The thymus is a T-cell producing lymphoid organ in the anterior mediastinum that plays a role in the development of the immune system, particular the maturation of T-cells. It typically has a retrosternal location and hence can mimic retrosternal pathology. In Infants presenting with repeated respiratory tract infection, after ruling out other system involvement, Higher imaging techniques must be utilized to differentiate physiological from pathological lesions so as to clinch diagnosis and implement relevant intervention. This rare case in a 7-month infant shows how a left upper zone persistent shadow, a rare X-ray findings of left thymus is misdiagnosed as persistent pneumonia or pulmonary sequestration and how imaging helps in avoiding unnecessary treatment.

Keywords: T-cell; Lesions; Immune system; Pneumonia.