.e. , the largest tcc ) was included in this study . in our hospital ,
the routine us follow - ups of postlobectomy patients who received treatment for ptmc were performed as follows : the initial 3 us follow - ups were performed at a 1-year interval , and the later us follow - ups were performed at 1- or 2-year interval depending on patient agreement . in this study , patients were excluded if they had 3 or less us follow - ups or did not have at least 1 us follow - up after the 5-year or more interval from thyroid surgery . an interval increase or decrease for each tcc was defined as a positive or negative interval change of 10% or more in the largest diameter of a tcc during the us follow - ups . on the basis of the us follow - ups ,
each tcc was retrospectively classified into 1 of 7 diagnostic categories by a single radiologist : ( 1 ) no interval change : an interval change of < 10% occurred in the largest diameter of the tcc ; ( 2 ) gradual increase : an interval increase occurred in the tcc at its largest diameter but did not have any fluctuations during the sequential us follow - ups ; ( 3 ) gradual decrease : an interval decrease occurred in the tcc at its largest diameter but did not have any fluctuations during the sequential us follow - ups ; ( 4 ) positive fluctuation : an interval decrease occurred in the tcc during the early us follow - ups and an interval increase occurred in the tcc during the late us follow - ups ; ( 5 ) negative fluctuation : an interval increase occurred in the tcc during the early us follow - ups and an interval decrease occurred in the tcc during the late us follow - ups ; ( 6 ) disappearance : no tcc was visualized during the us follow - ups ; and ( 7 ) new detection : a new tcc was observed during a late or the last us follow - up .
of the 437 patients , 268 patients ( 61.3% ) underwent a long - term follow - up with us examinations ( range 6078 months ; mean 65.7 months ) .
of the 268 patients , 41 patients ( 15.3% ; 32 women and 9 men ; range 2466 years ; mean age 42.2 years ) had tccs  3  mm at the largest diameter of the tccs ( range 3.08.2  mm ; mean 3.9  mm ) . among them , 35 patients ( 13.1% ) had tccs during both the preoperative thyroid us examination and us follow - ups ; however , 6 patients ( 2.2% ) had tccs only during the us follow - ups . through the preoperative thyroid us examinations and us follow - ups , the interval change for the tccs was classified as follows : no interval change ( n = 8) , gradual increase ( n = 8) ( figure 1 ) , gradual decrease ( n = 5 ) , positive fluctuation ( n = 3 ) , negative fluctuation ( n = 6 ) , disappearance ( n = 5 ) , and new detection ( n = 6 ) .
of the 41 patients with tccs , no patient had a tcc  10  mm at its largest diameter during both the preoperative thyroid us examinations and us follow - ups . during the thyroid
us follow - ups , no tccs demonstrated an increase that was 2 or more times of their largest diameter .
further , no patients had any sonographically suspected intracystic hemorrhages or complained of any relevant symptoms .
the clinical significance of a tcc is very low because a tcc is not associated with a thyroid malignancy and is easily diagnosed by a thyroid us examination [ 24 , 7 ] . in particular ,
a tcc can be sonographically diagnosed because a tcc has some typical sonographic features ( i.e. , pure thyroid cyst with intracystic comet - tail artifacts ) , and thus many radiologists do not recommend us - guided fine - needle aspiration for a tcc [ 24 , 7 ] .
sometimes , a tcc results in an intracystic hemorrhage , and thus patients can complain of local pain or a palpable neck mass .
however , a long - term interval change in a tcc has not been reported .
this study attempted to investigate the long - term sonographic interval changes of tccs in postlobectomy patients who were treated for ptmc . in the present study ,
tccs had various interval changes , although no tcc had largest diameter  10  mm . among them ,
the most common patterns were no interval change ( 19.5% ) and gradual increase ( 19.5% ) .
however , the incidence of a gradual decrease ( 12.2% ) and disappearance ( 12.2% ) was not low . in this study ,
various interval changes were observed with respect to tccs , but none of the tccs demonstrated an abrupt increase or acute onset of symptoms .
therefore , the author believes long - term us follow - up for tcc is unnecessary .
high - resolution thyroid us examinations have been used worldwide for the evaluation of thyroid nodules that resulted in the general acceptance of certain characteristics that mark benign and malignant thyroid nodules [ 48 ] .
a thyroid us examination has been considered the most accurate imaging tool for evaluating thyroid nodules despite its operator dependency [ 4 , 7 , 8 ] . in this study , an experienced radiologist who had 10 years of experience in thyroid us ( > 2500 cases / year )
only a thyroid nodule showing an anechoic thyroid nodule with comet - tail artifact was considered to be a tcc .
first , of the 437 patients , 169 patients ( 38.7% ) were not included because of insufficient us follow - ups .
further , only patients who underwent lobectomy because of ptmc were included ; thus , a selection bias was possible .
in addition , a comparison analysis was not performed for tcc interval changes secondary to thyroxine - replacement therapy during the maintenance periods because of the small number of cases in each category .
several reports have shown that shrinkage of thyroid nodules occurs more frequently in patients with long - term thyroid - stimulating hormone suppression than in untreated patients [ 10 , 11 ] . for clarity , a large - scale study involving a general population may be required .
finally , a single radiologist performed all the thyroid us examinations , including preoperative thyroid us and postoperative us follow - ups . in conclusion ,
tccs show various interval changes in the patients who underwent lobectomy for papillary thyroid microcarcinoma , but tccs rarely have an abrupt increase or acute onset of symptoms .
objective . this study aimed to assess the interval changes of thyroid colloid cysts ( tccs ) by performing long - term ultrasound ( us ) follow - up examinations 
 . methods . from 2007 to 2008 
 , 437 patients underwent a lobectomy for the treatment of papillary thyroid microcarcinoma . among them , 268 patients underwent 4 or more postoperative us follow - ups after surgery . 
 this study investigated the prevalence and interval changes of tccs 3  mm by using us follow - ups . results . among 268 patients , 
 35 ( 13.1% ) had tccs 3  mm by a preoperative thyroid us , and 6 ( 2.2% ) had newly detected tccs at a us follow - up . through long - term us 
 follow - up , the interval changes for tccs were classified as follows : no interval change ( n = 8) , gradual increase ( n = 8) , gradual decrease ( n = 5 ) , positive fluctuation ( n = 3 ) , negative fluctuation ( n = 6 ) , disappearance ( n = 5 ) , and new detection ( n = 6 ) . 
 none of the tcc cases had a tcc that was 10  mm at its largest diameter , and no patient complained of any relevant symptoms pertaining to the tccs . 
 conclusions . in this study , 
 tccs demonstrated various interval changes , but no abrupt increase was found or acute onset of symptoms occurred .