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Imaging findings in an infant with congenital pulmonary venolobar syndrome (scimitar syndrome)
T Westgarth-Taylor, MB ChB, FC Rad Diag (SA)
Department of Radiology, Groote Schuur Hospital, Cape Town
T Kilborn, MB ChB, FRCR
Department of Radiology, Red Cross War Memorial Children’s Hospital, Cape Town
Corresponding author: T Westgarth-Taylor (twestgarthtaylor@gmail.com)
Abstract
Congenital
venolobar syndrome (CVLS) is a rare complex malformation that includes
hypoplasia of the lung, partial anomalous pulmonary venous drainage
and, in a quarter of patients, associated cardiac anomalies. We present
the chest radiograph and multidetector CT findings in a case of
congenital venolobar syndrome in an infant, and describe the history of
the condition.
Introduction
Congenital venolobar syndrome (CVLS) is a unique
and rare form of lobar hypoplasia associated with other anomalies of
the pulmonary vessels.1 The reported incidence is 0.4 - 0.7% of all congenital lung anomalies.3
The syndrome’s variable components include: lung hypoplasia
(right more commonly affected than left), partial anomalous pulmonary
venous drainage (to right atrium, coronary sinus, inferior vena cava
(IVC), or hepatic circulation), absent or small pulmonary artery,
systemic arterial supply to the lung, cardiac anomalies (atrial septal
defect (ASD), ventricular septal defect (VSD), patent ductus arteriosus
(PDA), tetralogy of Fallot, coarctation, hypoplastic left heart or
endocardial cushion defects), diaphragmatic hernia, and anomalies of
the bony thorax or thoracic soft tissues.2
,
4
Embryologically ,it is thought to represent a primary developmental
anomaly of the right lung with secondary anomalous venous drainage.4
George Cooper and Raoul Chassinat are credited with
the earliest description of the anomaly in the medical literature. In
1836, they individually described single cases of a rare congenital
malformation that included venous drainage from the lung beneath the
diaphragm.5
,
6 The first authors to use the term ‘scimitar’ were Halasz et al. in 1956.7
They referred to a vertical curvilinear vein resembling a scimitar,
draining all or a portion of the right lung to the right atrium or more
commonly to the IVC.
The first detailed radiographic description
of the ‘scimitar sign’ (the presence of a scimitar vein on
a chest radiograph) was by Dotter et al. in 1949; they were also the first to use angiography and cardiac catheterisation to document the anomaly.8 The term ‘scimitar syndrome’ first appears in the 1960 article by Neill et al.,
referring to the combination of anomalous venous drainage of all or
most of the right lung to the right atrium or IVC together with
hypoplasia of the right lung and associated with systemic arterial
collaterals.9
The name of the syndrome has subsequently been refined, and the
preferred term ‘congenital pulmonary venolobar syndrome’
was coined by Dr Ben Felson in 2003.3
The clinical presentation of CVLS is variable.
Patients may be completely asymptomatic or symptomatic early in life;
it depends on the associated cardiac abnormalities and degree of
shunting.3
,
4 Surgery is considered in patients who are symptomatic, and requires detailed and accurate preoperative imaging.
Case report
Our patient presented at 7 weeks of age with a
2-day history of cough and fever, and was initially diagnosed with
right-sided pneumonia. At the time of presentation, a murmur was
documented.
Chest radiography showed volume loss of the right
lung with mediastinal shift to the right and opacification of the right
hemithorax. The right lung was therefore difficult to assess and the
heart size could not be accurately measured. The left lung showed air
trapping and pulmonary plethora (Fig. 1).
In view of the clinical and radiographic findings,
an echocardiogram was performed which revealed multiple cardiac
anomalies including a large ASD, small VSD, and dilated right atrium,
ventricle and main pulmonary artery. The right and left pulmonary
arteries were not well defined. This explained some of the clinical
findings; however, the volume loss of the right lung remained a
concern, and a chest CT was performed to further define the anatomy.
The chest CT was done in the arterial phase and
showed a hypoplastic right upper lobe bronchus and consequently also a
hypoplastic right lung – this explained the mediastinal shift to
the right (Fig. 2). The right pulmonary artery was small, with normal
main and left pulmonary arteries (Fig. 3). Assessment of the venous
drainage revealed an anomalous right pulmonary vein entering the IVC at
the junction with the right atrium – a so-called ‘scimitar
vein’ (Fig. 4). The left pulmonary veins showed normal drainage
into the left atrium.
The heart was enlarged and the pulmonary
vasculature prominent, in keeping with the echo findings of a left to
right shunt (ASD and VSD). The study also documented coarctation of the
aorta at the level of a PDA, neither of which had been shown on
echocardiography (Fig. 5).
Discussion
Congenital venolobar syndrome refers to a
wide spectrum of pulmonary developmental anomalies, which may occur
singly or in combination.3
Our case highlights the main components of
CVLS i.e. hypoplastic right lung with a small right pulmonary artery
and anomalous pulmonary venous drainage of the right lung. In 25% of
cases there is an associated cardiac abnormality, most commonly septal
defects, as in our case.3
,
4
Coarctation of the aorta is associated with CVLS, but is uncommon and
the actual incidence unknown. Our patient did not exhibit co-existent
diaphragmatic or soft-tissue abnormalities.
The present case also demonstrates the diagnostic
difficulties that may be encountered with CVLS. It is a rare disorder,
not often diagnosed at initial presentation. Mediastinal shift and
dextroposition of the heart on plain film are indicators of pulmonary
hypoplasia, which warrants further investigation. This is particularly
important if there is a co-existing cardiac anomaly or a suspicion of
the scimitar sign on the radiograph. In these patients, the venous
drainage and arterial supply of the lung need to be defined in order to
direct management.4
Echocardiography is the initial additional imaging
method used in suspected cardiac anomalies. However, in the case of
infants, small or absent pulmonary arteries and anomalous venous
drainage can be very difficult to define.10
Angiography has traditionally been used as an adjunct to
echocardiography in the investigation of suspected pulmonary arterial
and venous anomalies but is time-consuming, invasive, uses radiation,
requires general anaesthetic and can have complications related to
arterial access.
More recently, MDCT has been shown to be useful in
accurately identifying both the pulmonary arteries and anomalous
pulmonary venous return in CVLS.4
,
10
,
11
As well as the source images, 3D reconstructed images are particularly
helpful in depicting the entire course of the anomalous scimitar vein
and its point of drainage as well as any systemic arterial supply to
the lung.4 MDCT also
eloquently defines the tracheo-bronchial tree and associated lung
abnormalities, as well as the cardiac and other non-vascular anomalies.1
,
4
,
10
MDCT has the advantages of not requiring an anaesthetic or arterial
access and is a fast, non-invasive investigation that has assumed a
pivotal role in evaluating patients with congenital lung anomalies. The
radiation dose delivered at MDCT should be modified by using dose
reduction techniques and paediatric protocols.
Magnetic resonance angiography using
contrast-enhanced 3D MRI has also been shown to have a good correlation
with surgical findings and does not share the radiation burden of CT
and angiography.12 However, it does require expertise that is not readily available at most institutions – ours included.
CVLS in isolation is compatible with life; symptoms
in these patients are usually due to the associated cardiac
abnormalities, and the severity thereof determines prognosis.5
,
6
When patients are symptomatic, surgical correction of the cardiac
abnormality along with scimitar vein ligation or embolisation may be
considered. Our patient underwent aortic coarctation, and ASD and VSD
repair at age 14 weeks. At follow-up echocardiogram at age 7 months,
the coarctation had recurred and required balloon dilation. No other
complications were present.
Conclusion
In patients with mediastinal shift on chest
radiograph due to suspected lung hypoplasia, MDCT is a non-invasive and
appropriate investigation aiding in the diagnosis of congenital
pulmonary venolobar syndrome and possible associated cardiac defects.
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Fig. 1. Frontal chest radiograph showing opacified
right hemithorax with mediastinal shift to the right and small right
lung when compared with the left. The left lung is hyperinflated and
plethoric.
Fig. 2. Coronal minimum intensity projection (MINIP) showing the hypoplastic right upper lobe bronchus and right lung.
Fig. 3. Axial maximum intensity projection (MIP) showing the small right pulmonary artery (arrow).
Fig. 4. Coronal MIP showing the scimitar vein (arrow) and its point of insertion into the IVC. Note the plethoric left lung.
Fig. 5. Oblique sagittal MIP image showing the aortic coarctation (arrow).