case_images: PMC9259802_01
case_images: Successive ultrasonography (US) and contrast-enhanced ultrasonography (CEUS) images of the same largest lymph node, with dynamic changes during progression and regression. (A) The initial US showed the lymph node was in deep position, flat oval in shape, 40 mm on the long axis and 15 mm on the short axis, with a long/short ratio of >2. The lymphatic cortex was notably thickened to 12 mm and presented as a homogeneous hypoechoic area with a visible lymphatic hilum. (B) The second US showed indistinctive decrease in cortical thickness and the same lymph node size from the previous examination. (C) The third US in the follow-up showed a distinctive decrease in lymph node size and cortical thickness having irregular shape. (D) The last US showed normalized lymph node (indicated by hollow arrows). (alpha) The initial diagnosis of CEUS was based on centripetal perfusion enhancement in the asynchronous type, with a notable area in the deviated center showing hypoperfusion, covering half of the area of the lymph node. (beta) The second CEUS showed distinctive decrease in hypoperfusion area. (gamma) The third CEUS in the follow-up showed normalized enhancement and near invisibility of the hypoperfusion area (indicated by arrows).
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case_images: Ultrasonography (US) revealed multiple abnormal left axillary lymph nodes with "alarming" signs ( Figures 1A ,  2A-C ). Contrast-enhanced ultrasonography (CEUS) using SonoVue (sulfur hexafluoride microbubbles, Bracco, Netherlands) revealed an internal hypoperfusion area ( Figure 1alpha ). The US features of the abnormal lymph nodes remained nearly the same, whereas CEUS revealed a noticeable reduction in the hypoperfusion area ( Figures 1B, beta ). In the follow-up at 6 months after vaccination, US demonstrated a notable decrease in the size and cortical thickness of the largest lymph node; the previous hypoperfusion area shown on CEUS was hardly visible ( Figures 1C, gamma ). The US indicated complete resolution on the second follow-up at 8 months after vaccination ( Figure 1D ).
case_images: (A-E) Images of multiple abnormal lymph nodes (indicated by arrows) at 4 months after vaccination. (A) One small abnormal lymph node in the nearly spherical shape, with a long/short ratio of <2, the notably thickened lymphatic cortex with an invisible lymphatic hilum, yet superb microvascular imaging confirmed the blood distribution of hilar type. (B, C) Elastography of one of the same abnormal lymph nodes. (B) Shear wave elastography demonstrated a modulus of 9.7 kPa. (C) Real-time tissue elastography demonstrated the hardness ranging from 'median' to 'soft'. (D) US-guided fine-needle aspiration of one superficial lymph node. (E) Computed tomography demonstrated the left axillary lymphadenopathy. (F) Hematoxylin and eosin staining under 100x magnification showed reactive hyperplasia.
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case_images: Ultrasonography (US) revealed multiple abnormal left axillary lymph nodes with "alarming" signs ( Figures 1A ,  2A-C ). The relevant diagnostic workup revealed the following: complete blood count (CBC) demonstrated a slight decrease in eosinophils (0.01 x 109/L), the computed tomography (CT) of the head, neck, and chest was normal, and the US of the thyroid, breast, and lymph nodes in other parts of the body and abdomen was also normal ( Figure 2E ). Macroscopically, the resected abnormal lymph node was soft and yellow-grayish; the microscopy revealed nonspecific reactive hyperplasia ( Figure 2F ), and the immunohistochemistry was negative for tumors.
case_images: Timeline of diagnosis, interventions, and prognosis. US, ultrasonography; CEUS, contrast-enhanced ultrasonography.
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case_images: The timeline of diagnosis, interventions, and prognosis for this case is shown in  Figure 3 .