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The chest X-rays of these groups of children are pneumonia? Or a normal image? Doctor Gu Pei is stunned *Only for medical professionals. What are the characteristics of pediatric thymus images? Recently, there are several chest radiographs of children with respiratory diseases, which have caused doubts among young training physicians, as shown in Figure 1 and Figure 2 below: Figure 1 shows: the left chest radiograph shows signs of pneumonia in the upper right; the right chest radiograph shows signs of pneumonia Figure 2 shows the thymus shadow: the left chest X-ray shows signs of pneumonia in the upper right; the right chest X-ray shows the thymus shadow in the above two groups of pictures, can you distinguish which one is a pneumonia sign and which is a normal thymus image? Read the following text first, then click and slide up to view the answer. Figures 1 and 2 on the left both show that large flakes and cloudy blurred shadows can be seen in the upper right lung. Combined with the clinical manifestations of the child, such as fever, cough, audible auscultation, and decreased breath sounds, The appearance of phlegm sounds or fine moist rales can be clearly identified as signs of pneumonia; the right image of Figure 1 shows a unilateral dense and uniform triangle, the inner edge is connected to the mediastinum, the lower edge is located at the horizontal lobe fissure, and the edges are clear and sharp. The right image in Figure 2 shows that the inner edge is located in the mediastinum and the outer edge extends obliquely from the inside to the outside. Although it seems that the edge is not clear due to the influence of the hilar shadow, the radiologist can visualize it at different levels. Signs of the same tissue were observed. The chest X-rays of the two groups are very similar, as the saying goes: two rabbits walk next to the ground, can Anneng tell whether I am male or female? This requires our clinicians, especially young doctors in the imaging department, to understand and be familiar with the imaging manifestations of the infant thymus. The imaging manifestations of the thymus in infants and young children vary widely, which often leads to doubts and difficulties in diagnosis. It is often misdiagnosed as lobar pneumonia, atelectasis, mediastinal tumor, heart disease, etc. So the question arises: where is the thymus located? What is the function of the thymus? What are the imaging findings on X-rays of the thymus? The normal thymus is divided into left and right lobes and the middle isthmus, and the general shape is conical. Each lobe has an independent fibrous capsule, located in the anterior and superior mediastinum behind the sternum, up from the lower border of the thyroid, down to the level of the 4th to 6th anterior ribs, and occasionally up to the level of the diaphragm. The anterior is close to the posterior border of the sternum, and the posterior is close to the trachea, innominate artery, aortic arch and pericardium from top to bottom. As shown in Figure 3. The thymus gland weighs about 10g-12g at birth, and weighs about 30g-50g at puberty, and then gradually shrinks with age, and is basically replaced by fat at the age of 60. Figure 3. Anatomical diagram of normal thymus and adjacent tissues. Source: Baidu Encyclopedia The thymus is an important lymphoid organ in the body. Its function is closely related to immunity and plays an important role in human immunity, especially cellular immunity. The thymus gland secretes thymic hormones and hormone-like substances, and is an organ with endocrine function. It is also the site of T cell differentiation, development and maturation, which can continuously induce all stages of T cell differentiation and development and enhance the response of mature T cells to antigens or other stimuli. The thymus also has the function of regulating the immune balance of the body, so when the thymus has lesions, it will have a serious impact on the immune function of the body. Many factors can affect the size of the thymus, such as fever, hunger, disease can shrink, and then increase in recovery. The thymus can be shown on the chest X-ray of children under 2 years old, and the performance is more obvious. Occasionally seen in children 2 to 8 years old, rarely seen above 8 years old. Various imaging manifestations of the thymus The thymus has a variety of X-ray manifestations, including the following imaging manifestations: 1. Sail type: unilaterally distributed, dense and uniform, in the shape of a spinnaker, the inner edge is located in the mediastinum, and the outer edge is It descends from the inside to the middle of the lung, and the edge is sharp. As shown in Figure 4 below. Figure 4: sail-shaped thymic shadow 2. Triangle: Unilateral, dense and uniform, the tip of the triangle points to the hilum, the inner edge is connected to the mediastinum, the lower edge is located at the horizontal lobe fissure, and the edges are clear and sharp. As shown in Figure 5 below. Figure 5: Triangular thymic shadow 3. Strip: bilateral or unilateral, dense and uniform, the inner edge is connected to the mediastinum, the lower edge is located at the horizontal lobe fissure, and the edges are clear and sharp. As shown in Figure 6 below. Figure 6: Bar-shaped thymic shadow 4. Circle: one or both sides, dense, round or semi-circular, with no obvious demarcation between the inner edge and the mediastinum, and the outer edge of the arc is clear and sharp, and the outer edge is blurred. As shown in Figure 7 below. Figure 7 shows: round thymic shadow 5. Huge mass shape: unilateral or contralateral, dense, the density of the outer band gradually decreases, occupying the entire upper lung field and part of the middle lung field, the lower edge is clear and sharp, and the outer edge is blurred. As shown in Figure 8 below. Figure 8: After roughly grasping the characteristics of the thymus shadow in the giant mass-like thymus shadow, let's look at the difference between the two groups of X-ray shadows encountered by young doctors (slide up the question, click the blank to see the answer). How should indistinguishable thymus glands be identified? It is worth noting that: (1) The rare ectopic thymus is caused by the disorder of thymus transition during fetal development. Most commonly in the neck, but can also occur in front of the trachea or behind the superior vena cava. Ectopic thymic tissue can cause airway obstruction or have a neoplastic effect on other tissues. It must be differentiated from true mediastinal tumors, and MRI may be better used in the differentiation. (2) Normal thymic shadow sometimes needs to be differentiated from thymic cyst, lymphoma, thymoma, teratoma and thymic lipoma. As shown in Figures 9 and 10 below. Figure 9: A phyllodes thymic lymphoma (image via Medscape). Figure 10: A thymoma at the right cardiac border (image via Medscape). When X-rays cannot clearly diagnose normal thymic shadows, CT and MRI examinations should be performed in a timely manner, and age and clinical manifestations can be used for identification. (3) Some patients with myasthenia gravis often have thymic hyperplasia, and X-ray and CT scans in these patients may have normal thymic shadows. (4) Individual differences in the size of the thymus in children are relatively large, and it is difficult to compare the size and shape of the thymus in different children at different ages. (5) A professor of respiratory department once said: For infants with thymic shadows, if the child takes hormone drugs for a few days, the normal thymic shadows on the chest X-ray will disappear. It may be because hormones are immunosuppressive agents. We have not tried to verify, but this can also be used as a method of identification. (This article has been helped and guided by radiologists Sun Gang and Guo Xiuhu, and I would like to express my gratitude.) Source of this article: Medical Pediatrics Channel Author of this article: Zhang Guangcheng Editor in charge: Xiang Yu The pediatric clinical knowledge doctor station app you want to see is all Yes 👇 1. Scan the QR code below the code 2. 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