Paediatric multidetector CT angiography: spectrum ... - BIR Publications

The British Journal of Radiology, 80 (2007), 376–383

PICTORIAL REVIEW

Paediatric multidetector CT angiography: spectrum of congenital thoracic vascular anomalies B OGUZ,

MD,

M HALILOGLU,

MD

and M KARCAALTINCABA,

MD

Department of Radiology, Hacettepe University School of Medicine, Sihhiye, Ankara 06100, Turkey

ABSTRACT. Multidetector row CT (MDCT) is a non-invasive and rapid technique used for the evaluation of paediatric vascular diseases as an alternative to conventional angiography. Three-dimensional (3D) images allow excellent display of vascular anomalies that can be used as a vascular road map by surgeons. The aim of this pictorial review is to demonstrate diagnostic MDCT angiographic findings of various congenital thoracic vascular anomalies in paediatric patients. It is important to recognize these anomalies early for proper treatment and follow-up, and also to prevent morbidities and mortalities.

Congenital anomalies of the thoracic vascular system are an important cause of morbidity and mortality in infants and children. Multiple imaging modalities, such as chest radiography, barium oesophagography, echocardiography, CT, MRI and conventional angiography, are used to diagnose the anomalies and plan possible treatment. Conventional radiology detects the presence of anomalous compressions of the trachea and oesophagus. However, in most cases, it is not sufficient alone to accurately diagnose the vascular abnormalities. Although echocardiography is a useful and safe technique for the diagnosis of thoracic vascular anomalies, angiography is usually necessary for definitive anatomical evaluation, especially before surgery. Conventional angiography is an invasive technique that has several disadvantages including long procedure time, need for sedation, arterial puncture and rare potential complications such as dissection and occlusion [1]. With advances in imaging technology, the introduction of multidetector row CT (MDCT) has dramatically expanded the applications of CT in the evaluation of vascular and airway diseases [1–7]. The advantages of MDCT, compared with single detector row CT, include improved temporal and spatial resolution, greater anatomic coverage, more consistent contrast material enhancement, faster scan speed and higher quality three-dimensional (3D) reconstructions [1–7]. Three-dimensional images allow excellent display of vascular anomalies that can be used as a vascular road map by surgeons. CT angiography is a preferable modality of diagnosis for arterial disease as an alternative to conventional angiography, because it is safer, less time consuming and also more cost-effective. In addition to displaying vascular anatomy, thoracic CT angiograms provide information about both airway and Address correspondence to: Berna Oguz, Elvankent Emlak Bankasi Bloklari A 13/25, 06930 Ankara, Turkey. E-mail: oguzberna@ yahoo.com

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Received 1 August 2005 Revised 13 September 2005 Accepted 11 November 2005 DOI: 10.1259/bjr/47124005 ’ 2007 The British Institute of Radiology

lung parenchyma, which is important in patients who have thoracic vascular anomalies [2, 3, 5]. MDCT has also gained increasing acceptance as an alternative to MRI in the screening of vascular abnormalities [2–9]. Compared with MR angiography, CT angiography has the advantage of the ability to acquire high spatial resolution in a shorter acquisition time that means a reduced need for sedation and less intensive anaesthetic management [5–9]. During sedation or general anaesthesia in critically ill patients, the open and non-magnetic environment around a CT scanner facilitates monitoring and resuscitation if necessary [6]. The speed of CT examinations makes the maintenance of thermal stability, which is critical in the care of neonates, more feasible than with MR examinations [5]. The short examination time also reduces motion artefact. In addition, CT provides information about both the lung parenchyma and bony structures that are not evaluated accurately by MRI. CT examinations can be performed immediately post-operatively without risk in patients with any type or location of metallic fragments such as stents or surgical clips and there is no contraindication for patients with pacing systems [5–7]. Because children are more sensitive to the effects of radiation than adults, the issue of radiation exposure is extremely important. Although radiation exposure and administration of iodinated contrast material may be considered as disadvantages of CT angiography, it must be considered that, in critically ill children, the risks of prolonged anaesthesia may be greater than that of radiation and iodinated contrast material [2, 3, 5, 6, 8]. Allergic reaction to iodinated contrast material and renal failure are contraindications for CT angiography. Contrast doses required for CT angiography studies decreases with multidetector CT [5, 6, 9]. Nowadays, these considerations make MDCT angiography the preferred imaging modality for the detection of vascular anomalies in infants and young children [2, 3, 5, 6, 8, 9]. The British Journal of Radiology, May 2007

Pictorial review: Paediatric multidetector CT angiography

The decision to perform CT or MR angiography for the diagnosis of vascular anomalies in paediatric patients must be based on a reasonable risk–benefit analysis that depends on the individual situation of every patient. This pictorial review demonstrates diagnostic MDCT angiographic findings of various congenital thoracic vascular anomalies in paediatric patients.

Imaging technique Thoracic MDCT angiography studies were performed using a four-channel multidetector scanner (VolumeZoom; Siemens Medical Systems, Erlangen, Germany) in infants and children with suspected thoracic vascular anomalies. Very brief sedation was used for children younger than 5 years old. The remaining patients cooperated without sedation. Nonionic iodinated contrast material (300 mg ml21) was injected by a power injector at a rate varying from 0.8 ml s21 to 2 ml s21, not to exceed 2 ml kg21 of body weight, via an angiocath placed in the right antecubital vein. Using a modified bolus tracking method, when the contrast material arrived in the right ventricle (determined visually by the on-site radiologist), acquisition was initiated manually by the technician. Scans extended from just above the level of the thoracic inlet, so that proximal aspects of the common carotid and subclavian arteries were included, to the level of the diaphragm. Technical parameters used for CT examinations were as follows: detector collimation, 461 mm; pitch, 1.75; slice thickness, 1.25 mm; reconstruction interval, 1 mm; table speed, 14 mm s21; gantry rotation time, 0.5 s;

(a)

80–120 kVp and 60–100 mAs (according to the age and weight of the child).

Image processing All image sets were evaluated for vascular and airway anomalies, using multiplanar reformations and 3D volume-rendered images to highlight the vascular and airway anatomy. Three-dimensional images were formed at a Leonardo 3D post-processing workstation with Syngo software (Siemens Medical Systems). Diagnostic images were obtained in all patients and the spectrum of congenital anomalies detected by MDCT angiography included vascular ring anomalies, interrupted aortic arch, aortic coarctation and pulmonary atresia with ventricular septal defect (VSD).

Spectrum of congenital anomalies Vascular rings Vascular rings are a group of congenital anomalies of the aortic arch caused by errors in the development of the embryonic aortic arches. These abnormal vascular structures completely or incompletely encircle the trachea, oesophagus or both, which can cause respiratory or feeding problems in infants and children [10, 11]. Double aortic arch is the most common type of symptomatic vascular ring (Figure 1). It is characterized by two aortic arches originating from the ascending aorta. Usually, a right arch is larger and higher than the

(b)

Figure 1. A 3-month-old boy with double aortic arch. (a) Sagittal oblique and (b) cranial view volume-rendered threedimensional images show double aortic arch surrounding the trachea (t). Right arch (R) is wider than the left arch (L). DA, descending aorta.

The British Journal of Radiology, May 2007

377

B Oguz, M Haliloglu and M Karcaaltincaba

(a)

(b)

Figure 2. A 6-year-old boy with a right-sided aortic arch and aberrant left subclavian artery. Volume-rendered threedimensional images in (a) anterior and (b) posterior projection show right-sided elongated aortic arch (A) with ipsilateral descending aorta (DA) and aberrant left subclavian artery originating from the right-sided aortic arch being the last branch which passes to the left (arrow). ALSA, aberrant left subclavian artery; RSA, right subclavian artery; LVA, left vertebral artery; RVA, right vertebral artery; LCCA, left common carotid artery; RCCA, right common carotid artery.

left arch and the descending aorta is on the left side (Figure 1). Right-sided aortic arch results from involution of the left aortic arch. There are two main types: right aortic arch with mirror image branching and right aortic arch with aberrant left subclavian artery (ALSA) (Figure 2). ALSA arises from the aortic diverticulum originating from the posterior right aortic arch. Aberrant right subclavian artery (ARSA) is the most common congenital anomaly of the aortic arch originating as the last vessel of the aortic arch, from the junction of the aortic arch with the descending aorta [10, 11] (Figure 3). Patients with this anomaly are usually asymptomatic. It is 378

often an incidental finding on imaging studies. Aneurysm of this vessel is extremely rare and may present with symptoms due to compression of the adjacent structures (Figure 3). In Figure 3 we present a case of type I truncus arteriosus with aneurysm of the aberrant right subclavian artery. Truncus arteriosus is an anomaly characterized by a single vessel arising from the ventricles, overriding a VSD, and supplying the systemic, pulmonary and coronary circulations [10]. Anomalous left pulmonary artery (pulmonary sling) is a rare abnormality that occurs due to involution of the proximal left sixth arch. The blood to the left lung comes from an aberrant left pulmonary artery which arises The British Journal of Radiology, May 2007


(a)

(b)

(c) Figure 3. Aneurysm of aberrant right subclavian artery (AARSA) in a 23-month-old boy with truncus arteriosus. Volumerendered three-dimensional images in (a) posterior and (b) anteriocranial projection show aneurysmatic aberrant right subclavian artery (arrow) arising from the left-sided arch (A) and passing from the left to the right. (c) Multiplanar coronal reformation demonstrate narrowing of the pulmonary artery (arrow) between the aberrant right subclavian artery (*) and the aorta (A) and moderate cardiomegaly. R, right side; L, left side.

from the right pulmonary artery and courses to the left, passing between the oesophagus and trachea [10, 11]. We detected an anomalous left pulmonary artery using CT angiography in a 13-month-old boy who also The British Journal of Radiology, May 2007

had right tracheal bronchus anomaly (pig bronchus) (Figure 4). In the diagnosis of vascular rings it is important to detect the presence of airway or oesophageal compression. CT 379


(a)

(b)

(c)

(d)

Figure 4. A 13-month-old boy with pulmonary sling anomaly and tracheal bronchus (pig bronchus). (a–c) Axial consecutive CT images show the anomalous left pulmonary artery (arrow) which arises from the right pulmonary artery and passes to the left behind the trachea (t). In the same patient, (d) coronal multiplanar and (e) three-dimensional volume-rendered reformations show the tracheal bronchus (arrow) arising from the right lateral wall of the trachea just above the carina and directed toward the right upper lobe. Note that all images show narrowing of the trachea (t) at the level of the anomalous left pulmonary artery coursing to the left.

(e)

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(a)

(b)

Figure 5. New diagnosis of type A interrupted aortic arch with large systemic collaterals in a 4-month-old girl. (a) Sagittal multiplanar reformation and (b) volume-rendered three-dimensional images show aortic interruption (arrow) just beyond the left subclavian artery (S) with dilated posterior collateral intercostal arteries (arrowheads). A, aortic arch; DA, descending aorta.

(a)

(b)

Figure 6. A 12-month-old girl with short-segment aortic coarctation. (a) Sagittal and (b) coronal multiplanar reformations clearly demonstrate the location and extent of the narrowing (arrow) just beyond the left subclavian artery (S), which is mildly dilated. Posterior collateral intercostal arteries (arrowheads) arising distal to the coarctation and post-stenotic dilatation of the proximal descending aorta are also seen. A, aortic arch; DA, descending aorta.


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(a)

(b)

(c)

(d)

Figure 7. Pulmonary atresia and ventricular septal defect in an 8-year-old girl with tetralogy of Fallot anomaly. (a) Axial CT image, (b) axial and (c) sagittal volume-rendered 3D reformations show aplasia of the main pulmonary artery (*). Non-confluent right (RPA) and left (LPA) pulmonary arteries filling by collateral arteries are seen. Ascending aorta (AA) is dilated. (d) Axial volume-rendered 3D reformation at the level of the ventricular system also shows ventricular septal defect (arrow). DA, descending aorta.

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angiography with 3D reconstructions does provide more definitive pre-operative information concerning vascular anatomy and the relationship between the oesophagus and the tracheal lumen (Figure 1–4).

Interrupted aortic arch Interrupted aortic arch (IAA) is an extreme form of aortic coarctation and is characterized by discontinuity of the aortic arch between the ascending and descending aorta. IAA is classified according to the site of the interruption [10]. Approximately 42% of the infants with interrupted aortic arch have the type A interruption, which means that the interruption occurs just beyond the left subclavian artery (Figure 5). In type B, the most common form (53%), the interruption occurs between the left common carotid artery and the left subclavian artery. In type C, the least common form (5%), the interruption occurs between the innominate artery and the left common carotid artery [10]. MDCT angiography can be used safely for the diagnosis of aortic interruption [2, 5, 8]. 3D reformations show the origin of the great arteries and collateral vessels. CT angiography may also serve as a follow up investigation after intervention or surgical treatment.

Aortic coarctation This anomaly occurs when there is partial involution of the left dorsal aortic arch. Collateral blood flow via intercostal arteries may result in notching of the inferior aspect of the ribs [10, 11]. Coarctation can be demonstrated accurately with MDCT angiography (Figure 6). In the setting of coarctation, the location, relative size and extent of the stenosis, the relationship of the coarctation to the great vessels and the extent of collateral vessel formation become better defined with imaging planes customized to the course of the aorta [2, 3, 5]. Multiplanar and 3D volume-rendered images have more average accuracies and sensitivities than axial images for the detection of aortic coarctation (Figure 6) [2, 3, 5]. On the axial imaging, especially short segment coarctations can be missed [3]. MDCT angiography may also provide valuable information in post-operative evaluation of the aorta, because the positions and patency of endovascular stents and their relationships to the origin of the great vessels can be clearly demonstrated [2].

Pulmonary atresia with ventricular septal defect Pulmonary atresia with VSD is considered the extreme end of the anatomic spectrum of tetralogy of Fallot. There is no main pulmonary artery arising from the right


ventricle. It may also be named as pseudotruncus (type IV truncus arteriosus) where no pulmonary arteries originate from the ascending trunk [10]. In this anomaly, the lungs are supplied by extracardiac sources such as patent ductus arteriosus and major aortopulmonary collateral arteries. Most frequently, the right and left pulmonary arteries are patent. However, they may also be hypoplastic. To diagnose this uncommon anomaly, the complex curving anatomy of the pulmonary artery is well demonstrated by MDCT angiography using multiplanar and 3D volume-rendered images (Figure 7).

Conclusion MDCT angiography with higher quality multiplanar and 3D imaging is a rapid and non-invasive technique that is an alternative to conventional angiography for the evaluation of thoracic vasculature in infants and children with suspected congenital vascular anomalies.

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