Davachi and colleagues, in 1971, were one of the first to systematically assess and classify congenitally malformed mitral valves based on postmortem assessment (Davachi et al. 1971). They used a segmental classification according to whether the lesion affected the leaflets, commissures, tendinous chords, or papillary muscle arrangements. In 1977, Collins-Nakai et al. critiqued this segmental classification as they noted 97 % (37 out of 38) of their patients with congenital mitral stenosis had more than one segment of the mitral valve apparatus affected (Collins-Nakai et al. 1977). They concluded that it was misleading to classify patients based on one anatomic segment of the mitral valve (Collins-Nakai et al. 1977). They proposed a classification based on associated cardiac defects (e.g., associated left-sided lesion, tetralogy of Fallot, or no associated defects) (Table 22.1).

In 1978, Ruckman and van Praagh focused their attention on stenotic mitral valve defects and noted that typically congenital mitral stenosis affected multiple valve segments (Ruckman and van Praagh 1978). Commonly, the leaflet margins were thickened, tendinous chords appeared shortened, interchordal spaces were obliterated, and the two papillary muscles were underdeveloped and closely spaced. They coined the term “typical congenital mitral valve stenosis” to describe this most common defect with two distinct papillary muscle arrangements. The remainder of stenotic mitral valve defects were classified as “parachute mitral valve” (a single papillary muscle variant), “hypoplastic mitral valve” (miniature valve as seen in hypoplastic left heart syndrome), “double orifice mitral valve,” and “supramitral ring.” “Supramitral ring” earned a category of its own even though from their work it was clear that it was rarely an isolated defect. As a result, by necessity, some patients were classified into multiple categories based on this system. In 1994, Moore et al. (1994) expanded van Praagh’s classification by adding “atypical congenital mitral stenosis” to differentiate between groups with symmetrical (typical mitral stenosis) and asymmetrical (atypical mitral stenosis) papillary muscle arrangements. His description of “atypical congenital mitral stenosis” resembled Oosthoek’s (Oosthoek et al. 1997) description of “parachute-like asymmetrical valve” (see complex mitral valve lesions).

In 1976, Carpentier et al. (1976) introduced a surgical classification system to specifically facilitate the development of tailored techniques for congenital mitral valve repair. It was based on the “predominant lesion,” as he also observed that multisegment pathology was the most prevalent. His description and classification was based on observations at surgery made via the left atrium. Prior to this all classifications were based on the pathologists’ view of the defect. The Carpentier classification was based on leaflet motion: normal, restricted, or prolapsed. In addition it considered the predominant anatomic and hemodynamic effects (Table 22.1). This description of congenital mitral valve defects was widely accepted and utilized over the next three decades (Serraf et al. 2000; Carpentier et al. 1976; Chauvaud et al. 1998; Oppido et al. 2008; Uva et al. 1995; McCarthy et al. 1996; Prifti et al. 2002; Stellin et al. 2010; Wood et al. 2005; Zias et al. 1998). His team dramatically expanded the repertoire of operative techniques and in doing so popularized mitral valve repair for congenital defects. In 2008, Oppido and colleagues (Oppido et al. 2008) further refined the classification system by adding a further level to Carpentier’s classification, the quality of leaflet tissue: normal or dysplastic. In their surgical series, dysplastic leaflets were associated with less favorable and less durable repairs.

Anatomical pathologists and cardiac surgeons introduced descriptive terms for what they perceived as very distinct congenital mitral valve lesions. However, many have argued that the majority of cases do not fit the classic morphologic pattern but are the incomplete forms or the so-called forme fruste (Rosenquist 1974; Mitruka and Lamberti 2000). As a result these descriptive terms are not stand-alone terms and require further clarification to facilitate effective communication.

“Parachute mitral valve” refers to an anomaly of the mitral valve apparatus where all tendinous cords insert into one papillary muscle as noted by Edwards in 1963 (Schiebler et al. 1961). The other papillary muscle is either absent or severely hypoplastic. As a pathologist, he observed the mitral valve through the incised left ventricle and noted that the anomaly had a parachute-like appearance. Others later observed that in the setting of isolated papillary muscle, the tendinous chords are often short and fused with interchordal spaces partially or completely obliterated (Hoashi et al. 2010; Davachi et al. 1971; Chauvaud et al. 1998; Shone et al. 1963). Commissures are frequently underdeveloped and the leaflets may be dysplastic or deficient. The combination of these lesions can give rise to a funnel rather than a parachute-like appearance. It is frequently associated with a “supramitral ring” (Davachi et al. 1971; Ruckman and van Praagh 1978) that is often an integral part of the mitral valve leaflets (Banerjee et al. 1995; Asante-Korang et al. 2006). It is a membranous or fibrous shelf that arises from the atrial side of the anterior mitral valve leaflet and posteriorly attaches to the leaflet, annulus, or the left atrial wall below the level of the left atrial appendage (Banerjee et al. 1995). Parachute mitral valve is commonly classified as a malformation of the papillary muscles. However, that is too simplistic. It is often the associated lesions of other valve segments (e.g., commissural underdevelopment, dysplastic leaflets, and shortened and fused tendinous chords) that determine the severity of valvar dysfunction (stenosis and regurgitation) and hence the need for cardiac intervention.

In addition to a supramitral ring, parachute mitral valves are frequently associated with subaortic obstruction and coarctation of the aorta. When obstruction at all four levels is present, it is then referred to as Shone’s complex (Shone et al. 1963).

Parachute-like asymmetrical valve was described by Oosthoek et al. (1997) in 1997 as an anomaly that is an incomplete form of the true parachute valve with two papillary muscles: one hypoplastic and the other dominant receiving the majority of tendinous chords. He further described that one of the papillary muscles was often elongated, located higher in the left ventricle with its tip reaching to the annulus, and attached at both its base and lateral side to the left ventricular wall. The valve leaflets could be directly attached to the hypoplastic papillary muscle. Parachute-like asymmetrical valves formed a spectrum of anomalies, rather than a well-defined entity. Only one out of Oosthoek’s 29 cases could be described as a “true” parachute valve (Oosthoek et al. 1997). Two decades earlier Rosenquist also demonstrated that most papillary muscle anomalies were often mild or incomplete forms (which were common among patients with coarctation) and that the “true” parachute anomaly, with a single papillary muscle, was rare (Rosenquist 1974).

Anomalous mitral arcade was first described by Layman and Edwards in 1967 as “an anomaly of the mitral valve that consisted of connection of the left ventricular papillary muscles to the anterior mitral valve leaflet, either directly or through the interposition of unusually short tendinous chords” (Layman and Edwards 1967). When viewed from the left ventricle, the two papillary muscles resembled two pillars, and the bridging fibrous tissue in-between the papillary muscles resembles the arch of an arcade.

Hammock mitral valve was first described in 1976 by Carpentier et al. (1976), and it referred specifically to the appearance of the mitral valve apparatus from its left atrial aspect as viewed at cardiac surgery. The hammock appearance arose when the valvar orifice was at least partially obstructed by intermixed tendinous chords that attached to abnormal papillary muscles implanted just beneath the posterior leaflet (Carpentier and Brizard 2006).

Double orifice mitral valve is a rare anomaly (0.05 % of congenital cardiac abnormalities) that is usually found incidentally or in combination with other abnormalities, most commonly AV canal defects. In itself, it is rarely a cause of significant regurgitation or stenosis (Zalzstein et al. 2004).

Although it is not a true mitral valve lesion, it is convenient to include cor triatriatum (heart with three atria) in the discussion. It is rare – 0.5 % of congenital cardiac defects – and may be associated with other defects including ASD (see below), anomalous pulmonary venous drainage, VSD, bicuspid aortic valve, coarctation of the aorta, Fallot’s tetralogy, DORV, common AV canal, persistent left SVC with unroofed coronary sinus, and hypoplastic mitral valve.

The nature and severity of symptoms in patients with congenital mitral valve anomalies relate to etiology, rate of onset and progression, left ventricle function, pulmonary artery pressure, and the presence of coexisting valvular or myocardial diseases.

The diagnosis of congenital mitral valve anomaly relies on the clinical findings, the chest radiography, the electrocardiogram (ECG), and most importantly the echocardiographic assessment. The positive diagnosis can often be made before the echocardiographic evaluation in the presence of an isolated mitral valve anomaly.