Dynamic Right Ventricular Outflow Tract Obstruction Due to a Swinging Echolucent Cyst on Interventricular Septum in a 4-Year-Old Girl
A 4-year-old girl was referred to our hospital for evaluation of an incidentally found heart murmur. She had a history of perimembranous ventricular septal defect in infancy, which was reported to be spontaneously closed sonographically in a nearby hospital at 1 year of age. She had no history of traumatic injury. On examination, a grade 4/6 systolic ejection murmur was audible at the left upper sternal border. Chest radiograph and ECG were unremarkable. Echocardiography (Figure 1; Movies I and II in the online-only Data Supplement) revealed that an echolucent cyst (10 mm in diameter) originating from the membranous interventricular septum (IVS) was swinging like a pendulum and obstructing the right ventricular outflow tract, as represented by a peak flow velocity of 4.0 m/s. There was no visible shunt jet across the IVS or the cystic wall. Cardiac catheterization and angiography (Figure 2; Movies III and IV in the online-only Data Supplement) showed that a large swinging filling defect protruded from the IVS into the right ventricular outflow tract. The defect produced a pressure gradient of 45 mm Hg between the right ventricle and pulmonary artery. Left ventriculography revealed a bulging membranous septum with no obvious shunt flow into the right ventricle or the cyst. T2-weighted magnetic resonance imaging (Figure 3) showed a high-intensity-mass lesion arising from the IVS toward the right ventricle.
A surgical procedure was performed to relieve right ventricular outflow tract obstruction by resecting the cyst. Under cardiopulmonary bypass, a collapsed aneurysmal tissue tag was found that originated from the IVS. When the tissue tag (12 mm) was resected at the origin, a perimembranous ventricular septal defect was found (Figure 4). The resected tag was a soft aneurysmal sac with no holes, composed of fibrous tissue histologically. The tissue tag was considered to be a “closed” aneurysm of the membranous septum that originated from the membranous IVS, with potentially a tiny anatomic communication with the left ventricle. The defect was closed directly, and hypertrophied muscle was resected on the anterior wall of the right ventricle. Postoperative echocardiography revealed no cyst on the IVS (Movies V and VI in the online-only Data Supplement).
Aneurysm formation in the membranous septum is a common mechanism to reduce interventricular shunting in patients with ventricular septal defects and is believed to be usually benign in nature. Although there are a few old case reports showing that such aneurysms were complicated by right ventricular outflow tract obstruction,1–4 information related to prognosis or to the dynamic nature of the aneurysm is scarce in the era of contemporary modalities, including cineangiography, color Doppler ultrasound, and magnetic resonance imaging. In the present case, a swinging aneurysm of the membranous septum dynamically obstructed the right ventricular outflow tract in a pendulum-like manner, which suggests that it may progress3 or potentially cause sudden cardiac events even in children. Furthermore, such an aneurysm was a diagnostic challenge in the present case because of the lack of any obvious shunting between the aneurysm and left ventricle in vivo, which was not the case with previous reports.1–4 The series of images, including movies, in the present case should lead to a reappraisal of the clinical significance of an otherwise benign aneurysm of the membranous septum in caring for children and adults with ventricular septal defects.
The online-only Data Supplement is available with this article at http://circ.ahajournals.org/cgi/content/full/121/12/e250/DC1.
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