PMC9889852_01
Ultrasonography images of adult-type rhabdomyoma of the thyroid. (A) Conventional gray-scale sonography revealed a solid and hypoechoic thyroid nodule (arrow) in the left lobe. (B) Color Doppler flow imaging showed a relatively rich blood flow signal inside this nodule (arrow). (C) Contrast-enhanced ultrasound image showed hypoenhancement of the nodule (arrow) in the arterial phase. (D) Shear wave elastography showed a lower stiffness of the nodule (arrow) compared with that of the thyroid.
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A hypoechoic solid nodule (measured 50 mmx 23 mm x 23 mm) with a clear boundary was found in the enlarged left lobe of the thyroid, and punctate echogenic foci was not detected on ultrasonography ( Figure 1A ). Blood flow signals within and around the nodule were shown by Color Doppler flow imaging ( Figure 1B ). The lesion showed heterogeneous hypoenhancement during the whole procedure of CEUS ( Figure 1C ). Moreover, the lesion was soft according to the stiffness measurement by shear wave elastography (SWE) (Emax=5.3 kPa, Emean=4.2 kPa, Emin=3.2 kPa, Ratio=0.4) ( Figure 1D ).
CT images of adult-type rhabdomyoma of the thyroid. Plain CT images revealed the left thyroid lobe was obviously enlarged, and there was a lesion (arrow) with slightly low density in the left thyroid lobe.
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The lesion showed slightly low density with unclear boundary in the enlarged left thyroid lobe on plain computed tomography (CT) ( Figure 2 ).
Pathological findings of adult-type rhabdomyoma of the thyroid. (A) Histopathological section (hematoxylin and eosin staining). (B) Immunohistochemistry result showing the expression of desmin. (C) Immunohistochemistry result showing the expression of MyoD1. (D) Immunohistochemistry result showing the expression of myogenin. (E) Immunohistochemistry result showing the expression of smooth muscle actin. (F) Immunohistochemistry result showing the expression of S-100 protein.
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Histologic examination of the tumor showed that it consisted of bland spindle cells, immature elongated cells with bipolar cytoplasmic extensions, strap-type rhabdomyoblasts with abundant eosinophilic cytoplasm and round vesicular nuclei displaying a fascicular growth pattern ( Figure 3A ). On immunohistochemistry, the tumor had strong desmin ( Figure 3B ) and weak sparse myoD1 expression ( Figure 3C ), while myogenin ( Figure 3D ), smooth muscle actin ( Figure 3E ), S-100 protein ( Figure 3F ), thyroglobulin, thyroid transcription factor 1, cytokeratin, and paired box protein 8 were negative.