Management for Warthin Tumor of the Parotid Gland: Surgery or Observation. A 21-Year Retrospective Study of 387 Cases

Abstract

Purpose

This study investigated the characteristics, diagnosis, and treatment of Warthin tumors (WTs) to explore the possibility of managing patients by observation.

Methods

We reviewed the records of 1167 patients with benign parotid tumors who were seen in our department between September 1999 and April 2021. Among them, 387 cases were WT and 668 cases were pleomorphic adenoma. We evaluated preoperative diagnoses of WT by symptoms/signs, fine-needle aspiration cytology (FNAC), imaging, such as ultrasonography and magnetic resonance imaging, and technetium-99m pertechnetate (Tc-99m) scintigraphy. Fisher’s exact test and the Mann–Whitney U test were used in statistical analyses.

Results

Warthin tumors were treated by surgery in 238 cases and follow-up in 149 cases. The 238 patients were diagnosed as WT at the final pathology after surgery. Among them, 172 patients (72.3%) were determined as benign histological type by preoperative FNAC; in these 172 patients, 170 (71.4%) were correctly diagnosed as WT in the final pathology. Preoperative Tc-99m scintigraphy was performed in 69 patients diagnosed with WT by final pathology or FNAC, and the positive rate of Tc-99m scintigraphy in WT was 75.4%.

Conclusions

Combining FNAC and Tc-99m scintigraphy, as well as considering clinical findings, enables the diagnosis of WT in most cases. In particular, WT is more common in the elderly, grows more slowly, and is less likely to be malignant. Therefore, if WT can be diagnosed preoperatively with a high rate of correct diagnosis, it could be an accurate and effective means of managing patients through follow-up without surgery.

Keywords

parotid tumor Warthin tumor observation fine-needle aspiration cytology technetium-99m pertechnetate scintigraphy

Introduction

Pleomorphic adenoma (PA) is the most common benign tumor occurring in the parotid gland and accounts for 60% to 70% of cases.¹ The second most common type is Warthin tumor (WT), and PA and WT combined account for approximately 90% of all benign parotid tumors.^2,3 However, the prevalence of WT has been increasing, and a report indicates that it is now more common than PA.⁴

Because WT and PA comprise such a large percentage of benign parotid tumors, it is crucial to differentiate between them for preoperative diagnosis. Malignant transformation of PA can occur⁵ and it develops in relatively young people; thus, most cases are indicated for surgery. In contrast, WT is more common in older adults and rarely transform to malignancy; therefore, it can be managed by observation, although aesthetic issues may remain.⁶ Because of these differences between PA and WT, a reliable differential diagnosis is critical for determining the appropriate treatment approach. Besides symptoms/signs, fine-needle aspiration cytology (FNAC) and imaging, such as ultrasonography and magnetic resonance imaging, can be used for the preoperative diagnosis of parotid tumors. Moreover, technetium-99m pertechnetate (Tc-99m) scintigraphy may also be used to diagnose WT.⁷

In our department, we have been diagnosing and treating parotid tumors for over 21 years. In recent years, the number of cases in which WT is managed without surgery has increased. Because we have now seen a total of over 1000 cases of PA and WT, we decided to investigate the differential diagnosis and other features of the two conditions, as well as the clinical characteristics and management of WT.

Materials and Methods

Patients

We reviewed the records of 1167 patients with benign parotid tumors (excluding recurrences) who were seen in our department between September 1999 and April 2021. Among them, WT (238 cases) and PA (668 cases) were confirmed by the final pathology of surgical specimen and WT (149 cases) which were managed by observation. In patients who underwent surgery, the tumors were histopathologically classified according to the 2017 WHO classification.⁸ During the same period, we treated 222 cases of malignant parotid tumors.

The study was approved by our institutional review board (approval no. #2621-1).

Characteristics of WT and PA

In patients receiving surgery for WT or PA, we evaluated age, sex, duration of disease, tumor diameter, tumor location, symptoms/signs, operation time, bleeding volume, and postoperative facial paralysis. A lower pole tumor was defined as a tumor whose center was more caudal than the marginal mandibular branch of the facial nerve.⁹ The age distribution of patients with WT was examined separately for men and women.

Fine-Needle Aspiration Cytology

Ultrasound-guided FNAC was performed preoperatively in all patients undergoing surgery. We examined the preoperative FNAC findings in patients who were diagnosed with WT at the final pathology after surgery and the final pathology results in patients who were diagnosed as having WT at the preoperative FNAC. Fine-needle aspiration cytology results were categorized according to the Osaka Medical College salivary gland cytology classification system, which consists of 11 categories.¹⁰

Technetium-99m Pertechnetate Scintigraphy

Preoperative Tc-99m scintigraphy was performed for the patients with parotid tumor according to the following principal. Preoperative Tc-99m scintigraphy was performed for the patients with 65 surgery cases and 46 observation cases. In surgery cases, Tc-99m scintigraphy was performed for the cases that WT was suspected by symptoms/signs and image findings, but not confirmed by FNAC. In observation cases, it was performed for the cases that WT was suggested strongly by various signs such as history, FNAC, symptoms/signs, and image findings. Lemon juice stimulation was used to measure Tc-99m.

Surgery

During the period targeted in this study, parotid tumors were diagnosed and treated under a predefined policy.¹¹ In principle, surgery was performed by a partial superficial parotidectomy under general anesthesia. An S-shaped incision was made in the skin to reveal the operative field. For processing the nerve, the main trunk of the facial nerve was identified, followed by the identification and dissection of the branch required for tumor resection. An electronic scalpel was used to resect parotid tissues. If a tumor was located just above the superficial layer of the main trunk, a peripheral nerve was then identified to perform a retrograde dissection due to the difficulty of nerve identification in the main trunk. For cases of deep lobe tumor, superficial lobe tissue was dissected to identify nerves then returned to its original position after resection of the tumor. Facial nerve monitoring was used from September 2014. No medication, such as steroids, was used when facial paralysis developed postoperatively.

Patients With WT Treated by Surgery or Observation

We compared the age, sex, tumor diameter, tumor location, symptoms/signs, use of Tc-99m scintigraphy, and FNAC findings between patients with WT who underwent surgery and those who were managed by observation.

Postoperative Facial Paralysis

We examined factors associated with postoperative facial paralysis in WT and PA, including age, sex, histopathological type, tumor diameter, tumor location, symptoms/signs, operation time, and bleeding volume. We also examined the time to recovery from paralysis in patients with WT or PA who developed postoperative facial paralysis and were followed up for at least 24 months after surgery.

Statistical Analysis

For WT and PA, Fisher’s exact test was used to compare sex, tumor location, pain/tenderness, adhesion, and presence of facial paralysis, and the Mann–Whitney U test was used to compare age, tumor diameter, operation time, and bleeding volume. Univariate and multivariate analyses were used to evaluate postoperative facial paralysis in WT and PA, respectively. In the univariate analysis, Fisher’s exact test was used for sex, tumor location, pain/tenderness, and adhesion, and the Mann–Whitney U test was used for age, tumor diameter, operation time, and bleeding volume. In the multivariate analysis, binomial logistic-regression analysis was used, with the presence or absence of postoperative facial paralysis as the dependent variable. In binomial logistic regression, bleeding volume was estimated to depend on operation time because correlations were observed between the 2 items (WT, r = .501; PA, r = .448; both P < .05 by Spearman’s rank correlation coefficient). Therefore, operation time was used, and bleeding volume was excluded from independent variables. To enable independent variables to be studied in detail, the following variables were recoded as categorical variables on the basis of the respective frequency distribution: age, which was divided into 3 categories (<45, ≥45 to <70, and ≥70 years); tumor diameter, which was divided into 2 categories (<25 and ≥25 mm); and operation time, which was also divided into 2 categories (<120 and ≥120 min). The reference categories for the independent variables were as follows: age, less than 45 years old; sex, male; tumor diameter, < 25 mm; tumor location, superficial lobe; pain/tenderness, none; adhesion, none; and operation time, < 120 minutes. In all analyses, a P value less than .05 was considered statistically significant.

Results

Characteristics of WT and PA

During the study period, 149 patients with WT were managed by observation; definite or suspected WT was diagnosed by FNAC in 141 of these patients and by Tc-99m scintigraphy in the remaining 8 patients. The symptoms/signs and other examinations in these patients did not contradict a diagnosis of WT.

We have compared WT with PA in surgical cases. The mean age of the patients with WT was 62.9 years, and 87.4% of them were men. The mean tumor diameter was 31.9 mm, and tumors were located in the lower pole in 57% of patients. The percentage of patients who experienced pain/tenderness was 7.2%, and the percentage of patients with adhesion to surrounding tissue was 3.8%. The mean operation time and bleeding volume were 117.9 min and 28.3 mL, respectively. Postoperative facial paralysis was observed in 17.6% of patients and was transient in all cases. We found significant differences between patients with WT and those with PA in age, sex, tumor diameter, tumor location, adhesion to surrounding tissue, and bleeding volume (Table 1). In patients of WT with surgery, the age distribution ranged from 20 to 85 years (mean, 62.9 years) in men and from 38 to 84 years (mean, 63.0 years) in women (Table 2). In terms of changes by year, the number of cases of PA increased markedly from 2012. The number of observation cases increased from 2011 and almost reached a surgery to observation-ratio of 1:1. The ratio of total WT to PA was 1:1.7 (Figure 1).

Table 1.

Patient demographic and clinical features of Warthin tumor and pleomorphic adenoma.

	Warthin tumor	Pleomorphic adenoma	p-value
	N = 238	N = 668	p-value
Age, mean, y	62.9	48.0	< 0.001
Sex ratio, male to female	208:30	206:462	< 0.001
Tumor diameter, mean, mm	31.9	24.4	< 0.001
Tumor location	79:136:23	436:75:157	< 0.001
Ratio of superficial to lower pole to deep	79:136:23	436:75:157	< 0.001
Pain/tenderness, n	17	41	0.586
Adhesion	229:9	602:66	0.002
Ratio of mobile to limited/fixed	229:9	602:66	0.002
Operation time, mean, min	117.9	125.1	0.402
Bleeding volume, mean, mL	28.3	19.6	< 0.001
Postoperative facial paresis, n	42	145	0.184

Table 2.

Number of patients with Warthin tumor by age and sex.

Age, y	Warthin tumor (N = 238)
Age, y	Male, n	Female, n
20–29	2	0
30–39	1	1
40–49	12	1
50–59	58	6
60–69	80	15
70–79	48	5
80–89	7	2

Figure 1.

Cases of pleomorphic adenoma (PA) and Warthin tumor (WT) by year (1999–2021). In WT, management by observation has increased since 2011. The number of cases of PA has increased from 2012. The overall WT:PA ratio is 1:1.7.

Fine-Needle Aspiration Cytology

238 patients were diagnosed with WT at the final pathology after surgery. Among them, 172 patients (72.3%) were determined as benign tumor (histology confirmed, Category 4-1) by preoperative FNAC; in these 172 patients, 170 (71.4%) were correctly diagnosed as WT in the final pathology and PA in the remaining 2. Only 2 cases were diagnosed as malignant by FNAC (Category 6) (Table 3).

Table 3.

Fine-needle aspiration cytology (FNAC) results according to the Osaka Medical College (OMC) system.

	Preoperative FNAC results (OMC system)	FNAC results for cases diagnosed with Warthin tumor by final pathology, n (N = 238)
OMC classification	1-1 Inadequate	35
	1-2 Cyst contents	3
	2 Non-neoplastic	10
	3 Atypia of undetermined significance	4
	4-1 Benign tumor (histology confirmed)	172
	4-2 Benign tumor (histology unconfirmed)	8
	5 Uncertain malignant potential	4
	6-1 Suspicious for malignancy	1
	6-2 Malignant (grade/histology unconfirmed)	1
	6-3 Malignant (grade confirmed)	0
	6-4 Malignant (grade/histology confirmed)	0
	Final pathology	Results of final pathology for cases diagnosed with Warthin tumor by preoperative FNAC, n (N = 193)
	Warthin tumor	173
	Pleomorphic adenoma	6
	Basal cell adenoma	4
	Oncocytoma	3
	Inflammation	3
	Cyst	1
	Muceopidermoid carcinoma	1
	Carcinoma ex plemorphic adenoma	1
		Acinic cell carcinoma	1

On the other hand, a total of 193 patients among all surgical cases were diagnosed with WT by preoperative FNAC. In these patients, the final pathology after surgery identified WT in 173 patients (89.6%), PA in six, and malignancy in three (1.6%) (Table 3).

Technetium-99m Pertechnetate Scintigraphy

Preoperative Tc-99m scintigraphy was performed in 111 patients. Of these patients, 65 underwent surgery to remove the tumor and 46 were treated by observation (Table 4). In those patients treated by surgery, 43 were confirmed at the final pathology to have WT; 34 (79.1%) of these patients showed accumulation in Tc-99m scintigraphy that matched the tumor. Among the 4 false-positive cases for WT, 2 were a malignant tumor; 1 was a malignant lymphoma, and 1 was acinic cell carcinoma. Tc-99 m scintigraphy had a sensitivity of 79.1% and a specificity of 81.8% for WT. On the other hand, among 46 observation cases which underwent Tc-99m scintigraphy, 26 patients were diagnosed with WT by FNAC, and Tc-99m was positive in 18 of these cases. Overall, the positive rate of Tc-99m scintigraphy in WT was 75.4%.

Table 4.

Results of preoperative technetium-99m pertechnetate scintigraphy in cases (N = 111) managed by surgery or observation.

Surgery cases (n = 65)		Observation cases (n = 46)
Tc-99m result	n	Tc-99m result	n
Tc-99m-positive	38	Tc-99m-positive	33
Warthin tumor^a	34	Warthin tumor^b	18
Others	4	Others	15
Tc-99-m-negative	27	Tc-99-m-negative	13
Warthin tumor^a	9	Warthin tumor^b	8
Others	18	Others	5

^aWarthin tumor was confirmed by final pathology

^bWarthin tumor was confirmed by fine-needle aspiration cytology

Abbreviations: 99m-Tc, technetium-99m pertechnetate scintigraphy

Patients With WT Treated by Surgery or by Observation

The comparison of patients treated by surgery or by observation revealed that the latter had a higher mean age (P < .001), smaller tumor diameter (P < .001), and a higher rate of being diagnosed with WT by FNAC (P < .001). The rate of Tc-99m performed was higher in observation cases (P = .004) (Table 5).

Table 5.

Characteristics of patients with a Warthin tumor managed by surgery or observation.

	Warthin tumor
	Surgery cases	Observation cases	p-value
Age, mean, y	62.9	69.9	<0.001
Sex ratio, male to female	208:30	129:20	0.877
Tumor diameter, mean, mm	31.9	26.1	<0.001
Tumor location, n (%), lower pole	136(57.1%)	95 (63.8%)	0.203
Pain/tenderness, n (%)	17 (7.1%)	11 (7.4%)	1.000
Adhesion (limited/fixed), n (%)	9 (3.8%)	6 (4.0%)	1.000
Tc-99m performed, n (%)	43 (18.1%)	46 (30.9%)	0.004
FNAC diagnosis of Warthin tumor, n (%)	170 (71.4%)	141 (94.6)	<0.001

Abbreviations: Tc-99m, Technetium-99m pertechnetate scintigraphy; FNAC, fine-needle aspiration cytology.

Postoperative Facial Paralysis

Postoperative facial paralysis occurred in 42 patients with WT and 145 patients with PA. In patients with WT, we found significant differences between those with and without paralysis in tumor diameter (P = .049), tumor location (P = .001), operation time, and bleeding volume (both P < .001). The highest odds ratios in multivariate analysis were for tumor location (deep lobe; 3.3) and operation time (≥120 min; 2.8) (Table 6). In patients with PA, the differences were similar to those in patients with WT (ie, in tumor diameter, tumor location, operation time, and bleeding volume), although we also found a significant difference for adhesion to surrounding tissue. As in WT, multivariate analysis in PA found the highest odds ratios for tumor location (deep lobe; 2.7) and operation time (≥120 min; 2.0) (Table 7). Patients with WT (n = 28) or PA (n = 102) who developed postoperative facial paralysis were followed up for at least 24 months after surgery. Time to recovery was less than 8 months (median, 3 months) in all patients with WT. Although 16 patients with PA (15.7%) required 9 months or longer for recovery, the median time was the same as in those with WT (3 months).

Table 6.

Univariate and multivariate analyses for risk factors of postoperative facial paralysis in Warthin tumor.

Risk factors	Total N = 238	Postoperative facial paralysis		p-value
Risk factors	Total N = 238	Yes n − 42	No n − 196	p-value
Age, mean, y	62.9	62.6	63.0	0.745
Sex ratio, male to female	208:30	36:6	17:24	0.798
Tumor diameter, mean, mm	31.9	34.1	31.4	0.049
Tumor location ratio of superficial to lower pole to deep	79:136:23	14:17:11	65:119:12	0.001
Pain/tenderness, n	17	3	14	1.000
Adhesion ratio of mobile to limited/fixed	229:9	39:3	190:6	0.199
Operation time, mean, min	117.9	136.5	113.9	<0.001
Bleeding volume, mean, mL	28.3	35.7	26.8	<0.001
Risk factors	Odds ratio	95 % confidence interval for partial regression coefficient		p-value
Risk factors	Odds ratio	Lower limit	Upper limit	p-value
Age, < 45 years	Reference
≥45 to <70 years	0.921	0.163	5.190	0.925
≥70 years	0.621	0.098	3.960	0.615
Sex, female	1.710	0.599	4.860	0.317
Tumor diameter, ≥25 mm	2.130	0.817	5.570	0122
Tumor location, superficial	Reference
lower pole	0.676	0.305	1.500	0.334
Deep	3.310	1.130	9.710	0.029
Pain/tenderness	1.080	0.245	4.790	0.916
Adhesion, limited/fixed	1.530	0.310	7.560	0.602
Operation time, ≥120 min	2.810	1.250	6.300	0.012

Table 7.

Univariate and multivariate analyses for risk factors of postoperative facial paralysis in pleomorphic adenoma.

Risk factors	Total N = 668	Postoperative facial paralysis			p-value
Risk factors	Total N = 668	Yes n − 145		No n − 523	p-value
Age, mean, y	48.0	50.4		47.3	0.285
Sex ratio, male to female	206:462	40:105		166:357	0.338
Tumor diameter, mean, mm	24.4	27.2		23.7	0.011
Tumor location ratio of superficial to lower pole to deep	436:75:157	71:11:63		365:64:94	<0.001
Pain/tenderness, n	41	9		32	0.968
Adhesion ratio of mobile to limited/fixed	602:66	123:22		479:44	0.026
Operation time, mean, min	125.1	160.1		115.4	<0.001
Bleeding volume, mean, mL	19.6	32.8		15.9	<0.001
Risk factors	Odds ratio	95 % confidence interval for partial regression coefficient			p-value
Risk factors	Odds ratio	Lower limit	Upper limit		p-value
Age, <45 years	Reference
≥45 to <70 years	1.820	1.190	2.770		0.005
≥70 years	1.660	0.828	3.340		0.153
Sex, female	1.570	1.010	2.450		0.045
Tumor diameter, ≥25 mm	1.180	0.792	1.770		0.411
Tumor location, superficial	Reference
lower pole	0.913	0.452	1.850		0.801
deep	2.650	1.700	4.130		<0.001
Pain/tenderness	1.020	0.450	2.310		0.964
Adhesion, limited/fixed	1.500	0.824	2.720		0.185
Operation time, ≥120 min	1.990	1.290	3.090		0.002

Discussion

Pleomorphic adenoma is generally perceived to be the most common histological type of benign parotid tumor and WT to be the second most common histological type.¹² However, recent studies, primarily from Europe, found that cases of WT are increasing. Luers et al.1 showed that cases of WT increased approximately two-fold from 1990 to 2014, to a PA:WT ratio of almost 1:1. Psychogios et al.⁴ reported on 201 patients with WT and 138 with PA who underwent surgery between 2014 and 2018 and found that WT was the most common type of benign parotid tumor. Reasons for the increase in WT may be that it is more common in advanced age people, and life expectancy has been increasing in recent years; furthermore, surgery is becoming safer to perform in older people. Other reasons may be related to improved detection rates because of advances in imaging technologies and increased awareness of parotid tumors among general practitioners. Moreover, advances in surgical techniques may have increased the safety of operations on parotid tumors. Our study shows that cases of PA increased markedly from 2012 onward. Furthermore, the number of cases of WT that were managed by observation only rose from 2011 to 2021, increasing the ratio of surgery cases to observation cases to approximately 1:1. However, in the overall study period, the case number ratio of PA to WT was 1.7:1, and the number of cases of PA remained higher. When examining the PA to WT ratio in the future, studies will need to clarify whether the sample consists of only surgery cases or hospital-based cases.

Transient postoperative facial paralysis, the most problematic postoperative complication after surgery for parotid tumors, occurred in both PA and WT, and the frequency did not differ significantly between the two histological types. Multivariate analysis showed that the odds ratio for facial paralysis in both WT and PA was higher in patients with a tumor in the deep lobe than in those with one in the superficial lobe. Regardless of histological type, deep lobe tumor resection requires a larger area of nerve dissection and the operation time is often longer, which may explain the higher odds ratio for this tumor location. The time to recovery from postoperative facial paralysis was 6 months in 80% to 90% of patients, which was similar to previous reports.^13-15 Time to recovery was slightly shorter in patients with WT than in those with PA, and all patients with WT recovered within 8 months, whereas some with PA needed longer time to recover. The reason for this difference may be that WT occurs more often in men, who tend to have larger nerve diameters than women and are therefore less likely to experience paralysis in case of nerve damage, and that WT is often located in the lower pole, thereby requiring only a small amount of dissection.

Because WT is more common in advanced age people, progresses slowly, and rarely becomes malignant, managing patients by observation without surgery is a valid option for this type of tumor. A study on the rate of enlargement of WT reported an increase of .26 cm per year.⁶ When deciding to treat patients with WT by observation only, a histological diagnosis of WT should be established preferably. In the present study, about 90% of cases proved to be an accurate histopathology (WT) by the final pathological diagnosis when the parotid tumors were diagnosed as WT by preoperative FNAC, and only 3 patients (1.6%) were diagnosed as having a malignant tumor at the final pathology. Jechova et al.¹⁶ reported that 93.1% of 216 patients diagnosed with WT by FNAC were confirmed to have WT and 7 (3.2%) were found to have a malignant tumor. Borsetto et al.¹⁷ conducted a similar study and found that 89% of patients were diagnosed with WT and only 4.2% had a malignant tumor, while the rate of correct histological diagnosis in preoperative FNAC among patients diagnosed with WT at the final pathology was approximately 70% in our study.

Another useful tool for preoperative diagnosis of WT is Tc-99m scintigraphy. In this study, the positive rate of Tc-99m scintigraphy in WT was 75.4%. Miyake et al.⁷ reported that acid-stimulated Tc-99m scintigraphy had a positive rate of 94% in WT. The positive rate in benign tumors other than WT is only 8%; thus, suggesting that this test is specific to WT. The present study found good sensitivity and specificity of Tc-99m in WT.

Taken together, the above findings suggest that more than 90% of parotid tumors can be correctly diagnosed preoperatively as WT by combining FNAC and Tc-99m scintigraphy. In addition, the preoperative diagnosis rate may improve by including the typical characteristics of WT, such as advanced age, male sex, lower pole location, and bilaterality.

In theory, if WT is found to require less invasive surgery and to have fewer postoperative complications compared with PA, surgical treatment may be seen as the best treatment approach. However, we saw no evidence to support that kind of treatment strategy. Rather, because WT is more common in advanced age people and can be accompanied by systemic complications at a constant rate, an observation-only strategy is preferable in many patients. Although a reliable preoperative histological diagnosis of WT is necessary when deciding to manage a patient by observation only, this study demonstrated that this approach is nevertheless feasible in the majority of cases. If WT can be reliably diagnosed by histology, the observation approach becomes a viable option, although aesthetic issues may remain. In the future, the indication of extracapsular dissection, a less invasive operative method, may be expanded to include WT because WT commonly occurs in the lower pole and recurrence is rare¹⁸; however, this procedure also requires a reliable preoperative histological diagnosis.

One limitation of this study was the handling of observation cases because patients with WT that were either confirmed or suspected on the basis of FNAC or Tc-99m scintigraphy were considered as having WT. The correct diagnosis rate of WT by FNAC is about 90%, and the false-positive rate of Tc-99m scintigraphy is about 20%. Therefore, this group may have included about 10% of histological types other than WT. However, because the characteristic findings of WT were also used as the basis for the diagnosis, we believe that misdiagnosis was likely limited to a small percent of patients. Another limitation is that observation cases were followed up by outpatient visits for about 1 year after the decision was made to take the observation approach. However, few patients continued to visit our hospital after that time. Some of these patients may have received surgery at other hospitals, depending on the subsequent course of their condition.

Conclusion

In patients with WT, 238 underwent surgery, and 149 were managed by observation. Among the 238 patients confirmed by the final pathology to have WT, 170 (71.4%) were diagnosed with WT preoperatively by FNAC. The positive rate of Tc-99m scintigraphy in WT was 75.4%. Combining FNAC and Tc-99m scintigraphy, as well as considering clinical findings, enables the diagnosis of WT in most cases. If a reliable histological diagnosis can be made preoperatively for WT, managing patients by observation may be a viable approach, in particular because WT is more common in older adults and rarely undergoes malignant transformation.

Footnotes

Author Contributions

Ryo Kawata designed and supervised the study. Hiromi Nishimura, Ichita Kinoshita, and Ryo Kawata wrote the manuscript. Masaaki Higashino, Tetsuya Terada, and Shin-Ichi Haginomori acquired all clinical data. Takeshi Tochizawa and Ichita Kinoshita assisted in the statistical analyses. All authors performed data analysis and interpretation and approved the manuscript.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethical Approval

This study was approved by our Institutional Review Board (approval no. #2621-1, 2020).

Informed Consent

Informed consent was obtained from all individual participants included in the study.

Date Availability

Data available on request due to privacy/ethical restrictions.

ORCID iDs

Ichita Kinoshita

Masaaki Higashino

Tetsuya Terada

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