Postoperative Evaluation of Vascular Structures

Evaluation of the postoperative vascular status can be a diagnostic challenge because of confusing anatomy with aberrant circulatory characteristics. Strategies for thoracic surgery comprise a large variety of anastomotic or conduit techniques involving the connection of major vascular or cardiac structures for the restitution of adequate physiologic hemodynamic status. A typical example is represented by the Blalock-Taussig shunt which connects the right or left subclavian artery with the main pulmonary artery branch of the ipsilater-al side in order to bypass pulmonary atresia or stenosis (Fig. 15). In addition, a combined patent ductus arteriosus can usually be found. Another example of surgical strategies which can be performed in cases of double outlet right ventricle, is a Glenn-shunt which connects the right superior vena cava with the corresponding pulmonary artery branches (Fig. 16). Under these circumstances a modified Fontan conduit connecting the inferior vena cava to the left or right pulmonary artery is often combined. Evaluation of a postsurgical vascular status of this type with catheter angiography would require an invasive preparation of the left internal jugular vein, puncture of an iliac vein and arterial catheterisation. In cases in which the left superior vena cava persists, even both jugular veins may have to be punctured.

MR imaging is a valuable diagnostic tool for non-invasive assessment of the postsurgical outcome. In particular, CE 3D MR angiography is very helpful for a complete anatomic description of the area of interest. Due to the requirement for accurate detection of arterial and venous perfusion, multiphase acquisitions involving up to six perfusion phases, are mandatory. Best results are obtained under breath-hold conditions after intubation. For the diagnostic evaluation, thick slab MIP reformations or 3D surface rendered reconstructions may provide an overview of the anatomic situation. Vessel anastomosis or single vascular areas should be assessed by means of multiplanar reformations with reconstruction of thin slabs of variable thickness covering the individual structure of interest.With a focussed diagnostic approach, reliable detection of vessel stenosis in an area of anastomosis can be achieved even when the vessel diameters are extremely small [36].

Common therapeutic approaches in cases of aortic coarctation include interventional treatment with dilatation of the stenosis (Fig. 17), sur-

Image Surface Rendered Vascular

Fig. 16. Surface rendering of a 3D CE MRA dataset in anterior-posterior view in a patient with pulmonary atresia (Gd-BOPTA, 0.1 mmol/kg). This study demonstrates the postoperative situation following bilateral Glenn anastomosis. A persistent left upper vena cava was connected to the left pulmonary artery (arrow) and the normal right upper vena cava was connected to the right pulmonary artery (arrowhead)

Fig. 16. Surface rendering of a 3D CE MRA dataset in anterior-posterior view in a patient with pulmonary atresia (Gd-BOPTA, 0.1 mmol/kg). This study demonstrates the postoperative situation following bilateral Glenn anastomosis. A persistent left upper vena cava was connected to the left pulmonary artery (arrow) and the normal right upper vena cava was connected to the right pulmonary artery (arrowhead)

Fig. 17. Patient with coarctation following percutaneous transar-terial angioplasty. On MR angiography a remaining low grade stenosis distal to the branching left subclavian artery can be seen (arrow). However, no dissection or rupture of the vessel wall due to angioplasty was found. The case shows that MRA is an excellent imaging modality for follow-up of post-operative or post-therapeutic studies of aortic coarctation gical resection of the involved segment combined with end-to-end anastomosis (Fig. 18) and patch angioplasty. When a concomitant hypoplastic aortic arch is present, flow turbulence can lead to aneurysm formation with the possibility of fatal complications. Finally, the combination of coarc-tation and aortic valve malformation has to be considered in follow up studies of patients with aortic stenosis (Fig. 19).

MR angiography is extremely reliable in detecting aneurysm formation in the postsurgical follow up of patients and diagnosis based on MR fre quently results in therapeutic approaches such as surgical intervention with graft implantation [37]. In addition MR angiography is a valuable diagnostic instrument for the detection of pulmonary artery stenosis, pulmonary shunting or pulmonary vein stenosis after thoraco-surgical treatment [38].

For complete postoperative evaluation MR an-giography should always be combined with unen-hanced multiplanar T1w and T2w imaging techniques to detect or exclude perivascular complications such as hematoma or seroma as a possible cause for vascular obstruction [39].

Post Operative Seroma

Fig. 18a-c. A 16-year-old female patient with surgical and interventional therapy of aortic coarctation. a shows a CINE trueFISP sequence orientated along the axis of the descending aorta. Recurrent stenosis (arrow) indicated by a jet phenomenon as a sign of accelerated blood flow can be seen distal to the left subclavian artery. On T1w sequences orientated perpendicular to the axis of the aorta a thickening of the wall of the descending aorta is demonstrated (arrowsin b). Surface rendering of a 3D CE MRA dataset of the same patient (c) reveals a significant stenosis distal to the left subclavian artery (arrow)

Fig. 19a-c. MIP reconstruction (a) of a thoracic CE MRA study (Gd-BOPTA, 0.1 mmol/kg) in a patient with surgical reconstruction of aortic coarctation. This follow-up study revealed a slight residual stenosis distal to the branching of the left subclavian artery (arrowin a, b). However a newly developed ectasia of the aortic root was also depicted on both the MIP (a) and the surface rendered image (arrowheads). Further examination using CINE trueFISP sequences perpendicular to the aortic valve (c) revealed a biscupid aortic valve (arrow). This may occur in approximately 30% of patients with aortic coarctation and may result in aneurysm formation of the ascending aorta due to flow turbulence

Arterial Tortuosity Syndrome

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