Discussion

Mitral ring is a rare congenital anomaly, which was first described as a component of Shone's syndrome.Reference Anderson ⁴ In fact, two different entities must be distinguished: intramitral ring, which is a shelf located within the two mitral leaflets, and supramitral ring whose origin is just above the mitral annulus. As for our patient, an intra-operative visualisation of a fibrous shelf that arose beneath the orifice of the left atrial appendage eliminates the diagnosis of the divided left atrium – also named cor triatriatum sinister – and, at the same time, confirms that of the supramitral ring. Indeed, the origin of the divided left atrium is necessarily located above the opening of the left atrial appendage. The two types of mitral rings might still have different embryological origins. Owing to the fact that the intramitral ring is always combined with abnormal subvalvular apparatus, it seems to be a part of an intrinsic mitral valve disease; because the supravalvular ring was found above the tricuspid valve of a congenitally corrected transposition of the great arteries, it was suggested that the supramitral ring would rather be a form of left atrial outlet obstruction – it means a left atrial disease.Reference Marino, Sanders, Parness and Colan ⁵ This hypothesis is supported by the fact that, in case of the supramitral ring, the subvalvular apparatus is always normal. Both intramitral and supramitral rings are responsible for stenosis that leads to elevated left atrial pressure and post-capillary pulmonary hypertension. Classically, cross-sectional echocardiography reveals dilated right cardiac chambers, whereas the left ventricle is not filled. The definitive treatment of the supramitral ring consists of its surgical removal, which is, most of the time, completely efficient.Reference Toscano, Pasquini and Iacobelli ⁶

In their series of 15 patients, Collison et alReference Collison, Kaushal and Dagar ⁷ showed that, using transthoracic cross-sectional echocardiography, the pre-operative diagnosis of mitral ring was possible only for 73% of patients. Moreover, real-time transthoracic three-dimensional echocardiography was proved to be efficient to visualise mitral ring in children.Reference Pawelec-Wojtalik, Iorio, Anwar and El Midany ³ Indeed, this technique allows to see the ring from the left atrium (en face view), as a surgeon. Three-dimensional echocardiography is also helpful to analyse both chordal attachments and papillary muscles. We believe that the combined use of cross-sectional and three-dimensional echocardiography allows both to clarify the diagnosis of congenital mitral stenosis and to provide better morphological analysis of these valves. This is of interest when considering the fact that need for re-operation is 50% in case of intramitral ring, whereas removal of supramitral ring is usually definitive.Reference Toscano, Pasquini and Iacobelli ⁶ Finally, this observation is unique because, to our knowledge, no other case of multi-perforated mitral ring has ever been reported so far. The two orifices were perfectly depicted by three-dimensional echocardiography, highlighting again its high descriptive value even in small children with congenital heart disease.