congenital thoracic vascular anomalies

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  • Congenital ThoracicVascular AnomaliesJose A. Maldonado, MDa, Travis Henry, MDb,Fernando R. Gutierrez, MDc,*

    TECHNIQUE

    Although infants and children are the mostfrequently affected by congenital vascular

    conscious sedation with chloral hydrate (50100mg per kilogram body weight, maximum dose of2000 mg) in patients younger than 18 months andwith intravenous pentobarbital sodium (up to 6 mgper kilogram body weight, maximum dose of

    , University of Puerto Rico School of

    Medicine, 660 South Euclid Avenue,Campus Box 8131, St Louis, MO 63110, USA

    ersity, St Louis, MO, USA

    ital

    iologic.thec

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    .comRadiol Clin N Am 48 (2010) 85115c Cardiothoracic Section, Mallinckrodt Institute of Radiology, Washington Univ* Corresponding author.E-mail address: gutierrezf@mir.wustl.edu (F.R. Gutierrez).a Cardiothoracic Imaging Section, Department of Diagnostic RadiologyMedicine, San Juan, Puerto Ricob Mallinckrodt Institute of Radiology, Washington University School offoundation, clinical presentation, and imagingcharacteristics, especially those of MDCT.

    atric patients undergoing imaging and therapeuticprocedures.3 At our institution, we induceCongenital vascular anomalies of the thorax repre-sent an important group of entities that can occureither in isolation or in association with differentforms of congenital heart disease. From a clinicalviewpoint, they can be totally silent or, becauseof associated cardiac anomalies or compressionof the airway and esophagus, result in cardiovas-cular, respiratory, or feeding problems that resultin morbidity andmortality. It is extremely importantthat radiologists have a clear understanding ofthese entities, their imaging characteristics, andtheir clinical relevance.The imaging armamentarium available to diag-

    nose these diverse conditions is ample, and hasevolved from such traditional methods as chestradiography, barium esophagography, and angi-ography to new modalities that include echocardi-ography, multidetector row CT (MDCT), and MRimaging. These imaging modalities have addedsafety, speed, and superb resolution in diagnosisand, as in the case of MDCT, provide additionalinformation about the airway and lung paren-chyma, resulting in a more comprehensive exami-nation with greater anatomic coverage.1,2 Thisarticle reviews the most important congenitalthoracic vascular anomalies, their embryologicKEYWORDS

    Multidetector computed tomography Congen Vascular Anomaliesdoi:10.1016/j.rcl.2009.09.0040033-8389/09/$ see front matter 2010 Published by Eanomalies of the thorax, such anomalies can alsobe seen in adults, sometimes incidentally and aspart of an examination for a totally unrelated indica-tion. Therefore, examinations should be tailored totake into account radiation issues, need for seda-tion, and other indications so that that diagnosisis safe, comprehensive, and efficient. To accom-plish this, those indications, along with availableclinical and imaging data, should be systematicallyand carefully reviewed in consultationwith referringphysicians before the examination is prescribedaccording to the patients individual needs.Radiation exposure, particularly in infants and

    children, must be carefully considered whendeciding whether MDCT or MR imaging is moreappropriate. This risk should be weighed againstthe longer imaging time required for MR imaging,which necessitates expanded sedation or anes-thesia with their inherent risks.Due to the fast scanning times of MDCT, seda-

    tion is seldom required for older children andadults. For infants and children younger than 5years of age, however, sedationmaybe necessary.The American College of Radiology has issuedhelpful guidelines to assist radiologists in the safeand effective use of conscious sedation for pedi-lsevier Inc. rad

  • dimensional volume-rendered images from anexternal and internal perspective (virtual bronchos-

    Maldonado et al86200 mg) in those older than 18 months. Scans areobtained during a single breath-hold. In sedatedand uncooperative patients, images are obtainedduring quiet respiration. In general, anatomiccoverage extends from the thoracic inlet to belowthe level of the diaphragm. In a 64-row MDCT,scanning of the entire thorax can be accomplishedin a single breath-hold of less than 5 seconds.For vascular opacification, a nonionic low-osmo-

    larity contrast agent that contains 300 mg of iodineper milliliter or greater is injected via an antecubitalvein using a mechanical injector. A saline boluschase is applied. In adult patients, a contrast mate-rial doseof 1.5mL/kgbodyweight anda flow rate of3 to 4 mL/s through an 18-gauge catheter areprescribed. In pediatric patients, the flow ratevaries with the size of the intravenous catheter.Suggested rates are 1.5 to 2.0 mL/s for a 22-gaugecatheter and 2 to 3 mL/s for a 20-gauge catheter.For catheters smaller than 22 gauge, the contrastmedium should be administered by hand. An auto-mated bolus tracking system is used to determinethe scanning delay time. A cursor is placed in theregion of interest and the attenuation thresholdset at 120 Hounsfield units. In pediatric patients,an empiric delay of 12 to 15 seconds after the startof intravenous contrast injection can be used forpatients who weigh less than 10 kg. A delay of 20to 25 seconds is used in larger patients.4

    We use a 64-section CT scanner (Sensation 64;Siemens Medical Solutions, Forchheim, Germany)with a detector collimation of 64 0.6 mm, pitch of1.4, and gantry rotation time of 330 ms. In adultpatients, tube current is set to 220 mA and tubevoltage to 120 kV. In pediatric patients, low radia-tion dose techniques are used. Tube current isadjusted by weight in the following manner: 25mAs in patients weighing less than 15 kg, 30mAs in patients weighing between 15 and 24 kg,45 mAs in patients weighing between 25 and 34kg, 75 mAs in patients weighing between 35 and44 kg, 100 mAs in patients weighing between 45and 54 kg, and 120 to 140 mAs in patients weigh-ing more than 54 kg. Tube voltage dosages of 80kV are used for patients weighing less than 50kg. For patients weighing more than 50 kg, tubevoltage dosages of 100 to 120 kV are used.For the evaluation of congenital thoracic vascular

    anomalies, we do not routinely synchronize the CTdata acquisition with the ECG tracing. An ECG-gated CT of the thorax increases scanning timeand, more importantly, the radiation dose. In somecases, however, ECG-gating may be necessary toevaluate concomitant complex cardiac abnormali-ties, to assess ventricular and valvular function, orto reducemotionartifacts thatobscure theanatomy.

    Scanning parameters then include a detectorcopy) readily show the extent.6

    EMBRYOLOGY

    Familiarity with the embryologic development ofthe thoracic vasculature is crucial in the properunderstanding of the potential anomalies andanatomic variations. So, a brief review of thisdevelopment follows, with an emphasis on thesystemic and pulmonary circulations.By the third week of embryonic development,

    paired angioblastic cords canalize to form endo-thelial tubes that quickly fuse into a single cardiactube beginning at the cranial end. The cardiac tubeelongates and develops alternate dilatations andconstrictions that mark its several segments. Pro-gressing caudally, these are truncus arteriosus,bulbus cordis, ventricle, atrium, and sinusvenosus.Separation of the aorta and pulmonary trunk is

    brought about by ingrowth of a spiral aorticopul-monary septum within the truncus arteriosus,which develops cephalad to caudad. The truncusarteriosus at the cranial end is continuous withthe aortic sac from which symmetric aortic archesarise. Six paired aortic arches develop. Theseterminate in the dorsal aortas of the correspondingside. Portions of these arches regress and disap-collimation of 32 0.6 mm, section collimation of640.6mmbymeansofa z-flying focal spot, gantryrotation timeof 330ms, pitch of 0.2, and tubepoten-tial of 100 to 120 kilovolt (peak) (kv[p]). We routinelyuse ECG-controlled tube current modulation. Thesupervising physician must determine on a patient-by-patient basis if the benefit of the additional infor-mation to be obtainedbyECG-gating outweighs therisks of the increased radiation dose.With the advent of MDCT, postprocessing tech-

    niques have become routine. They are helpful inconveying relevant imaging data to the referringphysicians and can provide surgeons with detailedanatomic information for surgical planning.Althoughthe source axial images are in most instances suffi-cient for diagnosis, two-dimensional reformattedand three-dimensional volume-rendered recon-structions can provide additional information aboutthe nature and extent of the lesion in question.During thoracic CT angiography for the evaluationof congenital thoracic vascular anomalies, thesepostprocessed images are particularly useful in as-sessing stenoses and change of caliber of smallstructures that run obliquely to the imaging plane.5

    If concomitant airway narrowing is present, three-pear, but several remnants normally persist.

  • descending aorta. Currently, this latter type is

    Congenital Thoracic Vascular Anomalies 87The first and second aortic arches regress,except for small portions that form parts of themaxillary and stapedial arteries, respectively. Inhumans, the fifth aortic arches are rarely or onlytransiently present.7 The third, fourth, and sixthaortic arches are the most important for finalvascular development. The third pair of aorticarches forms the common carotid arteries andpart of the internal carotid arteries. The left fourthaortic arch forms part of the definitive left aorticarch. The aortic sac contributes to the proximalpart of the aortic arch, and the left dorsal aortacontributes to the distal part of the aortic arch.The right fourth aortic arch forms the proximalsubclavian artery; the distal su