Department of Radio diagnosis, Nair Hospital, Mumbai, India

^*Corresponding author: Naukarkar V, Department of Radio diagnosis, Nair Hospital, Mumbai, India, Phone: +91 8767207597; E-mail: naukarkarvikrant@gmail.com

Copyright: © 2023 Naukarkar V, et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Proximal interruption of the pulmonary artery (PIPA) is a rare congenital anomaly. Presentation varies from mild breathlessness to life-threatening hemoptysis. In isolation, this anomaly has a very good prognosis. But when associated with cardiac abnormalities the prognosis depends on the associated conditions. Therefore, accurate and prompt diagnosis is very essential. Here we describe a case of proximal interruption of the pulmonary artery presenting with mild hemoptysis which was managed conservatively.

Pulmonary Artery Anomalies; Interrupted; Radiology; Case Report

Proximal interruption of the pulmonary artery is an abnormality where a proximal portion of a pulmonary artery shows abnormal development with preserved, normally developed intrapulmonary vasculature. It creates a condition of chronic hypoxia which leads to a lot of physiological alterations. Here, we describe an interesting case, where PIPA led to collateral vessel formation, the rupture of which caused the patient to present with mild hemoptysis which was managed conservatively.

A 31-year-old male presented to the casualty department with complaints of acute onset on-and-off fever, mild hemoptysis, vomiting, abdominal pain, and loose stools. On probing further, he also gave a history of mild chronic dyspnea on exertion. The patient was mildly hypotensive with tachypnoea and tachycardia but maintained oxygen saturation. He denied any addictions.There was no history of any surgery in the past. A respiratory examination revealed reduced respiratory sounds on the right side of the chest. Cardiovascular, neurological, and abdominal examinations were normal.

Routine investigations were ordered as per the hospital protocol. Electrocardiographic findings were within normal limits. Hematological cell counts were adequate. Chest X-ray revealed mild elevation of the right dome of the diaphragm and apical pleural thickening. Mild blunting of the right costophrenic recess was noted. Bony thorax and heart size were appropriate. What was surprising to us was the inconspicuous right hilum and indiscernible opacity of the right pulmonary artery (Figure 1). It was decided to go ahead with computed tomography pulmonary angiography with high-resolution thoracic sections. CT revealed the right proximal pulmonary artery interruption after 1 cm of origin. The left pulmonary artery was hypertrophied (Figure 2). There was a paucity of peripheral pulmonary vasculature which appeared narrow in caliber as compared to the left side. Multiple enlarged bronchial, Trans plural collateral vessels were observed supplying right lung parenchyma. The right internal mammary artery was larger in caliber than the left. Mild pleural thickening was noted. The lung window revealed right-sided smooth interstitial septal thickening suggestive of hypertrophied collateral vessels. The tracheobronchial tree revealed no abnormalities.

Due to the recent Leptospira outbreak in the rainy season, the patient was evaluated with anti-leptospiral antibodies which came positive. Because of mild symptomatology, it was decided to treat the patient conservatively. The patient was started on ceftriaxone and adequate hydration was maintained to tackle hypotensive status. The patient improved dramatically within a week. For interrupted rightsided pulmonary artery follow-up was suggested as the patient only had associated mild chronic dyspnea on exertion (Figure 3).

Proximal interruption of the right pulmonary artery (PIPA) is a rare congenital anomaly with a reported prevalence of 1:2,00,000. Usually, PIPA occurs on the side opposite to that of the aortic arch. It is more common on the right side. When on the left side it is associated with cardiac anomalies and a right-sided aortic arch. The most common cardiac anomalies are tetralogy of Fallot, patent ductus arteriosus, and atrioventricular septal defects. Left-sided anomaly presents earlier and at a young age. Proximal pulmonary arteries develop from the proximal 6th aortic arch in the first trimester of pregnancy. The distal part of the left 6th aortic arch forms ductus arteriosus while the distal part is involuted on the right side. PIPA develops from abnormal development of the proximal part of the 6th aortic arch. Intrapulmonary vasculature has a separate origin and hence is developed normally. Three groups of the anomaly are recognized. In group 1 there is the presence of a left to right shunt most commonly patent ductus arteriosus. In group 2 associated pulmonary hypertension is present. An isolated anomaly without associated pulmonary hypertension is seen in group 3 [1].

Patients with PIPA are mostly asymptomatic or present with mild symptoms. The most common symptoms include chronic exertional dyspnoea, decreased exercise tolerance, recurrent infections, and hemoptysis. Reduced blood flow and hypoplasia of the lung lead to progressive dyspnoea on exertion. Recurrent respiratory infections are caused by the decreased delivery of systemic immunomodulators due to the interruption of blood supply proximally. Rupture of hypertrophied thin-walled collateral vessels can cause hemoptysis [2].

Diagnosis of the abnormality can be suspected on chest radiography based on findings of absent pulmonary artery opacity, and inconspicuous hilum. Other associated findings include ipsilateral lung volume loss with ipsilateral cardio mediastinal shift and elevation of the hemidiaphragm. Compensatory hyperinflation of the contra lateral lung with herniation to the opposite side can be seen. Collateral vessel formation leads to peripheral reticular opacities, pleural thickening, and rib notching. Recurrent infection can cause cystic-bronchiectasis changes.

Computed tomography pulmonary angiography (CTPA) is widely done to diagnose PIPA since it is rapid, readily available, and hasan excellent spatial resolution (Figure 4). Collateral vessels are better appreciated. Thin 0.625 mm sections are obtained from lung apices to the top of the diaphragm after giving 1.5 ml/kg contrast at the rate of 3.5-4 ml/sec bolus dose. Maximum intensity projection reformats are made. A high-resolution lung window better assesses the bronchial tree and lung parenchyma. Normally developed bronchial tree is seen. CT findings include proximal interruption of the pulmonary artery with preserved or paucity of the distal pulmonary vasculature. Lung parenchyma is perfused by systemic hypertrophied collateral vessels from bronchial, trans-pleural intercostal, internal mammary, phrenic, subclavian, and brachiocephalic arteries. These changes can lead toperipheral reticulations, pleural thickening, and rib notching. Sometimes an aberrant artery arising from the aorta can be seen supplying the lung parenchyma. Ipsilateral volume loss of lung parenchyma with mediastinal shift, crowding of ribs, and elevation of the hemidiaphragm is seen. Compensatory contra lateral lung volume expansion and hypertrophy of the pulmonary artery are noted. Intraparenchymal and subpleural cysts and bronchiectasis changes can be seen in cases of recurrent infections.

Magnetic resonance angiography (MRA) of the thorax is an alternative to a CT scan. Respiratory and electrocardiographic gating is used to acquire better images. T1 and T2 weighted TSE images in axial and coronal planes are obtained in minimum free breathing or breath holding as per the patient’s condition. Pre- and post-gadolinium contrast images with subtraction are also acquired. However, due to limited availability, long duration, and cost consideration CT is preferred over MRI. The only indication of MRI is in young patients to avoid radiation exposure (Figure 5).

Digital subtraction angiography best depicts proximal interruption of the pulmonary artery and offers simultaneous intervention in cases of hemoptysis.

Other investigations include a ventilation-perfusion scan (V/Q scan). It shows decreased perfusion on the side of interruption with maintained ventilation. Echocardiography can be done to look for associated cardiac anomalies [3].

PIPA is managed conservatively depending on the symptomatology. Rarely in case of severe symptoms intervention is needed. Recurrent infections are treated with appropriate antibiotics. Chronic breathlessness due to pulmonary hypertension seen in 19- 27% of patients requires treatment with phosphodiesterase inhibitors and endothelin receptor antagonists. Hemoptysis is seen in 10-20 % of cases. It is self-limiting most of the time. When significant, percutaneous trans-arterial embolization of bleeding collateral vessels is done. Various embolization materials include gel foam, polyvinyl alcohol, glue, and coils. It carries a success rate of 73-99 % and a recurrence rate of 10-55 %. In cases of recurrent hemoptysis even after embolization, pneumonectomy is performed. Surgical reconstruction of interrupted pulmonary artery can be done but the procedure carries high morbidity and mortality [4] (Figure 6).

Hypogenetic lung syndrome is one of the differentials where hypoplasia of lung parenchyma with anomalous venous drainage is seen. A scimitar-shaped abnormal draining vein along the right heart border differentiates this condition from PIPA. Swayer James syndrome can mimic PIPA where unilateral lung hypoplasia with increased lucency will be seen due to post-infectious obliterative bronchiolitis. Unlike PIPA air trapping will be seen on expiratory images. Primary pulmonary hypoplasia is characterized by the hypoplasia of normal lung parenchyma, bronchial tree, and pulmonary vasculature. On the contrary in PIPA bronchial tree is normal. Pulmonary artery branch stenosis is one of the differentials but can be ruled out by the absence of post-stenotic dilatation [5].

Proximal interruption of the pulmonary artery is an uncommon congenital anomaly with varied presentation. Due to the benign nature of the disease, it needs to be differentiated from other more ominous conditions by appropriate investigations. PIPA is mostly managed conservatively unless complicated by significant hemoptysis, where in percutaneous transarterial embolization or pneumonectomy is performed.