unresponsive to conventional angioplasty by using high-pressure balloons.42 Trauma can also be produced to the pulmonary arteries, usually with the tear occurring distal to the area of the stenosis.153 Pulmonary hypertension was found to be a significant risk factor for such trauma Cutting balloons, as produced by Boston Scientific (Fig 18.23), and used successfully in resistant coronary and peripheral arterial lesions, are now being used for resistant stenotic lesions in the pulmonary arteries that are undilatable even at high pressures The balloon has three or four microtome blades, attached along the length of the balloon, which protrude on inflation to create controlled cuts on the walls of the stenosed vessels On deflation, the balloon folds over the blades Early results in lesions resistant to conventional balloon angioplasty have been encouraging.154,155 Overall, cutting balloons improve the gain in luminal diameter, albeit with a slight increased risk of vascular trauma FIG 18.23 Cutting balloon with microtome blades (arrows) (From Engelke C, Sandhu C, Morgan RA, Belli AM Using 6-mm cutting balloon angioplasty in patients with resistant peripheral artery stenosis: preliminary results Am J Roentgenol AJR 2002;179:619–623 Copyright of American Roentgen Ray Society.) Pulmonary Arterial Stenting Endovascular stenting has been increasingly used in older patients and in hemodynamically significant stenosis in infants and young children Stents are particularly effective in abolishing stenosis that reappears after successful balloon angioplasty due to elastic recoil and for dynamic stenosis related to folds and kinks in surgically repaired pulmonary arteries.156 Stenting of complex stenoses involving the pulmonary arterial bifurcation remains a challenging procedure (Fig 18.24) Due to close proximity of the origins of the right and left pulmonary arteries, it is advisable to deploy stents simultaneously into both arteries In patients who have undergone the LeCompte maneuver as part of the arterial switch operation, the pulmonary arterial bifurcation lies anterior to the ascending aorta Coronary arteries that have been transferred during arterial switch may be in close proximity to the site of implantation of stents, and the risk of arterial occlusion should be considered Much debate existed earlier about the wisdom of early postoperative PA balloon angioplasty or stenting However, as Zahn and Nicholson have reported, early postoperative PA stenting can be accomplished, but care must be taken to avoid oversizing the stent.157,158 FIG 18.24 Bilateral pulmonary arterial stenting for stenosis at the bifurcation of the pulmonary trunk Simultaneous inflation of balloons in both pulmonary arteries The left anterior oblique projection with a cranial tilt profiles well the pulmonary arterial bifurcation Systemic Venous or Baffle Stenosis Stenosis of major systemic veins, such as the superior or inferior caval vein, may follow surgical manipulation, such as following bypass, or in superior caval anastomosis surgery for the Glenn procedure or the Warden procedure Also frequent, the superior vena cava can become obstructed due to thrombotic occlusion from an indwelling central venous catheter When these venous obstructions become severe, venous collateralization almost always occurs but is never sufficient to relieve upstream venous hypertension Hence the presence of large venovenous collaterals should not be considered a reassuring sign but rather an indication of significant venous obstruction with upstream venous hypertension! Obstruction to systemic venous drainage can be treated with balloon dilation as a palliative measure in young infants or children or with stenting for older patients, with good long-term outcome Angiography to delineate the stenosis is a very important step in planning the treatment If stenosis is severe, access may be required from both ends with cannulation of femoral and jugular veins Very thin wires may be used to cross the lesion If there is venous atresia, recanalization will be required using a variety of methods and approaches More recently, the use of chronic thrombotic obstruction coronary wires and even radiofrequency-energy wires have been used to successfully recanalize occluded venous pathways.159 In rare cases, a Brockenbrough needle may have to be used Long sheaths are then used to cross the stenotic segment and an appropriate stent is deployed Balloon-expandable (Fig 18.25) and self-expanding stents have also been successfully used to relieve obstruction, with good long-term results.160–162