Discussion: Congenital ventricular diverticulum are extremely rare anomalies. The true incidence remains unknown as estimates of occurrence are predominately based on very small series and scattered case reports. Additionally, because many affected infants remain asymptomatic, the lesion often remains unrecognized until a functional murmur, incidental chest x-ray or EKG leads the patient to further evaluation. A prevalence of 0.05/10,000 births has been reported, with occurrence in males more common than females, and the left ventricle more commonly affected than the right.1, 2 The communicative base of the lesion is broad, and the diverticulum wall is thin, composed of dysplastic myocardium and varying degrees of fibrous tissue. Diverticulum can be unilobulated or multilobulated with walls that are dyskinetic or akinetic. Locations include the ventricular apex, interventricular septum, or the free ventricular wall. Lesions in the latter location often extend to the level of the A-V valves.
Etiology: The etiology of ventricular diverticulum remains speculative. However, there is a substantial amount of evidence to support the role of myocardial infarction in the pathogenesis 3,4,5. At all other stages of life including infancy, myocardial infarction is the most common predecessor to ventricular aneurysm 5, 6 Fetal lesions bear multiple similarities to the aneurysms that develop in adults following myocardial infarct. Like adult aneurysms, fetal defects are areas of thin fibrous scar-like tissue with attenuated myocardium with abnormal kinesis. They have been found at autopsy in association with abnormalities of the coronary vessels such as anomalous origin of the left coronary artery, coronary ostia stenosis, hypoplasia, rupture 5 or thrombosis. These abnormalities may be the sequelae of inflammatory/degenerative changes of coronary arteries secondary to occlusive fibroelastosis or Kawasaki disease. The role of myocardial infarct in the genesis of fetal aneurysms has been supported by case reports in which infarct is confirmed utilizing postnatal EKG 3, 7 and thallium myocardium perfusion imaging, and postmortem histopathological confirmation 3,4,5,8. The finding of myocardial infarct has also been reported in conjunction with normal coronaries 4. In these instances, damage to the myocardium from congenital viral infection 9 or arrhythmia associated vascular accident may be the pathogenic factor7. Inheritance may also play a role in the pathogenesis of ventricular aneurysm 10. In many infants with ventricular diverticulum there is no evidence of infarct or preexisting ischemia. In these children, an inherited error 10, 11, 12 in embryogenesis is theorized to produce weakened, dysplastic myocardium. Several authors have reported familial occurrence in aneurysms of muscular interventricular septum. This may be due to a genetic defect in mesnchymal cell migration in the embryologic development of the interventricular septum 12.
Differential Diagnosis: A suspected ventricular aneurysm should be differentiated from a ventricular diverticulum. Whereas aneurysms are broad-based, thin-walled lesions projecting through disrupted myocardium, diverticula are small, narrow-necked, finger or ballon-like projections with thicker, well-developed three-layer muscular walls composed of normal myocardium. Diverticulae typically have normal wall kinesis and do not generally produce cardiovascular compromise. They occur more commonly at the ventricular apex. Unlike aneurysms, which are typically isolated anomalies, diverticulae are associated with midline defects of the fetal thorax and abdomen including Pentology of Cantrell, omphalocele, and ectopic cordis as well as limb malformations 13. Associated intracardiac anomalies include VSD in virtually all cases, ASD in 50% of cases and pulmonary stenosis in 33 % 14.
The differential of right ventricular diverticulum also includes Uhl’s anomaly (congenital absence of the right ventricular pericardium), arrhythmogenic right ventricular dysplasia, and atrialized myocardium in Ebstein’s anomaly 15.
Ultrasound Findings/Diagnosis: Most commonly, the prenatal detection of ventricular aneurysm or diverticulum arises incidentally from the detection of an abnormal, distorted cardiac contour on the four-chamber view of the heart 3,6,8,16,17 or detection of fetal arrthymia 4, 7, 15, 18. A suspected aneurysm is confirmed sonographically utilizing color-flow pulsed Doppler in conjunction with real-time 2-D imaging. A large, wide-based echolucency is found that is contiguous with the ventricular cavity. The use of color-flow Pulsed Doppler demonstrates to and fro, low velocity blood flow, entering the cavity during diastole and exiting with systole. Hypokinesis or akinesis of the aneurysm wall can be observed. If the aneurysm ends near the level of the mitral or tricuspid valves, A-V insufficiency is often present secondary to aneurismal distortion of the valve attachment. Isolated pericardial effusion in the absence of other signs of cardiac failure has been reported, particularly when the aneurysm arises from the right ventricle 21.
Complications: While the majority of affected fetuses maintain normal cardiac function, the potential exists for a variety of significant complications. Fetal arrhythmias are common and may be of either atrial or ventricular origin 4, 15. Congestive heart failure and fetal hydrops develop as the end result of valvular insufficiency, ventricular dysfunction, progressive enlargement of the aneurysm, or sustained tachycardia 2, 5,8,16, 17. Thrombi can form as the result of the low velocity blood flow in and out of the dyskinetic aneurysm. A large pericardial effusion or aneurysm can result in compression of the fetal lung with subsequent pulmonary hypoplasia 16, 17 as well as mediastinal shift leading to hydrops 8.
Prognosis: Outcome is generally favorable if the size of the aneurysm remains stable and normal cardiac function is preserved 6, 14,15,17,18. However, the prognosis is dismal in hydrops is present or cardiac failure evolves in utero 2, 5,8, 16, 17. Several sonographic findings accurately predict poorer prognosis. These include large volume of the aneurysm at diagnosis and/or progression in the dimensions of the lesion 16, early gestational age at diagnosis 8,16, location of the defect higher in the ventricular wall, near or encompassing the A-V valve attachment 16, and presence of cardiac failure or hydrops 2, 5, 8, 16, 17 . In postnatal life, 40% of children remain asymptomatic with their aneurysms ultimately detected incidentally. The remaining 60% however will present for diagnosis because of serious complications including congestive heart failure 19, ventricular tachyarrhythmia, thromboembolism 20, endocarditis, rupture and sudden death 8.
Antenatal Management: Ventricular aneurysm may be an evolving disease, progressing through a spectrum of severity with cardiac growth. As above, a favorable outcome requires that the fetus maintains normal cardiac function. Hence, antennal management requires surveillance for early detection of complications. Serial fetal sonographic evaluation with Doppler echocardiogram identifies fetuses with poor prognostic factors that are at risk for adverse outcome, and provides an opportunity for intervention. Such surveillance should include:
-Two-D real time cross-sectional imaging: evaluation for dynamic progression in size of the aneurysm (measure ratio of aneurysm to ventricle), any evidence of cardiac failure such as pericardial effusion, mediastinal shift, and fetal hydrops. Pericardiocentesis may be indicated if a large effusion results in cardiac tamponade or significant compression of the fetal lungs 16. However, in the absence of any evidence of dysfunction, pericardial effusions have been reported to spontaneously resolve 18.
-Color-flow Doppler evaluation for thrombus formation, A-V valve regurgitation, reversed atrial shunting. Doppler insonation of the venous system can reveal ensuing cardiac failure, which should be anticipated if any of the preceding is present.
-M-mode documentation of the fetal heart rate and rhythm
With the paucity of reported cases and follow-up of ventricular aneurysms detected prenatally, no standard exists to dictate peripartum management. Hence, timing and mode of delivery should be individualized based on the perinatal assessment. Early intervention is not necessary in the absence of fetal cardiac compromise, thus such pregnancies should be allowed to progress to term. Conversely, delivery is indicated with the evolution of hydrops fetalis in the near term fetus. The very premature fetus with cardiac failure may sometimes be temporized with aggressive digoxin therapy to prolong gestation long enough to achieve pulmonary maturity or the benefits of antenatal corticosteroids 5, 15. Cesarean delivery is prudent for the compromised fetus with hydrops fetalis whereas the safety of vaginal delivery has been reported in the asymptomatic fetus with ventricular aneurysm. Delivery should occur at a tertiary care facility to provide immediate availability of neonatal intensive care and pediatric cardiology.
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