Sonographic appearance of intrathyroid ectopic thymus in children

Case 320: Intrathyroidal Thymic Tissue

HISTORY

A 7-year-old boy with a history of pleuropulmonary blastoma after resection 6 years prior and germline DICER1 mutation was being monitored by physicians at a multidisciplinary genetic predisposition clinic. He demonstrated no evidence of recurrent pleuropulmonary blastoma, and his renal US, chest radiographic, and ocular screening examination results remained normal. Per age-directed screening guidelines, he underwent thyroid US. He had no signs or symptoms of hyper- or hypothyroidism. Physical examination was notable for the absence of thyromegaly or palpable nodule. US at 12-month follow-up showed no change in size or appearance of the left lobe (not shown). However, at this time, the Thyroid Imaging Reporting and Data System (TI-RADS) classification scheme was applied to the stable left lobe finding. The findings were discussed at a multidisciplinary thyroid nodule conference, and the decision was made to bring the patient back for a short-term follow-up for limited unenhanced MRI without sedation. A diagnosis was made based on the follow-up imaging findings.

[Intrathyroidal thymus can cause confusion in the diagnosis of a thyroid mass. A case report]

Intrathyroidal thymus tissue (ITTT) is a rare, benign condition; its diagnosis can prove challenging due to unfamiliarity with this entity. However, it has ultrasonographical and cytological characteristics which can suggest its presence and thus should be considered in the differential diagnosis of thyroid nodules. Presently, immunohistochemistry can be used with fine needle aspiration (FNA) cytology, thus decreasing the need for unnecessary surgery. We discuss the usefulness of immunohistochemistry in thyroid cytology, with reference to a case of a 10-year-old patient, who underwent partial thyroidectomy for a suspicious thyroid nodule which was eventually diagnosed as ITTT by the histopathology of the surgical specimen.

Ultrasound findings of the thyroid gland in children and adolescents

Ultrasonography (US) is an important diagnostic tool in evaluating thyroid diseases in pediatric patients. This pictorial essay reviews the application of various ultrasound techniques such as B-Mode ultrasound and color Doppler, elastography and contrast enhanced ultrasound (CEUS) in children and adolescents in various thyroid pathologies including congenital thyroid abnormalities, diffuse thyroid diseases (DTD), focal thyroid lesions and thyroid malignancy.

Echographic findings in ectopic intrathyroidal thymic tissue in children. A systematic review

Intrathyroidal ectopic thymic tissue (IETT) is an indulgent, unusual entity and is part of the differential diagnosis of thyroid nodules in the pediatric population. Because of the low prevalence of IETT, the diagnosis may be difficult. Awareness of this diagnosis is definitive to avoid surgical interventions. The aim of this study was to review the literature on the echographic characteristics of IETT. We conducted a search of Ovid, PubMed and the virtual health library. A total of 619 patients with a mean age of 6.2 years old were included. IETT was located in the lower portion of both of the thyroidal lobes in 556 children, the echographic shape was reported for 173 patients, with the fusiform shape as the most representative, the appearance of the IETTs was reported for 121 patients, the most common was the hypoechogenic pattern with multiple internal echogenic foci. The average lesion diameter was 5.53 mm, and Doppler findings reported a hipovascular pattern in 56% of the lesions. In conclusion, IETT is an infrequent entity; nonetheless, it must be considered in the differential diagnosis of neck nodules in children and should be study and follow with echography to avoid unnecessary surgery.

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.

The paediatric thymus: recognising normal and ectopic thymic tissue

The appearance of the paediatric thymus changes as the normal process of thymic involution occurs. Thymic tissue may be orthotopic within the anterior mediastinum or ectopically located along the course of its embryological development. The variable appearance of orthotopic and ectopic thymic tissue in children on imaging studies may lead to misinterpretation of the normal thymus as pathology. Recognition of normal thymic tissue can mitigate unnecessary further diagnostic testing and patient anxiety. In this review, we discuss the embryological development and anatomical variants of normal thymus, and demonstrate the multimodality imaging features of the normal thymus in children, including positron-emission tomography, and diffusion-weighted imaging and in- and opposed-phase imaging on magnetic resonance imaging. We demonstrate the normal thymus mimicking pathological processes and discuss features that distinguish normal thymus, including thymic rebound hyperplasia, from pathology.

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.

Long-term ultrasound follow-up of intrathyroidal ectopic thymus in children

OBJECTIVE

To present the sonographic follow-up of intrathyroidal ectopic thymus (IET) in children and adolescent patients.

PATIENTS

Out of the 507 children referred to FNAB between 2006 and 2018, 30 (5.9%) pediatric patients (10 females), mean age 5.7 years (1.2-13.8, median 4.9 years) were diagnosed with IET.

METHODS

A retrospective analysis of medical files of patients diagnosed with IET between 2006 and 2018. Assessed data included ultrasound characterisation, elastographic strain ratio (SR) results and hormonal evaluation.

RESULTS

Analysis of thyroid US scans revealed that the mean age at the first thyroid ultrasound was 5.7 (1.2-13.8, median 4.9) years, and at the last US 10.7 (3.7-18, median 10.5) years. The mean time of the IET observation was 59.6 (2-148, median 53.5) months. On US, IET was hypoechoic with multiple linear and punctate echoes, hypovascular, fusiform on longitudinal plane and round or polygonal on an axial plane, more common in the right thyroid lobe (66.7%) and located in the posterior part of the lobes (54.5%), bilateral in two patients and multifocal in one patient. SR of IET was similar to the surrounding normal thyroid tissue. Complete regression of IET was observed in 12/30 patients after a mean time of 81.7 months (median 76.5), at the mean age of 13.7 (9.2-18, median 13.9) years. FNAB was performed in 10/30 and a hemithyroidectomy in 1/30 IET patients. In the FNAB (+) group, patients were younger (5.08 vs 6.08 years) and lesions were larger (0.12 ml vs 0.05 ml) than in the FNAB (-) group. All patients with IET were euthyroid with negative TPOAb and TgAb levels.

CONCLUSION

The reproducibility of unique ultrasound features of IETs allows for safe long-term follow-up of these benign lesions in the majority of pediatric patients: not only monitoring the regression of IET but also screening towards the rare occurrence of a tumor arising from the IET.

Pharyngeal Ectopic Thymus: A Case Report

Pharyngeal ectopic thymus is a rare cause of pharyngeal masses and is rarely considered in the differential diagnosis of neck and head masses in children. In this paper, the case of an infant with a pharyngeal ectopic thymus is presented and our intraoral surgical approach in the patient's treatment is described.

Fusiform Cervical Mass in a 6-Year Old Boy; Do not Forget the Thymic Cyst

Cervical thymic cyst is a rare clinical entity, with approximately one hundred cases reported in the literature so far. The purpose of this case report is to highlight some certain features, along with an extensive research of the relevant literature. A 6-year-old boy was admitted to the Otorhinolaryngology Department due to the presence of a left-sided, painless, latero-cervical swelling, first observed by his parents 2 weeks ago. Physical examination revealed a painless, well-delineated mass, with no signs of inflammation. No enlarged cervical nodes were present. The mass extended from the mandibular angle, under the sternocleidomastoid muscle, in proximity with the ipsilateral neurovascular bundle. Ultrasound transverse gray-scale panoramic view detected a wellcircumscribed lesion, with fine echogenic foci, appearing in close proximity with the upper pole of the left thyroid lobe and the ipsilateral common carotid artery. Elective surgical intervention with complete mass excision was performed. Histopathological examination confirmed the diagnosis of a cervical thymic cyst. Cervical thymic remnants represent a group of neck masses that pediatricians and pediatric surgeons should consider in differential diagnosis of both cystic and solid neck masses. Most cystic cervical thymic masses are found in the lower third of the anterior neck, extending deep to the sternocleidomastoid muscle, featuring close anatomic relationship with the composites of the ipsilateral carotid sheath. Elective surgery is kept as the treatment of choice, after ruling out the possibility of subject immunologic disturbance.

Multi-parametric Ultrasound Evaluation of Pediatric Thyroid Dyshormonogenesis

The aim of this study was to assess the diagnostic contribution of gray-scale ultrasonography, color Doppler, superb microvascular imaging and shear wave elastography in thyroid dyshormonogenesis (TD). From October 2017 to February 2018, the prospective study included 31 patients (13.6 y; 11-14 y) diagnosed with TD based on thyroid scintigraphy and perchlorate discharge tests and 40 healthy pediatric volunteers (12.8 y; 10-16 y). Median resistive indices (RIs), peak systolic and end-diastolic velocities, vascularity indices (VIs) via superb microvascular imaging and shear wave elastography parameters were evaluated. Median VI values were significantly higher and median RI values were significantly lower in the study group than the control group. No significant difference was found between shear wave elastography parameters of the TD and control group. VI was significantly correlated with median total thyroid gland volumes (p = 0.002, r = 0.28), medication dosage (p = 0.03, r = 0.48) and 2-h radioactive iodine uptake values (p = 0.008, r = 0.57). VI is a clinically significant and novel parameter useful for diagnosing TD.

Intrathyroidal Thymic Tissue in an Adolescent with Graves' Disease: Case Report and Review of Current Literature

Intrathyroidal thymic tissue (ITT) is a benign entity found in children and young adolescents that often mimics a concerning thyroid nodule with microcalcifications on ultrasound. It is challenging for the clinician to distinguish between these two entities, which may lead to unnecessary invasive procedures. We report an adolescent female patient with Graves' disease who underwent total thyroidectomy for a thyroid nodule concerning for malignancy for which the surgical pathology ultimately revealed ITT. As ITT is rarely found beyond childhood, the concurrent Graves' disease may have led to persistence of thymic tissue in this patient. Several sonographic features can help in differentiating ITT from a concerning thyroid nodule. Once identified, ITT should be followed by serial imaging with anticipation of decreasing size or complete resolution over time.

Intrathyroidal ectopic thymus tissue: a diagnostic challenge

OBJECTIVES

The prevalence of thyroid nodules in pediatric population is 0.2-2%, which is lower than adults. However, the probability of the nodule to be malignant is higher than adults (20-73%). Differential diagnosis of thyroid lesions in children includes intrathyroidal ectopic thymus tissue (ITT). ITT can present as a thyroid nodule, and be confused with malignancy with its hyperechoic pattern; this might cause unnecessary fine-needle aspiration biopsies and/or surgical interventions. In the current study, we mainly aim to define both US and color Doppler ultrasonography (CDUS) characteristics of ITT. We also aim to describe the most sensitive and most specific diagnostic parameters of ITT.

METHODS

We have evaluated US examination reports of 56 children for whom differential diagnosis included ITT between February 2015 and August 2018. We have recorded sonographic characteristics of the lesions, CDUS data, and thyroid hormone levels.

RESULTS

Study population consists of 56 patients (22 ITT, 34 other diagnoses). Median age of the population is 10 years. Age, sex, laboratory results, and follow-up change in lesion diameters do not show any significant difference between ITT and other diagnosis groups. Typical US appearance, fusiform lesion shape, and isovascular CDUS characteristics are higher in ITT group. The median value of the lesion's highest diameter is smaller in ITT group. The most valuable criteria to predict ITT presence were the fusiform shape and the longest diameter of the lesion.

CONCLUSIONS

Fusiform shape and a maximum diameter of ≤ 9 mm are the most selective criteria to predict ITT diagnosis.

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

Thyroid nodules with ultrasound (US) cancer risk features and extra-thyroid lesions suggesting malignant lymph nodes, require prompt diagnosis, especially in children. The US pattern of intrathyroidal ectopic thymus (IET) can strongly suggest papillary thyroid carcinoma (PTC). The extra-thyroid ectopic thymic tissue (EET) can mimic pathological lymph nodes in US. The aim of the study has been to demonstrate US features and diagnostic methods, allowing finally to confirm the presence of IET and EET in children. The US and elastographic features of 16 ectopic thymic tissue (ET) lesions were analyzed so as to describe the typical characteristics of ET and to define the best method to differentiate ET and malignant lesions. Among 16 analyzed lesions, 11 lesions were IET, and 5 were EET adjacent to the thyroid connective tissue capsule. Most of IET were located in the middle part of the right lobe and were fusiform or oval in shape. All the lesions were solid, hypoechoic, and heterogeneous with bright internal echoes. Among IET, 73% of lesions had well- or very well-defined margins. In strain elastography of IET lesions, the strain ratio was similar in all lesions, and its value ranged from 0.95 to 1.09. Despite the low prevalence of IET and cervical EET, clinicians and radiologists should be aware of US characteristics of such lesions. The confirmation of their benign character is absolutely required. Elastography is a useful tool to initially differentiate PTC and IET. However, due to high risk of malignancy in thyroid lesions in children, similarity of US features of PTC and IET, and due to the possibility of malignancy in ET, only cytological evaluation provides definitive diagnosis.

Prevalence and sonographic features of ectopic thyroidal thymus in children: A retrospective analysis

PURPOSE

To assess the prevalence of ectopic thyroidal thymus tissue detected by sonography (US) in children and to analyze the US features.

METHODS

We retrospectively reviewed images of 216 children who had undergone a thyroid or neck US examination from February 2015 to June 2015. Lesions within or adjacent to the thyroid gland that showed echopatterns consistent with thymic tissue were diagnosed as ectopic thyroidal thymus tissue. Lesions were reviewed according to their side, location, level, size, shape, echo pattern, internal content, and vascularization.

RESULTS

A total of 216 children (119 girls, 97 boys) with a mean ± SD age of 8.6 ± 5.2 years were enrolled the study.Thirty children (13girls, 17 boys) (13.9%) had 35 lesions compatible with ectopic thyroidal thymus tissue.Nine children had intrathyroidal (4.2%) and 21 children had extrathyroidal (9.7%) ectopic thymus tissue.The mean ± SD ages of the children with and without ectopic thyroidal thymus tissue were 6.0 ± 3.6 years and 9.1 ± 5.2 years, respectively (P = .002). Twenty-five of the lesions were extrathyroidal and 10 were intrathyroidal. All extrathyroidal and most (8/9) intrathyroidal ectopic thymuses had fusiform shape with well demarcated contours. Ectopic thymuses were located either in the midportion (n = 23) or lower portion of the neck (n = 12). Both extrathyroidal and intrathyroidal ectopic thymuses showed typical hypoechoic (n = 22/25, n = 9/10, respectively) or hyperechoic (n = 3/25, n = 1/10, respectively) echo patterns with internal linear and punctate echoes.

CONCLUSIONS

Ectopic thyroidal thymic tissue is common in children. Radiologists should be vigilant about the unique US features of ectopic thyroidal thymus, including a hypo- and hyper-echoic echo pattern with multiple linear and punctate echoes, a fusiform shape, well-demarcated contours, and middle or low-lying location to differentiate it from other neck or thyroid lesions.

Intrathyroidal thymic tissue in children: Avoiding unnecessary surgery

BACKGROUND/PURPOSE

Intrathyroidal thymic tissue may be misinterpreted as a thyroid lesion in children, leading to invasive tests or resection. We sought to describe the characteristic imaging features of these lesions and to evaluate the safety of non-operative management.

METHODS

A retrospective review of all patients less than 18years old with intrathyroidal thymic tissue from 2000 to 2016 was performed. Data collection included patient demographics, imaging results, interventions, and outcomes.

RESULTS

Eleven patients were identified using institutional radiology and pathology databases. Median patient age and lesion size at presentation were 5years old (range 2 to 8years old) and 0.9cm (range 0.4 to 9.2cm), respectively. Six lesions were incidentally identified, six were left-sided, and the most common location was the lower pole. Ultrasonographic features were reproducible and included well demarcated (10/11), hypoechoic lesions (11/11), containing punctate/linear internal echoes (11/11), and occasional mild hypervascularity (6/11). All cases demonstrated interval size and echotexture stability over a median surveillance period of 3years (range 1 to 8years). While 9 patients were simply observed, the first patient in this series underwent excision, while another had a fine needle aspiration to confirm pathology.

LEVEL OF EVIDENCE

Study of diagnostic test, Level IV.

CONCLUSION

Intrathyroidal thymic tissue has typical clinical and sonographic characteristics which allow for appropriate diagnosis and avoids thyroid resection.

Intrathyroidal ectopic thymus in children: A benign lesion

As ultrasound is commonly used these days, more and more lesions are found incidentally, including simple cysts, isoechoic nodules, and hypoechoic nodules, such as ectopic thymus. We here report the prevalence of ectopic thymus and its natural course.We retrospectively reviewed the charts of 690 subjects (342 males, 348 females) who were under 18 years old and had undergone neck or thyroid ultrasound at Hallym University Sacred Heart Hospital from January 2014 to June 2017. Ectopic thymus was defined when the incidental lesion was hypo- to iso-echoic compared to adjacent muscles with vascularity and did not have a connection to the thymus in the mediastinum.Of the 690 children, 16 (9 males, 7 females; median and ranges of age at diagnosis, 13 months and 18 days to 10 years) were diagnosed as having ectopic thymus. The most common location of ectopic thymus was in the inferior aspect of the left thyroid lobe. The median and ranges of the longest diameter at the time of initial diagnosis was 22.5 mm and 8 mm to 38 mm, respectively. Four cases underwent follow-up ultrasound, of which 3 cases showed no change in size and 1 case showed decreased size.Ectopic thymus should be kept in mind when a lesion is found in the neck and thyroid incidentally, and physicians should reassure parents about its benign course.

Ectopic Intrathyroidal Thymic Tissue Mimicking Thyroid Nodules in Children

Ectopic intrathyroidal thymic tissue is a benign lesion of nonthyroid origin occasionally found in the pediatric thyroid gland. Accurate diagnosis of such lesions is critical to avoid unnecessary biopsy or surgery. Twelve children referred to our center for the concern of thyroid nodules were found to have intrathyroidal thymic tissue. Most of the lesions had a classic sonographic appearance of a hypoechoic mass with sharp margins and multiple focal internal nonshadowing echogenicities identical to thymic tissue. Sonography and, in select cases, fine-needle aspiration can be used to diagnose benign thymic tissue within the thyroid and avoid unnecessary surgery.

Surveillance Neck Sonography After Thyroidectomy for Papillary Thyroid Carcinoma: Pitfalls in the Diagnosis of Locally Recurrent and Metastatic Disease

A sonographic examination of the neck performed 6 to 12 months after thyroid surgery in patients with differentiated thyroid cancer is strongly recommended by the American Thyroid Association and considered mandatory by the European Thyroid Association for locoregional surveillance. The aim of this article is to review the normal anatomic changes expected after thyroid surgery and the pathologic mimics of thyroid carcinoma recurrence in post-thyroidectomy patients as they appear on neck sonography. We hope to offer some pearls to increase diagnostic confidence in this setting.

Ectopic Intrathyroidal Thymus in Childhood: A Sonographic Finding Leading to Misdiagnosis

BACKGROUND

During gestation, the primordial thymus migrates from the pharynx to the anterior mediastinum, thus thymic tissue can remain at any point along this path. Intrathyroidal thymic remnants are rare, and their sonographic patterns have only recently been described. This retrospective study presents the sonographic appearance of ectopic intrathyroidal thymus and emphasizes the role of sonography in order to avoid misdiagnosis.

METHODS

The population consisted of 42 children, 3.5-14 years old, who had a thyroid sonogram performed due to a positive family history or symptoms indicative of thyroid disease, and ectopic intrathyroidal thymus was recognized.

RESULTS

In all patients, the same pattern was revealed: a fusiform intrathyroidal lesion, with no mass effect, homogeneously hypoechoic, with diffuse bright internal echoes. The similarity to the characteristic sonographic pattern of the normal mediastinal thymus was crucial for the diagnosis of ectopic intrathyroidal thymic tissue. In 8 cases, a normal elongated thymus was found connected to the thyroid with an accessory lobe embedded in the lower thyroid pole. The above sonographic appearances mimicked a thyroid nodule.

CONCLUSIONS

Awareness of the sonographic patterns of the ectopic intrathyroidal thymus is mandatory to avoid misdiagnosis. In most cases, further investigation is unnecessary, but sonographic follow-up should be recommended.

Intrathyroidal Ectopic Thymus in Children: Retrospective Analysis of Grayscale and Doppler Sonographic Features

OBJECTIVES

The purpose of this study was to define grayscale and color Doppler sonographic features of an ectopic intrathyroidal thymus and to differentiate it from other thyroid nodule etiologies.

METHODS

We retrospectively reviewed imaging findings from 30 children who had a diagnosis of an ectopic intrathyroidal thymus from November 2005 to January 2013. Nodular thyroid lesions that were enclosed by the thyroid parenchyma and showed a typical echo pattern consistent with the thymus were accepted as the enclosed form of an intrathyroidal ectopic thymus. Eleven of these 30 children had an intrathyroidal ectopic thymus enclosed by the thyroid parenchyma, and they were enrolled in the study. The recorded sonograms were reviewed according to side, location, size, shape, echo pattern, internal content, and vascularization.

RESULTS

The enclosed forms of ectopic intrathyroidal thymuses were unilateral in all children and located in the mid portion (n = 10) or lower portion (n = 1). All lesions were well demarcated, and the most common shape was fusiform (n = 8). Nine lesions showed a typical hypoechoic echo pattern with internal linear and punctate echoes resembling a mediastinal thymus. On color Doppler imaging, 6 lesions showed hypovascularity compared to the thyroid parenchyma, and 5 lesions showed internal vascularity.

CONCLUSIONS

Unique sonographic features of the enclosed form of an ectopic intrathyroidal thymus, including a hypoechoic echo pattern with multiple linear and punctate echoes, a fusiform shape, a well-demarcated contour, and a mid- or low-lying location with hypovascularity or internal vascularity, can help radiologists differentiate it from other thyroid nodule etiologies.

Prevalence of ectopic intrathyroidal thymus in Japan: the Fukushima health management survey

BACKGROUND

Ectopic intrathyroidal thymus is thought to be a rare entity, often discovered incidentally, and is due to aberrant thymic migration during embryogenesis.

OBJECTIVE

The aim of this study was to determine the prevalence of ectopic intrathyroidal thymus in children using ultrasound screening.

METHODS

This study was cross-sectional and was conducted with the initial preliminary survey of the Fukushima Health Management Survey between October 9, 2011, and March 31, 2012, after the Fukushima Daiichi Nuclear Power Plant accident. A total of 37,816 children were examined in the survey.

RESULTS

Diagnostic criteria are based on the ultrasonographic appearance of ectopic intrathyroidal thymus, which were round, oval, or polygonal hypoechoic or hyperechoic areas, with multiple granular and punctate echogenic foci. A total of 375 (0.99%) cases (164 girls) with ectopic intrathyroidal thymus were observed. The mean age was 7.0 years (range 0-18 years). Ectopic intrathyroidal thymus was located in the right (n=180), left (n=178), or bilateral (n=17) thyroid lobes. The incidence of ectopic intrathyroidal thymus was inversely correlated with age and body mass index.

CONCLUSION

The results reflect the prevalence of ectopic intrathyroidal thymus using ultrasonography in the general population. Further examination will be needed by way of longitudinal follow-up.

Thymus and aging: morphological, radiological, and functional overview

Aging is a continuous process that induces many alterations in the cytoarchitecture of different organs and systems both in humans and animals. Moreover, it is associated with increased susceptibility to infectious, autoimmune, and neoplastic processes. The thymus is a primary lymphoid organ responsible for the production of immunocompetent T cells and, with aging, it atrophies and declines in functions. Universality of thymic involution in all species possessing thymus, including human, indicates it as a long-standing evolutionary event. Although it is accepted that many factors contribute to age-associated thymic involution, little is known about the mechanisms involved in the process. The exact time point of the initiation is not well defined. To address the issue, we report the exact age of thymus throughout the review so that readers can have a nicely pictured synoptic view of the process. Focusing our attention on the different stages of the development of the thymus gland (natal, postnatal, adult, and old), we describe chronologically the morphological changes of the gland. We report that the thymic morphology and cell types are evolutionarily preserved in several vertebrate species. This finding is important in understanding the similar problems caused by senescence and other diseases. Another point that we considered very important is to indicate the assessment of the thymus through radiological images to highlight its variability in shape, size, and anatomical conformation.

Changes in pediatric thyroid sonograms in or nearby the Kanto region before and after the accident at the Fukushima Daiichi nuclear power plant

Following the accident at the Fukushima Daiichi Nuclear Power Station which occurred on March 11, 2011 due to the Eastern Japan Great Earthquake (the Accident), there have been concerns over elevation of the risk of thyroid cancer among children due to internal exposure to radioactive iodine. In Fukushima Prefecture, screening of children with thyroid ultrasonography has been carried out, yielding numerous findings, suggesting a possible influence from the Accident. We report thyroid ultrasonographic findings, used by similar device at Fukushima Prefecture's study, at Ito-hospital. Of the 2721 children aged 15 or less who visited our hospital between January 2005 and March 2013, 1214 children (330 boys and 884 girls; median age, 12; range of age, 4-15) were covered by evaluation of thyroid ultrasonographic findings, excluding children known in advance to have thyroid disease on the basis of disease history, palpation and blood tests. Among these 1214 children, 709 children (58.4%) were found cysts (≤ 5 mm in 665 cases) by ultrasonography, 43 children (3.5%) were found nodules (≤ 5 mm in 18 cases) and 9 children (5.2%) were found an intrathyroid ectopic thymus. Analysis of the data before and after the Accident using the same device, involving age adjustment on the basis of the standard population in 2010, showed no difference in the incidence rate of cysts or nodules. In children examined, the incidence rate of cyst formation (particularly ≤ 5 mm) was higher, and there was no difference in the incidence rate of cysts or nodules between the pre- and post-accident period.

Thyroid ultrasound findings in children from three Japanese prefectures: Aomori, Yamanashi and Nagasaki

Due to the likelihood of physical and mental health impacts following the unprecedented accident at the Fukushima Dai-ichi Nuclear Power Plant, the Fukushima prefectural government decided to conduct the Fukushima Health Management Survey to assist in the long-term health management of residents. This included thyroid ultrasound examination for all children in Fukushima. For appropriate evaluation of ultrasound screening of the thyroid, it is important to understand its reference data of thyroid findings in children in general. In order to analyze the frequencies of specific thyroid findings, we conducted ultrasound screening of the thyroid by the same procedures as used in Fukushima in 4,365 children, aged 3 to 18 years, from three Japanese prefectures. Overall, thyroid cysts were identified in 56.88% and thyroid nodules in 1.65% of the participants. Thyroid cysts and nodules with a maximum diameter of more than 5 mm were identified in 4.58% and 1.01%, respectively, and age-adjusted prevalences were 3.82% and 0.99%, respectively. Although the prevalence of cysts and nodules varied among the examination areas, no significant differences were observed among the three examination areas in the prevalence of cysts and nodules with a maximum diameter of more than 5 mm. Also, the prevalence of thyroid cysts and nodules, especially those with a maximum diameter of more than 5 mm, significantly increased with age, and showed a female predominance. We also identified ectopic thymus (1.95%), diffuse goiter (1.40%), ultimobranchial body (0.73%), lymph node swelling (0.21%) and thyroid agenesis (0.05%). This is the first ultrasound description of the age-adjusted prevalence of thyroid cysts and nodules, or of the prevalence of abnormalities other than cysts and nodules, such as ectopic thymus, in relation to age, in the general Japanese child population. We contend that this can provide relevant information for the Fukushima Health Management Survey and future population studies.

Intrathyroidal thymic tissue mimicking a malignant thyroid nodule in a 4-year-old child

Intrathyroidal thymic tissue is rare and may be confused with a malignant thyroid nodule because of hyperechoic dots mimicking calcifications. We report the case of a thyroid nodule with malignant ultrasonographic findings in a 4-year-old child, which was confirmed cytologically as ectopic thymic tissue. The sonographic findings of ectopic thymus were similar to those of the thymus; therefore, clinicians should be familiar with ultrasonography findings of normal thymic tissue.