We present an unusual case of mitral regurgitation in an adult caused by anomalous mitral arcade. Adults diagnosed with MA tend to have milder valve pathology compared to children, which explains their delay in diagnosis until adulthood [3]. Although the exact cause of MA remains unclear, it is hypothesized to be due to arrested development of the chordae tendineae apparatus during mitral valvulogenesis, notably at a stage after collagenization (conversion of muscle to fibrous tissue) but before attenuation and elongation of the tensor apparatus [4].  The premature interruption of the maturation and elongation of the tensor apparatus yields the characteristic absent or shortened chordae tendineae, and frequent direct attachment of the papillary muscles onto the valve leaflets[10,11]. This is often accompanied by a decrease in inter-chordal spaces, or their loss due to fusion of the chordae tendineae by an interconnecting fibrous band that gives rise to the classic “arcade” or “hammock” appearance of the mitral valve apparatus [3].  This malformation of the subvalvular apparatus also causes undue restraint on the interposed papillary-chordae-mitral leaflet structure, which results in improper positioning of the MV apparatus, aberrant leaflet apposition and consequent suboptimal motion of either/both leaflet(s) that leads to valve stenosis and/or regurgitation [12].

The diagnosis of mitral arcade is made through cardiac imaging. TTE is often the initial test of choice to evaluate mitral valve anatomy and pathology. In one systematic review, the diagnosis of mitral arcade was made in 50% of patients through TTE imaging alone [3].

The key defining features on TTE are: (1) Normal size of the mitral valve annulus; (2) thickened mitral leaflets with restricted motion; (3) elongated papillary muscles; (4) short or absent chordae tendinae that attach very close to or directly onto the free edge of the anterior mitral leaflet; and (5) narrow interchordal spaces and/or hammock-shaped fibrous connection between the papillary muscles [2,6]. Usually there is relatively preserved structure of the posterior leaflet apparatus but this can be affected in more severe cases of MA [12]. When assessment by TTE is suboptimal, TEE can be used to further investigate mitral valve pathology and diagnose MA. More advanced imaging such as cardiac CT or MRI is mainly used for pre-surgical planning if warranted, or to help evaluate other cardiac disease such as a concurrent cardiomyopathy. Our patient’s TTE and TEE exhibited many of these characteristic findings, which lead to her diagnosis of mitral arcade and consequent management.

The management of adult MA patients first lies in accurate diagnosis. Given the high morbidity of childhood MA, most patients are diagnosed early in life [6]. Therefore, a high index of suspicion for MA is required when evaluating the etiology of mitral regurgitation or stenosis in adult patients. Once diagnosed, symptomatic adults with significant valve regurgitation or stenosis have typically undergone valve replacement based on pediatric experience rather than valve repair. This matches with numbers from literature: Of the 18 adult cases that have been reported, 13 patients underwent valve surgery; 11/13 (85%) underwent valve replacement (3 bioprosthetic; 8 mechanical) and 2/13 (15%) underwent valve repair [6,10,11,13]. Of the other 5/18 patients: 3 were treated medically (one due to incidentally diagnosed lung cancer), 1 died from heart failure prior to intervention, and no follow up or intervention was reported for 1 patient.

Only short- to mid-term outcome data are available. Of the 13 patients who underwent valve surgery, all 13 were live at discharge; 5/13 had no further follow up; 1/13 (8%) died suddenly at home 4 months after mitral valve repair, which had been complicated by residual mitral regurgitation and severe LV dysfunction (LV ejection fraction 22%); 7/13 (54%) were well at follow up – 3/7 had unknown duration of follow up, the remaining 4/7 were followed up to 2 weeks to 1 year after surgery. Only 1/3 medically-treated patient had follow up and was well at 48 months. These numbers are to be interpreted with caution as the true numerator and denominator are unknown.

For our patient, mitral valve repair rather than replacement was chosen in order to avoid the risks associated with anticoagulation in a young, childbearing woman who also had a history of fibroids with menorrhagia. Our patient underwent successful complex mitral valve repair and is well at more than 5 months since surgery.