Looking beyond the thrombus: essentials of pulmonary artery imaging on CT

Abstract

Background: Pulmonary arteries are not just affected by thrombus. Congenital and acquired conditions can also involve the pulmonary arteries. An awareness of these conditions is important for the radiologist interpreting chest computed tomography (CT).

Methods: The anatomy of the pulmonary arteries was reviewed. CT and magnetic resonance (MR) acquisition protocols for imaging the pulmonary arteries were discussed. The imaging appearances of congenital and acquired anomalies involving the pulmonary arteries, using CT and other modalities, were presented.

Results: Imaging features of congenital anomalies presented include pulmonary agenesis, partial pulmonary artery agenesis, patent ductus arteriosus, pulmonary artery sling, congenital pulmonary artery stenosis and coronary to pulmonary artery fistula. Acquired pulmonary artery anomalies discussed include arteritis, infected aneurysm and sarcoma. Pulmonary artery filling defects besides thromboembolism are also discussed, including foreign body emboli. Imaging features of bronchogenic carcinoma and mediastinal fibrosis demonstrating compression of the pulmonary arteries are presented, followed by a brief discussion of post repair appearance of the pulmonary arteries for congenital heart disease.

Conclusions: Congenital and acquired pulmonary artery anomalies have a characteristic appearance on a variety of imaging modalities. An acquaintance with the imaging features of these anomalies is needed to avoid misinterpretation and reach the correct diagnosis. Teaching Points • Discuss a variety of congenital and acquired anomalies of the pulmonary arteries. • Discuss the imaging appearance of the presented congenital or acquired pulmonary artery anomalies. • Describe CT and MR acquisition protocols for imaging the pulmonary arteries. • Review the anatomy of the pulmonary arteries.

Fig. 1

a Frontal radiograph of a patient with sinus venosus atrial septal defect demonstrates a dilated pulmonary artery, pulmonary oedema, left pleural effusion and cardiomegaly. The right lower lobe pulmonary artery measures 26 mm. b Contrast-enhanced axial CT image demonstrates an enlarged main pulmonary artery in the same patient. The pulmonary artery to aorta ratio is 1.9. c Axial steady state free precession images in the same patient demonstrate enlarged pulmonary artery (arrow). d Pulmonary artery distensibility (1.8 %) can be calculated using cine MR, by measuring the diastolic minimal (10.9 cm²) and systolic maximal (11.1 cm²) cross-sectional area obtained perpendicular to direction of blood flow. e Average velocity obtained with phase contrast MR in the main pulmonary artery is 11.6 cm/s

Fig. 2

a Illustrations depicting the developing six paired aortic arches with the left and right dorsal aorta during early embryogenesis. b Further development leads to formation of right and left pulmonary arteries from the sixth aortic arches, primitive truncus arteriosus and adjacent arteries. Arrest in this normal development can lead to agenesis, partial agenesis, pulmonary sling, etc.

Fig. 3

Contrast-enhanced CT image (a) shows complete agenesis of left lung and left pulmonary artery. The left hemithorax is smaller with mediastinal shift toward the left and the elevation of the left hemidiaphragm. The abdominal contents are seen in the left hemithorax. Contrast-enhanced axial CT image (b) demonstrates partial agenesis of the left pulmonary artery (arrow) with hypoplasia of left lung. There is no mediastinal shift, but the abdominal organs extend into the thorax

Fig. 4

Contrast-enhanced axial CT image (a) and a volume rendered image (b) in a patient with patent ductus arteriosus (PDA) depicting the persistent communication between the pulmonary artery and descending aorta (arrow). The flow direction in the post-natal period is aorta to pulmonary artery as the pulmonary pressures decrease. This can lead to pulmonary hypertension, which on CT will present as enlarged pulmonary trunk as seen on the volume rendered image

Fig. 5

Illustration (a) and contrast-enhanced axial CT image (b) depicting the left pulmonary artery coursing between the trachea and oesophagus to reach the left pulmonary hilum. Patient’s symptoms correlate with the degree of upper airway obstruction present from narrowing of the trachea

Fig. 6

Contrast-enhanced axial CT image (a) from a patient with tetralogy of Fallot (TOF) and a prosthetic pulmonic valve demonstrates severe stenosis of the left and mild stenosis of the right pulmonary artery (arrows). In addition there is an ascending aortic aneurysm. In a different patient (b) with an unrepaired TOF, an aneurysm of the pulmonary trunk (arrow) formed with a chronic thrombus in the right and left pulmonary arteries. Also note the multiple dilated aortopulmonary collaterals. CT angiogram c performed with 30 ml of contrast in a patient with chronic renal failure and a prosthetic pulmonary valve demonstrates a main pulmonary artery aneurysm (measuring 44 mm)

Fig. 7

Contrast-enhanced axial CT image in systemic arterial phase demonstrates contrast blush within the pulmonary trunk emanating from a tubular enhancing structure along the left anterior descending coronary artery. Communication is noted between this and the pulmonary artery, suggesting a coronary to pulmonary artery fistula (arrow)

Fig. 8

Contrast-enhanced axial CT image (a) in a 16-year-old patient with progressive dyspnea and absent left upper extremity pulse shows a focus of smooth narrowing and aneurysmal dilatation of the left main pulmonary artery (arrow). Late venous phase axial MR image from a 3D GRE acquisition (b) shows delayed enhancement of an aneurysmal left pulmonary artery branch (arrow). Also note the wall enhancement of descending thoracic aorta (arrowhead) consistent with vasculitis. These findings are suggestive of Takayasu arteritis

Fig. 9

Contrast-enhanced axial CT (a) in a patient with Bechet’s disease demonstrate a focal aneurysm of the right lower lobe pulmonary artery with eccentric mural thrombus (arrow). Volume rendered image (b) better depicts the eccentric saccular aneurysm (arrow). This patient underwent right lower lobectomy for recurrent haemoptysis

Fig. 10

Contrast-enhanced axial CT image demonstrates aneurysmal formation with irregular thick walls in the segmental branches of right and left lower lobe pulmonary arteries (arrow) in this patient with a known infected aneurysm. These findings were new compared with prior chest CT

Fig. 11

Contrast-enhanced axial CT image (a) demonstrates a large filling defect in the left pulmonary artery (arrow). The lesion remained stable after a course of anticoagulation, which raised the suspicion for a malignancy. Subsequently obtained FDG-PET (b) demonstrated the central part of this filling defect to be hypermetabolic, consistent with a primary pulmonary artery sarcoma. Gadolinium-enhanced cardiac MR (c) performed 60 s post contrast for preoperative evaluation demonstrates a lesion in the left pulmonary artery with an non-enhancing central portion, consistent with a bland thrombus, and an enhancing component in the pulmonary arteries and left lower lobe, suggestive of a tumour

Fig. 12

Different patients with non-thrombotic emboli to the pulmonary arteries: catheter fragment (a), non-target emboli from N-butyl-2-cyanoacrylate injection of gastric varices (b), inferior vena cava filter prong (c) and bone cement for vertebropasty (d)

Fig. 13

Contrast-enhanced axial CT image in a patient with left hilar lung cancer demonstrates the left main pulmonary artery being completely encased and narrowed by the left upper lobe mass (arrow), which also extends into the mediastinum

Fig. 14

Axial CT images in a patient with prior histoplasmosis demonstrates an enlarged pulmonary trunk (36 mm). The proximal right and left pulmonary arteries are normal in calibre but taper and are severely narrowed at the level of hila. In addition, there are calcified mediastinal lymph nodes, calcified pulmonary granulomas and interlobular interstitial thickening. These findings represent fibrosing mediastinitis

Fig. 15

Illustration (a) demonstrates stage 1, the Norwood procedure, for correcting hypoplastic left heart syndrome with the creation of a neoaorta from the pulmonary artery. Post-repair images (b) have a characteristic appearance with a rudimentary proximal ascending aorta and the proximal main pulmonary artery (arrow) reconstituting flow to the distal ascending aorta (arrowhead). During the procedure, the pulmonary trunk is ligated and the pulmonary arterial flow is re-established from either the subclavian artery or the brachiocephalic trunk. After completion of stage 3 (c, d), by attaching the inferior vena cava to the right pulmonary artery, the Fontan procedure, complete systemic venous flow is directed through the right pulmonary artery into the lungs. Note the right pulmonary artery (arrow) shows higher attenuation secondary to the contrast injection from the right arm veins compared with the left pulmonary artery (arrowhead) which has lower attenuation due to blood flow from the inferior vena cava

Fig. 16

Contrast enhanced axial CT images in a patient with transposition of great vessels demonstrates the characteristic appearance post-arterial switch. The pulmonary arteries (arrow) are positioned anterior to the aorta with the left and right main branches draping around the aorta. There is a higher incidence of pulmonary artery stenosis in these patients