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

Abstract

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.

Thyroid nodules in children and adolescents

“…The majority of adult criteria for selection of nodules for FNA apply to children and adolescents with the following exceptions; first, ultrasound features and clinical context should be used rather than size alone to identify nodules that warrant FNA [9]; second, solid nodules appear to have an increased risk of malignancy in pediatric patients compared with adults; third, intrathyroidal thymic tissue, a variation of normal embryology and thyroid-thymic migration, may mimic a thyroid nodule (Fig. 1) [62,63]; and fourth, a widely invasive form of PTC called diffuse sclerosing variant PTC (dsvPTC) presents with nonnodular, diffuse infiltration of the thyroid associated with microcalcifications throughout the gland, a 'snow storm' appearance on ultrasound (Fig. 1) [64][65][66].…”

Fine needle aspiration of hematolymphoid lesions of the thyroid: Onsite adequacy and ancillary testing

“…[ 17 ] Ultrasound findings that suggest malignancy include microcalcifications, irregular borders, and hypoechogenicity. [ 18 ] Features which indicate malignancy may be determined using the thyroid imaging reporting and data system (TI-RADS). TI-RADS refers to any of several risk stratification systems for thyroid lesions usually based on ultrasound characteristics.…”

“…[ 1 , 20 , 21 ] Identification of some of these features on ultrasound prompts the provider to pursue testing to rule out malignancy. [ 18 ] Rarely, ectopic non-thyroidal tissue may be detected on ultrasound as a thyroid nodule with concerning features. Thus, in accordance with current guidelines, any thyroid lesion found in a child, except for pure cysts, requires thorough evaluation including FNA.…”