Pseudoaneurysm of mitral-aortic intervalvular fibrosa in a child: Demonstration by MDCT and MRI.

Subaortic left ventricular outflow tract pseudoaneurysms are rare lesions that are associated with aortic valve diseases, infective endocarditis, trauma or surgery. We present dynamic multidetector computerized tomography and cine magnetic resonance imaging features of a case of subaortic aneurysm arising from interaortic-mitral valvular region in a child with past history of infective endocarditis.

INTRODUCTION

Psedoaneurysms in the mitral-aortic intervalvular fibrosa are rare, but well recognized. Left ventricular outflow tract aneurysms have been associated with aortic valve diseases, valvular surgery, infective endocarditis and tuberculosis.[1-3] In the past, these lesions have been diagnosed with echocardiography and catheterization; presently, multidetector computerized tomography (MDCT) and magnetic resonance imaging (MRI) are emerging as the imaging modalities of choice, and have tremendous capabilities to demonstrate the three dimensional anatomy and hemodynamics of these lesions to much greater clarity and detail. We describe the dynamic MDCT and cine MR features of a subaortic left ventricular outflow tract aneurysm in the region of mitral-aortic intervalvular fibrosa in a child.

CASE REPORT

A 10-year-old boy with history of aortic valve disease (bicuspid aortic valve with severe aortic regurgitation) and infective endocarditis 6 months ago was referred for evaluation of echocardiographic finding of a cystic lesion. The lesion was posterior to the aortic root and anterior to left atrium with turbulent flow on color Doppler. The lesion was thought to represent a ruptured myocardial ring abcess; the patient was advised further imaging with MRI. Cardiac MRI was done using ECG gated breath-hold SSFP (TRUFI) sequences in left ventricular short axis and LVOT (3 chamber plane) and transaxial (aortic valve planes). The aneurysm was seen filling during the systole and emptying during the diastole and showed a swirling flow (manifested by hypo intense signal secondary to rapid dephasing due to turbulent flow); the aortic valve was bicuspid with severe aortic regurgitation and thickening of valve margins [Figure 1 and Videos 1 and 2]. The patient was lost to follow-up and turned up after 6 months. A repeat study was requested but the child developed claustrophobia in the MR suite. CT angiography was performed on a 64-slice scanner (Sensation, Siemens Medical Solutions) using a pediatric cardiac CT protocol and retrospective ECG gating. The images were processed on dedicated workstation; reformatted MPR and MIP images in different planes were analyzed. CT angiography revealed an aneurysmal out pouching (measuring 1.9 × 2.9 × 3.0 cm in diastole as compared to previous MRI when the lesion measured 1.7 × 2.5 × 2.7 cm in the same cardiac phase) arising from left ventricular outflow tract below the aortic annulus; the aneurysm was related anteriorly to the aortic root and posteriorly to left atrium [Figures 2 and 3]. Multiphasic images revealed that the aortic valve was bicuspid with thickening of the free edges of the valve and dilation of ascending aorta (measuring 3.9 × 3.9 cm). When the size of the pseudo aneurysm was compared to the previous MRI for same cardiac phase a definite increase in the size of lesion was observed and the child was advised surgical repair.

Figure 1

TRUFI image in the LVOT plane shows the pseudoaneurysm (delineated by open arrows) between aortic root and left atrium with relatively hypointense signal (due to dephasing secondary to turbulence)

Figure 2

CT (MPR) image in 3-chamber plane shows the subannular aneurysm (horizontal arrow) between the root of ascending aorta (up arrow) and left atrium (down arrow)

Figure 3

MPR image of MDCT shows the pseudoaneurysm (delineated by arrows)

DISCUSSION

Congenital subaortic aneurysms are rare and were initially described in African population, and subsequently it is also reported in other racial groups.[1-5] Many of the subaortic aneurysms arise from mitral aortic intervalvular fibrosa, a fibrous structure between aortic and mitral valves. This is a relatively avascular area and prone to infection during endocarditis and subsequent aneurysm formation. Bicuspid aortic valves have a congenital weakness of mitral aortic intervalvular fibrosa and hence, a propensity to the formation of pseudo aneurysms; the regurgitant jet of aortic regurgitation may also be a contributing factor in such patients.[4-6] The most common antecedents are aortic valve surgery and infective endocarditis. Subaortic aneurysms have also been associated with tuberculosis, syphilis, takayasu arteritis, rheumatic carditis.[27-9] Some of these lesions are thought to be congenital in origin.[10]

The symptomatology of subaortic aneurysms is dominated by the underlying clinical condition. Clinical features include congestive cardiac failure, breathlessness, features of infection (due to endocarditis), palpitations, murmurs, angina (due to compression of left coronary artery); sudden death has also been reported. The aneurysms can rupture and communicate with the ascending aorta or left atrium. Thrombus formation with systemic embolism, myocardial infarction secondary to left coronary compression and rupture into pericardium have been described.[411]

Transthoracic echocardiography is the first imaging modality to pick up these lesions; however, the anatomic detail and precise relationship with the cardiac chambers often requires transesophageal echocardiography. In one series of 16 patients with intervalvular pseudo aneurysms, TEE had a sensitivity of 90% and transthoracic echo had a sensitivity of 43% only; Aortography could identify only 3 out of 10 pseudo aneurysms. A distinct dynamic pattern of systolic expansion and diastolic collapse was seen in case of pseudo aneurysms on Doppler. With advent of MDCT and cardiac MRI, invasive catheterization is unnecessary. CT angiography has the advantage of simultaneous evaluation of valvular structures, coronary arteries, thrombi, and the precise relationship of the pseudo aneurysm with other cardiac chambers, aortic root and pulmonary artery. Cine MR sequences (TRUFI and FLASH sequences) with their high temporal resolution and sensitivity to fast and turbulent flow can show the filling and emptying of the aneurysm during different phases of cardiac cycle, ascertain the relationship of aneurysm neck with left ventricular outflow tract and in conjunction with phase contrast sequences, can help in quantification of aortic regurgitation, stroke volume and ejection fraction. MRI also has the advantage of avoiding ionizing radiation which is a concern in young children. However, patient cooperation with breath-hold can limit an optimal study in severely symptomatic or uncooperative patients. Till now very few of these patients have been studied by MRI and MDCT.[1213]

The exact localization of the opening and neck of aneurysm is essential; MDCT and MRI both provide excellent multi-planar and 3D images of the aneurysm, its relationship with coronaries, aortic root and cardiac chambers and are invaluable to the operating surgeon.

The treatment is surgical and involves primary repair of the aortic valve, closure of the aneurysmal mouth with or without the use of a pericardial or Dacron patch. Excision of the pseudo aneurysm with replacement of aortic root has also been performed.[414]