Chest wall depressions most often involve the lower sternal segment. It has previously been divided into a limited cup-shaped depression, and a relatively wide and shallow saucer-shaped depression. A careful review of a large number of preoperative photographs and CT films of patients with funnel chest reveals that some patients present with long groove-like depressions of the anterior chest wall, which are often asymmetric, and some patients with a mixture of corpus cavernosum and funnel chest.
The extent of asymmetry, rib protrusion, sternal torsion, and cephalic aspect of the depression should be noted prior to surgery, and the presence of a short anterior-posterior diameter of the thorax should also be noted. Female patients may exhibit significant asymmetry of both breasts. High-quality preoperative photographs should be obtained for each patient to allow comparison with the postoperative period, making the parents and relatives of the child forget the severity of the preoperative deformity.
Although most patients present with a shortened anteroposterior thorax, occasionally a chest wall depression may occur on top of a barrel chest, when the anteroposterior thorax may still be large and may not compress the heart even if the deformity is severe. Also, CT films may suggest a smaller thoracic index than in those with complete depression. Some families tend to have similar concave morphology over several generations.
Careful morphologic evaluation may be clinically predictive of treatment outcome. The proportion of each type is unknown, but it is predominantly the cup-shaped depression type, with far fewer saucer-shaped depressions and even fewer mixed types of long sulcus depressions and funnel chests with chicken breasts.
1.Classification and evaluation index
Chest wall deformity can be symmetrical or asymmetrical. The symmetry of the depression can be checked by preoperative CT scan and photography. On the photographs, the symmetry can be determined by the degree of deviation of the location of the elliptical depression area from the center of the anterior chest wall. On CT films, symmetry can be determined by the ratio of the left to right diameter measurements of the thorax (R/L), which can then be used to confirm the diagnosis. the R/L ratio can also be used to identify different types of asymmetrical deformities.
One of the advantages of CT scanning is that it clearly shows sternal torsion and the degree of torsion can be easily determined. Therefore, sternal torsion is further classified as mild (torsion <30°) to severe (torsion >80°). The degree of torsion is not inferred from preoperative photographs.
The assessment of the degree of torsion is to provide a method of comparison of outcomes and also to determine the need for surgical treatment. There are several methods of grading the severity of funnel chest, but none are widely accepted.
Haller et al. introduced the concept of a “thoracic index” to assess the need for chest wall correction on CT films. The thoracic index is calculated as the ratio of the maximum transverse diameter of the thorax to the distance from the back of the sternum to the front of the spine at the most depressed part of the anterior chest wall, and the indication for surgery is greater than 3,25.
In 2004, Lee and Park et al. proposed a series of indices for the evaluation of funnel chest based on CT films, including depression index (DI), asymmetry index (AI), eccentricity index (EI), and imbalance index (UI), and used these indices to evaluate the effect of surgical correction.
They analyzed the relevant indices on CT films of 308 patients with funnel chest before and after surgery and found that the depression index (DI) and asymmetry index (AI) were significantly reduced after surgery. Comparison between symmetrical and asymmetrical patients revealed that there was a significant difference in the asymmetry index (AI) between the two before surgery and no significant difference in AI after surgical correction with different shapes of shaped plates according to the staging, suggesting that the asymmetrical funnel chest could become symmetrical after correction. The eccentricity index (EI) and imbalance index (UI) were also significantly reduced after surgery.
1. Morphological classification (Park) and significance
From August 1999 to June 2002, Park et al. treated 322 patients with funnel chest, including 71 adults, by applying the Nuss procedure and its modification. in 2004, they reported the classification of funnel chest by CT films.
Because funnel chest has a wide range of morphologic manifestations of variation, they concluded that technical improvements for each variant type were needed to achieve satisfactory results. Therefore, a morphologic classification system based on CT slices was proposed.
It was first divided into symmetrical (type 1) and asymmetrical (type 2). type 1 was further divided into two subtypes 1A and 1B, with the common feature that the median sternum (point C) coincides with the center of the depression (point P). type 1A is a deep symmetrical depression typical of the lower sternum. type 1B is a wide and flat symmetrical depression.
In the asymmetric type (type 2), the center of the depression is not in the midst of the sternum but to one side. type 2 is further divided into three subtypes: 2A, 2B, and 2C. type 2A, also known as the eccentric type, has the midst of the sternum in the midline of the body, but the deepest part of the depression is in the rib cartilage on one side. type 2B, also known as the unbalanced type, has the center of the depression in the midline of the body, but the degree of depression is not uniform on both sides, so that the chest wall on both sides is at the same angle as the mid-sagittal plane of the body. The center of the depression is located in the midline of the body, but the degree of depression is not uniform on both sides, so that the angle between the two sides of the chest wall and the sagittal plane of the body is not equal.
Funnel chest subtype (Park)
Symmetrical (type 1): the center of the depression is located in the middle of the sternum
1A: Typical symmetrical deep depression of the lower sternum
1B: wide and flat symmetrical depression of the lower sternum
Asymmetric type (type 2): the center of the depression is not in the middle of the sternum but to one side
2A: the eccentric type, where the center of the sternum is located in the midline of the body, but the deepest part of the depression is located in the rib cartilage on one side
2A1: confined type
2A2: Wide and flat type
2A3: Grand Canyon type, with a deep longitudinal sulcus running from the clavicle down to the lower thorax, with the depression mostly located in the cartilage next to the sternum rather than in the sternum
2B: Imbalanced type, the center of the depression is located in the midline of the body, but the degree of depression is not uniform on both sides
2B1: Restricted type
2B2: wide and flat type
2C: mixed type of 2A and 2B
1-Classical Nuss plate; 2, -Park modified bridge shaping for symmetrical funnel chest (type 1), which prevents overcorrection; 3-Asymmetrical shaping for type 2A, where the highest P point of the plate corresponds to the deepest part of the sternal depression; 4-Gull wing shaping for types 2B and 2C, where the V-shaped notch (E point) of the plate corresponds to the chest wall projection; 5 (hump shaping) and 6 (composite shaping)-used for symmetrical funnel chest in adults, which enhances the lifting force of the middle part of the plate on the sternum.
C-plate midpoint; D-arc diameter; E-sternal elevation point; H-hinge point; P-deepest point of chest wall depression.
According to Park, in the evaluation of 322 postoperative outcomes of funnel chest, 294 cases were rated as excellent and 28 as good, while there were no cases rated as poor. The proportions of patients with symmetrical, eccentric and unbalanced postoperative outcomes rated excellent were 99, 5%, 98, 9% and 95, 8%, respectively. Thus, we can see that the use of different shaped plates according to the different morphological types of patients can significantly improve the surgical results.