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Original Report |
1 Mallinckrodt Institute of Radiology, Washington University School of Medicine,
510 S Kingshighway Blvd., St. Louis, MO 63110.
2 Department of Pediatric Surgery, St. Louis Children's Hospital, Washington
University School of Medicine, One Children's Pl., St. Louis, MO 63110.
Received November 20, 2003;
accepted after revision January 12, 2004.
Address correspondence to M. J. Siegel
(siegelm{at}mir.wustl.edu).
Abstract
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CONCLUSION. MDCT angiography with 3D rendering shows the anomalous feeding artery and the draining veins that allow a diagnosis of pulmonary sequestration. These features may prove useful in distinguishing intra- and extralobar sequestration and in surgical planning.
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Helical CT has proven to be of considerable value in the diagnosis of arterial feeders and parenchymal changes in sequestration [8–12]. The 3D capability of MDCT is particularly valuable in depicting the relationship of the aberrant artery to adjacent structures [9]. Thus, the definite diagnosis of pulmonary sequestration has become possible with CT angiography, obviating more invasive angiography.
The treatment of choice for sequestration is surgical excision. Because the vascular communications are variable, imaging studies are integral to the evaluation of patients with sequestration. Although it has been suggested that identification of venous drainage is not of primary importance for treatment planning and that only information related to the presence and location of the aberrant artery is essential [9], in our experience, knowledge of venous drainage can be helpful in planning the surgical procedure and in communicating with the child's parents.
Helical CT usually shows the anomalous arteries associated with pulmonary sequestration. Although the use of 3D MDCT imaging to show venous drainage associated with sequestration has been described in adults [8], to our knowledge, its usefulness in defining the venous anatomy in the pediatric population has not been established. The purpose of this study was to show the ability of 3D MDCT angiography to reveal the venous and the arterial angioarchitecture of pulmonary sequestration. This information may be helpful in distinguishing intra- and extralobar sequestrations and in surgical planning.
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Four pediatric patients, who ranged in age from 6 days to 6 months, were sedated with orally administered chloral hydrate (50–100 mg per kilogram of body weight; maximum dose, 2,000 mg). One 9-year-old patient cooperated for the CT examination without sedation.
Imaging Technique
CT was performed on either a Somatom Plus-4 scanner or Sensation 16 scanner
(Siemens Medical Solutions). All patients received nonionic IV contrast
material (320 mg I/mL) at a dose of 2 mL per kilogram of body weight. Scan
initiation was 12–15 sec after the start of the IV contrast injection in
the four younger patients. An automated tracking system with a density of 100
H in the ascending aorta was used to initiate scanning in the older
patient.
On the 4-MDCT scanner, we used a collimator width of 2.5 mm and a table speed of 15–20 mm per rotation. On the 16-MDCT scanner, we used a collimator width of 1.5 mm and a table speed of 36 mm per rotation. All examinations were performed with low–radiation dose techniques. Studies were performed at 30 mAs in the four younger patients and at 50 mAs in the older patient. An 80-kV dose was used for all five patients.
Scanning extended from just below the level of the thoracic inlet to just above the level of the renal arteries. CT scans were acquired during quiet respiration in sedated patients and during a single breath-hold in the 9-year-old patient. All images were processed with standard soft-tissue settings (e.g., 400–450 H width; 40–50 H level) and lung window settings (e.g., –160 to –1,800 width; –450 to –550 H level).
Imaging Review
Three-dimensional volume-rendered and maximum-intensity-projection MR
images were obtained using a freestanding workstation. All reconstructions
were performed by a radiologist experienced in 3D postprocessing techniques,
and reconstruction time for each patient was approximately 30 min. The volumes
of interest were selected from the axial source to include the aorta and its
branches, the pulmonary arteries, the pulmonary veins, and the superior vena
cava. Images were reconstructed at a 3-mm slice thickness on the 4-MDCT
scanner and at a 2-mm slice thickness on the 16-MDCT scanner. Patient
identifying information was removed before review by two observers.
The axial images and the 3D reconstructions were reviewed by two radiologists, and the arterial supply and venous drainage to and from the sequestration were recorded. The axial images were interpreted first. The order of image review was randomized for the 3D interpretation to decrease recall of patient diagnosis. The observers reviewed the reconstructed 3D images in real time and thus could optimize depiction of the course of the vessels.
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In the one patient with extralobar sequestration, the arterial supply was from the celiac artery. Venous drainage was into a congenital cystic adenomatoid malformation in the right lower lobe. On gross examination, the sequestered lung was contained in its own pleura. On microscopy, sections from the sequestration in the left lung showed changes of mild chronic interstitial inflammation and histologic features of type II cystic adenomatoid malformation. Sections from the right lung showed a congenital cystic adenomatoid type II malformation. The microscopic findings included numerous columnar epithelial-lined cysts (< 2.0 cm). No tissue continuity was found between the left lower lobe sequestration and the right lower lobe cystic adenomatoid malformation. The one patient without surgical confirmation most likely had an extralobar sequestration because the venous drainage was into the portal vein. Arterial supply was from the thoracic aorta.
MDCT Findings
The sequestered lungs appeared as enhancing solid masses in two of the
three intralobar sequestrations and in the two extralobar sequestrations on
soft-tissue and lung window settings. In one patient with an infected
intralobar sequestration, CT showed cystic changes in the sequestration and
enhancement of surrounding lung parenchyma.
Table 1 summarizes the ability of axial and 3D MDCT images to depict the vascular anatomy of sequestration in pediatric patients. Axial images and 3D reconstructions allowed identification of the arterial supply to the lesion and its course in all patients (Figs. 1A, 1B, 1C and 2A, 2B, 2C, 2D). In one patient, the arterial supply was more obvious on 3D reconstructions (Fig. 3A, 3B, 3C, 3D). The arteries had a transverse or slightly oblique course from the aorta to the sequestration.
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The presence and course of the anomalous draining vein were identified on axial views in the patient with surgically proven extralobar sequestration (Fig. 2A, 2B, 2C, 2D). In this patient, the vein from the sequestration in the left lower hemithorax crossed the midline and drained into a congenital cystic adenomatoid malformation in the right lower lobe. In the three patients with intralobar sequestrations, the veins draining from the sequestrations could not be identified on axial images. In the neonate with suspected extralobar sequestration, the drainage into the portal vein was not recognized prospectively on axial images, but only in retrospect after review of the 3D MDCT images (Fig. 3A, 3B, 3C, 3D). In all patients, the draining veins were identified on the 3D reconstructions. With the exception of the patient in whom the vein crossed transversely from the left to right hemithorax, the course of the veins was nearly perpendicular to the imaging plane. The veins, therefore, were more difficult to identify on axial images, especially given the associated inflammatory changes.
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Other investigators have concluded that the venous drainage of pulmonary sequestration may not be clearly shown on CT [9, 11]. We believe that the CT angiography techniques that we have reported allow display of the venous anatomy. In our opinion, as well as that of others [1], knowledge of the anatomy of the venous drainage is potentially useful before surgical resection. Most intralobar sequestrations require lobectomy or at least a segmentectomy of the involved lung. In contrast, with an extralobar pulmonary sequestration in which venous drainage is often into the azygous vein, the anomaly can be removed without resection of the normal lung tissue. If it can be determined preoperatively whether a sequestration is intra- or extralobar on the basis of the venous drainage, an assessment can be made regarding the possible need for lung resection and can be conveyed to the child's parents. In four of our five patients with sequestration, CT angiograms with 3D images provided the clearest visualization of the detailed anatomy of the vein.
The draining vein of pulmonary sequestration is particularly amenable to 3D reconstruction because it is often oriented in the z-axis. Unlike the aberrant artery which usually has an axial course or minimally oblique course through the image plane to reach the sequestration, the vein courses obliquely to reach the left atrium or systemic veins such as the azygous system. The ability to rotate the 3D volume-rendered display in any orientation in real time is helpful in discerning the relationships of the pulmonary veins [13, 14].
One of the obvious disadvantages of MDCT is the radiation exposure, especially in pediatric patients. Our study has shown that a single phase contrast injection can show the location and course of both the artery and the vein. The use of a single phase of contrast material is critical to reduce radiation exposure. In addition, we used relatively low-exposure factors (30–50 mAs and 80 kV) and achieved superb diagnostic-quality images.
Although it involves exposure to ionizing radiation, CT angiography has obviated catheter angiography, which has a substantially higher radiation exposure. MRI is an attractive alternative to CT, but it requires relatively prolonged sedation times in infants and younger children. The shortened imaging time of CT compared with that of MRI decreases the duration of sedation. In addition, MRI cannot accurately evaluate lung parenchyma. Sonography is the other alternative to CT, but it requires a favorable acoustic window and its use is generally limited to evaluating the neonatal chest.
In conclusion, we believe that low-dose 3D CT angiography can provide useful information about the arterial and venous angioarchitecture in pulmonary sequestration in children. Although axial images are diagnostic for evaluation of arterial feeders, 3D images enhance the visualization of small and tortuous venous vessels and, in some cases, the arterial feeders. This information can allow more confident diagnosis and treatment.
Acknowledgments
We thank Sanjeev Bhalla for technical assistance with
Figure 3D.
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