In this study, patients’ age ranged from 1 month to 14 years with a mean of 2.84 ± 3.77 years and slightly higher male predominance. Their BMI mean was 15.27 ± 1.99 kg/m2 (underweight), while heart rate and blood pressures were normal. Most of the cases presented with either cyanosis (73%) or cardiac murmur (87%), while other manifestations as clubbing, squatting, and hypoxic spells were noted in 53%, 47%, and 33% of cases.
In the study of Hu et al. [6], the mean age of TOF patients was 2.85 ± 2.30 years (range 5 months to 10 years) with 56% of them males. The mean body mass index was 14.05 ± 6.48 kg/m2, heart rate 122.50 ± 16.73 bpm, systolic blood pressure 91.25 ± 24.84 mmHg, and diastolic pressure 54.15 ± 18.68 mmHg. The common symptoms noticed were heart murmurs (64.23%), followed by cyanosis (24.39%), post-exercise tachypnea (4.07%), and squatting (1.63%) that were comparable to the present study results.
In fact, clinical presentation varies based on severity of right ventricular outflow tract (RVOT) obstruction and amount of pulmonary blood flow. Often, cyanosis is not present at birth but appears later within a few months after birth, except in severe cases of (RVOT) obstruction. According to Loh et al., cyanosis appeared in 73% of cases from 3 months to 1 year of life, hypoxic spells in 45%, and squatting in 50% of cases [15]. The pulse and blood pressure are usually normal [16].
All the cases in the present study were diagnosed by their clinical manifestations and confirmed by echocardiography finding for major four TOF criteria. Searching for other associated vascular anomalies that are frequently present in these cases was done according to standard guidelines, before they were referred for MDCT assessment preoperatively [5, 8].
Although TTE combined with Doppler imaging is the first-line method for diagnosis of complex CHD, however, due to its small acoustic window, low spatial resolution, and operator-dependent nature, it is preferred mainly for diagnosing intra-cardiac anomalies with difficulty in detecting extra-cardiac ones [9, 11]. Also, the invasive nature, catheter problems and high radiation dose of cardiac catheterization deferred it as diagnostic method in many cases, although it is the gold standard for this purpose [17].
On the other hand, magnetic resonance imaging was considered as a promising imaging modality for delineating vascular defects in recent years; however, it has many limitations such as presence of pacemakers, lengthy sedation, and relatively low spatial resolution which limit its use for assessing smaller extra-cardiac vascular anomalies [18].
The development of MDCT, with its excellent image quality, rapid acquisition speed that decreases the need for sedation or anesthesia, lower radiation doses, high-resolution, and so excellent visualization of anatomic structures, made it a rapid reliable non-invasive tool for detecting various anomalies in children with complex CHD, even critically ill patients [9, 19]. It may be superior to echocardiography in detecting extra-cardiac anomalies as those of coronary artery, pulmonary artery branches, and multiple aorto-pulmonary collaterals (MAPCVs) [5, 13, 20], which is going with these study findings.
It was interesting to find that many vascular anomalies were newly detected by using MDCT other than those detected before during echocardiography examination. By using MDCT, 85% of our cases showed associated extra-cardiac anomalies compared to only 55% detected by TTE and this difference was statistically highly significant. Moreover, when following up the postoperative findings of these patients, MDCT was found to be superior to TTE assessment for detection of these anomalies, as regards its sensitivity (98% vs. 76.9%), specificity (88.9% vs. 85.7%), positive predictive value (98% vs. 90.9%), negative predictive value (88.9% vs. 66.7%), and so its diagnostic accuracy (96.6% vs. 80%).
These are going with the findings of Hu et al.’s [6] study who compared MDCT to TTE and found that MDCT had greater value in detecting associated extra-cardiac vascular anomalies in TOF patients {diagnostic accuracy 99.13% vs. 97.39%; sensitivity 92.45% vs. 77.07%; specificity 99.81% vs. 99.42%; positive predictive value 98.00% vs. 93.08%; and negative predictive value 99.24% vs. 97.74%}. Also, Bu et al. [21], after finding similar results, mentioned that MDCT not only had overall higher sensitivity than TTE (97.2% vs. 90.6%; P < 0.05), but also was much more sensitive for the diagnosis of extra-cardiac vascular abnormalities (92.0% vs. 68.0%; P < 0.05).
Due to the small field of view during echocardiography examination from the supra-sternal direction in addition to the short neck of pediatric patients, the overlying bone, and aerated lung, all these factors may influence the diagnostic value of TTE compared to MDCT in identifying accurately the great vessels and extra-cardiac anomalies [6, 9].
Moreover, Nie et al. [9], in addition to finding significant differences in the diagnostic accuracy and sensitivity of high pitch MDCT angiography and TTE for detecting congenital extra-cardiac vascular anomalies (P < 0.05), mentioned that MDCT offers more information about the relations of these thoracic vascular anomalies to the airways and lung parenchyma, resulting in greater anatomic details, that help the surgeon during correction procedures.
Also, Abd El-Rahman et al. [22] found that the overall sensitivity of MSCT angiography in diagnosis of extra-cardiac vascular anomalies was 98.1% which was higher than that of TTE (80%) and they concluded that it provides important complementary information to TTE with regard to extra-cardiac vascular structures and coronary artery anatomy.
More recently, Alsalihi et al. [23] confirmed these findings and they concluded that MDCT can provide confident detection and exclusion of extra-cardiac vascular abnormalities with superb anatomical description (sensitivity 98.41%, specificity 99.76%, PPV 96.88%, and NPV 99.88%).
It is worthy to mention that the most common anomalies detected in our patients by MDCT were those of pulmonary artery (80%), followed by aorto-pulmonary vessels (45%), then aortic artery (40%), coronary arteries (20%), and lastly vena cava connection anomalies (6.7%).
Patients with pulmonary artery (PA) defects included 18 patients with main PA atresia, 8 with hypoplastic main PA, 10 with abnormal atretic right PA, and 12 with abnormal atretic left PA. Patients with aorto-pulmonary vessels defects included 14 patients with patent ductus arteriosus and another 14 with major aorto-pulmonary collateral vessels (MAPCS). On the other hand, those with aortic artery anomalies included 16 patients with right-sided aortic arch (AA), and 2 patients with each of double AA, hypoplastic AA, persistent 5th AA and aberrant left subclavian artery. As regards coronary arteries (CA) malformations, there were 2 patients with each of coronary AVF, anomalous origin of right CA from PA (ARCAPA), and anomalous origin of right CA from left main CA, in addition to 3 patients with each of left anterior descending artery dual coarse and anomalous origin of left CA from PA (ALCAPA). Lastly venous connection anomalies included 2 patients with double superior vena cava and another 2 with pulmonary venous connection anomalies.
Also, Zakaria et al., by using multi-detector CT for diagnosis of TOF associations, found pulmonary artery abnormalities in 100% of their cases, either atresia or stenosis of the main artery or its right or left branches, infundibular pulmonary artery stenosis in 43%, deformities of the MAPCVs in 57%, and right aortic arch in 30%. In addition to that, 4% of their cases had abnormal coronary arteries and 44% had patent ductus arteriosus [7].
Recently, Chelliah et al. [13] and others, when comparing MDCT to TTE, found that it was of greater value in the visualization of anomalies of the pulmonary artery [11, 21] and valve, as well as deformities of the MAPCVs [12], abnormal vena cava connections, and aortic artery and valve disorders [24]. They mentioned that TTE can only identify relatively large ones, while MDCT can visualize the number, origin, and supplied lung lobes of MAPCVs, regardless of the size of the vessels [25]. Moreover, MDCT was found to have both 100% sensitivity and specificity for the detection of coronary artery anomalies in these patients [10].
It should be mentioned that MDCT highlights the importance of specific critical extra-cardiac vascular anomalies with its implication to management plane as in the following categories:
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1
Finding needs immediate intervention as anomalous right coronary artery origin from pulmonary artery (ARCAPA) especially if associated with severe degree of MPA stenosis, coronary arteriovenous fistula (AVF).
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2
Findings important to be clarified before the time of operation such as size and numbers of major aorto-pulmonary collateral vessels (MAPCVs), persistent left sided SVC, right sided AA, pre-pulmonic course of dual LAD, and total anomalous pulmonary venous return (TAPVR).
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3
Findings of implication in surgical access or dating like double AA, and partial anomalous pulmonary venous return (PAPVR).
Lastly, although MDCT provide accurate, non-invasive, rapid, diagnostic imaging of the extra-cardiac vascular structures, however, many limitations for its use are present as the need for sedation of children especially those below 6 years of age in addition to exposing these young developing individuals to higher doses of ionizing radiations and to iodinated contrast material. In this study, we use chloral hydrate for sedating these children and non-iodinated contrast materials to avoid side effects of these drugs as much as it could be however MDCT is indispensable prior to operative correction as the most accurate imaging technique for this purpose.
The study used a relatively small sample size; for better analysis and results, it would have been presented with a larger sample size. The imaging technique used was a retrospective ECG-gated one which still provides more irradiation than its prospective counterpart, with however using low dose according to the ALARA dose lowering protocol. In future studies, it might be warranted using prospective ECG-gated technique with low dose radiation adaptive statistical iterative reconstruction (ASiR) technique to benefit from high image quality with dose reduction.