Asymmetric normal thymus

Case contributed by Dr Yusra Sheikh


Presented to the Emergency Department with shortness of breath.

Patient Data

Age: 4 months
Gender: Male

There is a large mass in the right hemithorax appearing contiguous with the cardio-mediastinal contour on this side. The right pulmonary vasculature is seen behind the mass. There is no mediastinal shift. In particular, there is no tracheal displacement. Left lung is clear.  There is no pleural effusion on either side.

This was felt to represent a normal thymus, likely asymmetric. An ultrasound was subsequently performed to confirm the above.


Ultrasound confirms that the mass is lobulated and appears contiguous with the thymus, lying predominantly to the right of the pericardium without any underlying mass effect on the heart or vessels. No suspicious or concerning features.

Case Discussion

The normal thymus is a great mimicker of lung pathology. Anytime a mass is identified on a child's chest radiograph, it is important to ask oneself if that could be the thymus. A normal thymus, no matter how big it is, does not displace the trachea. In a younger child, ultrasound can easily be used to assess the thymus.

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Case information

rID: 68935
Published: 20th Jun 2019
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included

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