Cytomorphology and sonographic features of ectopic thymic tissue diagnosed in paediatric FNA biopsies

Abstract

Ectopic thymic tissue is rarely present as a neck mass or thyroid nodule on FNA biopsy. The ultrasound imaging findings reveal a well-defined fusiform lesion with punctate bright echoes that could be misinterpreted as papillary thyroid carcinoma. The aspirates show a small lymphoid population, immunophenotypically compatible with thymic T-cells, in addition to scattered epithelial cells. Therefore, knowledge of the typical ultrasonographic and cytopathological features can help make a definitive diagnosis and avoid more invasive procedures in paediatric patients.

Ectopic cervical thymus in children: Clinical and radiographic features

“…Limitations of the current study include lack of pathology results to confirm diagnosis of ECT, and the fact that some children did not have follow‐up after initial diagnosis. Previous studies have used biopsy or FNA testing to confirm the high correlation between characteristic ultrasound features and the diagnosis of ectopic thymic tissue . Because this correlation has been demonstrated in the literature, we do not routinely biopsy lesions exhibiting these features unless the child is symptomatic or the diagnosis unclear.…”

“…Most children underwent ultrasound imaging alone. Ultrasound imaging may be a reasonable option for diagnosis and surveillance in many cases as long as providers proceed with FNA or biopsy if there is growth or concerning features . Ultrasound is particularly useful in children as it avoids the need for general anesthetic and prevents radiation exposure.…”

“…Figure contains separate images of an intrathyroidal ECT lesion and a nodule suspicious for papillary thyroid carcinoma. These lesions appear quite different; however, fine needle aspiration or excisional biopsy should be performed if providers are unable to rule out malignancy with surveillance alone . On the other hand, providers may feel more comfortable with ultrasound surveillance of lesions with benign‐appearing characteristics that seem to be an extension of mediastinal thymic tissue (Type A).…”

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

“…Some studies have confirmed that the presence of an intrathyroidal thymus through cytology or surgery due to the fear that children with suspicious thyroid lesions are misdiagnosed ( 4 5 12 13 15 16 21 22 ). However, a few studies on the ultrasound characteristics and the prevalence of intrathyroidal thymus were based on US images only, without cytological evaluation, and suggested that US could be used as a common diagnostic tool to identify a benign intrathyroidal thymus ( 11 13 17 23 ).…”

“…However, because US has become more frequently used in children, the characteristic features of intrathyroidal thymic tissue used to distinguish it from thyroid nodules have been reported more often, and this intrathyroidal thymus is now more frequently found as a common variant ( 8 11 12 13 14 15 ). Until 2015, 59 cases of ectopic thymic tissue mimicking thyroid nodules or neoplasia detected on US had been published and more cases have been reported since ( 12 13 15 16 17 18 ). The US features of an intrathyroidal thymus are similar to those of a normal thymus.…”