Systemic arteriopulmonary venous fistula (APVF): case presentation of an asymptomatic individual and a review of the literature

Abstract

Abnormal communications between the systemic and pulmonary venous systems are rare but can present as a opacity on chest radiograph. A solitary vessel communicating as a fistula directly between the systemic arterial circulation and the pulmonary venous system is not widely described. These may have significant implications in the long-term cardiovascular health of an individual acting as a left to right shunt. There is no clear consensus as to the management, but surgical management and endovascular embolisation have been successfully used. We present a case where a systemic arteriaopulmonary fistula originating from the abdominal aorta and connecting to the right inferior pulmonary vein manifested as an incidental finding on a chest radiograph and was further evaluated on cross-sectional imaging in a young patient. Chest radiographs are non-specific and it is important to be aware of the less frequent but important pathologies that can be picked up on plain chest radiographs, which inturn should warrant further investigation. This is presented in conjunction with a review of the available literature along with a discussion regarding the differential diagnosis and management applicable to the general clinician.

Background

Abnormal vascular communications as an unusual but potential diagnosis of a chest X-ray opacity is often not considered. An angiographic phase contrast-enhanced chest CT provides clarity regarding abnormal vascular connections. The associations and treatment of a variety of chest vessel malformations depend on the exact location and connections as well as an assessment of physiological impact. An arterial pulmonary fistula is a rare anomaly, which has limited literature base and no management consensus. It is important to recognise as it can develop elevated right heart pressures with associated sequalae. Due to concerns about right-sided cardiac failure embolisation, surgery or conservative management have been considered as a treatment option.^1–4

The fundamental issue with pulmonary and systematic vascular communications is a physiological shunting of blood either from the right-sided circulation to the left, thereby bypassing the lungs or from the left back to the right without passing through the peripheral circulation. Symptoms of shunts are well established and primarily related to the specific type of shunting, whether left to right or right to left.⁵

Right to left shunts can include dyspnoea, haemoptysis, chest pain, cough and paradoxical embolism (thrombotic and infective), whereas left to right shunts can lead to right-sided heart failure and pulmonary hypertension. Due to increased pressures, ‘Eisenmenger’ phenomena whereby the right-sided pressure exceeds the left-sided pressures, resulting in flow reversal and decompensation.⁶

Case presentation

A 40-year-old woman with no significant previous medical history or radiological imaging received an emergency chest X-ray due to concerns regarding aspiration after excessive alcohol intake. An ill-defined density was noted within the right lower zone on an AP radiograph, and interval Posterior-Anterior (PA) chest radiograph was advised. The subsequent film demonstrated a well-defined opacity with tubular conformation in the right lower zone, mid clavicular line (figure 1). A contrast-enhanced CT study of the thorax was arranged (figure 2A–E). This demonstrated a right-sided systemic arterial to pulmonary venous communication between the subdiaphragmatic aorta and the right inferior pulmonary vein, which passed through the right lower lobe. Use of reconstruction (figure 3) and maximal intensity projection (MIP) significantly aided the determination of the vascular connections. These were also appreciable on coronal and axial MIP (figure 4). This vessel measured maximally 15 mm in diameter and enhanced during the systemic arterial phase imaging that was acquired. The right lower lobe pulmonary veins and some upper lobe pulmonary veins drain into this dilated structure, which returned blood to the left atrium. Discussion with the interventional radiology team and cardiothoracic team regarding management was undertaken with a decision to monitor the patient for any developing of right-sided heart failure.

Figure 1.

PA chest radiograph demonstrating the right mid zone opacity.

Figure 2.

Axial image reconstruction on lung windows with maximal intensity projection demonstrating abnormal right-sided vessel connecting to the left inferior pulmonary vein.

Figure 3.

Reconstruction of right lower lobe vessel communicating with the right inferior pulmonary vein and aorta.

Figure 4.

Diagram from Shovlin⁶ indicating the major functions of the pulmonary capillary bed that are bypassed in the setting of pulmonary arteriovenous malformations (red arrow).

Investigations

Chest radiographs and chest CT are standard studies used in daily practice by a large number of clinicians. Unexpected findings such as soft tissue densities with tubular conformations are unusual, but an awareness of a wide differential and possibilities is essential to ensure appropriate management. In our individual, plain film findings were significantly abnormal and differential diagnosis of a bronchocoele, arterio venous malformation (AVM), pulmonary sequestration, rounded pneumonia, focal consolidation and nodular lesion were considered.

There were no previous films to assess growth or longevity and further imaging was appropriately sought. Subsequent evaluation with a chest CT demonstrated a large intrapulmonary vessel (figure 2). MIP reconstruction demonstrated the vessel anatomy (figure 3) with its originating and destination connections appreciated. Further assessment of the physiological impact of the abnormal vasculature was performed by echocardiogram, which demonstrated no significant evidence of right ventricular hypertrophy or strain.

Differential diagnosis

While unusual, an accurate diagnosis may be achieved through understanding of an appropriate differential and recognition of the origin and insertion of the abnormal vasculature. The prime differentials of abnormal cardiopulmonary vasculature would include pulmonary AVM (PAVM), pulmonary sequestration, Scimitar syndrome, partial anomalous venous return or pulmonary vein varix.

Pulmonary arteriovenous malformations are a capillary-based lesion with abnormal connection between the pulmonary artery and pulmonary vein considered to result from a defect in the terminal capillary loops, causing dilation and formation of thin-walled vascular sacs. They are usually congenital and comprise of a feeding vessel or vessels and an efferent venule. Multiple PAVMs are commonly associated with hereditary haemorrhagic telangiectasia.^{7 8} While physiologically acting as a low pressure shunt, PAVMs (figure 4) are distinct from systemic arterial to pulmonary venous fistulae (APVF) as the latter do not involve the capillary bed and are connected to the systemic arterial system.

Other differentials of abnormal pulmonary vasculature include pulmonary sequestration, which may appear similar on the chest radiograph, although it would demonstrate a segmental of lung tissue without connection to the bronchial tree on CT supplied by the systemic arterial circulation. Further differentials included scimitar syndrome, a specific type of partial anomalous pulmonary venous return (PAPVR) characterised by a hypoplastic lung drained by an anomalous vein into the systemic circulation, so-called after its characteristic radiographic appearances of a ‘Turkish sword’ like opacity. This similarly leads to a right to left shunt with associated complications and is almost exclusively right sided and is related to a hypoplastic lung that was absent in this case. Similar scimitar syndrome drains the pulmonary veins into the systemic venous system rather than a connection between the systemic arterial system and pulmonary veins in this patient.

PAPVR is a range of rare congenital cardiovascular condition in which some of the pulmonary veins draining oxygenated blood back from the lungs, drain into the systemic circulation rather than in the left atrium. This can cause a left to right shunt with associated sequalae. This is distinct from a systemic APVF, whereby the abnormal connection is between the systemic circulation and a pulmonary vein feeding back towards the left atrium, not connected to lung parenchyma. Pulmonary vein varix, a localised aneurysmal dilation of a pulmonary vein, is a further differential that should be considered with regards to the finding of a dilated tubular pulmonary structure. This would be distinct from a fistula by its normal communication between the lung parenchyma and the left atrium.

Treatment

Due to the scarcity of the literature, there is little consensus as to the management of APVFs. Conservative management may be appropriate in vessels of small calibre where volume of blood shunted is unlikely to have a lasting impact on right atrial pressures. Similarly, depending on the presentation, comorbidities and life expectancy of the individual at presentation, many communications are unlikely to have a long-term health consequences and overtreatment is a real possibility. MR angiography may be used to demonstrate the flow gradient to guide appropriately timed intervention.⁹ Although cases have been surgical resected and embolised under ⁷Interventional Radiology within the literature,^1–4 this patient was managed conservatively. A case by case management plan tailored to the individual patient requirements based on their risk profile and multi disciplianary team discussion is mandatory as these are complex lesions.

Outcome and follow-up

The patient was seen in clinic and following discussion, a plan was adopted to keep this finding under surveillance with follow-up imaging with a rapid access pathway put in place—as the patient is relatively young and the proposed treatment options have significant risks and complications. The patient has had serial echocardiograms, which showed normal right and left heart pressures with no significant evidence of volume overload to indicate a significant extra cardiac shunt. The patient was alive and well at 2 years follow-up.

DISCUSSION

Although rare, the differential of an aberrant intrapulmonary vessel is considerable and diligent tracing of the vessel origin and insertion is essential. The use of multiplanar reformats and MIP techniques can be useful in determining the connections. Although digital subtraction angiography is considered the gold standard of angiographic imaging⁹ contrast-enhanced CT should suffice.

A congenital fistula between the infradiaphragmatic aorta and the right inferior pulmonary vein returning to the left atrium is rarely described within the literature, with only one other case presenting as a fistula between the abdominal aorta and the right inferior pulmonary vein.¹ Two further cases presented as a fistula between the descending thoracic aorta and the right (one inferior and one superior) pulmonary veins^{2 3} and four cases presenting as fistulas between the descending thoracic aorta and the left inferior pulmonary vein.^{4 10 11} All the cases were adults except one neonate² and were alive at the publication of the reports.

Learning points.

• Abnormal communications between the systemic arterial circulation and the pulmonary venous system are rare, with a limited literature base relating to systemic arterial to pulmonary venous fistula.

• CT scans with the use of multiplanar reconstructions and maximum intensity projection is essential to accurately identify the vascular origin and connections.

• Left to right shunts can have long-term health effects and consideration to treatment, in particular embolisation, should be considered.

Ethics statements

Patient consent for publication

Obtained.