Unilateral Absence of Pulmonary Artery: An Uncommon Cause of Pulmonary Hypertensio

Abstract

INTRODUCTION: Congenital absence of one pulmonary artery is a rare entity, with a prevalence of 1 in 200,000(1). Unilateral absence of the right pulmonary artery (UARPA) often presents in adulthood, with recurrent pulmonary infections, dyspnea, hemoptysis, and pulmonary hypertension (PH; 19-25%). Unilateral absence of the left pulmonary artery (UALPA) is typically associated with congenital heart defects and diagnosed in childhood(1). We report a case of UARPA presenting with severe pulmonary hypertension who was managed with vasodilator therapy. CASE PRESENTATION: A 33 year old Filipino male was referred for the finding of UARPA on chest tomography (CT). He presented with worsening exertional dyspnea over two months, limiting him to walking 20-30 yards. Review of systems was notable for ankle swelling, and loud snoring. His past medical history was significant for obstructive sleep apnea treated with CPAP therapy. Reported medications included albuterol and fluticasone inhalers. On examination he was morbidly obese (BMI 45.2 kg/m2) in no apparent distress. His pulse was 97/minute and his oxygen saturation was 94%. He had jugular venous distension and 2+ pitting edema. Six minute walk distance was 1250 feet, with desaturation from 99% to 92% on room air. Chest CT demonstrated absence of the right main pulmonary artery with an atrophic right lung. Spirometry showed moderate restriction, and a decreased DLCO (49%). Echocardiogram revealed normal left ventricular ejection fraction, a dilated right ventricle with an RVSP of 65 mmHg, and a negative saline contrast study. VQ scanning revealed 38% ventilation with 12% perfusion to the right side. Laboratory studies demonstrated mild polycythemia, and an elevated brain natriuretic peptide (448 pg/mL). Right heart catheterization demonstrated a right atrial pressure of 17 mmHg, a pulmonary artery pressure of 124/65(mean 90mmHg), pulmonary capillary wedge pressure of 17 mmHg, Fick cardiac output of 3.23L/m and an index of 1.52L/min/m2. The patient was admitted for treatment with IV diuresis and tadalafil, and significant symptomatic improvement was noted within three days. He was discharged with an improved 6-minute walk test, and will follow up in our PH clinic for optimization of his vasodilator therapy DISCUSSION: Unilateral absence of the pulmonary artery presenting in adults is uncommon. The defect is rooted in aberrant embryogenesis (involution of the 6th aortic arch). Collaterals develop from multiple sources (bronchial, aortopulmonary, systemic, and coronary) and may cause hemoptysis(1). Recurrent infection may be due to inadequate blood supply and impaired mucociliary function(1). PH occurs when the existing pulmonary circulation has insufficient elasticity to cope with increased flow(1). Patients are often diagnosed by CXR or CT scan. CXR often shows an absent right hilum, and hyperlucent, atrophic lung. Echocardiography can detect pulmonary hypertension and exclude cardiac anomalies. VQ scanning often demonstrates diminished ventilation and absent perfusion on the affected side. CT and MRI delineate anatomic variation and collateral supply, and negate the need for pulmonary angiography (except for intervention)(1). Management strategies are limited. Pneumonectomy has been used in patients with recurrent infection or hemoptysis, but may be difficult in cases with extensive collateralization(1). Pulmonary vasodilator therapy is effective in treating associated PH(1,2). CONCLUSIONS: We present a case of an adult patient with UARPA, OSA and severe PH. This case highlights the evaluation and management of this rare condition, and attests to the efficacy of vasodilator therapy if patients develop PH.