A systemic shunt redirects blood from the aorta or a branch of the aorta to the pulmonary arteries in order to increase oxygen saturation. These include central shunts (surgical graft to the pulmonary arteries from the ascending aorta) (Fig. 1A, 1B, 1C), Potts shunts (from descending aorta to left pulmonary artery, no longer performed), Waterston shunts (from ascending aorta to right pulmonary artery), and Blalock-Taussig shunts (subclavian artery to ipsilateral pulmonary artery). The contemporary modified Blalock-Taussig shunt is performed by interposing a prosthetic graft from the subclavian or innominate artery to the ipsilateral branch pulmonary art ery via an end-to-end anastomosis [4]. Postoperative complications include distortion of the ipsilateral pulmonary artery, identified in 24–33% after a modified Blalock-Taussig shunt [5, 6], occurring more commonly in those who undergo shunt placement earlier in life [5]. Major (≥ 50%) pulmonary artery stenosis occurs in 14% of cases, and rarely, there is complete occlusion of the pulmonary artery or the shunt [5]. In approximately 50%, shunt narrowing occurs, usually at the anastomosis [6].

Although echocardiography is often the initial imaging technique used to evaluate the branch pulmonary arteries, usually only the central pulmonary arteries are imaged because of acoustic interference by the lungs. Frequently in the postoperative patient, surgical clips or catheter-placed coils create imaging artifacts on MRI, which may obscure visualization of the branch pulmonary arteries. In this case, MDCT is helpful, particularly for the left pulmonary artery. The appearance of the left pulmonary artery and the extent of distortion are important to define preoperatively, before any additional sur gical intervention. If the area of distortion is too posterior to adequately visualize from a midsternotomy incision, the surgeon must approach it from a left thoracotomy.

Venous shunts, although not performed in neonates because of elevated pulmonary resistance, can be used to increase pulmonary blood flow after infants are approximately 3 months old. A classic Glenn shunt is a surgical connection between the vena cava and the transected ipsilateral pulmonary artery. These have been performed in the setting of tricuspid atresia and single ventricle [7], but they are essentially no longer used because of the undesirable creation of discontinuous branch pulmonary arteries. The currently performed bidirectional Glenn shunt connects the cranial segment of the transected superior vena cava to the right pulmonary artery via an end-to-side anastomosis, allowing blood to flow to both lungs [4] (Fig. 2A, 2B, 2C). A hemi-Fontan procedure, a variant of the bidirectional Glenn shunt, involves a second anastomosis of the caudal superior vena cava segment with the inferior right pulmonary artery and may facilitate a subsequent Fontan procedure. Sequelae after a Glenn shunt include decreased arterial diameter and flow in the contralateral pulmonary artery as well as development of decompressing venous collaterals (superior vena cava-to-inferior vena cava circulation), resulting in reduced oxygen saturation [7, 8]. Patients are also at risk for developing pulmonary arteriovenous fistulas (AVFs) (20%); the incidence correlates with the number of years after the procedure [7].

A Kawashima procedure is performed in the setting of heterotaxy syndrome and refers to placement of a bidirectional Glenn shunt in a patient with interruption of the inferior vena cava and azygous extension to the superior vena cava. This therefore redirects all systemic venous blood to the lungs except the hepatic and coronary venous return. A left-sided Kawashima vascular connection is anasto mosed to the left branch pulmonary artery. Postoperatively, patients have mild cyanosis because the desaturated hepatic venous blood is pumped along with the pulmonary venous blood to the body. Surgeons sometimes avoid redirecting hepatic venous drainage in patients with an interrupted inferior vena cava because of the complexity of incorporating this return. Unfortunately, failure to incorporate hepatic venous blood results in a number of patients after Kawashima repair developing a pulmonary arteriovenous malformation (AVM) [9]. When an AVM is present, a conduit may be placed to incorporate hepatic blood flow into the pulmonary circuit to facilitate its resolution [10]. Difficult to visualize with echocardiography, these conduits from the hepatic veins to the innominate vein can be evaluated with MDCT to exclude thrombosis or stenosis (Fig. 3A, 3B, 3C, 3D).

The Fontan procedure was initially conducted for tricuspid atresia and is currently performed as the final palliative procedure in any heart with single-ventricle physiology, such as hypoplastic left heart syndrome. This procedure involves separation of the systemic and pulmonary circulations. Systemic venous blood is routed directly to the lungs, which may be performed initially during a staged hemi-Fontan procedure or a bidirectional Glenn shunt. The single ventricle pumps exclusively (or nearly exclusively) to the body. Historically, the inferior vena cava connection involved an anastomosis between the superior aspect of the right atrium with the right pulmonary artery. More recently, the connection is made using an intraatrial baffle or an external conduit from the inferior vena cava to the pulmonary artery [11, 12] (Fig. 4A, 4B, 4C, 4D).

The Fontan cavopulmonary pathway is at risk for thrombosis or suboptimal flow dynamics [11, 12]. Systemic circulation complications include subaortic obstruction, systemic ventricular dysfunction, and atrioventricular valve regurgitation [12]. Aortocollateral vessels and pulmonary AVFs may also develop, and alterations in venous pressure result in an increased propensity for pleural effusion and protein-losing entero pathy [12]. In the early postoperative period, an unusual complication is a large fluid collection adjacent to the external conduit (Fig. 5A, 5B). MDCT with IV contrast material can delineate the extent of such a collection, determine whether it represents a contained collection or a pseudoaneurysm, and show resolution after treatment.

In truncus arteriosus, a rare congenital anomaly, the pulmonary arteries arise from the aorta, which overrides a ventricular septal defect. Classification systems reflect the origins of the branch pulmonary arteries and whether the aortic arch is interrupted. During surgical repair, the ventricular septal defect is closed, and the pulmonary arteries are anastomosed to the right ventricle using a conduit. Follow-up requires evaluation for conduit or truncal valve stenosis or regurgitation, adequacy of ventricular septal defect closure, stenosis of the pulmonary arteries (Fig. 6), dilatation of the aortic root, and ventricular dysfunction [13]. Cardiac angiography can assess for hemodynamically significant stenosis and residual ventricular septal defects; however, the conduit to pulmonary artery anastomosis may not be fully visualized to enable adequate assessment of the pulmonary artery origins, which are seen well with MDCT (Fig. 6).

A Norwood procedure is the initial palliation for patients with hypoplastic left heart; it establishes a reliable egress of systemic arterial blood from the systemic right ventricle via the main pulmonary artery to the reconstructed aortic arch [11, 14]. Pulmonary blood flow is then provided by either a systemic shunt or a restrictive conduit from the right ventricle to the branch pulmonary arteries (Sano modification) [14]. After a Norwood procedure, CT is performed to visualize the aortic arch and ventricular or aortic pulmonary artery anastomoses (Fig. 7A, 7B, 7C). Distal aortic arch narrowing is an important complication to identify in order to avoid a pressure overload on the systemic right ventricle. Elevation in ventricular end-diastolic pressure related to ventricular dysfunction will raise pulmonary venous pressure (and then pulmonary artery pressure) and increase the risk of subsequent Glenn or Fontan procedures.

In patients with severe pulmonary atresia resistant to interventional dilatation, arterial stents or surgical conduits may be required to augment pulmonary artery flow distal to the region of narrowing (Fig. 8A, 8B).

Older techniques used to correct transposition of the great vessels include the Senning and Mustard procedures, aimed at revising the venous return. This was accomplished with an atrial baffle composed of autologous tissue (Senning) or synthetic material (Mustard) in conjunction with atrial septal resection [15]. Venous inflow was diverted via the baffle to the contralateral atrio ventricular valve and ventricle [15]. Com plications include arrhythmia, sudden death, right ventricular dysfunction, tricuspid regurgitation, obstruction of the atrial baffle due to narrowing, systemic and pulmonary venous obstruction, and atrial baffle leak [16, 17]. Repair for transposition of the great vessels is currently most commonly performed with an arterial switch procedure; however, not all patients are candidates. The pulmonary artery and aorta superior to the sinotubular junction (i.e., distal to coronary artery origins) are transected and reattached in the alternative location, and the coronary arteries migrate to the neoaortic root [15, 18]. Potential cardiopulmonary complications after an arterial switch operation include anastomotic obstruction (most commonly pulmonary), ventricular dysfunction, central and peripheral pulmonary stenosis (with branch pulmonary artery distortion occurring more commonly on the left side), neoaortic insufficiency, mitral regurgitation, left mainstem bronchus compression resulting from posteriorly displaced aorta, and less frequently, coronary artery stenoses [15, 18]. In the setting of compromised oxygenation postoperatively, MDCT can add considerable information in addition to that provided by echocardiography to determine whether a pulmonary artery anomaly is the underlying cause (Fig. 9A, 9B, 9C, 9D).