Teaching Case

57-year-old male on bike, hit a car. Fractures of left 3rd-8th ribs on plain radiographs. CT scan (Figure 1) showed a small hemothorax and a pseudoaneurysm of a segmental or subsegmental branch of the left lower lobe pulmonary artery. Hemodynamically stable. No hemoptysis or dyspnea.

What caused the pseudoaneurysm?

Transcatheter angiography was obtained via right common femoral vein approach (7 French sheath).
Mean pulmonary arterial pressure was normal. Angiograms showed filling of an ellipsoid pseudoaneurysmal sac, the opacification of which was slightly delayed (within seconds) relative to the parent vessel and adjacent pulmonary arterial vasculature (Figure 2).
A subsegmental, laterobasal pulmonary artery branch was the single feeding vessel of that PAP and was embolized with detachable microcoils (from 4 to 6 mm in diameter and 10-20 cm in length).
Post-embolization angiograms (Figure 3) confirmed occlusion of the parent subsegmental vessel and exclusion of the pseudoaneurysmal sac at the late phase.
Patient underwent subsequent surgical rib fixation. No complications were observed after a 5 months follow-up.
Motion of an adjacent rib close to the pseudoaneurysmal sac could be seen in real-time (Video 1): the mobile rib fragment migrated medially during inspiration and laterally in expiration, consistent with flail chest pathophysiology).

Background

Pulmonary arterial pseudoaneurysms (PAP) are uncommon and usually arise in context of thoracic infections (e.g., tuberculosis (aka Rasmussen PAP), pneumonia, mycotic tricuspid endocarditis) (33%), trauma (17%), and neoplasms (13%) [1-4]. In traumatic etiologies, they are seen in penetrating injuries, either external stab wounds to the chest or iatrogenic manipulations (e.g., pulmonary arterial catheter insertion [2], cardiothoracic surgeries, percutaneous lung tumour ablations and biopsies [5,6]). They may arise either early or years later [1,7].

Clinical Perspective

While true aneurysms of the pulmonary arterial system are more often central in location, pseudoaneurysms are more commonly peripheral (83% of lesions) and solitary (83% of patients). Clinical presentation can be asymptomatic or include hemoptysis, dyspnea, or both [1]. Mortality (reportedly in the 50-100% range) can result from vessel rupture with asphyxia and aspiration from intrapulmonary haemorrhage or from sudden cardiac death due to pulmonary arterial dissection [8].

Imaging Perspective

The key finding on both contrast-enhanced multidetector computed tomography and transcatheter angiographic imaging studies is the focal saccular outpouching of a pulmonary arterial branch. The lesion may be unsuspected clinically prior to its detection by imaging (9%) and can be easily missed on early CT studies (46% in one series of PAP from all causes) [1].

Outcome

Endovascular treatment is the first-line option, consisting typically of embolization of the PAP sac and/or the parent vessel. Although coils and microcoils were initially the embolic agents of choice, newer devices too are now available for parent vessel occlusion, 2 such as Amplatzer plugs (currently being increasingly used for pulmonary arteriovenous malformations) and microvascular plugs; yet their relative rigidity and the peripheral location of PAPs can at times make this option difficult and potentially unsafe. Percutaneous injection of cyanoacrylate or thrombin under CT guidance has been reported as an alternative when endovascular treatment is not feasible [9]. Surgery, consisting of arterial ligation or lung resection, is often avoided in these critically ill patients [3,7,10].

Take-Home Message / Teaching Points

PAP in trauma are typically related to penetrating trauma. In this case with blunt external trauma and flail chest pathophysiology, the PAP likely
resulted from an internal “penetrating injury” due to paradoxical motion of an adjacent rib fragment in and out of the chest during respiratory cycles and shearing forces exerted on the adjacent lung parenchyma (Video 1). The patient did not develop subsequent bronchopleural fistula or recurrent PAP or bleeding.