Sonographic and Elastographic Features of Extra- and Intrathyroidal Ectopic Thymus Mimicking Malignancy: Differential Diagnosis in Children

Case Reports: A role of postoperative radiation therapy in completely resected early stage intrathyroid thymic carcinoma: a case report and literature review of the diagnosis and treatment

Background

Intrathyroid thymic carcinoma (ITTC) is a rare malignant tumor of the thyroid, probably arising from ectopic thymus or branchial pouch remnants. Most of the literature recommended radical resection as the fundamental treatment for ITTC, and postoperative radiation appears to be able to reduce the recurrence rate in patients with advanced ITTC. However, the issue of adjuvant radiotherapy in completely resected early-stage ITTC has been controversial.

Case presentation

Here, we reported a new case of early-stage ITTC that treated with total thyroidectomy and the right central neck dissection. Postoperative external beam radiation therapy (50.0 Gy/25 fractions) was given to the thyroid bed and bilateral cervical lymph node area since the tumor involved part of the sternal thyroid muscle. At 4-year follow-up after completion of radiotherapy, she is without evidence of locally recurrent or distant disease.

Conclusion

Since there are no current guidelines for early-stage ITTC, in combination with this case and previous literature, we may suggest routine adjuvant radiotherapy should be considered in patients with incompletely resected tumors and extraparenchymal extension of ITTC. Moreover, we summarized comprehensive and advanced diagnosis, treatment, prognosis of ITTC and comparison between ITTC, primary squamous cell carcinoma of thyroid gland, differentiated thyroid cancer, and anaplastic thyroid cancer.

Intrathyroidal ectopic thymus: Ultrasonographic features and differential diagnosis

Intrathyroidal ectopic thymus (IET) is defined as an ectopic thymus tissue that is generally found incidentally and rarely in the thyroid gland in the pediatric group. It occurs as a result of disruption of the embryological migration path and the settling of the thymus tissue into the thyroid gland. In the differential diagnosis, it is mostly confused with thyroid nodules. Although thyroid nodules are less common in children than adults, the rate of malignancy is much higher. Therefore, knowing the general ultrasound findings of IET better may prevent unnecessary invasive attempts and surgical procedures. In this article, we tried to compile the key imaging findings of IET.

The Role of Superb Microvascular Imaging and Shear Wave Elastography in Differentiation of Thyroid Nodules from Intrathyroidal Ectopic Thymus in Children

BACKGROUND

Ectopic thymus could be located intrathyroidal, therefore fine ultrasound details are useful for this differentiation.

AIM

To investigate differences in stiffness and vascularity properties among thyroid nodules and intrathyroidal ectopic thymus (IET) by obtaining quantitative data in children.

PATIENTS AND METHODS

Twenty-seven thyroid nodules and 20 IET in children were evaluated in terms of vascularity index (VI) via superb microvascular imaging (SMI) and stiffness by shear wave elastography (SWE). Differences in the volume, VI, and SWE parameters of the lesions were assessed by using the Mann-Whitney U test. Association of the age, lesion volume, SWE, and VI parameters was investigated by using Spearman's correlation analysis. The optimal cut-off values for stiffness and vascularity in the differentiation of nodules from IET were calculated with ROC analysis.

RESULTS

The median (range) age of the participants with thyroid nodules and IET were 15.6 (10-18) years and 8.8 (3-14) years, respectively. The medians (range) VI of the IET and thyroid nodules were 4.7 (0.2-16) % and 23.8 (7.5-40)%, respectively. The median SWE values were 7.6 (4.4-9.5) kPa and 15.58 (8.5-23.4) kPa for IET and nodules, respectively. There have been highly significant differences among medians of volume, SWE, and VI values of the lesions. Significant positive correlations were found between VI and SWE parameters (p=0.001, r=0.64), and volume with VI (p=0.018, r=0.34) and SWE (p:0.001, r= 0.5). The diagnostic accuracies were 93%, 91% with the cut-off values as 9.2 kPa, 13% for the SWE and SMI, respectively. IETs were found to be less vascular and less stiff than thyroid nodules.

CONCLUSIONS

IETs could be easily and confidently differentiated from nodules using SWE and SMI quantifications. This discrimination prompts the reduction of unnecessary interventional procedures.

Intrathyroidal Ectopic Thymus and Sonoelastographic Findings

BACKGROUND

Intrathyroidal ectopic thymus (IET) can be misdiagnosed as thyroid nodules.

PURPOSE

To evaluate the sonoelastographic findings of IET in pediatric population.

METHODS

Twelve children who had been examined with ultrasound (US) and strain elastography between December 2012 and December 2019 were included in this retrospective study. The patients' demographics and ultrasonographic findings including the location, margin, shape, diameters, volume, structure, vascularity, and elastography values of the lesions were evaluated.

RESULTS

Twelve lesions were detected in 12 asymptomatic patients (3 females and 9 males) with a mean age of 4.67 ± 2.27 years. The most common location of the IET was in posterior part and middle third of thyroid, and the most common appearance on US was a well-defined, ovoid-shaped, and predominantly hypoechoic solid lesion with punctate/linear branching hyperechogenities. The lesions were mostly hypovascular on Doppler US. The mean strain ratio on elastography was found to be 1.10 ± 0.04. In the follow-up of 7 patients with available information, there was not any significant change in size or appearance of IET on US.

CONCLUSION

IET should be considered in the differential diagnosis of the lesions within the thyroid. The first step to accurately diagnose an IET is to consider it in the differential diagnosis. In addition to US, strain elastography findings can be used to distinguish IETs from papillary thyroid cancers which can have similar US appearance, and help avoid unnecessary biopsies.

Interobserver Agreement and Plane-Dependent Intraobserver Variability of Shear Wave Sonoelastography in the Differential Diagnosis of Ectopic Thymus Tissue

Shear wave elastography (SWE) has been demonstrated to be a useful tool in the differential diagnosis of ectopic thymus tissues (ETs), providing quantitative values of the shear wave stiffness (SWS) of both ETs and adjacent thyroid tissue. However, no data are available on the potential influence of the imaging plane (transverse vs. longitudinal) on the obtained SWS and shear wave ratio (SWR) values in SWE of these tissues. Moreover, no reports on the interobserver repeatability of SWE were published in regard to ETs. The aim of this study has been to evaluate the potential influence of the examination plane—transverse vs. longitudinal—on the SWS and SWR results, as well as to determine whether SWE of ETs is subjected to interobserver variability. SWE was demonstrated to have high inter- and intraobserver agreement in the evaluation of ETs and adjacent thyroid tissue. Significant differences between SWS values, but not SWR values, obtained in the transverse and longitudinal planes were observed. This phenomenon is probably a result of anisotropy-related artifacts and does not reduce the reliability of the method. SWE operators should be aware of the presence of plane-dependent artifacts to properly interpret the obtained results.

Normative values of thymus in healthy children; stiffness by shear wave elastography

PURPOSE

Thymus grows after birth, reaches maximal size after the first few years and involutes by puberty. Because of the postnatal developmental and involutional duration, we aimed toinvestigate normal stiffness values of mediastinal thymus by shear wave elastography (SWE) in different age groups of children and discuss imaging findings of thymus.

METHODS

We prospectively examined 146 children (90 girls, 56 boys) who underwent a thyroid or neck ultrasound examination. All subjects underwent ultrasound and SWE evaluation of mediastinal thymus by parasternal and suprasternal approach. We subdivided the subjects based on the ages as 0 to 2 months (group 1), >2 to 6 months (group 2); >6 months to 2 years (group 3), >2 to 5 years (group 4), >5 to 8 years (group 5), and greater than 8 years old (group 6).We investigated differences of mean shear wave elasticity (kPa) and shear wave velocity (m/sec) values among age groups and the association of SWE values with age, body mass index (BMI), height, and weight of the patients.

RESULTS

Medians and ranges of age, height, weight, and BMI were 24 (2-84) months, 85 (55-120) cm, 12(4.55-22) kg, 15.37 (13.92-17.51) kg/m2, 11 (2.64-23.15) cc, respectively. Mean shear wave elasticity of thymus when all participants were included was 6.76±1.04 kPa. Differences of mean elasticity values among age groups and also gender groups were not statistically significant. There were highly significant negative correlations among age (r:0.3), height (r:0.26), weight (r:0.3) with elasticity and also velocity values (p<0.001). The thymus elasticity is negatively correlated with age.

CONCLUSION

Quantitative evaluation of the thymus by SWE provides normative stiffness values based on age and gender groups. The thymus elasticity decreases with increased age, height and weight.

Application of Shear Wave Sonoelastography in the Differential Diagnosis of Extra- and Intra-Thyroidal Ectopic Thymic Tissue

The ultrasound (US) pattern of intrathyroidal ectopic thymus (IET) can resemble papillary thyroid carcinoma (PTC) while the extrathyroidal ectopic thymus (EET) can mimic pathological lymph nodes. Recently, the usefulness of strain elastography (SE) was demonstrated in the differential diagnosis, however this method has several limitations. The aim of the current study was to assess the usefulness of shear wave elastography (SWE) in this field. The US, SE, and SWE were performed in 31 children with 53 ectopic thymuses (ETs) and quantitative values of SWE parameters were calculated, so as to generate potential normative values of ET elasticity and of the shear wave ratio (SWR). The mean SWR_IET was 0.89 ± 0.21 and the mean shear wave stiffness (SWS) was 7.47 ± 1.93 kPa. The mean SWR_EET was 0.84 ± 0.15 and the mean SWS_EET was 11.28 ± 2.58 kPa. The results have proven that the stiffness of ETs is lower or equal to the thyroid’s. SWE was demonstrated to be a useful diagnostic method for ET evaluation. Therefore, the application of SWE in ET diagnosis allows more accurate evaluation of ET-like lesions and, in many cases, allows one to avoid invasive procedures, simultaneously providing a precise monitoring method based on combined US and SWE evaluation.

Long-Term Follow-Up Ultrasonographic Findings of Intrathyroidal Thymus in Children

Objective

To analyze long-term follow-up sonographic findings of intrathyroidal thymus in children.

Materials and Methods

Among 1259 patients with congenital hypothyroidism under 15 years of age who underwent thyroid ultrasonography (US), 41 patients were diagnosed with an intrathyroidal thymus based on US criteria, i.e., hypoechoic solid lesion with punctate and linear echogenicity. In 26 patients aged one to 14 years old, the last follow-up US was performed after 6 to 132 months and compared with the initial US. The lesion was considered to decrease in size if there was a change of more than 2 mm in any dimension. The margin change was divided into well-defined and indistinct, blurred. When the echogenicity changed to a hyperechoic from a characteristic thymic echogenicity pattern, the pattern was considered a hyperechogenic. The changes in size were compared with the changes in shape, margin, and echogenicity pattern. The changes in size, shape, margin, and echogenicity were analyzed the association with the age of last follow-up. Statistical analysis was conducted using the chi-squared test and logistic regression.

Results

Fifteen (57.7%) cases were stable in size, and 11 (42.3%) decreased in size, including one that disappeared. Ten (38.5%) cases changed to indistinct margins from initially well-defined margins including one case of initially indistinct margin. Six (23.1%) changed to hyperechogenic, from initially characteristic thymic echogenicity patterns. When follow-up change was compared, decreases in size were significantly associated with lesion changes to indistinct margins (p = 0.004). The age at last follow-up was significantly associated with change to hyperechogenicity (odd ratio, 2.141; 95% confidence interval, 1.144–4.010, p = 0.017).

Conclusion

On follow-up US, an intrathyroidal thymus may be decreased in size, with indistinct margins, or show changes to a hyperechoic mass. Decreases in size may be associated with changing to indistinct margins, and changes to hyperechogenicity may be associated with increasing age.

Ectopic thymus as a cause of Horner's syndrome

Ectopy of the thymus is a rare anomaly arising during fetal development, where the thymus does not make a complete decent into the thoracic cavity where it should involute in adolescence. The most common complications of an ectopic thymus include tracheal or esophageal compression presenting in childhood. This is a report of a single case of ectopic cervical thymus identified in a 2-month-old infant presenting with Horner's syndrome. Thymic ectopy should be on the differential when performing a radiologic evaluation of a neck mass when imaging characteristics are similar to thymic tissue.