Unilateral absent pulmonary artery in an adult - A diagnostic and therapeutic challenge.

Unilateral absent pulmonary artery (UAPA) is a congenital abnormality rarely diagnosed in adults. UAPA has a myriad of clinical presentations and pulmonary hypertension is present in a quarter of all cases. Isolated UAPA commonly affects the right pulmonary artery and occurs as a result of abnormal development of the sixth aortic arch segment. Due to its rarity, it remains a diagnostic and therapeutic challenge. We describe a case of UAPA in an adult presenting with severe pulmonary hypertension. We describe the appropriate diagnostic approach to a patient with pulmonary hypertension and illustrate the importance of a detailed evaluation to determine the underlying aetiology, particularly in rare causes. Furthermore, we review the clinical presentation, diagnosis and management challenges of UAPA in adults.

Introduction

Unilateral absent pulmonary artery (UAPA) is a rare congenital abnormality due to pulmonary artery agenesis, most commonly of the right pulmonary artery, and may present as a cause of pulmonary hypertension in adults [1]. No consensus exists regarding therapy and it is a diagnostic challenge [2]. We highlight this condition presenting with pulmonary hypertension, review therapeutic principles for UAPA in adulthood and demonstrate that to ensure an accurate diagnosis of rare causes of pulmonary hypertension a high index of clinical suspicion and close scrutiny of investigations is necessary.

Case report

A 53-year-old woman, with well-controlled hypertension and hypothyroidism, presented to the emergency department with sudden onset of dyspnoea associated with palpitations. On examination, her blood pressure was 60/40 mmHg with a pulse rate of 160 beats per minute and she was noticeably cyanosed. Her respiratory examination was normal but on cardiovascular examination she was tachycardic and on auscultation a loud pulmonary component of the second heart sound and a murmur of tricuspid regurgitation were present.

An electrocardiogram (ECG) showed a supraventricular tachycardia (SVT), which was terminated following synchronized electrical cardioversion, using intravenous midazolam titrated to effect for sedation under the direction of an emergency medicine physician (Fig. 1). The subsequent ECG demonstrated features of right ventricular hypertrophy with pressure overload: a right axis; an associated S1T3 pattern; a qR pattern in lead V1; T wave inversion in leads V2–V4 and p - pulmonale (Fig. 2). Subsequently, the patient was started on therapeutic low molecular weight heparin along with intravenous amiodarone, to maintain sinus rhythm and prevent the possible recurrence of the hemodynamically unstable supraventricular tachycardia, and admitted to the Intensive Care Unit for monitoring.

Fig. 1

Supraventricular tachycardia with features of right ventricular strain.

Fig. 2

Sinus rhythm, right axis deviation, p – pulmonale, an S1T3 pattern, a qR pattern in V1 and T wave inversion in V2–V4 suggesting right ventricular hypertrophy and pressure overload.

Transthoracic echocardiography showed a dilated right ventricle with severe tricuspid regurgitation and a pulmonary artery pressure of 120 mmHg. The left atrium and ventricle were normal with an ejection fraction of 73%. The pulmonary function test showed a low diffusion capacity of 45% with a normal FEV1, FVC and FEV1/FVC ratio. Due to her initial SVT and marked pulmonary hypertension a diagnosis of chronic thromboembolic pulmonary hypertension (CTEPH) was initially suspected. On chest radiograph, a small oligaemic right lung field and empty right pulmonary bay (hilum) was noted with hyperinflation and plethora of the left lung field and a prominent left pulmonary artery (Fig. 3). A radionuclide ventilation/perfusion scan showed a barely visible right lung field on perfusion images but was well visualized on ventilation images. The computed tomography pulmonary angiogram (CTPA), following close review, demonstrated an absent right pulmonary artery with abrupt cutoff and atresia after its origin and no collateral circulation to the right lung was noted (Fig. 4, Fig. 5). A massive right pulmonary artery clot was excluded and the atretic right pulmonary artery was confirmed on cardiac magnetic resonance imaging (MRI), which also showed an increased right ventricular mass and end-systolic volume with reduced systolic function (Fig. 6). A right heart catheterization confirmed high pulmonary pressures measuring 130/38 mmHg; a mean pulmonary artery pressure of 76 mmHg and 23.4 Woods units. A nitric oxide vasoreactivity test was negative with pulmonary pressures measuring 121/41 mmHg, a mean pulmonary artery pressure of 76 mmHg and 18.02 Woods units post the administration of inhaled nitric oxide. This was performed with a senior anaesthetist and cardiologist present, as great care should be taken in the sedation of patients with severe pulmonary hypertension.

Fig. 3

A chest radiograph with oligemia and volume loss of the right lung field and an empty right pulmonary bay. The left lung filed is plethoric with compensatory hyperinflation and an enlarged left pulmonary artery.

Fig. 4

Computed tomography pulmonary angiogram showing an absent right pulmonary artery with abrupt cut – off and atresia at its origin (arrow).

Fig. 5

3D - Reconstructed computed tomography pulmonary angiogram showing an absent right pulmonary artery with abrupt cut – off and atresia at its origin (arrow).

Fig. 6

Cardiac magnetic resonance imaging showing an absent atretic right pulmonary artery (arrow).

The patient remained stable throughout the admission but due to her age surgical re-vascularization was deemed not possible. She was started on supplemental home oxygen therapy, sildenafil for her pulmonary hypertension, oral furosemide due to clinically evident right heart failure and an antiarrhythmic and has remained stable on therapy.

Discussion

Unilateral absent pulmonary artery (UAPA), first described by Frentzel in 1868 [3], is a rare congenital malformation and occurs in 1 in 200,000 adults with a median age of presentation of 14 years [1], [4], [5]. Agenesis of the pulmonary artery occurs due to altered development of the sixth aortic arch segment that does not connect to the pulmonary trunk and in two thirds of cases affects the right pulmonary artery, the side opposite to the aortic arch [4], [5], [6]. Often it occurs in association with other cardiac defects, such as tetralogy of Fallot or septal defects, but it can occur in isolation, as in our patient [1], [2], [4]. The distal vessels of the affected lung remain intact and are vascularized by bronchial vessels and abnormal collaterals from bronchial, subclavian, intercostal and sub-diaphragmatic arteries [4], [7], [8].

In UAPA the pulmonary hypertension occurs on the basis of pulmonary arterial vascular remodeling where increase pulmonary blood flow to one lung, through the single patent pulmonary artery, results in increase shear stress with subsequent endothelial intimal injury. This increased pulmonary blood flow stimulates the release of endothelin, which acts as a potent vasoconstrictor and stimulates vascular smooth muscle proliferation with resultant intimal hyperplasia, medial hypertrophy and, ultimately, collagenous replacement of the intima in late disease. A similar phenomenon occurs to some patients who have undergone a pneumonectomy, particularly of the right lung, who develop pulmonary hypertension [9], [10], [11], [12].

The clinical presentation of patients with UAPA is varied and some patients may be asymptomatic. A review of 108 cases in 2002 showed that 40% of patients presented with poor effort tolerance and dyspnea; 37% presented with a combination of recurrent chest infections, pleural effusion and chest pain and 12% with high altitude pulmonary oedema – although the reason patients with UAPA were predisposed to high altitude pulmonary oedema could not be elucidated in the study [5]. Haemoptysis, which may be life threatening, originating from hypertrophied bronchial vessels or peripheral arteriovenous fistulas was present in 20% [2], [4], [5], [6]. Pulmonary hypertension was present in 25% of patients with UAPA and, in conjunction with pulmonary haemorrhage, is an important determinant of long-term survival [5], [7], [13]. Common causes of death in UAPA include: massive pulmonary haemorrhage, respiratory failure and right heart failure with an overall mortality rate of approximately 7% [5], [7].

The diagnosis requires a high index of clinical suspicion and subsequent close scrutiny of radiological imaging, particularly when no other cause for pulmonary hypertension can be identified. Features that would provoke clinical suspicion of the diagnosis on a chest radiograph may include the presence of asymmetric lung fields with a reduced lung volume and shift of mediastinal structures to the affected side. Furthermore, an empty pulmonary bay reflecting the absent hilar vasculature on the affected side may be noted, whilst compensatory hyperinflation or a plethoric lung field, due to increased pulmonary blood flow, may be seen on the opposite side [5], [7], [13]. The diagnosis can subsequently be confirmed using non-invasive radiological imaging such as CT or MRI [2], [4], [7]. Ventilation-perfusion scintigraphy will demonstrate normal ventilation but absent perfusion on the affected side [7]. Although pulmonary angiography remains the gold standard for diagnosis, it is rarely performed due the reliability of non-invasive imaging [2], [4], [7], [13].

Other differential diagnosis for UAPA with a hyperlucent lung field would include: a massive pulmonary embolism, which in this case was ruled out with the use of cardiac MRI that demonstrated pulmonary artery atresia. The Swyer – James syndrome, a childhood viral or mycoplasma infection with resultant bronchiolitis, is most frequently diagnosed in childhood but can remain asymptomatic until adulthood; additionally the chest CT scan would have evidence of bronchiectasis and air trapping [14], [15]. Another congenital cardiovascular syndrome characterized by a hypoplastic right lung and pulmonary artery is the Scimitar syndrome (pulmonary venolobar syndrome), where a curved anomalous right pulmonary vein, resembling a scimitar sword, drains into the systemic venous system and the mediastinal structures are displaced into the right hemithorax [16], [17].

In adults, there is no consensus on therapy and as such UAPA remains a therapeutic challenge. Asymptomatic patients can be monitored for the development of pulmonary hypertension with serial echocardiography [4]. Surgical re-vascularization, through an aortopulmonary shunt or connection to the main pulmonary artery, is most successful in the paediatric population and not favored in older patients due to the presence of irreversible lung hypoplasia [2], [18], [19]. Rather, in adults therapy is tailored to the patient's clinical presentation. In those with pulmonary hypertension, vasodilator therapies such as endothelin receptor antagonists, calcium channel blockers and intravenous prostacylcins have been used [2], [5]. Selective embolization of the systemic collateral circulation may be used to treat massive haemoptysis [2], [20]. However, due to the technical challenges associated with embolization as a result of the extensive collateral circulation that is present in UAPA, pneumonectomy may be favored - except in those patients with a high operative risk [2], [20]. In patients with recurrent infections: pneumonectomy or lobectomy is recommended as therapy of choice, as the affected lung does not contribute to ventilation [2], [4], [5]. Heart-lung transplant has also been suggested as a modality of therapy in a patient with established pulmonary hypertension and pre-existing congenital heart disease with UAPA [6].

Conclusion

In our patient CTEPH was considered as the initial clinical diagnosis, but after close evaluation of the radiological investigations, this diagnosis was revised to UAPA. This case highlights the diagnostic challenges that may be faced in patients presenting with rare causes of pulmonary hypertension and the high index of suspicion and close scrutiny of basic and specialized investigations that is necessary when considering the aetiology. In adults UAPA remains a rare entity and may prove difficult to diagnose, moreover, it may present in several ways and therapy should be tailored to the patient's clinical presentation.

Disclosure

The authors have no conflicts of interests to declare.