Incomplete Shone syndrome in a 44-year-old woman: a case description

Introduction

Shone syndrome, first described by Shone and colleagues in 1963, is a rare and complex congenital cardiovascular disorder characterized by a spectrum of obstructive lesions affecting the left side of the heart (1). The classical or complete form of the syndrome includes four components: supramitral ring, parachute mitral valve (PMV), subaortic stenosis, and coarctation of the aorta (CoA). These abnormalities result in combined obstruction of the left ventricular inflow and outflow tracts, ultimately impairing systemic circulation and increasing cardiac workload.

The complete form is rare, and most cases are diagnosed in infancy or early childhood due to severe symptoms such as congestive heart failure, failure to thrive, or cyanosis. In contrast, incomplete Shone syndrome, defined by the presence of two or three of the classical components, accounts for a larger proportion of clinical cases but remains underdiagnosed, particularly in asymptomatic or mildly symptomatic adults (2). Epidemiological studies estimate that Shone syndrome accounts for approximately 0.67% of all congenital heart diseases (3), with a median age at diagnosis of approximately 8 years. Adult cases are exceedingly rare, and there are only a few reports in the literature describing the natural history and variable manifestations of the syndrome beyond childhood.

The PMV—a hallmark feature of Shone syndrome—results from an abnormal mitral valve apparatus in which all chordae tendineae insert into a single papillary muscle, limiting leaflet mobility and leading to mitral stenosis (4,5). Similarly, CoA, another frequent component, involves segmental narrowing of the aortic arch or descending thoracic aorta and is often associated with systemic hypertension and collateral vessel formation (5,6). The pathophysiological consequence of these obstructive lesions is increased left ventricular afterload and impaired diastolic filling, which contribute to hypertrophy, fibrosis, and ultimately heart failure if untreated. Whereas the complete form often necessitates early surgical intervention, the incomplete form can be asymptomatic or oligosymptomatic for years (2), with diagnosis frequently delayed due to atypical anatomical features or overlapping symptoms with other cardiac conditions (7). Echocardiography remains the cornerstone of diagnosis and can be supplemented by advanced imaging modalities such as cardiac computed tomography angiography (CTA) or cardiac magnetic resonance imaging (MRI) for detailed anatomical assessment.

This case report describes a unique adult presentation of incomplete Shone syndrome in a 44-year-old woman with nonclassical anatomical variants, including an unusual mitral valve morphology that mimicked PMV function. To our knowledge, adult presentations with this type of mild anatomical obstruction and preserved functional status are uncommon, and this case contributes to a growing body of literature emphasizing the importance of multimodal imaging, longitudinal surveillance, and clinician awareness in recognizing atypical forms of congenital heart disease in adults.

Case presentation

A 44-year-old woman was admitted to the cardiology outpatient clinic with over 1 year of progressive chest tightness, exertional dyspnea, and decreased exercise tolerance. She had a known history of hypertension. Physical examination was unremarkable, and laboratory tests showed no significant abnormalities.

Initial transthoracic echocardiography revealed a bicuspid aortic valve (BAV) (type 0) (Figure 1A), with three major branches arising from a tortuously shaped aortic arch. The aortic isthmus had a reverse-S morphology with a peak velocity of 219 cm/s at a protrusion opposite the left common carotid artery and 194 cm/s at a membranous ridge within the isthmus (Figure 1B,1C). The descending thoracic aorta measured 37 mm proximally, while the abdominal aorta measured 20 mm.

Figure 1 Obstruction of the LVOT and inflow tract. (A) The short-axis view of the aorta suggested a BAV (type 0). (B,C) The suprasternal notch view showed a descending aortic arch with a tortuous course, and color Doppler indicated a mosaic blood flow. (D) The apical four-chamber view showed that the mitral valve had a “doming” shape. (E,F) The long-axis view of the LV and the two-chamber section revealed that the anterolateral papillary muscle of the mitral valve was almost directly attached to the valve leaflets (indicated by the yellow arrows). BAV, bicuspid aortic valve; LV, left ventricle; LVOT, left ventricular outflow tract.

Mitral valve assessment revealed thickened, hyperechoic leaflets with limited mobility. Most chordae tendineae were attached to a hypertrophied posteromedial papillary muscle, resulting in a parachute-like configuration (Figure 1D). The valve opening was restricted, with an orifice distance of 0.94 cm, a traced orifice area of 2.52 cm², and a pressure half-time-derived area of 2.12 cm². The peak transvalvular velocity was 176 cm/s, and the mean gradient was 4 mmHg.

The patient was hospitalized twice for unrelated conditions—knee joint pain and abnormal uterine bleeding. During one of these admissions, repeat echocardiography revealed direct insertion of the anterolateral papillary muscle into the mitral leaflet (Figure 1E,1F), and there was further evidence of mitral stenosis, including an orifice distance of 1.7 cm, a traced area of 2.6 cm², a pressure half-time area of 2.0 cm², and a mean gradient of 5 mmHg. Additional findings included aortic sinus dilation, mild coarctation of the proximal descending aorta, and mild mitral regurgitation. CTA confirmed severe localized narrowing at the proximal aortic arch near the left subclavian artery with proximal aortic arch dilation (Figure 2A,2B).

Figure 2 Head and neck CTA. (A) The results indicated severe localized narrowing of the aortic arch near the left subclavian artery with proximal aortic arch dilation (indicated by the yellow arrow). (B) Overall observation of the aorta. CTA, computed tomography angiography.

The constellation of findings—BAV, mitral valve with restricted mobility due to anomalous papillary muscle insertion, and aortic arch hypoplasia—supported the diagnosis of incomplete Shone syndrome. Notably, the supramitral ring and subaortic stenosis were absent.

The definition of Shone syndrome has now been significantly expanded to encompass various categories of congenital mitral valve disease combined with at least one type of left ventricular outflow tract obstruction. This case had left ventricular outflow tract obstruction due to BAV malformation, CoA, and mitral valve morphological abnormalities, meeting the diagnostic criteria for incomplete Shone syndrome.

All procedures in this study were performed in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

Shone syndrome is a rare congenital cardiac disorder characterized by progressive obstruction of the left heart inflow and outflow tracts. The complete form includes four classic lesions: supramitral ring, PMV, subaortic stenosis, and CoA. However, the incomplete form, involving two or three of these anomalies, is more frequently encountered in clinical practice and is often associated with additional congenital defects such as atrial or ventricular septal defects, PDA, or persistent left superior vena cava (8).

Most reported cases are diagnosed in early childhood due to symptomatic obstruction. In contrast, adult presentations, particularly with incomplete variants, are rare and diagnostically challenging due to subtle clinical manifestations and atypical anatomical variations. Our patient exhibited certain key features of the incomplete syndrome. A parachute-like mitral valve configuration was causing functional mitral stenosis, but it was not a classic single papillary muscle. The asymmetric distribution of chordal attachments led to restricted leaflet mobility, consistent with a parachute morphology (9,10). Interestingly, this presentation did not involve a supramitral ring, which is traditionally considered part of the inflow tract obstruction in Shone syndrome. BAV was present, which despite not being obstructive, constitutes a common left-sided congenital anomaly and is reported in up to 25% of Shone syndrome cases (7). Moreover, there was mild coarctation of the proximal aortic arch, which was confirmed by Doppler velocities exceeding 200 cm/s and was further corroborated by CTA findings of discrete narrowing with poststenotic dilation. The severity of obstruction was subclinical, explaining the patient’s preserved functional status.

Through her pioneering case observations and analyses, Maude Abbott was the first to systematically document and describe the significant association between BAV deformity and aortic pathology, including stenosis, in the work The Atlas of Congenital Cardiac Disease (11). Her work laid the cornerstone for subsequent generations to establish that this common congenital cardiac anomaly constitutes a major underlying cause of secondary aortic valve stenosis.

The uniqueness of this case lies in its subtle mitral stenosis caused by anomalous papillary muscle insertion, rather than by a fibrous supravalvular ring or classical PMV. This variant adds to the spectrum of mitral abnormalities observed in Shone syndrome and highlights the diagnostic value of detailed echocardiographic imaging (12).

According to published reports, the severity of mitral inflow obstruction is the most critical determinant of prognosis in Shone syndrome (13,14). Severe mitral stenosis typically becomes apparent in infancy or early childhood and requires early surgical intervention (15). In contrast, patients with milder variants, such as in our case, may remain asymptomatic until adulthood, with good long-term outcomes if carefully monitored. Management strategies for adult patients with Shone syndrome are individualized. Surgery is indicated in the presence of significant obstruction or heart failure symptoms. Our patient’s hemodynamic parameters were within the mild range, and her symptoms were well-controlled with medical therapy and lifestyle adjustments. Surveillance with serial imaging is essential to detect any progression.

Our case contributes to the limited body of literature on adult-onset incomplete Shone syndrome and demonstrates the importance of recognizing nonclassical anatomical variants. A high index of suspicion and multimodal imaging, including echocardiography and CTA, are critical to achieving a timely diagnosis. Early recognition can guide appropriate management and improve long-term prognosis.

Conclusions

Incomplete Shone syndrome can present in adulthood with atypical anatomical variants and mild symptoms. Recognition of these subtle anomalies, particularly involving the mitral valve apparatus and aortic arch, is essential. Multimodal imaging plays a pivotal role in accurate diagnosis and management planning. This case contributes to the limited literature on adult presentations of Shone syndrome and highlights the need for individualized patient evaluation.

Acknowledgments

None.

Footnote

Funding: This study was supported by the Innovative Research Program of Xiangyang No. 1 People’s Hospital (No. XYY2025SD09).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1429/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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