How to differentiate Lung Mass from Mediastinal mass?

Sometimes, it might be quite difficult..

Sometimes, it might be quite difficult to differentiate a lung mass from a mediastinal mass, especially when the mass in lying close to the mediastinum. In such cases, you can differentiate the two by following the table and looking at the images.

Lung mass

Mediastinal mass

It projects usually on one side of the hemithorax

It may project on both sides of the thorax or on one side. But if you see a mass projecting on both sides of the mediastinum, it is definitely a mediastinal mass

It will have poorly defined margins with the lung, in most cases.

The margins of the mass with the lung with be well defined.

The centre of the mass will lie in the lungs

Centre of the mass with lie in the mediastinum

The mass will make acute angle with the mediastinum

The mass will make obtuse angle with the mediastinum.

Fig- Lung mass ( first figure) and mediastinal mass ( second figure).

Note the centre of the mass, the angle with the mediastinum , and the outline of the mass . In the first image, the mass is making acute angles with mediastinum, has irregular margins and centre of mass lies in the lung. But in the second image, the mass is arising from the mediastinum and extending to the area of lung, so it is making obtuse angle with the mediastinum. The mass has sharp margins

Note the lesion in the left hilar region, which is having irregular interface with the adjacent lung, acute angles with the mediastinum and with centre of the circle drawn outlining the mass in the lung, suggesting the lesion to arise from the lung. This is a left hilar bronchogenic carcinoma.Case courtesy of Dr Ian Bickle, Radiopaedia.org, rID: 50353

Note there is opacity in the right apical region, which has obtuse angle with the mediastinum. The lesion has sharp interface with the adjacent lungs. This is a mediastinal mass arising from the superior mediastinum, and not a lung mass.  Case courtesy of Dr Henry Knipe, Radiopaedia.org, rID: 30542.

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