British Journal of Radiology (2006) 79, e99-e102
© 2006 British Institute of Radiology
doi: 10.1259/bjr/45058144
3D multidetector CT angiographic evaluation of extralobar pulmonary sequestration with anomalous venous drainage into the left internal mammary vein in a paediatric patient
E Y Lee, MD, MPH
J E Dillon, MD
M J Callahan, MD
and
S D Voss, MD
Department of Radiology, Children's Hospital Boston and Harvard Medical School, 300 Longwood Ave., Boston, MA 02115, USA
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Abstract
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Pulmonary sequestration is a congenital lung malformation, defined by dysplastic and non-functioning lung tissue lacking normal tracheobronchial connections and accompanied by an anomalous systemic blood supply. Recognition of anomalous arteries and veins in pulmonary sequestration is paramount to making the correct diagnosis. In contrast to intralobar pulmonary sequestration, where anomalous venous drainage is usually into the pulmonary venous system, the pattern of anomalous venous drainage is more varied in extralobar pulmonary sequestration. To the best of our knowledge, anomalous venous drainage to the internal mammary vein in extralobar sequestrations has not been reported. We report an anomalous venous drainage into the internal mammary vein in an extralobar sequestration which was evaluated with 3D multidetector CT angiography.
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Introduction
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Pulmonary sequestration is a congenital malformation in which a focal area of dysplastic and non-functioning lung parenchyma is present without a normal connection to the tracheobronchial tree and the pulmonary arteries [1, 2]. There are two types of pulmonary sequestration, intralobar and extralobar, both of which have an anomalous arterial supply, usually from the descending aorta [1, 2]. Venous drainage, however, is different in the two types of pulmonary sequestration, making it possible to differentiate between them. In an intralobar sequestration, the anomalous venous drainage is typically via the inferior pulmonary vein. In an extralobar sequestration, however, the anomalous venous drainage is systemic, commonly via the azygous vein, although unusual drainage into the portal vein or left subclavian vein has been reported [3–5]. To our knowledge, anomalous venous drainage into the internal mammary vein in extralobar sequestrations has not been reported in paediatric patients, especially with 3D multidetector CT (MDCT) angiography.
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Case report
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A 5-week-old girl was referred to our hospital for post-natal evaluation of a left lower thoracic mass seen on a pre-natal ultrasound examination. Post-natally, the patient was asymptomatic and underwent an ultrasound examination which demonstrated an approximately 3.1 cm x 3.0 cm solid mass located in the left lower thorax, superior to the left hemidiaphgram. Careful evaluation of this mass with colour and duplex Doppler demonstrated a small artery arising from the descending aorta and coursing to the anterior aspect of the mass. Venous drainage could not be clearly identified by ultrasound examination.
Subsequently, the patient underwent MDCT angiography on 16-MDCT (Lightspeed Ultra 16; GE Healthcare, Milwaukee, WI). The patient received non-ionic intravenous contrast material (Optiray 320; Mallinckrodt, Inc., St. Louis, MO) at a dose of 2 ml per kilogram of body weight. An automated tracking system with a density of 100 HU in the descending aorta was used to initiate scanning. We used a collimator width of 1.25 mm and a table speed of 10 mm per rotation. The examination was performed at 120 mAs and 80 kV. Scanning extended from just below the level of the thoracic inlet to just above the level of the renal arteries. CT images were acquired during quiet respiration without sedation.
Axial CT images (Figure 1a
) showed an approximately 3.1 cm x 3.2 cm solid, heterogeneously enhancing mass located within the left lower thorax, above the diaphragm. A small anomalous vessel anterior to the mass and an enlarged left internal mammary vein were identified (Figure 1a). A small vessel adjacent to the descending aorta (Figure 1b) was also visualized. Evaluation of the origin as well as the entire course of these vessels was difficult with axial images alone. For further evaluation, 3D volume-rendered images were obtained using a freestanding workstation (Vitrea 2 workstation; Vital Images, Plymouth, MN) by a paediatric radiologist experienced in 3D post-processing techniques. A sagittal 3D volume-rendered image (Figure 1c) demonstrated the full course of an anomalous artery arising from the descending aorta and coursing to the left lower thoracic mass, as well as an anomalous vein arising from the mass and draining into the left internal mammary vein, most consistent with an extralobar sequestration. The right hemithorax was smaller than the left; however, there was no other abnormality.
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Figure 1. A 5-week-old female infant with left lower lobe extralobar sequestration. (a) Enhanced axial CT image demonstrates heterogeneously enhancing, solid mass located within the left lower thorax (S). Also noted is an anomalous vessel anterior to the mass (short arrows), which 3D volume-rendered images identified as an anomalous vein draining into the left internal mammary vein. Enlarged left internal mammary vein is also seen (long arrow). (b) Enhanced axial CT image shows a small vessel (long arrow) adjacent to the descending aorta (short arrow) and coursing toward left lower thoracic mass (S), most likely representing anomalous arterial vessel supplying extralobar sequestration. The entire course of the vessel could not be obtained on axial CT images alone. Again noted is anomalous draining vein (arrowhead). (c) Sagittal 3D volume-rendered image demonstrates entire course of anomalous vein (short arrows) from extralobar sequestration (S), coursing anteriorly toward the heart and draining into left internal mammary vein. Anomalous artery (long arrow) arising from descending aorta is also well visualized.
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The patient has not yet undergone surgery. She remains asymptomatic and clinically stable 10 months after the CT findings confirmed the clinical suspicion of an extralobar sequestration.
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Discussion
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Pulmonary sequestration is part of a wide spectrum of congenital lung malformations, defined by dysplastic and non-functioning lung tissue lacking normal tracheobronchial connections and accompanied by an anomalous systemic blood supply [1, 2]. Recognition of anomalous arteries and veins in pulmonary sequestration is paramount to making the correct diagnosis and preventing confusion with other benign congenital lung parenchymal lesions such as cystic adenomatoid malformations, or malignant disease processes such as neuroblastoma.
In contrast to intralobar pulmonary sequestration, where anomalous venous drainage is usually into the pulmonary venous system, the pattern of anomalous venous drainage is more varied in extralobar pulmonary sequestration. Although anomalous venous drainage to systemic veins such as the azygous, hemiazygos, or inferior vena cava occurs in most cases of extralobar pulmonary sequestration, there may rarely be a connection to the portal vein or subclavian vein [3–5]. To the best of our knowledge, anomalous venous drainage to the internal mammary vein has not been reported, and 3D MDCT angiographic findings and its usefulness have not been described.
The recognition of an anomalous venous drainage in sequestration is not only important for differentiating between intralobar and extralobar sequestrations, but has implications for pre-operative surgical evaluation as well. Pre-operative identification of anomalous venous drainage in a sequestered segment can prevent massive intraoperative haemorrhage due to the accidental trans-section of an unanticipated vessel [6]. Defining anomalous patterns of venous drainage also facilitates surgical planning, since most intralobar sequestrations require lobectomy or segmentectomy of the involved lung, while the sequestered segment can be removed without resection of normal lung tissue in an extralobar sequestration. Furthermore, optimally defining an infradiaphragmatic anomalous vessel is important because it necessitates transabdominal surgery rather than transthoracic intervention.
In the past, imaging modalities such as ultrasound, CT, MRI, and conventional angiography, all of which can demonstrate anomalous vessels in patients with pulmonary sequestration, have been used to make this diagnosis. The CT evaluation of pulmonary sequestration has evolved, however, with the recent advent of MDCT and its associated 3D imaging capabilities. Although 3D MDCT angiography examination exposes paediatric patients to low doses of ionizing radiation, it avoids many of the limitations encountered with alternative imaging modalities. For example, ultrasound requires a favourable acoustic window and often fails to visualize the small anomalous arterial and venous structures inherent to pulmonary sequestrations identified in infants. MRI, which is frequently used for the evaluation of pulmonary sequestration, usually requires the sedation of paediatric patients and the lung parenchyma cannot be completely evaluated. The need for sedation is reduced in MDCT, or even eliminated, due to decreased imaging time [8]. In our case, the 16-MDCT angiographic examination was successfully completed in less than 4 s and without sedation. Conventional catheter-based angiography has been considered the gold standard. However, it is invasive, has a substantially higher radiation exposure, and is associated with post-catheterization complications, including bleeding, vascular injury and pseudoaneurysm formation. Furthermore, cross-sectional imaging capabilities of MDCT, in contrast to angiography, allow simultaneous evaluation of the congenital anomalies frequently associated with pulmonary sequestration, including diaphragmatic hernia and congenital heart defects.
In the past, axial CT images obtained from conventional single detector CT have been of limited value in demonstrating both the arterial supply and especially the venous drainage of sequestration [9]. Ikezoe et al reported that conventional axial CT images demonstrated an anomalous arterial supply in 16 of 24 sequestrations and failed to show the venous drainage in all cases [9]. In our case, the recognition of an anomalous arterial supply and an anomalous venous drainage was difficult with axial CT images alone, but could be readily accomplished with 3D MDCT angiography. These findings are in agreement with the published reports of Lee et al, in which 3D MDCT angiography was found to be useful in the evaluation of paediatric patients with small and tortuous congenital vascular anomalies [7] and anomalous venous drainage in pulmonary sequestration [4]. The anomalous vein in our case was oriented in the z-axis, anteriorly toward the heart and draining into the left internal mammary vein. This orientation was amenable to 3D reconstruction, and the ability to rotate 3D images in any direction in real-time was helpful for purposes of following the entire course of the anomalous vein.
In summary, the diagnosis of extralobar sequestration with unusual venous drainage can be challenging in paediatric patients, especially when there is a small, tortuous vessel with an unusual course. In the present case, 3D MDCT angiography was useful in making the correct diagnosis of extralobar sequestration by visualizing the full course of the unusual anomalous venous drainage into the internal mammary vein, a finding which can be missed on axial images alone.
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Addendum
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While this manuscript was under review, the patient underwent surgical resection of the left lung mass, 13 months after the original diagnosis. Final pathological diagnosis confirmed extralobar pulmonary sequestration. In addition, CCAM-like histological changes were described within the lesion, emphasising the complex nature of these lesions, and the likelihood of overlap between congenital cystic malformations of the lung and the spectrum of bronchopulmonary foregut malformations.
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Acknowledgments
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This work was supported in part by NIH grant 5K08CA093554-04 (SDV).
Received for publication November 1, 2004.
Revision received June 13, 2005.
Accepted for publication October 26, 2005.
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References
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Abstract
Introduction
