Radiological Diagnosis

Rasmussen's Aneurysm

Axial CECT section of the thorax shows a left upper lobe cavity with an eccentric enhancing nodule (white arrows in [Figure - 1],[Figure - 2]. Coronal reconstruction shows a pseudoaneurysm arising from a branch of the left upper lobar pulmonary artery (arrow in [Figure - 3]). These findings suggest Rasmussen's aneurysm. The patient succumbed to massive haemoptysis two days later.

Discussion

Rasmussen's aneurysm, named after the Danish physician Fritz Valdemar Rasmussen (1837 - 1877) is the dilatation of a small-medium sized pulmonary artery in a tuberculous cavity. It is a rare phenomenon caused by weakening of the pulmonary artery wall from adjacent cavitary tuberculosis [1]. Historically it was termed a pulmonary artery erosive pseudoaneurysm. The destructive process can affect a systemic artery of the lung or chest wall or the thoracic aorta itself. When a pulmonary artery branch is tangentially approached by cavitary tuberculosis, there is a rupture of the media and an eccentric protrusion of the thickened intima in the cavity. Progressive weakening of the arterial wall occurs as granulation tissue replaces both the adventitia and the media. The granulation tissue in the vessel wall is then gradually replaced by fibrin, resulting in thinning of the arterial wall, pseudoaneurysm formation, and subsequent rupture [2],[3].

Haemoptysis of variable amount results from the intimal rupture. Bleeding in the cavity is expectorated or results in autocompression of the ruptured aneurysmal sac. A review of autopsy findings in patients with a history of chronic cavitary tuberculosis showed a 5% prevalence of Rasmussen aneurysm [3]. It is usually solitary, located in the upper lobe. It may lead to rupture and haemorrhage. Haemoptysis is present in one third of the patients and is the usual presenting symptom. It may be life-threatening when the haemoptysis is massive. It is fatal in 5% of cases. It can also be multiple. Rasmussen aneurysm has to be systematically searched for in patients with haemoptysis from a destructive process of the lung. Once revealed, its treatment is imperative.

Spiral CT angiography, including pulmonary and systemic phases; help plan the surgical or endovascular treatment. It can be simultaneously perfused by the pulmonary and the systemic circulation. With an appropriately timed bolus of iodinated contrast material, pulmonary artery pseudoaneurysms appear as enhancing, round lung masses that are isodense to the central pulmonary arteries. Apart from the diagnosis of pulmonary arterial lesion, spiral CT can also provide useful pretherapeutic information, especially prior to embolotherapy. In the latter situation, it is important to identify the feeding vessels prior to hyperselective catheterization and occlusion. In addition to transverse CT scans, 3D SSD and 3D MIP can help identify the relationship of the aneurysmal sac with the artery to be occluded, the number of aneurysms and the spatial orientation and diameter of the arteries before catheterization. Immediately after a bleeding episode, the aneurysm sac can be collapsed in the cavity. Consequently further CT angiography is advised a few hours after an episode of haemoptysis. Spiral CT is considered the noninvasive modality of choice in the work-up of pulmonary artery aneurysms prior to therapeutic interventions [4],[5].

These pulmonary artery aneurysms may lead to the formation of arteriovenous fistulas. Both the aneurysms and fistula can be treated by percutaneous intervention if necessary. The initial treatment of choice for this entity is percutaneous catheter embolization [3],[5][6].