Andersons pediatric cardiology 1110

aspect (compare with Fig 42.5) Right, Arrangement of the opened valve The fusion of the leaflets creates a more circular attachment within the root, producing the annular paradox This feature, in which ring-like attachments of the leaflets become evident only when the valve is malformed, can be considered to represent an annular paradox Thus, although the orifice of the normal pulmonary valve is often described in terms of the “annulus,” the measurement taken at this level by the echocardiographer is a virtual diameter at the level of the basal ring (Fig 42.7) FIG 42.7 Section across the pulmonary root The measurement usually taken by the echocardiographer as the “annulus” (red line) is at the level of the basal attachment of the leaflets This is a virtual ring, having no anatomic counterpart The true anatomic rings in the root, the sinutubular and anatomic ventriculoarterial junctions―shown by the green and blue lines, respectively―are rarely measured by the echocardiographer In some instances it is possible to identify four raphes, suggesting that the valve itself initially had four leaflets.3 Commissural fusion can also produce pulmonary stenosis in the setting of a bifoliate valve (Fig 42.8A), whereas in other instances the pulmonary valve can be not only bifoliate but also bisinuate (see Fig 42.8B) FIG 42.8 Bifoliate pulmonary valves (A) Trisinuate valve with a conjoined leaflet (B) In contrast, a valve with only two sinuses supporting the two leaflets Nonetheless, the typical lesion producing pulmonary valvar stenosis is uniform fusion of the peripheral zones of apposition of a trifoliate valve, leaving a central aperture Usually this arrangement is associated with some degree of thickening at the union of the zones of apposition with the sinutubular junction This is described surgically as tethering (see Fig 42.4) Accentuation of such tethering can produce marked narrowing at the sinutubular junction, often described as being supravalvar In reality the sinutubular junction is an integral part of the valvar complex In some instances valvar stenosis is the consequence of dysplasia of the leaflets, making them thick and mucoid Such thickening is sufficient to produce obstruction of the valvar orifice, even when the leaflets themselves are not fused along their zones of apposition (Fig 42.9A) Most of the patients with Ullrich-Noonan syndrome have this type of stenosis.4 Dysplasia can also be found when either the trifiliate or bifoliate valve is already itself stenotic, thus exacerbating the extent of the narrowing at the valvar orifice (see Fig 42.9B) FIG 42.9 Consequences of valvar dysplasia (A) With the pulmonary trunk amputated at the level of the sinutubular junction, the stenotic pulmonary valve is viewed from the arterial aspect Dysplasia of the three valve leaflets is seen to be narrowing the valvar orifice The stars show the so-called valvar commissures (B) The valve is itself bifoliate with a conjoined leaflet, and the orifice extends to the sinutubular junction at only two sites, as shown by the stars In this valve, the dysplastic leaflets excacerbate the narrowing because of the bifoliate nature of the valve Note the annular nature of the hinges of the two leaflets Although pulmonary valvar stenosis may be considered a simple lesion, it is rare for the lesion to be totally isolated There is almost always hypertrophy of the right ventricular walls In the neonate with critical valvar stenosis, such hypertrophy may be severe, with accompanying fibrosis of the endocardium and thickening of the tension apparatus of the tricuspid valve The right ventricle then resembles the situation seen at the functionally biventricular end of the spectrum of pulmonary atresia with intact septum (see Chapter 43) The findings of areas of subendocardial right ventricular infarction in the absence of coronary artery disease, coupled with extensive areas of disarray in the myocardial and arterial walls, point to the disease being more generalized than would be expected from a simple valvar lesion producing direct hemodynamic effects.5 In a good proportion of cases with pulmonary valvar stenosis of whatever type, there is an associated deficiency of the atrial septum In days gone by, so-called cardiac cirrhosis was noted in adults dying with pulmonary stenosis,6 but such hepatic changes are unlikely to be encountered now