Rupture of a mediastinal collateral aneurysm associated with unilateral absence of pulmonary artery

Abstract

Isolated unilateral absence of pulmonary artery is a rare congenital malformation and often asymptomatic in adults. However, aneurysm formation in the aortopulmonary collateral vessels carries a potential risk of life-threatening hemorrhage. This case report describes a 79-year-old woman who presented with rupture of a mediastinal collateral aneurysm associated with isolated unilateral absence of pulmonary artery. We discuss the clinical course, including vascular morphology changes, and subsequent endovascular treatment. Notably, this case demonstrates the rupture of a de novo collateral aneurysm rather than a preexisting one.

Unilateral absence of pulmonary artery (UAPA) is a rare congenital anomaly often associated with other cardiac malformations. However, it can also present alone, known as isolated UAPA (IUAPA), with an estimated prevalence of approximately 1 in 200,000 adults.¹ In the absence of a native pulmonary artery to provide adequate blood supply to the lung, systemic-to-pulmonary collateral vessels develop, forming an aberrant vascular network that may lead to aneurysm formation.² Although adult patients with IUAPA are often asymptomatic, rare but severe complications such as massive hemorrhage secondary to aneurysm rupture can occur.^3,4 We herein describe a patient with a ruptured mediastinal collateral aneurysm associated with an IUAPA and discuss the clinical course, including vascular morphology changes before and after rupture. The patient has provided written consent for publication of this case.

Case report

A 79-year-old woman with a history of IUAPA, right-sided aortic arch, aortic stenosis (without other congenital anomalies such as bicuspid aortic valve) treated with transcatheter aortic valve implantation 4 years prior, hypertension, hyperlipidemia, and rheumatoid arthritis presented to the emergency department with complaints of sudden-onset chest and back pain. Recent medication history included an oral corticosteroid for rheumatoid arthritis discontinued 1 month before presentation and oral lascufloxacin, a fluoroquinolone antibiotic, taken for parotid swelling for 2 days before admission. Hemodynamic status on arrival was stable. Blood biochemical findings were largely within normal reference ranges, except for a decreased hemoglobin level (10.1 g/dL). Acute myocardial infarction was excluded in the emergency department.

Computed tomography (CT) showed a 20-mm pseudoaneurysm arising from a fusiform 30 mm aneurysm in the mediastinal collateral vessels, surrounded by mediastinal hematoma without extravasation (Fig 1). This aneurysm had not been visible on CT performed four years earlier (Supplementary Fig, online only). In addition, four saccular aneurysms and one fusiform aneurysm (all <20 mm in diameter) were identified in collateral vessels (Fig 2). These aneurysms had not changed in size significantly from 4 years earlier. A diagnosis of ruptured mediastinal collateral aneurysm associated with IUAPA was made, prompting urgent endovascular intervention.

Fig 1.

Computed tomography angiography (CTA) image showing a 20-mm pseudoaneurysm surrounded by mediastinal hematoma. Arrow denotes the pseudoaneurysm.

Fig 2.

Reconstructed computed tomography angiography (CTA) images showing the absence of the left main pulmonary artery and excessive systemic-to-pulmonary collateral arteries with multiple aneurysms (red). Arrow shows a ruptured aneurysm. The scan also shows right-sided aortic arch.

A 6F guiding sheath (Destination; Terumo) was inserted through the right common femoral artery. A mediastinal collateral artery arising from the distal descending aorta was coaxially catheterized with a 5F polyurethane catheter (RLG; Hanako Medical) and a 1.7F microcatheter (Carnelian Pixie; Tokai Medical Products). Angiography demonstrated that this artery supplied the left lower lung lobe and revealed a saccular pseudoaneurysm originating from a fusiform aneurysm located in the middle third of the collateral artery (Fig 3, A). Advancement of the microcatheter to the aneurysm outflow vessel was unsuccessful owing to arterial tortuosity. Angiography performed with the catheter tip positioned proximal to the aneurysm did not demonstrate a pulmonary vein fistula. Although angiography did not visualize other systemic arteries, preprocedural CT suggested small anastomoses between the distal segment of the mediastinal collateral artery and other systemic arteries, including the subphrenic and bronchial arteries. Therefore, after test injections with contrast media, a 1:1 mixture of N-butyl cyanoacrylate (NBCA) (Histoacryl; B. Braun) and iodized oil (Lipiodol; Gerbet) was administered as a bolus injection to completely embolize the aneurysm, taking care to avoid embolization of the distal collateral anastomoses (Fig 3, B).

Fig 3.

(A) Angiogram showing a pseudoaneurysm (arrow) originating from the fusiform aneurysm in mediastinal collateral artery. Arrowheads show a fusiform aneurysm with focal stenosis. (B) Angiogram showing the N-butyl cyanoacrylate (NBCA)-iodized oil mixture (arrow) in the embolized mediastinal collateral aneurysm. (C) Reconstructed computed tomography (CT) arteriography image showing NBCA cast (arrow) in the aneurysm and adjacent arteries.

No postprocedural complications were encountered, and CT performed after the embolization confirmed NBCA filling within the aneurysm and adjacent arteries (Fig 3, C), with no evidence of pulmonary infarction. Oral lascufloxacin was changed to intravenous ceftriaxone after admission and the antibiotic was later discontinued when parotid swelling was ultimately determined to be noninfectious. The patient was discharged and remained well at the 1-month outpatient follow-up.

Discussion

Ruptured aortopulmonary collateral aneurysms associated with IUAPA are extremely rare. In this case, CT angiography (CTA) imaging from 4 years before the rupture allowed for longitudinal morphological assessment. Notably, no abnormalities were detected at the eventual rupture site on the prerupture CTA, although five other aneurysms visible on the same prerupture CTA that did not change in size on postrupture CTA. These findings indicate that new collateral aneurysms may form and rupture at a faster rate than preexisting ones. However, owing to the absence of interval imaging between the prerupture and postrupture CTAs, the growth rate of the ruptured aneurysm could not be evaluated.

Aneurysm formation observed in patients with aortopulmonary collaterals is thought to be caused by chronic high-flow velocities through excessive collateral arteries.⁵ This sustained hemodynamic stress on the vascular wall can disrupt the balance between mechanical load and vascular wall integrity, thus leading to aneurysm formation. In this case, we also considered other factors that may have compromised vascular integrity, including atherosclerosis, arterial dissection, infection, connective tissue disorders, and the concomitant use of fluoroquinolones with corticosteroids. Ultimately, clinical and microbiological findings from this patient did not support an infectious etiology. Based on the morphological characteristics of the ruptured aneurysm, arterial dissection was possibly associated with the aneurysm formation.⁶

Although no consensus exists on the risk of vascular injury with fluoroquinolone use, the US Food and Drug Administration has warned against their use in high-risk patients, including those with a history of aneurysms of the aorta or other blood vessels. Although the exact mechanism has not been confirmed, quinolones exhibit a high affinity for connective tissues. Adverse events such as Achilles tendon rupture can occur within 48 hours of starting fluoroquinolone treatment.⁷ Furthermore, concurrent and recent use of oral corticosteroids strongly increased the risk of Achilles tendon rupture in elderly patients receiving fluoroquinolones.⁸ Considering these concerns and the potential impact on vascular wall integrity, we decided to discontinue the fluoroquinolone treatment in this patient.

No consensus has been reached regarding the optimal management of hemorrhage from collateral vessels in patients with IUAPA. Therapeutic management should be guided by the clinical presentation and the patient's anatomy, including associated collateral circulation.^1,9 Treatment options include endovascular or surgical occlusion of collateral vessels or pneumonectomy on the affected side to control hemorrhage.¹ In this case, endovascular interventions were favored over surgery owing to the increased risk of bleeding from the extensive collateral circulation.¹⁰

Transcatheter treatment of pseudoaneurysms can be performed by embolization of the inflow and outflow vessels. Embolic agents such as coils and NBCA are commonly used materials. Coils are generally preferred when the microcatheter can reach the outflow vessels, because the risk of tissue ischemia is lower than with NBCA. However, NBCA provides an effective alternative in cases where catheterization of the outflow vessel is not possible,¹¹ as was the case in our patient. NBCA and iodized oil are not currently approved in the United States for embolization of a peripheral aneurysm. Before embolization, careful assessment of the flow rate and downstream arterial anatomy is essential. In this case, we considered the risk of pulmonary infarction after embolization to be low if the collateral circulation was preserved. Care must also be taken to avoid unintended reflux of the NBCA, especially in the presence of an excessive collateral network.

Conclusions

Aneurysm formation in the aortopulmonary collaterals in patients with IUAPA is a rare but potentially life-threatening condition. This case demonstrates the clinical course and vascular morphology changes before and after aneurysm rupture, highlighting the importance of careful observation not only of known aneurysms but also of the entire collateral vasculature on imaging.

Funding

None.

Disclosures

None.