Case report

The patient is an African-American male born as the first child of a 21-year-old female, with a history of one spontaneous miscarriage. The pregnancy was uncomplicated until 32 weeks gestation, when prenatal ultrasound revealed ventricular disproportion, with right ventricular hypertrophy, a small left ventricle, and possible coarctation of the aorta. With these antenatal concerns, labor was induced at 39 weeks gestation by artificial rupture of membranes. Since the labour failed to progress, the infant was delivered by cesarean section. Thick meconium and low Apgar scores, of 1 at 1 minute, 6 at 5 minutes, and 7 at 10 minutes complicated delivery. Despite immediate endotracheal suctioning, and ventilation through a mask with continuous positive airway pressure, respiratory distress persisted, and the patient was intubated at 30 minutes of life. Blood pressures obtained shortly after birth revealed values of 64 over 33 in the right arm, 68 over 34 in the left arm, 54 over 28 in the right leg, and 57 over 33 in the left leg. Due to the gradient of 10 millimetres of mercury between the upper and lower limbs, and the prenatal suspicion of aortic coarctation, umbilical lines were placed, and the patient was started on prostaglandin E at a dose of 0.05 micrograms per kilogram per minute.

An echocardiogram was performed and showed normal intracardiac anatomy with right ventricular hypertrophy, the anterior wall having a thickness of 5.6 millimetres. The left ventricle was compressed by the right ventricle but function was normal, with an ejection fraction of 78 per cent and shortening fraction of 44 per cent. There was no discernable evidence of aortic coarctation, the diameter of the transverse arch being measured at 4.2 millimetres, but there was a large patent arterial duct, making evaluation for coarctation difficult. The patient was weaned off prostaglandin E on the second day, and subsequent echocardiograms on the 4th, 6th and 12th days of life revealed near-complete closure of the arterial duct, and still no evidence of aortic coarctation. Over this period, however, the patient was noted to develop mild stenosis of the branches of the pulmonary trunk, with progression of the right ventricular hypertrophy, the anterior wall thickness measuring 6.8 millimetres.

In the second week of life, a new systolic ejection murmur, graded at two of six, was heard at the left sternal border, with radiation to the left scapula. Clinically, the infant now had decreased femoral pulses, and an increase was noted in the gradient between the upper and lower limbs. Due to these disconcerting clinical findings, the patient underwent cardiac catheterization on the 16th day of life (Fig. 1). By this time, the arterial duct had closed, and although no discrete coarctation was detected, diffuse hypoplasia of the aortic arch was seen, with a gradient of 10 millimetres of mercury measured from the ascending to the descending aorta. Over the next 6 days, the perfusion to the legs significantly worsened. Further echocardiography revealed a juxtaductal coarctation, with a gradient of 86 millimetres of mercury, together with moderate stenosis of the branches of the pulmonary trunk, with a gradient of 35 millimetres of mercury in the right, and 45 millimetres of mercury in the left pulmonary artery. To better visualize the aortic arch, and minimize exposure to radiation, we performed magnetic resonance imaging of the chest. Using gadolinium-enhanced three-dimensional magnetic resonance angiography (Fig. 2), diffuse stenoses were detected throughout the aorta and its branches, extending to below the renal arteries. In the thorax, the diameter of the ascending aorta was measured at 4.3 millimetres, with progressive diminution to 3.4 millimetres in the transverse aorta, and 1.5 millimetres just distal to the left subclavian artery. The segment with this smallest diameter continued for 1 centimetre, before the abdominal aorta opened up to a diameter of 3 millimetres. Diffuse hypoplasia of the pulmonary arteries was also confirmed, with the right and left pulmonary arteries having diameters of 2.5 millimetres.

Figure 1. Evaluation of the aortic arch by cardiac catheterization on the 16th day of life reveals no significant coarctation.

Figure 2. Evaluation of the aortic arch by magnetic resonance imaging combined with injection of gadolinium on the 22nd day of life reveals a long-segment of coarctation of the transverse aorta just distal to the left subclavian artery.

The patient underwent open heart surgery on the 24th day of life, a pulmonary allograft patch measuring 3 centimetres in length being used to replace the stenotic aortic segment. There was severe diffuse medial thickening of the thoracic aorta and its branches, deemed by the surgeon to be consistent with Williams' syndrome. Fluorescence in-situ hybridization studies were sent for analysis.

Although we considered using magnetic resonance imaging to follow longitudinally any changes in the morphology of the vessels, such a modality was deemed inappropriate, given the need for general anesthesia in an extubated infant. Instead, a follow up echocardiogram and computerized tomography angiogram, obtained on the 29th day of life, revealed no further narrowing in the region of the patch angioplasty, but there was increased stenosis in the abdominal aorta, the intraluminal diameter decreasing to less than 3 millimetres, and in the branches of the pulmonary trunk, with the gradient increasing to 70 millimetres of mercury across the left pulmonary artery, and 50 millimetres of mercury across the right pulmonary artery. Due to the diffuse and progressive nature of the arteriopathy, a pediatric rheumatologist was consulted, who recommended a temporal arterial biopsy. This revealed an intact intima and media, without evidence of inflammatory or giant cells. Direct and indirect immunofluorescence methods failed to detect antibodies or deposition of complement. The biopsy from the temporal artery was also stained with elastic-Van Gieson, which revealed decreased elastin staining in the intima, and disrupted elastic fibers within the media. These results were consistent with Williams' syndrome, and were supported by fluorescence in-situ hybridization analysis, which confirmed the 7q11.23 deletion.

Follow-up using echocardiography and computerized tomography angiography at 3 months of age demonstrated re-coarctation of the thoracic aorta in the region of the pulmonary homograft, the gradient having increased to 90 millimetres of mercury. The patient continues to have persistent, but non-progressive, stenosis of the right and left pulmonary arteries, the abdominal aorta, and the proximal parts of the brachiocephalic arteries, with biventricular hypertrophy. He is currently 4 months old, and at this time our estimates of his prognosis are guarded.

Discussion

Supravalvar aortic stenosis is the classic obstructive vascular lesion found in Williams' syndrome and can take the form of either localized or diffuse narrowing. In a study of the natural history of localized supravalvar aortic stenosis, Giddins et al.⁸ found that the mean left ventricular outflow pressure gradient increased from 25 to 59 millimetres of mercury over a period of 7 years during childhood. In the diffuse form of the disease, where long-segment coarctation of the thoracic and abdominal aorta is common, progressive arteriopathy has also been observed over time and typically leads to systemic hypertension in adolescents with Williams' syndrome.^{6, 7} A recent study suggests that progression in aortic stenosis over time results from failure of the aortic lumen to increase in size with age.⁹

Although the natural course of both localized and diffuse forms of supravalvar aortic stenosis is to progress over time, this process in most individuals appears to occur over a period of years.^{9, 10} In our patient, however, the diffuse arteriopathy progressed rapidly in infancy over a period of days. Instead of the patient being born with a fixed amount of arterial stenosis, with failure of the aortic lumen to increase in size with age, we observed postnatal proliferation of the arterial media, with progression to near complete obstruction of the proximal thoracic aorta. Even after the surgical repair, we presume ongoing proliferation of the arterial media to be the cause of re-coarctation in the same region. The aetiology of this process remains uncertain.