Accessory mitral valve tissue as a rare pathology has been reported to have an estimated incidence of 1 out of 26,000 adults . With reporting our case as the prenatal diagnosis of this anomaly, one might claim that AMVT could be an echocardiographic finding from fetal to late adulthood period. Despite the miniaturized anatomy of the fetal heart, the quality and resolution of the fetal echocardiographic images have been remarkably improved since the introduction of this imaging modality . With ongoing evolution in technology, the diagnosis of delicate structural heart defects such as AMVT in the fetus has become possible. Both three-dimensional (3D) and four-dimensional (4D) echocardiography enable to depict a more precise anatomical structure and provide en face visualization of the mitral valve. However, 3D and 4D fetal cardiac imaging require technical expertise [4, 5]. Likewise, although fetal cardiac magnetic resonance imaging has been used as a research tool, its clinical application in fetal heart diagnostic imaging has several limitations [3, 6].
The association of AMVT with other congenital cardiac defects has been frequently reported in the literature [1, 2, 7, 8]. This association might be attributed to the developmental pathophysiology of AMVT in the embryonic period. Normally, the endocardial cushion forms the mitral valve. If this embryonic process fails to develop normally, then AMVT might be separated from the cushion . Major associated anomalies such as ventricular and atrial septal defects, atrial septal aneurysm and subaortic stenosis also originate from the defects in the endocardial cushion development .
Several classifications have been used to describe the shape of AMVT in different case series [8,9,10,11]. The shape is dependent on the site where AMVT is attached. The site of attachment is on the left-sided heart structures including the anterior and posterior leaflets of the mitral valve, aortic valve, papillary muscles, chordae tendineae, interventricular septum and the left atrial/ventricular walls. For a more precise anatomical description of the lesion, Prifti et al. proposed a classification system . In this system, the accessory valves are divided into two shapes of fixed and mobile types. Fixed types (type I) include nodular (IA) and membranous (IB) accessory valves. Mobile type (type II) is also divided into two groups of pedunculated (IIA) and leaflet likes (IIB) accessory valves. Type IIB is further subdivided as rudimentary or well-developed chorda tendineae. Our case seems to be classified in the subdivision of IIB2 because of its mobile leaflets and well-developed chordae. A simpler classification method by Yetkin et al.  uses the true mitral valve leaflets as the primary landmarks for the AMVT typing. In this classification, the three types of I, II and III are described according to the attachments above, on or below the true mitral valve leaflets, respectively.
One-third of the patients with AMVT are asymptomatic. Symptoms of palpitation, chest pain, syncope and dyspnea have been reported. Patients with LVOT obstruction might experience dizziness and exertional dyspnea . Other serious, however, uncommon complications are hemiplegia, transient ischemic attack and retinal artery occlusion due to thromboembolic events [11,12,13]. Dysrhythmia including atrial fibrillation and ventricular tachycardia has been reported too [8, 11]. The prenatal presentation of ventricular extrasystoles in our fetus might be attributed to the AMVT. Anomalies of the conduction system have been reported in cases of AMVT . However, the co-existence of extrasystoles and AMVT in our case seems to be irrelevant because of the disappearance of both premature beats and LV apical diverticulum in post-partum echocardiograms [15, 16]. The ventricular ectopy and arrhythmia have been reported with LV wall defects including LV diverticulum. Moreover, there are reports of spontaneous fading of ventricular diverticulum before and after delivery . Concomitant disappearance of extrasystoles and diverticulum in our patient's follow-up might be a clue for their cause and effect relationship.
Some studies have reported that AMVTs might be overlooked in the echocardiographic examination for other cardiac anomalies, and even some cases of AMVT have been detected years after cardiac surgery. Hence, it is advised to improve echocardiographic imaging especially in the field of fetal echocardiography by optimizing image quality in different aspects of probe resolution, probe position, transducer pressure, depth and sector width.
Clinical assessment of patients is necessary for choosing the treatment in patients with AMVT. In asymptomatic patients without any associated conditions, only follow-up is recommended. However, in symptomatic patients, multiple factors including the symptoms, obstruction of the LVOT, valvar disease, heart failure and the concomitant anomalies must be considered in the therapeutic approach . Antiplatelet therapy has been suggested in all patients with AMVT . Surgery is a choice with relatively vague indications in the literature. Overall, surgical resection is indicated in symptomatic patients or those with prominent LVOT obstruction [1, 8].