Diseases of the pulmonary valve are most often congenital, and only rarely do acquired disorders such as carcinoid and rheumatic fever affect the pulmonary valve.  The pulmonary valve may be stenotic or atretic, or the leaflets of the valve may be absent. Pulmonary stenosis may be valvar, supravalvar, or subvalvar (ie, double-chambered right ventricle); it may also be in the branch pulmonary arteries. These lesions are collectively described as right ventricular outflow tract obstructions. In this article, only valvar pulmonary stenosis is reviewed.
A stenotic pulmonary valve usually occurs without associated congenital abnormalities, although it may be associated with other structural abnormalities of the heart. To distinguish the former from the latter, terms such as pulmonary stenosis with a normal aortic root or pulmonary stenosis with an intact ventricular septum have been used. However, the term isolated pulmonary valve stenosis is preferred.  The term isolated may be used even when a patent foramen ovale or a small atrial septal defect is present. The term congenital need not be used because most are congenital.
Pathologic features of the stenotic pulmonary valve vary.  The most common pathology is a dome-shaped pulmonary valve. The fused leaflets of the pulmonary valve protrude from their attachment into the pulmonary artery as a conical, windsock-like structure. The size of the pulmonary valve orifice varies from a pinhole to several millimeters. The orifice is most usually central but can be eccentric. Raphae, presumably fused commissures of the valve, extend from the stenotic orifice to a variable distance down into the base of the dome-shaped valve. The number of the raphe may vary from 0-7. Relatively uncommon variants are unicommissural, bicuspid, and tricuspid valves. The valve annulus is abnormal in most cases, and the fibrous back bone is partially or completely lacking; therefore, a true annulus may not be present. 
Hypoplasia of the pulmonary valve ring and dysplastic pulmonary valves may be present in a few of patients. Pulmonary valve dysplasia is characterized by thickened, nodular, and redundant valvular leaflets with minimal or no commissural fusion; hypoplasia of the valve ring; and lack of poststenotic dilatation of the pulmonary artery. [3, 4] The obstruction is mainly related to thickened, myxomatous, immobile pulmonary valve cusps and hypoplasia of the valve ring.
Changes secondary to pulmonary valve obstruction occur in the right ventricle and pulmonary artery. [1, 2] Hypertrophy of the right ventricular muscle is proportional to the degree (and perhaps the duration) of obstruction. The muscle hypertrophy is particularly prominent in the infundibular region and may become physiologically important; this appears to be related to the degree and duration of obstruction.  Mild dilatation of the right ventricular cavity is present. In extremely severe or critical obstruction, the right ventricular cavity may be markedly dilated. In rare cases, the right ventricle may be hypoplastic.
The main pulmonary artery is dilated in almost all cases. This dilatation is independent of the severity of the pulmonary valve obstruction and presumably related to a high-velocity jet across the stenotic valve. [6, 7] As noted above, such poststenotic dilatation is remarkably absent in patients with dysplastic pulmonary valves.
Supravalvar pulmonary stenosis is often associated with rubella syndrome and Williams syndrome (ie, elfin facies, supravalvar aortic stenosis, and hypercalcemia with or without mental retardation).
Isolated infundibular or subvalvar pulmonary stenosis is uncommon and usually associated with a ventricular septal defect (VSD), such as in tetralogy of Fallot.
Peripheral pulmonary stenosis is frequently observed in newborns. It is related to relative narrowing of the branch pulmonary arteries and the acute angle of the origin of the branch pulmonary arteries at this age. This represents fetal pattern and, in most cases, resolves over time.
Clinically significant narrowing of a valve or a blood vessel increases pressure proximal to the obstruction. This pressure gradient is necessary to maintain flow across the stenotic site. In pulmonic stenosis, hypertrophy of the right ventricle ensues and maintains this forward flow. The magnitude of right ventricular pressure and the pressure gradient across the pulmonary valve are generally proportional to the degree of obstruction. Under usual circumstances, proportional right ventricular hypertrophy maintains normal pulmonary blood flow. If the normal output is not maintained, right-sided heart failure ensues. This occurs in neonates with critical pulmonary stenosis and in patients with severe obstruction that occurs in childhood or adulthood.
Changes in the geometry of the left ventricle and decreased left ventricular function can also occur. [10, 11] The changes are proportional to the degree of right ventricular hypertrophy; however, they revert to normal after obstruction of the right ventricular outflow tract is relieved.
With increasing right ventricular hypertrophy, right ventricular compliance decreases with a resultant increase in end-diastolic pressure and with prominent a waves in the right atrium. As right atrial pressure rises, a right-to-left shunt may occur if the foramen ovale is patent or if an atrial septal defect is present; this change results in systemic arterial desaturation and clinically discernible cyanosis. This shunting may occur even without measurable elevation of right atrial pressure and is attributable to decreased right ventricular compliance.  Such a right-to-left shunt can also occur in patients with an underdeveloped (hypoplastic) right ventricle. 
Pulmonary stenosis represents 8-12% of all congenital heart defects in children. [14, 15] In adults, pulmonary stenosis represents approximately 15% of all congenital heart defects. [16, 17, 18] Isolated valvar pulmonary stenosis with an intact ventricular septum is the second most common congenital cardiac defect in children. It may occur in as many as 50% of all patients with congenital heart disease associated with other congenital cardiac lesions.
Racial difference in the prevalence of pulmonary stenosis is unlikely. 
The male-to-female ratio is 1:1. 
The patient's age at presentation is related to the severity of the obstruction. If the stenosis is severe, patients may present in the neonatal period or in infancy. Patients with mild obstruction may present in childhood with asymptomatic murmurs.
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