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case_images: Subglottic masses in the 2-year-old boy presenting with stridor. Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) scan of the neck showed (A) an abnormal soft-tissue density shadow on the medial side of bilateral thyroid upper pole with corresponding slightly narrowed airway (arrow). The thymus shadow was larger and seemed to extend to the neck. Transverse view of T1-weighted and Iterative Decomposition of water and fat with Echo Asymmetric and Least-squares estimation (IDEAL) T2-weighted MRI showed (B) isointense T1 and (C) hyperintense T2 masses in left of the trachea at the level of the thyroid gland and at the edge of the left and right lobe of the thyroid gland. (D) The masses enhanced slightly in contrast-T1-weighted transverse view. The trachea (arrow) was locally narrowed at the level of the thyroid gland.
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case_images: Abnormal signal was found at the thyroid level on neck Magnetic Resonance Imaging (MRI) scan (Fig. 1B-D); the abnormal signal measuring 7.8 x 5.7 x 12.6 mm was located on the left side to the trachea surrounding the thyroid gland. CT value of the mass was 76HU, followed by 80HU after contrast administration (Fig. 1A).
case_images: Intra-tracheal extension of the thymus in the 2-year-old boy presenting with stridor. Ultrasound showed (A) the tracheal ring (the dark area marked by an arrow) and thymus tissue (stars). Ectopic thymus was seen invading the trachea and presenting as heterogeneous hypoechoic masses of lymph nodes. (B) Color Doppler Flow Imaging (CDFI) blood flow chart; tracheal ring (arrow); ectopic thymus tissue (stars).
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case_images: Ultrasonographic appearance through the neck showed a hypoechoic lesion, characterized by multiple internal echogenic foci giving a "starry sky" appearance and ill-defined borders in the posterior aspect of the superior part of the left thyroid lobe (Fig. 2), which was similar to the thymus in the anterior mediastinum, suggesting the possibility of ectopic thymic tissue.
case_images: Direct Laryngoscopy and Bronchoscopy (DLB) showed (A) a subglottic semicircular mass with smooth mucosa, obstructed 70% laryngeal cavity (pre-operation). (B) Subglottic obstruction was significantly relieved (immediate post-operation). (C) Laryngeal obstruction was significantly relieved (a week after surgery).
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case_images: Direct Laryngoscopy and Bronchoscopy (DLB) examination under general anesthesia was performed, revealing a subglottic semicircular mass with smooth surface mucosa and obstruction of 70% of the subglottic cavity (Fig. 3).
case_images: Pathohistology and immunohistochemistry. (A) Ectopic thymic tissue with Hassall corpuscles (arrow), H&E x100. (B) Ectopic thymic tissue with Hassall corpuscles (arrow), H&E x200. (C) CD1a+, x200. (D) CK+ (epithelial expression), x200. (E) TdT+, x200.
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case_images: Postoperative pathohistological examination showed Hassall corpuscles (Fig. 4).