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syndrome.105 Ductal closure usually begins at the pulmonary arterial end of the vessel, and if closure at the aortic end fails to occur, it becomes in effect an aortic diverticulum under systemic pressure Although formation of such a diverticulum is common, it is less clear why this occasionally progresses to aneurysmal formation Structural abnormalities are possibly present in the aortic but not the pulmonary end of the duct, such as those associated with collagen vascular disorders Sepsis may be involved in the pathogenesis of some cases in infancy A diverticulum arising from the pulmonary trunk is also common Usually, the type found in infancy is asymptomatic and may not be uncovered until autopsy for death from other causes It presents as a tumorlike left-sided mediastinal mass In 20% of cases, rupture or embolism leads to death Dissection and infection may also occur Regression can occur, presumably due to thrombosis and organization, but progressive enlargement, or the onset of hoarseness (Ortner syndrome) because of damage to the recurrent laryngeal nerve or left bronchial obstruction, is an indication for surgical excision.110 In view of the frequency of life-threatening complications, prompt surgical removal is advisable Percutaneous occlusion of the aneurysm has not been established, but a potential approach is placement of a covered stent in the aorta to exclude the aneurysm and occlude the duct.111 Aneurysm of the duct is even more uncommon in adults.112 The duct may be patent at both ends but is usually closed at the pulmonary arterial end.113–115 Possible pathogenic mechanisms include arrested closure, with persistence of an aortic diverticulum, delayed spontaneous closure of the pulmonary arterial end, infective arteritis and external trauma in a patient with a persistent duct,116 or even coil occlusion of a preexisting patent duct.117 An aneurysm of the duct should be considered in the differential diagnosis of the adult with unexplained mediastinal masses seen on chest radiography The diagnosis can be confirmed by aortography or by computerized tomography.109,111–119 Like the pattern seen in infancy, the high incidence of rupture, embolization, and effects of pressure suggest that surgical excision is advisable Surgical ligation may itself be followed by aneurysmal formation,112,120 often associated with recanalization FIG 41.15 Anteroposterior retrograde aortogram showing a ductal aneurysm Note the associated moderate aortic insufficiency Thromboembolism Thrombosis of the duct as a source of neonatal embolus was first described in 1859.121 Several cases, mostly fatal, have since been noted.122,123 Early diagnosis can provide an opportunity for successful intervention, which may include thrombectomy, heparin, and resection of infarcted tissue Treatment Once the diagnosis of uncomplicated persistent patency of the arterial duct is established, elimination of the shunt should be recommended by catheter occlusion or surgery The justification for closure of small communications resides in the prevention of infective endarteritis, coupled with an extremely low procedural morbidity and mortality As noted earlier, in the setting of the socalled silent duct, there is little clinical evidence to justify any intervention or recommendation to prescribe coverage against subacute bacterial endocarditis.124 In the occasional patient who develops congestive heart failure, excluding those patients to be discussed later in the context of prematurity, drugs should be administered to combat the failure but only until intervention can conveniently be arranged Surgical Intervention In 1939 Robert Gross performed the first successful ligation of a persistent arterial duct in a 7-year-old girl.12,125 The duct is usually approached through a left posterolateral incision, using the third interspace in infants and the fourth space in children older than 1 year Uncommonly, the duct is on the right side, especially in the presence of a right aortic arch It must be approached from the right The duct may be ligated or divided The relative merits of each procedure continue to be hotly debated by surgeons Excellent results have been reported using both procedures The incidence of clinically apparent recanalization with ligation is approximately 1%,126–129 albeit that echo-Doppler studies have detected flow after ligation in clinically silent ducts, suggesting the incidence of residual flow to be higher.130 Large ducts exceeding 7 to 10 mm in diameter, or those associated with pulmonary hypertension, are generally divided Mortality reported from a large experience extending over 25 years for closure of the uncomplicated duct was no more than 0.2%,131 with a figure of 0.5% cited in another series.132 Once the safety of the operation was established in older children and adults, it was natural for surgeons to attempt closure in infancy,133 with Mustard already in 1951 reporting successful ligation in four infants.134 Many surgeons demonstrated the ease with which the duct could be ligated, even in those born prematurely.135 In most units, surgical ligation is reserved for those premature infants who have failed an adequate course of indomethacin or when there are contraindications to its administration However, treatment of the arterial duct is contentious, ranging from early targeted treatment, late (symptomatic) treatment, to no treatment at all (see later).136 When performed, surgical ligation can be done at bedside The need for accurate anatomic definition prior to intervention in the premature infant must be underscored.137 Complications are uncommon Injury to the recurrent laryngeal nerve injury can occur occasionally but is usually temporary,138 although it can be permanent Rarely, a false aneurysm may develop, prompting urgent surgical reoperation after ligation.139 Damage to the phrenic nerve has also been reported, occurring most frequently in the premature infant Chylothorax can also occur Inadvertent ligation of the distal left pulmonary artery occurs infrequently This is a hazard