case_images: PMC9664199_01
case_images: Cervical computed tomography scan (A, B).
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case_images: Cervical computed tomography (CT) showed a left thyroid mass (diameter: 5.5 cm) with uneven density and a plain CT value of 63 Hounsfield units (HU) ( Figure 1A ), suggestive of an adenoma. An enhanced scan showed multiple blood vessels in a heterogeneously enhanced lesion with a CT value of 133 HU ( Figure 1B ). The timeline with relevant data from the episode of care is presented in  Figure S1 .
case_images: Histological features of the intraoperative frozen sections of thyroid paraganglioma (A-D) and follicular adenoma (E, F). Scale bars: 400 mum (A, B), 200 mum (C, D), 300 mum (E), and 100 mum (F).
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case_images: Intraoperative frozen section showed an uneven fibrous septa and rich networks of delicate vessels surrounding tumor cell nests ( Figures 2A, B ). The tumor tissue comprised polygonal or epithelioid cells with eosinophilic cytoplasm arranged in a nesting, trabecular, or organoid pattern ( Figures 2C, D ). Follicular adenoma shows a mild, atypical, organizational structure comprising tumor cells ( Figures 2E, F ).
case_images: Histological features of the postoperative paraffin section (A-C) and immunohistochemical examination (D-J) of thyroid paraganglioma. Scale bars: 400 mum (A), 300 mum (B), and 100 mum (C-J). CgA, chromogranin A; CT, calcitonin; Syn, synaptophysin.
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case_images: Postoperative paraffin sections are shown in  Figures 3A-C . The tumor cells were negative for AE1/AE3, TTF1, and calcitonin ( Figures 3D-F ), and positive for chromogranin A and synaptophysin ( Figures 3G, H ). S-100 protein staining showed elongated sustentacular cells at the periphery of the tumor cell nests ( Figure 3I ). The Ki67 index was approximately 7% ( Figure 3J ).