Pulmonary Stenosis

Obstruction or narrowing at the pulmonary valve (valvular), subvalvular or supravalvular levels. 

Isolated pulmonary stenosis occurs approximately 0.4% to 0.6% per 1,000 live births and accounts for 10% of all congenital heart defects. It is the second most common defect with ventricular septal defects being the most common. 1-2

The cause of pulmonary stenosis is unknown. However, it can be associated with Noonan's syndrome involving dysplastic pulmonary valves in 50-62% of cases. 6 Pulmonary stenosis is a common heart defect seen in association with different types of congenital heart disease.

Pulmonary stenosis may occur at the pulmonary valve (valvular), subvalvular (infundibular) or supravalvular levels. In Infundibular pulmonary stenosis, the obstruction may be caused by abnormal growth of muscle or tissue. The abnormal growth involves unusual chordal or atrioventricular valve leaflet attachments that typically occurs in association with conotruncal defects. Also, infundibular thickening due to hypertrophic cardiomyopathy or obstruction secondary to malalignment of the conal septum is common causes of infundibular pulmonary stenosis. 7 Valvular pulmonary stenosis, typically due to the fusion of the valve commissures, characterized as a dome-shaped or conical valve with a small and narrowed orifice, is the most common cause of pulmonary stenosis. Relatively uncommon variants are unicommissural, bicuspid, tricuspid, dysplastic valves and hypoplastic annulus. In dysplastic valvular stenosis, the leaflets are markedly thickened, although unfused commissures with associated pulmonary regurgitation. Dysplastic, unfused valve leaflets are present in the majority of cases of Noonan's syndrome. 7,8 In Supravavular stenosis, obstruction occurs above the annulus of the pulmonary valve involving the main pulmonary artery or its branches. Isolated supravalvular pulmonary stenosis is a rare defect and is usually associated with other congenital anomalies. 

The varying degree of pulmonary stenosis can range from mild (often missed prenatally) to severe. Post-stenotic dilation of the main pulmonary artery may occur due to a high-velocity jet of flow through the narrowed orifice.  Tricuspid regurgitation may occur secondary to increasing pressures in the right ventricle. In severe cases, right atrial enlargement due to increased pressures within the hypertrophied right ventricle. Reversal of flow may be seen in the ductus arteriosus to supply pulmonary blood flow. 

Right ventricular hypertrophy and tricuspid regurgitation are often associated as resultant from the hemodynamic changes of pulmonary stenosis.
Pulmonary stenosis may be seen in association with different types of congenital heart disease, including conotruncal defects such as double-outlet right ventricle or tetralogy of Fallot. Also seen in tricuspid atresia with a ventricular septal defect, Ebstein's anomaly and corrected and complete transposition of the great arteries. 3 Extracardiac associated findings are rare, with the exceptions of syndromes. Pulmonary stenosis with dysplastic valve leaflets is present in most cases of Noonan's syndrome about 50-62 % of the time. 6 Infundibular or subvavular stenosis is a classic anatomic feature seen in tetralogy of Fallot. Other genetic syndromes associated with pulmonary stenosis may include neurofibromatosis, Beckwith-Wiedemann, LEOPARD (lentigines, electrocardiogram abnormalities, ocular hypertelorism, pulmonary stenosis, abnormal genitalia, growth retardation, and deafness) and William's syndrome.
Chromosomal abnormalities are rare associations with cases of pulmonary stenosis.

The recurrence rate for pulmonary stenosis is estimated at 2% when one previous child was affected but increased to 6% when two former children had congenital heart disease. 4-5

Mild forms of pulmonary stenosis may be challenging to detect during the second-trimester anatomic ultrasound. Diagnosis of pulmonary stenosis is made by careful evaluation of pulmonary valve morphology during systole, which shows thickened, dome-shaped valve leaflets that are visible throughout the cardiac cycle. Normal pulmonary artery valve leaflets are seen as thin and delicate leaflets that disappear in view during systole. Color Doppler interrogation is helpful to confirm pulmonary stenosis. A peak velocity more significant than 1 m/ sec across the pulmonary is abnormal and should prompt further evaluation. In moderate to severe stenosis, the four-chamber view may show right ventricular hypertrophy with tricuspid regurgitation on color, and post-stenotic dilation of the pulmonary artery may be seen. In some cases, reversal of flow within the ductus arteriosus. Pulmonary stenosis may progress over time from milder to a severe form, resulting in critical pulmonary stenosis and no growth of the annulus leading to pulmonary atresia. The three-vessel view and three-vessel trachea view will show post-stenotic dilation of the main pulmonary artery with thickened and echogenic pulmonary valve leaflets. Color Doppler interrogation of the pulmonary valve in the three-vessel view and three-vessel trachea view will demonstrate turbulent antegrade flow with color aliasing across the pulmonary valves. 3, 7, 8 

Pulmonary stenosis must be differentiated from pulmonary atresia. Improper use of color Doppler settings can lead to a false-positive diagnosis. Adjusting the velocity scale settings and use of pulsed Doppler may help in confirming the diagnosis. 

Prognosis for pulmonary stenosis is overall excellent except for the progression of severe cases of tricuspid regurgitation, dilation of the right atrium, cardiomegaly, hydrops fetalis and cardiac failure. Severe cases can also progress to critical stenosis leading to pulmonary atresia requiring surgical intervention with balloon valvuloplasty.3,7,9 Prenatal diagnosis has a worse outcome compared to postnatal diagnosis. Pulmonary stenosis diagnosed before 24 weeks has a prenatal survival rate of 66.6% based on reported case series.10

A detailed anatomic scan of the fetus at a tertiary referral center is highly recommended to exclude other cardiac or extracardiac structural abnormalities. Fetal karyotype with possible microarray should be offered to the patient to exclude chromosomal abnormalities. Genetic panel for Noonan syndrome should be taken into account.

In cases of critical pulmonary stenosis, evaluate for signs of hydrops fetalis, marked by the appearance of ascites, pericardial and pleural effusions, abnormal dopplers showing characterized reversed flow with atrial contraction within the ductus venosus or pulsations within the inferior vena cava, left ventricular dysfunction or restrictive foramen ovale. 

Ultrasound follow up should be offer in order to assess possible signs of progression. Perinatal management depends on the severity of the stenosis. A cesarean section may be recommended for fetuses with critical pulmonary stenosis. 

A formal fetal echocardiogram with a pediatric cardiologist is needed to further evaluate fetal cardiac structures and consultation for postnatal management and delivery at a tertiary care center. 

1.    Ferencz C, Rubin JD, Loffredo CA, et al. Epidemiology of Congenital Heart Disease.  The Baltimore-Washington Infant Study, 1981-1989. Perspectives in Pediatric Cardiology. Mount Kisco, NY: Futura Publishings;1993

2.    Hoffman JI, Kaplan S. The Incidence of Congenital Heart Disease. J Am Coll Cardiol. 2002;39:1890-1900

3.    Abuhamad A, Chaoui R. A Practical Guide to Fetal Echocardiography: Normal and Abnormal Hearts. Edition, 3. Lippincott Williams & Wilkins, 2015

4.    Nora JJ, Berg K, Nora AH. Cardiovascular Diseases: Genetics, Epidemiology, and Prevention. New York, NY: Oxford University Press; 1991

5.    Fesslova V, Brankovic J, Lalatta F. Recurrence of Congenital Heart Disease in Cases with Familial Risk Screened Prenatally by Echocardiography. J Pregnancy. 2011 

6.    Van der Burgt I. Noonan syndrome. Orphanet J Rare Dis. 2007;2:4. 

7.    Rychik J, Tian Z. Fetal Cardiovascular Imaging: A Disease-Based Approach. Elsevier Saunders, 2012

8.    Gikonyo BM, Lucas RV, Edwards JE. Anatomic features of congenital pulmonary valvar stenosis. Pediatr Cardiol. 1987. 8(2):109-16.

9.    Galindo A, Guiterrez-Larraya F, Velasco JM, et al. Pulmonary balloon valvuloplasty in a fetus with critical pulmonary stenosis and atresia with intact ventricular heart septum and failure. Fetal Diagn Ther. 2006;21:100-104

10.    Todros T, Paladini D, Chiappa E, et al. Pulmonary stenosis and atresia with intact ventricular septum during prenatal life. Ultrasound Obstet Gynecol. 2003;21:228-233

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