Discussion

Mitral valve aneurysm is a localised saccular bulging on the mitral leaflet towards the left atrium with systolic expansion and diastolic collapse. ^{Reference Kim, Cho and Jun1} It is most commonly caused by aortic regurgitant jet complicated by infective endocarditis of the aortic valve. ^{Reference Reid, Chandraratna and Harrison2} Perforation of the aneurysm may occasionally occur and lead to significant mitral regurgitation. ^{Reference Tewari, Moorthy and Sinha3} There are other acquired aetiology such as rheumatic diseases and suspected congenital or structural aetiology such as connective tissue diseases including osteogenesis imperfecta, Marfan syndrome, Ehlers–Danlos syndrome type IV, and pseudoxanthoma. ^{Reference Gajjar and Desai4,Reference Rückel, Erbel, Henkel, Kramer and Meyer5} Although these cases are rare, aneurysms caused by these aetiologies commonly occur in the anterior mitral leaflet. ^{Reference Kim, Cho and Jun1}

Mitral valve aneurysm in children, excluding acquired aetiologies such as infective endocarditis, rheumatic disease, and iatrogenic disorders, has rarely been reported in the literature. ^{Reference Saxena, Shrivastava and Kumar6} On the other hand, there are a few reports of isolated mitral valve perforation without infective endocarditis in children. ^{Reference Schranz, Oelert and Iversen7,Reference Oztunc, Saltik and Turkoglu8}

In our patient, the aneurysmal lesion was on the posterior mitral leaflet with no clinical evidence of infective endocarditis. Other congenital mitral valve diseases, such as prolapse, isolated cleft, double-orifice, tendon rupture, or severely hypoplastic leaflet or acquired mitral valve diseases, such as endocarditis, connective tissue disease, rheumatic fever, or trauma, were excluded. In our case, two mechanisms may have caused mitral aneurysm and regurgitation: congenital isolated mitral valve aneurysm that was subsequently complicated by sudden perforation or a small isolated mitral perforation that may have induced mitral valve aneurysm secondary to a jet lesion, while expansion of the hole eventually caused critical mitral regurgitation. Dilated left ventricle and atrium, as well as left ventricular hypertrophy with preserved pump function on echocardiography, suggested subacute onset. At the same time, the degenerative changes in the collagen fibre of the valvular leaflet and fibrosis on histopathological examination might have been caused by the long-standing jet lesion. Consequently, we believe that a small isolated mitral perforation may have progressed to severe mitral regurgitation complicated by mitral valve aneurysm. It is difficult to conclude with only a single instance. Therefore, there is a need for reporting similar cases with detailed graphics and pathologic information to elucidate the relevant aetiology and pathogenesis.

Mitral perforation and aneurysm are surgically repaired using various techniques. For isolated perforation in children, direct suture or patch closure using autologous pericardium is performed. ^{Reference Schranz, Oelert and Iversen7,Reference Oztunc, Saltik and Turkoglu8} For mitral valve aneurysm complicated by perforation in adults, resection of the aneurysm and mitral valve annuloplasty are done. ^{Reference Kim, Cho and Jun1,Reference Guler, Hatipoglu, Karabay and Kirma9} In our case, the outcome of surgical repair, that is, intentional perpendicular suture to achieve mitral coaptation, was excellent.

In summary, we reported a case of perforated mitral valve aneurysm not complicated by infective endocarditis in an 8-month-old male infant, with surgical and histopathological findings. Although its aetiology remains unclear, we suggest to include mitral valve aneurysm in differential diagnosis as a cause of mitral regurgitation in children.