Abstract: Mycobacterium tuberculosis in children with pulmonary tuberculosis under three years of age, of which immune organs are not mature, most likly spreads among blood circulation pathway, even lead to disabiling or lethal tuberculous meningitis. So it is essential that pulmonary tuberculosis of these children are diagnosed accurately and early. But these factors, including vague chief complicated with sympotoms or atypical sympotoms, collection of qualified sample and low reactivity caused by immature immune function, have made serious trouble for clinical diagnosis and treatment. Therefore CT imaging diagnosis for pulmonary tuberculosisin childre nunder three years of age is extremely important because CT imagines have high density resolution and image clarity.Based on achievements so far and our practical experience, characteristics of chest CT imagines of pulmonary tuberculosisin children under three years of age may be summarized as following: ①nodular, inflammatory, mass, interstitial and other forms shadows scattered in four or more lobes, especially at the lower. ②enlarged hilar and mediastinal Lymph node of moderately dense shadow among over 90% of cases and calcified lesion among over 50% cases, mainly located at the upper right tracheal (2R), lower right tracheal (4R), aortic arch (5 area), subcarinal (7 area), lower mediastinum (8 area) and right hilar (10R). ③ axillary lymph node enlargement more common on the left side. ④ miliary lesions or miliary nodules due to acute, subacute or chronic dissemination in about 10% of cases. more than 25% presented intracranial tuberculosis in head MR. ⑤emphysema next to the lesion and tracheobronchial lesion more than one quarter or about 6% respectively. These characteristics of chest CT images are very useful to help diagnosis of tuberculosis in children under three years of age.

Key words: Tuberculosis/Lung, Children, Tomography/X-ray computer