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Reference Curves for the Aortic Area by Age

Posted Dec 31, 2012 Updated Apr 10, 2023
By Li-An Wu MD , Chung-I. Chang MD , Jou-Kou Wang MD , Tiffany Ting-Fang Shih MD PhD , Mei-Hwan Wu MD PhD , Shyh-Jye Chen MD PhD
8 min read

Rationale and Objectives

The aim of this study was to establish reference curves and formulas for aortic cross-sectional area in patients from infancy to young adulthood.

Materials and Methods

Patients (aged 2 days to 18.1 years) who underwent electrocardiographically gated cardiac computed tomography between May 2004 and December 2011 were retrospectively examined. These patients were further divided into a group of normal controls (without aortic disease) and a group with coarctation of aorta. In the group of normal controls, the cross-sectional area of the aorta was measured at six locations: the sinotubular junction, distal ascending aorta, proximal arch, distal arch, aortic isthmus, and descending aorta (DAO). Interobserver and intraobserver variability, gender differences, the relationship between aortic cross-sectional areas and age, and the ratio to the DAO were also examined. The area ratio to the DAO was also examined in the group with coarctation of the aorta.

Results

A total of 65 patients and 365 measurable aortic segments were included in the analysis (55 normal controls and 10 patients with coarctation of aorta). Interobserver and intraobserver variability was limited (aside from measurements of the sinotubular junction). There were no gender differences in age and the cross-sectional areas of the different aortic segments. In the group of normal controls, the cross-sectional area of each aortic segment was highly correlated with age (all >0.90, P < .001). The reference curves and formulas for aortic cross-sectional area by age were also determined for further clinical use. In the normal controls, the <95% confidence intervals of the ratios of aortic isthmus to DAO, distal arch to DAO, and proximal arch to DAO were approximately 0.6, 0.8, and 1.0, respectively. In addition, in the group with coarctation, all area ratios of aortic isthmus to DAO were <0.6, which was significantly different from the group of normal controls ( P < .001). The area ratios of distal arch to DAO and proximal arch to DAO were also significantly different between two groups ( P < .001 for both).

Conclusions

Measurement of aortic area was reproducible. The established reference curves and formulas and minimal area ratios were convenient for further clinical use.

Aortic coarctation accounts for 5% to 10% of all congenital cardiac lesions . If left untreated, most patients die of stroke, coronary heart disease, or sudden death by the fourth decade of life . The conventional diagnosis of aortic coarctation is based on clinical presentation, echocardiography, and aortography . Although transthoracic echocardiography is a less invasive technique and allows pressure gradient measurements, the area of the coarctation and the collateral vessels can be difficult to visualize, particularly if a stent or prosthetic material has been used for repair of the coarctation . Aortography, an invasive procedure , is justified for use only in surgical planning or interventional procedures . Recently, multidetector computed tomographic (CT) imaging has been demonstrated to provide excellent depiction of the aorta, thoracoabdominal collateral vessels, and associated abnormalities and to provide high-quality arterial-phase imaging data suitable for multiple reformations . CT imaging is also a useful tool for pretreatment evaluation and posttreatment follow-up .

All previous studies pertaining to the use of CT for aortic diameter measurement have focused on one-dimensional assessment . This is in contrast to the measurement of two-dimensional cross-sectional area, which is more directly related to the severity of the pressure gradient in aortic stenosis, especially in the condition of coarctation, which is typically eccentric narrowing of the lumen . According to the definition of power, the severity of the pressure gradient in the stenotic segment is inversely proportional to the cross-sectional area of the aortic stenosis. In addition, deformation of aortic arch shape may occur following surgery ; hence, measurements of diameter may not necessarily give an accurate indication of true hemodynamic status.

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Materials and methods

Patient Enrollment

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Figure 1, Histogram showing the age distribution of the patients.

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Image Acquisition

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Table 1

Indications and Findings as Determined by Computed Tomographic Examination for All Patients (55 Normal Controls and 10 Patients with Coarctation of the Aorta) Included in the Study

n Abnormal Findings Controls ( n = 55) Intracardiac 20 Total anomalous pulmonary venous connection status post rerouting follow-up (2), partial anomalous pulmonary venous connection (2), infectious endocarditis (1) Coronary 9 Kawasaki disease (2), arteriovenous fistula (2) Tracheobronchial 8 Tracheal stenosis (3), innominate artery syndrome (2) Pulmonary arterial 7 Left pulmonary artery sling (1) Mediastinal 7 Pericardiac 2 Pericardial effusion (1) Systemic venous 2 Double inferior vena cava (1) Coarctation of the aorta ( n = 10) Isolated at isthmus 8 Associated with atrial septal defect (8), ventricular septal defect (6), patent ductus arteriosus (7), pulmonary hypertension (2) Hypoplastic aortic arch 2

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Image Reconstruction and Quantification

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Figure 2, Cross-sectional areas of the different aortic segments. (a) Parasagittal oblique view of the whole aorta. (b) Six levels of the aorta were identified: the sinotubular junction, distal ascending aorta (just before the origin of the innominate artery), proximal arch (midway between the innominate artery and left-sided common carotid artery), distal arch (midway between the left common carotid artery and left subclavian artery), aortic isthmus (ISTH), and descending aorta (DAO). (c) Reformatted slabs of the ISTH (slice thickness, 5 mm; interval, 5 mm). (d) Reformatted slab of 1-mm thickness (using central two slices). (e) A W-shaped curve was drawn to measure the enhancement threshold. (f) The curve of the enhancement threshold for the ISTH portion. Half the sum of the maximally enhancing luminal center and the outer lower density structure was used as a cutoff value (white line in the middle). (g) The threshold was automatically cuff off below the threshold, and a thin slab of the aorta was created. (h) The volume was automatically measured by the workstation and divided by 1 mm to give the aortic cross-sectional area in square centimeters.

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Statistical Analysis

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Results

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Table 2

Measurable Percentage for Each Aortic Segment

Segment of the Aorta_n_ % Descending 65 100 Isthmus 64 98.5 Distal aortic arch 60 92.3 Proximal aortic arch 58 89.2 Distal ascending aorta 62 95.4 Sinotubular junction 56 86.2 Total 365 93.6

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Figure 3, Reference curves for the cross-sectional area of aortic segments by age. The line in the center represents the mean value. The bilateral inner parallel lines are the 95% confidence limits for the regression line. The bilateral outer lines are the 95% confidence limits for the data points. (a) Descending aorta ( R 2 = 0.8633). (b) Isthmus ( R 2 = 0.8963). (c) Distal aortic arch ( R 2 = 0.8657). (d) Proximal aortic arch ( R 2 = 0.8847). (e) Distal ascending aortic arch ( R 2 = 0.8871). (f) Sinotubular junction ( R 2 = 0.8178).

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Figure 4, Reference curves for the area ratio of each segment of the aorta to the descending aorta by age. The line in the center represents the mean value. The bilateral inner parallel lines are the 95% confidence limits for the regression line. The bilateral outer lines are the 95% confidence limits for the data points. (a) Isthmus ( R 2 = 0.2695). (b) Distal aortic arch ( R 2 = 0.0550). (c) Proximal aortic arch ( R 2 = 0.0370). The <95% confidence limits for (a) , (b) , and (c) were approximately 0.6, 0.8, and 1.0, respectively.

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Figure 5, Bar chart of the group of normal controls and the group with coarctation of the aorta for the area ratio of (a) isthmus (ISTH) to descending aorta (DAO), (b) distal aortic arch (DR) to DAO, and (c) proximal aortic arch (PR) to DAO. CI, confidence interval.

Figure 6, Two cases of the eccentric narrowing of the isthmus of the aorta. (a,b) An 11-day-old male infant has coarctation at the isthmus portion of the aorta, an atrial septal defect, and patent ductus arteriosus. The cross-section of the narrowest portion of the aorta was ellipse shaped ( arrow ). The longest diameter measured 3.42 mm, while the short axis measured only 1.9 mm. (c) An 8-month-old female patient with coarctation of aorta at the isthmus portion, hypoplasia of the aortic arch, a ventricular septal defect, and an atrial septal defect. The cross-section of the narrowest portion of the aorta was also oval shaped. The longest diameter measured 4.01 mm, and the short axis was only 3.03 mm.

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Discussion

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Conclusions

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Academic Radiology, Volume 20, Issue 1
Journals General Radiology
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