Definition: Abnormal dilatation of the atrial septum with bulging of the septum at least half the distance to the left atrial wall. Prevalence: Fetal 60-588:10,0001,2 Postnatal 22:10,000, M1:F1.93. Etiology: Weakened or redundant septum primum stretched by increased right atrial pressures. Pathogenesis: Unknown. Associated anomalies: Atrial septal defect, tricuspid atresia, hypoplastic right heart, aortic stenosis, transposition4, and Ebstein"s anomaly3. Differential diagnosis: Normal foramen ovale flap, left atrial appendage, left atrial thrombus, anomalous left superior vena cava. Prognosis: Excellent, in absence of other anomalies. Recurrence risk: Unknown; probably small. Management: Exclude coexisting cardiac anomaly and arrhythmia, otherwise normal obstetrical care. MESH Heart-Aneurysm ICD9 745.5 CDC 745.580 Introduction Atrial septal aneurysm has been defined as an abnormally redundant septum primum flap which extends at least halfway across the left atrium5. In some cases these flaps have been large enough to prolapse through the mitral valve. Care must be taken not to confuse this appearance with the semicircular bulge or "pocket" of the normal flap of the foramen ovale. Although several series have reported echocardiographic and autopsy findings in children and adults with atrial septal aneurysms, few reports on the antenatal detection of such anomalies have been published. We present an atrial septal aneurysm diagnosed at 31 weeks gestation. Factors relevant to the management of such patients are discussed. Case report A 20-year-old G5P3 presented to the Vanderbilt Obstetrical Ultrasound unit at 31 weeks gestation for evaluation of gastroschisis. Ultrasound examination at that time revealed biometry consistent with 31 weeks and confirmed the presence of gastroschisis. In addition, the atrial septum was seen to bulge into the left atrium, consistent with an atrial septal aneurysm (fig. 1). No other anomalies were detected and no arrhythmias were noted. M-mode scan through the atrial septum demonstrated an abnormal septal excursion (fig. 2). Figure 1: Atrial septal aneurysm: note the position of the foramen ovale flap, far in the left atrium (arrow).
Figure 2: Abnormal monophasic M-mode of the septum primum (arrow).
The patient was electively delivered by cesarean section at 35 weeks of gestation. Gastroschisis was confirmed and repaired surgically. Cardiovascular examination after delivery was normal. An echocardiogram was not obtained. Four months later, both mother and child are well. Discussion Definition An atrial septal aneurysm is an abnormal dilatation of the atrial septum with bulging of the septum at least half the distance to the left atrial wall. Prevalence Atrial septal aneurysms are rare cardiac defects in children and adults, but not uncommon in fetuses. In 36,200 echocardiograms performed at the Mayo Clinic between 1978 and 1984, 80 cases (1 in 453) were diagnosed in patients ranging in age from 1 day to 89 years3. In contrast, in a series of 48 consecutive fetal echocardiograms, aneurysmal enlargement of the septum primum was seen in 3 (6%) patients.1 Pathogenesis Atrial septal aneurysm is a congenital cardiac defect that usually occurs in isolation, but occasionally may occur in association with other cardiac anomalies, especially those that lead to increased right atrial pressure such as hypoplastic right heart or tricuspid atresia. Diagnosis The defect, which involves the septum primum, can be seen antenatally as a bulge exceeding half the diameter of the left atrium on the four-chamber view. The normal biphasic excursion of the foramen ovale flap is shown in fig. 3. The biphasic motion of the foramen ovale flap is due to the atrial and ventricular contractions (fig. 4). This biphasic motion is lost in atrial septal aneurysms. M-mode of the septum primum flap may demonstrate loss of normal biphasic motion. Figure 3: M-mode of the septum primum (arrow) showing normal biphasic excursion. Figure 4: The normal biphasic motion of the foramen ovale flap (above) is compared with the motion of the flap in atrial septal aneurysm (below). Associated anomalies In most cases, abnormal findings are limited to the single anomaly of the fossa ovalis. However, when the aneurysm involves the entire atrial septum, hypoplasia of the right ventricle may be concurrent. One fourth of patients have been found to have atrial arrhythmias. Of 11 children with atrial septal aneurysms under the age of one year, 4 (36%) were found to have Ebstein"s anomalies and 7 (63%) had coexisting atrial septal defects3. A review of 105 fetuses evaluated for either arrhythmia or suspected congenital cardiac disease found an association between fetal arrhythmias and atrial septal aneurysm5. Of the 39 fetuses referred for arrhythmia, 25 (64%) were found to have atrial septal aneurysm, while 17 (26%) of 66 fetuses being scanned for suspected congenital heart disease also had atrial septal aneurysm. In a series of 148 fetuses evaluated for arrhythmia in the Netherlands2, 8 (5.4%) were found to have atrial septal aneurysm. Postnatal echocardiograms were performed in all infants and evidence of persistent atrial septal aneurysm was absent in all 8 antenatally diagnosed cases. There is a strong association between atrial septal aneurysm and fetal atrial arrhythmias2,5,-7. Evolution Atrial septal aneurysms are usually lost shortly after birth as left atrial pressure rises and eventually surpasses that of the right atrium, resulting in compression of the septum against the foramen ovale. Recurrence risk The recurrence risk is unknown. Management In the absence of associated anomalies, the prenatal management need not be altered. Management of associated anomalies will depend on their nature. Usually the arrhythmias associated with septal aneurysms do not require treatment.
References 1. Wilson AD, Rao PS, Aeschlimann S; Normal fetal foramen flap and transatrial doppler velocity pattern. J Am Soc Echo 3: 491, 1990. 2. Stewart PA, Wladimiroff J; Fetal atrial arrhythmias associated with redundancy/aneurysm of the foramen ovale. JCU 16: 643, 1988. 3. Hanley PC, Tajik AJ, Hynes JK, et al.; Diagnosis and classification of atrial septal aneurysm by two-dimensional echocardiography: report of 80 consecutive cases. J Am Coll Cardiol 6: 1370, 1985. 4. Casta A, Casta D, Sapire DW, et al.; True congenital aneurysm of the septum primum not associated with obstructive right- or left-sided lesions: identified by two-dimensional echocardiography and angiography an a newborn. Ped Cardiol 4:159-62, 1983. 5. Rice MJ, McDonald RW, Reller MD. Fetal atrial septal aneurysm: a cause of fetal atrial arrhythmias. J Am Coll Cardiol 12: 1292, 1988. 6. Hauser AM, Timmis GL, Stewart JR, et al. Aneurysm of the atrial septum as diagnosed by echocardiography: Analysis of 11 patients. Am J Cardiol 53:1401, 1984. 7. Varghese PJ, Simon AL, Rosenquist GL, et al. Multiple saccular congenital aneurysms of the atria causing persistent atrial tachyarrythmia in an infant: report of a case successfully treated by surgery. Pediatrics 44:429, 1969. 8. Katayama H, Mitamura H, Mitani K, et al.; Incidence of atrial septal aneurysm: echocardiographic and pathologic analysis. J Cardiol 20:411-21, 1990. 9. Barbosa MM, Pena JL, Motta MM, Fortes PR. Aneurysms of the atrial septum diagnosed by echocardiography and their associated cardiac abnormalities. Int J Cardiol 29:71-8, 1990.