Rasmussen aneurysm is an uncommon complication of pulmonary tuberculosis and represents a pulmonary artery aneurysm adjacent to or within a tuberculous cavity. Usually distributed peripherally and beyond the branches of the main pulmonary arteries.

A weakening of the pulmonary artery wall from adjacent cavitating tuberculosis is the cause of this condition. There is a progressive weakening of the arterial wall as granulation tissue replaces both the adventitia and the media. This is then gradually replaced by fibrin, resulting in thinning of the arterial wall, pseudoaneurysm formation, and subsequent rupture with hemorrhage. 

Hemoptysis is the usual presenting symptom and may be life-threatening when it is massive.