Ultrasonic diagnosis of congenital descending aortapulmonary vein fistula: a case description

Introduction

Congenital descending aortapulmonary vein fistula (cDAPVF) (1) is an extremely rare congenital vascular malformation, characterized by abnormal communications between the descending aorta (and its anomalous branches) and the pulmonary veins. Its incidence is exceedingly low, with only sporadic case reports in the literature (2). The core pathophysiological feature of cDAPVF is the shunting of high-pressure systemic blood flow—bypassing the normal capillary bed—directly into the low-pressure pulmonary venous system, forming a distinct left-to-left shunt. Despite its highly occult nature and heterogeneous clinical manifestations, many patients remain asymptomatic for long periods. The condition is often detected incidentally only in adulthood. In contrast, when the fistula orifice is large, it can induce severe hemodynamic disturbances, manifesting as exertional dyspnea, hemoptysis, or even progressive heart failure (3). Furthermore, the clinical symptoms of cDAPVF overlap with those of other congenital cardiovascular diseases [e.g., pulmonary sequestration (PS), transposition of the great arteries, and pulmonary arteriovenous malformations (PAVMs)], rendering initial diagnosis particularly challenging (4).

Traditionally, the diagnosis of cDAPVF has primarily relied on computed tomography angiography (CTA) or digital subtraction angiography (DSA) to delineate the anatomical structure and blood flow pathways of the lesion. However, these diagnostic modalities entail significant limitations, especially in pediatric patients: both CTA and DSA involve exposure to ionizing radiation. Epidemiological studies have shown that children are 2–3 times more sensitive to radiation than are adults. Additionally, international organizations generally concur that there may be no absolute safe threshold for low-dose radiation exposure (5). As a radiation-free imaging strategy, high-frequency ultrasound (HFUS) combined with transthoracic echocardiography (TTE) reduces ionizing radiation exposure. This approach shortens subsequent CT scanning ranges or can even replace CT as the initial diagnostic tool for highly suspected cases, minimizing unnecessary radiation in children (6).

This report presents a rare infantile case of cDAPVF to address the deficiencies in current diagnostic approaches and introduces HFUS combined with TTE screening as a noninvasive, radiation-free, first-line tool, validating its potential in diagnosing complex vascular anomalies. Notably, coexisting KCNT1 and SMAD2 gene mutations were identified in this patient, providing potential insights into the genetic etiology of this rare disorder.

Case presentation

All procedures performed in this case were 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’s guardians for publication of this case description and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

An 8-month-old female infant was admitted to our hospital on three occasions due to hemoptysis. Four days prior to admission, the patient developed overt hemoptysis with bright red blood, without an identifiable precipitating cause. No accompanying symptoms (e.g., fever, vomiting, or cough) were noted. On physical examination, her height was 65 cm and her weight was 11 kg. The patient exhibited drowsiness, mild anemia, decreased mental alertness, and moderate appetite. All physiological reflexes were present, with no other significant abnormalities detected. The laboratory findings were as follows: hemoglobin level, 104 g/L; red blood cell count, 3.5×10¹²/L; and N-terminal pro-B-type natriuretic peptide (NT-proBNP), 128 pg/mL. Chest X-ray demonstrated clear bilateral lung fields, without evidence of significant exudative lesions or space-occupying lesions. The cardiac silhouette was enlarged, with a cardiothoracic ratio of 0.61. TTE revealed the following: left-sided cardiac position with leftward displacement of the aortic arch, marked enlargement of both the left atrium (39 mm × 29 mm) and left ventricle (44 mm × 28 mm), a thickened endocardium with elevated echogenicity (measuring approximately 7.8 mm), mild impairment of left ventricular wall motion [ejection fraction (EF) 49%]; and discontinuity of the interatrial septum (measuring approximately 2.1 mm in width) (Figure 1A). Dynamic imaging of the subaortic plane revealed multiple disorganized collateral arterial echoes draining into the bilateral pulmonary veins, while color Doppler flow imaging (CDFI) showed abnormal high-velocity blood flow signals. The left inferior pulmonary vein (6.1 mm in diameter) and right inferior pulmonary vein (6.2 mm in diameter) exhibited “sausage-like” dilatation, while the diameters of the other pulmonary veins remained within the normal range (right upper pulmonary vein: 4.1 mm; left upper pulmonary vein: 3.9 mm) (Figure 1B).

Figure 1 Multimodal imaging [(A-E) ultrasound; (F-H) arterial CT] revealed the key abnormalities of cDAPVF: cardiomegaly, pulmonary vein dilation, abnormal collateral vessels, and transdiaphragmatic vascular communication. CT reconstruction confirmed the morphology of the aberrant vascular network. (A) Left enlargement of the heart. (B,F) Bilateral inferior pulmonary venous dilation. (C) Anomalous arterial vessels posterior to the IVC (arrow). (D) Abnormal blood vessels passing through the diaphragm (arrow). (E,H) Multiple abnormal collateral arteries located at the margins of the liver (arrows). (G) CT reconstruction technique showing the lesion to be composed of aberrant vasculature (arrows). cDAPVF, congenital descending aortapulmonary vein fistula; CT, computed tomography; IVC, inferior vena cava; LA, left atrium; LLPV, left lower pulmonary vein; LV, left ventricle; RA, right atrium; RLPV, right lower pulmonary vein; RV, right ventricle.

To further clarify the etiology of left heart enlargement and pulmonary vein dilatation and to better visualize the anatomical structure of deep thoracoabdominal fistulas, an HFUS probe (frequency >10 MHz) was subsequently used for examination. Continuous scanning at the 7^th–8^th intercostal space along the subscapular line and within the abdominal cavity revealed multiple tubular anechoic structures located posterior to the inferior vena cava (IVC) along the hepatic margin and near the diaphragm. Vascular tracking confirmed their origin from the posterior wall of the descending aorta. The largest vessel had an internal diameter of approximately 3.1 mm and a length of 2.8 cm, with a tortuous course. This vessel ascended obliquely anteriorly and superiorly before draining into the bilateral inferior pulmonary veins. No calcification or thrombus attachment was observed within the vessels (Figure 1C,1D). CDFI further demonstrated several abnormal high-velocity blood flow signals crossing the diaphragm and communicating with the pulmonary veins (Figure 1E). Ultrasound findings were highly consistent with hemodynamic characteristics, leading to the diagnosis of cDAPVF, complicated by patent foramen ovale and mild left ventricular systolic dysfunction.

To validate the ultrasound diagnosis, the patient underwent contrast-enhanced computed tomography (CT) after admission. CTA revealed multiple abnormally thickened branches of the celiac trunk, which traversed the esophagus, hepatic parenchyma, and perihilar region before entering the mediastinum. Multiple tortuous, thickened vascular shadows were observed around the trachea, bronchi, and esophagus, accompanied by segmental bronchial narrowing in both lungs. The CTA findings were fully consistent with the abnormal vascular anatomy identified on HFUS (Figure 1F-1H), providing definitive imaging evidence for the final diagnosis.

Genetic testing revealed mutations in the KCNT1 and SMAD2 genes in the patient. Following a multidisciplinary consultation involving specialists from the fields of pediatrics, cardiac surgery, radiology, ultrasound, and respiratory medicine, the patient’s family declined treatment due to the extremely high surgical risks attributed to the patient’s young age, complex vascular malformation, and associated genetic abnormalities. After discharge, the patient was followed up via outpatient visits and telephone consultations. Left ventricular function further deteriorated (EF 38%), with significant pulmonary venous congestion. Despite intensive supportive therapies, including blood transfusion, hemostasis, and heart failure management, the patient’s condition continued to worsen. At 1 year of age, she developed refractory heart failure and massive hemoptysis and ultimately died despite aggressive resuscitative efforts.

Discussion

cDAPVF is an extremely rare congenital vascular malformation, representing a specific subtype of systemic arteriovenous fistula (7). Its incidence is exceedingly low, with only sporadic case reports in the literature. The core pathophysiological mechanism involves direct shunting of high-pressure systemic blood flow (originating from the descending aorta) into the low-pressure pulmonary venous system. This abnormal connection bypasses the normal pulmonary capillary bed, resulting in aberrant flow of oxygenated blood and forming a distinctive left-to-left shunt (8), a pattern fundamentally distinct from the common left-to-right shunting observed in conditions such as patent ductus arteriosus (PDA) or atrial septal defect (ASD). For instance, PDA is defined as an abnormal channel between the aorta and pulmonary artery. In the absence of pulmonary hypertension, aortic blood flow continuously shunts into the pulmonary artery, increasing pulmonary circulatory volume and ultimately leading to pulmonary hypertension and right ventricular overload. Similarly, ASD induces left-to-right atrial shunting, which also increases pulmonary circulatory volume and may progress to pulmonary hypertension and left heart overload. In contrast, the left-to-left shunt in cDAPVF directly channels high-pressure blood flow into the pulmonary veins, imposing a massive volume load on the pulmonary venous system, left atrium, and left ventricle (9). This mechanism accounts for the significant left atrial and left ventricular dilation, manifestations of heart failure, and reduced left ventricular EF detected on echocardiography in this pediatric patient.

Given the nonspecific clinical manifestations of cDAPVF, differential diagnosis is critical. The diagnostic process in this case underscores the necessity of distinguishing cDAPVF from several common vascular malformations (10), as it exhibits distinct pathological and radiological features compared to PS, scimitar syndrome (SS), and PAVM. PS is a lesion in which feeding arteries derive from the systemic circulation, venous drainage empties into systemic veins—often with nonfunctional lung tissue—and radiology shows z well-defined solid or cystic mass. SS is characterized by abnormal drainage of the right pulmonary veins into the IVC or right atrium. Chest X-rays typically reveal the classic “scimitar” shadow, often accompanied by pulmonary hypoplasia and ipsilateral mediastinal shift. PAVM is an abnormal connection between the pulmonary artery and pulmonary vein, resulting in right-to-left shunting. Its most typical clinical manifestations include cyanosis and hypoxemia. Notably, this patient had no cyanosis, and the nature of the shunt (left-to-left) and its hemodynamic consequences were entirely distinct from the aforementioned conditions—providing clear indications for ultrasound-based differentiation.

Hemoptysis is a key clinical manifestation of cDAPVF, with its underlying mechanism likely involving persistent high-pressure blood flow damaging the pulmonary veins—leading to dilation, wall thinning, or even rupture, and subsequent hemoptysis. The combination of volume overload-induced heart failure and hemoptysis constitutes the primary clinical feature of this case. The diagnostic process in this patient demonstrates an optimized clinical pathway centered on TTE and HFUS as the core diagnostic strategy. TTE serves as the initial noninvasive screening tool, sensitively detecting indirect shunt-related signs (e.g., left atrial and left ventricular enlargement, pulmonary vein dilation). Additionally, CDFI can identify abnormal high-velocity blood flow signals, providing critical clues for further diagnosis. However, TTE is limited by its spatial resolution and tissue penetration depth and thus may be unable to clearly visualize small or tortuous fistula structures in the deep thoracoabdominal cavity.

Currently, the treatment of cDAPVF follows the principle of risk stratification: for patients with a single fistula, a diameter <1.0 cm and a clear anatomy, transcatheter closure is the preferred approach; for those with multiple tortuous fistulas, diameter >1.5 cm, or unsuitability for interventional therapy, open surgical repair is required; for asymptomatic patients with small shunts and normal cardiac function, ultrasound follow-up and monitoring are recommended. In our case, due to the infant’s multiple tortuous fistulas, young age, and concurrent genetic mutations, both interventional and surgical procedures entailed extremely high risk. The family ultimately declined invasive treatment, which is consistent with the aforementioned management principles for rare diseases (11).

HFUS addresses this limitation. By virtue of its high frequency (>10 MHz) and superior near-field resolution, HFUS can be used for ultra-high-resolution imaging that precisely delineates the anatomical structure and spatial relationships of deep vascular structures. In our case, HFUS successfully visualized tortuous vessels originating from the descending aorta near the diaphragm and traced their drainage into the bilateral inferior pulmonary veins. CDFI imaging further confirmed the presence of abnormal high-velocity blood flow. HFUS, a noninvasive, radiation-free, and bedside-accessible examination modality, is particularly valuable for pediatric patients (9), as it avoids the ionizing radiation risks associated with CTA and DSA. Thus, a layered diagnostic strategy is proposed: TTE for initial screening, HFUS for precise localization and anatomical assessment, and CTA or DSA for definitive verification or pretreatment planning. This approach not only improves diagnostic efficiency but also ensures a safer diagnostic and therapeutic experience for patients.

Genetic findings and implications

A notable finding in this case was the concurrent identification of mutations in the KCNT1 and SMAD2 genes. Both genes have been previously reported in the literature as being associated with cardiovascular defects although their link to cDAPVF remains unreported. The KCNT1 gene encodes a sodium-activated potassium channel (12). Variants in this gene primarily cause neuronal hyperexcitability, which manifests clinically as epileptic encephalopathy. Notably, approximately 10% of patients with KCNT1 mutations exhibit rare congenital heart defects, such as abnormal systemic–pulmonary collateral circulation. The SMAD2 gene functions as a key transcriptional regulator in the transforming growth factor-β (TGF-β) signaling pathway (13). Pathogenic variants in SMAD2 have been associated with complex congenital heart disease and vascular aneurysms. Although no literature has directly documented an association between these two gene variants and cDAPVF, their coexistence in this patient provides important genetic insights for investigating the etiology of this rare disease. We speculate that these two genes may exert synergistic or independent pathogenic effects on the cardiovascular system during embryonic development, collectively contributing to the formation of this extremely rare systemic arteriovenous fistula. This finding opens novel avenues for future basic research—specifically, the clarification of the mechanisms by which KCNT1 and SMAD2 contribute to the development of complex congenital vascular malformations—thereby deepening our understanding of the pathophysiology of cDAPVF.

Conclusions

This case report highlights the core value of TTE combined with HFUS in diagnosing complex congenital vascular malformations, using a rare case of cDAPVF as an example. TTE serves as an effective screening tool for the early detection of indirect signs, while HFUS—with its superior resolution—allows for the noninvasive visualization of anatomical structures and hemodynamic features of deep thoracic/abdominal fistulas, facilitating accurate localization and early diagnosis. This radiation-free strategy offers distinct clinical advantages, particularly for pediatric patients. Additionally, we found that concurrent KCNT1 and SMAD2 gene mutations were associated with cDAPVF, providing novel insights for pathophysiological research and the examination of potential genetic etiologies.

Acknowledgments

None.

Footnote

Funding: This study was supported by Natural Science Foundation in Gansu Provincial (23JRRA1383) and the Project for Cultivating Young Talents in Gansu Province (GSWSQNPY-2024-05).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1925/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 case were 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’s guardians for publication of this case description 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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