The etiology of pectus carinatum involves overgrowth of costal cartilage and undergrowth of ribs

Fig. 3. Measurement of the full length of the rib. (A) Three-dimensional volume rendering (VR) image is reconstructed automatically with a commercially available reconstruction program (Aquarius iNtuition Ver.4.4.6 TeraRecon, Foster City, CA). Unnecessary regions are manually deleted. (B) The full length of the left 4th rib is semiautomatically traced using the curved MPR technique with manual correction. (C) The tracing line passes through the center of rib. (D) The full length of the rib is measured by electronic caliper.

Purpose
Fig. 1. Measurement of the sternal rotation angle. (a) The sternal rotation angle is measured as the angle of sternal slope (Line C) against the baseline of the thorax (Line B) at a slice with a largest sternal slope. The baseline of thorax was defined as the perpendicular line to the vertical line traversing the T spine’s center (Line A).

Fig. 1. Measurement of the sternal rotation angle.

We compared the length of costal cartilage and rib between patients with symmetric pectus carinatum and controls without anterior chest wall protrusion, using a 3-dimensional (3D) computed tomography (CT) to evaluate whether the overgrowth of costal cartilage exists in patients with pectus carinatum.

Subjects and methods
Fig. 2. Measurement of the Haller index. The Haller index is defined as maximal internal transverse diameter of the chest (A) divided by the anteroposterior diameter between the sternum and the vertebral bodies (B) on axial CT images.

Fig. 2. Measurement of the Haller index.

Twenty-six patients with symmetric pectus carinatum and matched twenty-six controls without chest wall protrusion were enrolled. We measured the full lengths of the 4th–6th ribs and costal cartilages using 3-D volume rendering CT images and the curved multiplanar reformatted (MPR) techniques.

The lengths of ribs and costal cartilages, the summation of rib and costal cartilage lengths, and the costal index [length of cartilage/length of rib * 100 (%)] were compared between the patients group and the control group at 4th–6th levels.

Results
The lengths of costal cartilage in patient group were significantly longer than those of control group at 4th, 5th and 6th rib level. The lengths of ribs in patient group were significantly shorter than those of control group at 4th, 5th and 6th rib level.

The summations of rib and costal cartilage lengths were not longer in patients group than in control group. The costal indices were significantly larger in patients group than in control groups at 4th, 5th and 6th rib level.

Conclusion
In patients with symmetric pectus carinatum, the lengths of costal cartilage were longer but the lengths of rib were shorter than those of controls.

These findings may supports that the overgrowth of costal cartilage was not the only factor responsible for pectus carinatum.

The etiology of pectus carinatum involves overgrowth of costal cartilage and undergrowth of ribs, Chul Hwan Park, Tae Hoon Kim, Seok Jin Haam, Inhwan Jeon, Sungsoo Lee. Journal of Pediatric Surgery 49 (2014) 1252–1258. DOI: http://dx.doi.org/10.1016/j.jpedsurg.2014.02.044

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