Eur J Cardiothorac Surg 2008;34:150-154. doi:10.1016/j.ejcts.2008.03.044
Copyright © 2008, European Association for Cardio-thoracic Surgery. Published by Elsevier. All rights reserved.
Extreme eccentric canal type pectus excavatum: morphological study and repair techniques
Hyung Joo Park*,
In Sung Lee,
Kwang Taik Kim
Department of Thoracic and Cardiovascular Surgery, Korea University Medical Center, Ansan Hospital, 516 Gojan-Dong, Ansan 425-707, South Korea
Received 11 September 2007;
received in revised form 6 February 2008;
accepted 4 March 2008.
* Corresponding author. Tel.: +82 31 412 5060; fax: +82 31 414 3249. (Email: hyjpark{at}korea.ac.kr).
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Abstract
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Objective: Extreme eccentric canal type pectus excavatum (Grand Canyon type, GC, Type 2A3), is a distinct morphological variation, characterized by an eccentric longitudinal canal. Due to the extent of depression and asymmetry, repair is often challenging with the minimally invasive technique. Following, we present its morphologic characteristics and evaluate repair techniques according to morphology type. Methods: Extreme eccentric canal type pectus excavatum is an eccentric, long canal-like chest wall depression from the infra-clavicle to lower chest. Among 851 patients who underwent pectus excavatum repair from 1999 to 2007, 112 patients (13.2%) had the eccentric canal type. Morphologic type and repair techniques were evaluated; results were assessed by pectus indices (depression index (DI), asymmetry index (AI), and eccentricity index (EI)). Results: Of the asymmetric cases, 31% (112/361) were the eccentric canal type. Female proportion (male to female ratio = 2.3) was higher than in general pectus excavatum (4.1, p
< 0.05). Young female adults were more frequently affected (8/17, 47%, p
< 0.05). Repair techniques included asymmetric bar (n
= 97, 86.6%), seagull bar (n
= 53, 47.3%), crest compression (n
= 13, 11.6%), and parallel bar (n
= 79, 70.5 %) techniques. Pectus indices changes were: DI (pre 2.89 to post 1, p
< 0.01), AI (pre 1.11 to post 1.03, p
< 0.01), and EI (pre 1.69 to post 1, p
< 0.01). AI change represented asymmetric to symmetric correction. Conclusions: Extreme eccentric canal type pectus excavatum represents a distinctive morphology and requires special techniques for repair. Post-repair symmetry can be achieved by an asymmetric bar technique. Upper chest wall depression can be corrected by a parallel bar technique. Protruding ridge was relieved by a seagull bar or crest compression technique.
Key Words: Pectus excavatum • Asymmetry • Extreme eccentric canal type (Grand Canyon type) • Repair techniques
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1. Introduction
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Pectus excavatum encountered during surgical repair varies by morphologic type. A form of the most extreme eccentric asymmetry is longitudinal canal type (the Grand Canyon type, Type 2A3 according to the author's classification) [1]. This type of depression is one of the most unique variants that forms a deep furrow along the sternal border and looks like the Grand Canyon. A similar morphology of deformity was described once in brief [2] but the exact morphological characteristics of this extreme deformity were not portrayed and this variant has not been classified as a subset of pectus deformity in the literature. It was first denominated as a separate entity of pectus excavatum and successfully repaired with the minimally invasive technique by the principal author (HJP) [1]. Herein, we illustrate detailed morphological features and related abnormalities of this particular deformity, and describe and discuss the repair techniques.
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2. Materials and methods
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In a single surgeon's experience (HJP) between August 1999 and March 2007, 851 pectus excavatum patients underwent minimally invasive repair. Among them, 112 patients (13.2%) had the extreme eccentric canal type pectus excavatum (Grand Canyon type, Type 2A3) [1].
Morphology and associated disorders of the extreme eccentric canal type pectus excavatum (Grand Canyon type) were investigated. Surgical repair techniques were examined. Results were assessed via prospectively collected data analyses and pectus indices calculations from CT scan, including depression index (DI), asymmetry index (AI), and eccentricity index (EI) [3].
Statistical analysis was performed with SPSS. Categorical data was analyzed by Chi-square test and Fisher's exact test as appropriate. A p-value less than 0.05 was considered significant.
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3. Results
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Of the 361 patients with asymmetric type pectus excavatum, 112 (31%) had the extreme eccentric canal type (Grand Canyon type, type 2A3). Female proportion (male to female ratio = 2.30) was higher than in other pectus excavatum deformities (male to female ratio = 4.1) (p
< 0.05). Ages ranged from 3 to 51 years. Compared to other age groups, young female adults (age >20) were more frequently affected (8/17, male to female ratio = 1.2).
3.1 Morphology
The morphological characteristics of the extreme eccentric canal type pectus excavatum (Grand Canyon type) include a long furrow-like chest wall depression from the clavicle level to the lower thoracic cage (Fig. 1B, 2, Type 2A3). The main depression is usually located between the 6th and 9th costal cartilages, but extends up to the infraclavicular level at the 2nd costal cartilage. The deformity is eccentrically asymmetric, and mostly locates longitudinally along the right sternal border. Unlike the usual pectus excavatum that is formed by depression of the xiphisternal area, malformed costal cartilages off the midline comprise the floor of the asymmetric depression (Fig. 2A). The sternum, instead, rotates toward the depression and forms the left side wall of the depression (Fig. 2B). Frequently this deformity accompanies a ridge-like protruding crest of costal cartilages on the other side, usually at the left sternal border (Fig. 1C, Type 2B). The unique features of the malformed costal cartilages are forming a concavity (angulated downward) at the bottom of depression but convexity (angulated upward) at the opposite side where a protruded ridge forms (Fig. 2D, P).
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Fig. 1. Schematic drawing illustrates the location of depression and protrusion in extreme eccentric canal type (Grand Canyon type) pectus excavatum. (A) Usual symmetric pectus excavatum (Type 1A): a xiphisternal depression. (B) Extreme eccentric canal type (Grand Canyon type) pectus excavatum (Type 2A3): a longitudinal canal from the infra-clavicle to lower chest along the right sternal border. (C) Protruding ridge (Type 2B): a longitudinal crest along the left sternal border.
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Fig. 2. Patient photos and CT scans illustrate extreme eccentric canal type (Grand Canyon type) pectus excavatum (Type 2A3) and excavatum–carinatum complex (Type 2C). (A) Malformed costal cartilage forms the floor of the depression. (B) Rotated sternum forms a wall of the depression. (D) Depression of costal cartilage. (P) Protrusion of costal cartilage.
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Another notable feature is that young female adults characteristically manifest ipsilateral breast hypoplasia on the side of depressed chest wall (Fig. 3
). Two patients also had Marfan syndrome.
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Fig. 3. A 24-year-old female patient shows extreme eccentric canal type (Grand Canyon type) pectus excavatum and an ipsilateral (right side) breast hypoplasia (arrow). (A) Preoperative chest and breast contour and CT scan. (B) Postoperative chest and breast contour and CT scan.
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3.2 Repair technique
The key technique was the asymmetric bar technique for treating eccentric asymmetry; the principal morphologic element. In order to elevate eccentric depression selectively, the bar was shaped asymmetrically conforming the degree of eccentricity that places the maximum convexity of the bar corresponding to the deepest point of the pectus depression. This creates a symmetric chest wall, without residual depression or excessive protrusion at the other side (Fig. 4
).
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Fig. 4. Asymmetric bar technique for eccentric pectus excavatum repair. (A) Convexity of the bar corresponds to the center of the depression (arrow). (B) Rotating the bar along the hinge points selectively elevates the right-sided depressed chest wall (arrow), not affecting the left chest wall.
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When a single bar cannot elevate the entire depression as the depression extends to the level of clavicle, an additional bar at the upper chest can be used (the parallel bar technique). In the parallel bar technique, the main (lower) bar insertion point corresponds to the main depression, generally at 1 or 2 intercostal spaces below the nipple (6th to 7th intercostal space at the anterior axillary line). The second (supplementary) bar is usually positioned above the nipple (3rd or 4th intercostal space at the anterior axillary line).
A measure for the left parasternal crest is another consideration during repair, as it can result in protrusion. To avoid this, a notch in the bar at the point corresponding to the protrusion is created as a measure for minor protrusions (the seagull bar technique). A seagull shaped bar saves the protruded point from further elevation by the bar (Fig. 5
). In cases where the crest is too prominent for the seagull technique, crest compression technique was employed [1,4]. The crest compression actively compresses protrusions by placing the hinge point on the crest. The compressing pressure was generated by lever-action of rotating the bar on the crest that serves as a pivot (Fig. 6
).
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Fig. 5. Seagull bar technique for unbalanced pectus excavatum repair. (A) Convexity of the bar corresponds to the center of the depression (large arrow); notch of the bar corresponds to the points not to be elevated (small arrow). (B) Rotating the bar along the hinge points selectively elevates mainly the left sided depressed chest wall (large arrow); less affecting the right chest wall protrusion (small arrow).
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Fig. 6. Crest compression technique for unbalanced pectus excavatum repair. Preoperative CT scan shows midline depression and right side chest wall protrusion (excavatum–carinatum complex). *Right side hinge set on the crest. (Inset) Rotating the bar along the hinge points elevates the depressed chest wall (lower arrow) while it compresses the right chest wall protrusion (upper arrow) – dual action of the bar. Postoperative CT scan shows relief of midline depression and right side chest wall protrusion (post-repair symmetry). (a) Axis of the bar insertion; (H) hinge point; Preop: preoperative CT scan; Postop: postoperative CT scan.
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The crane technique is elevating the depressed sternum prior to rotating the bar in order to alleviate the pressure on the bar and hinge points [5]. Briefly the technique employs a wire suturing to the bony tissue on the xiphisternal area or other portion of the sternum as necessary and lifting the wire suture and the sternum by an operating table mounted crane system.
In repair of the extreme eccentric canal type pectus excavatum (Grand Canyon type), the asymmetric bar (n
= 97, 86.6%), parallel bar (n
= 79, 70.5%), and crest compression (n
= 13, 11.6%) techniques were used. The crane technique was employed for adult patients to elevate ossified and heavy chests, or for severe depressions of any age to facilitate the procedure (n
= 57, 50.9%).
To assess post-repair residual depression, asymmetry, and eccentricity, CT scan calculated indices were utilized. All pectus indices were decreased after repair: DI (pre 2.89 to post 1, p
< 0.01), AI (pre 1.11 to post 1.03, p
< 0.01), and EI (pre 1.69 to post 1, p
< 0.01).
Complication rates (37.9% vs 12.1%, p
< 0.01) and reoperation rate (5.6% vs 2.0%, p
= 0.031) were higher compared to general pectus excavatum repairs. Comparisons of individual complications are listed in Table 1
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Table 1 Comparison of complications and reoperation between extreme eccentric canal type (Grand Canyon type) and general pectus excavatum
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4. Discussions
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The minimally invasive repair technique introduced by Donald Nuss in 1997 started a new era for pectus excavatum surgical correction [6]. Over the past 10 years, many patients have benefited from this technique [7–9]. However, this new technique has been through a serious learning curve in the initial experiences of surgeons world-wide, mainly because of insufficient information on morphological diversity and lack of proper repair techniques to treat these varieties. Complications such as bar displacement or pneumothorax were frequent and others, including serious complications that led to fatal consequences, elicited a severe criticism. Having gained experience and developed some modified techniques, this minimally invasive procedure seems to be set up as a valuable armamentarium in the pectus surgery [7,9,10]
In spite of these advancements, there has been no insight on the various asymmetric pectus excavatum, and consequently no specific techniques for each element of morphology were developed. However, considering the large proportion of the asymmetry in the practice, this must be a significant obstacle on the road to establish this technique as a comprehensive procedure for pectus surgery. For that reason, we have been developing techniques for all varieties of pectus excavatum-related deformities, including diverse combinations of pectus excavatum and carinatum. The principal author (HJP) has created a morphological classification to facilitate surgical repair [1]. Principles of repair techniques by morphological type have also been established [4].
A typical characteristic of pectus excavatum is a wide variety of morphologic phenotype, as documented in other reports [11–13]. According to the author's observations, approximately 45% of patients undergoing repair are asymmetric, which includes various combinations of eccentricity and unbalance in pectus dysmorphology [1]. We first classified subtypes of asymmetry in the process of developing optimal techniques for each morphological entity (the morphology-tailored repair techniques) on the basis of minimally invasive repair-oriented approach. Later, a report from another group described morphologic variations of pectus excavatum; however, this does not categorize asymmetric subtypes systematically and the specific repair techniques for each variation were not offered [13].
The extreme eccentric canal type pectus excavatum (Grand Canyon type) is a distinctive subset of asymmetry, and is characterized by a long, canal-like eccentric excavation, where the depression lies longitudinally along the right sternal border (Type 2A3). The main depressed component is not the sternum but deformed costal cartilages. Malformed costal cartilages accompanying a rotated sternum differentiate the extreme eccentric type from classic pectus excavatum, which is presented as a midline xiphisternal depression (Figs. 1 and 2). Cartilages angulated in opposite directions (upward vs downward) at both parasternal area form an excavatum–carinatum complex (Fig. 2, Type 2C).
Compared to general pectus excavatum, this particular deformity affects more females (M:F = 2.3:1 vs 4:1 in general pectus excavatum). Young female adults are frequently affected and notably manifest ipsilateral breast hypoplasia on the side of the chest wall depression (Fig. 3). Frequent association with skeletal abnormalities such as spine deformity (scoliosis) is evident and under investigation. Future studies should include evaluating the genetic background associated with this set of disorders.
In the clinical setting, repair of the extreme eccentric canal type pectus excavatum (Grand Canyon type) is challenging. The degree of depression and asymmetry are usually too severe for conventional Nuss techniques. Consequently we have faced serious problems in our early experience, such as bar rotations, pneumothorax, hemothorax, and high reoperation rate (Table 1). Most of the major bar displacement (3/4, 75%) occurred in this morphologic subset. As a result, this subtype has been selected as a risk factor for complications [10] and this obstacle has driven us to create techniques to overcome it.
In the repair of this particular morphology, in addition to relief of intrathoracic organ compression by the main depression at the mid-chest, there are several points to be considered. Most of all, an extreme degree of asymmetry necessitates special attention for post-repair symmetry. The bar shaping needs to be accordingly tailored not only to the degree of depression but also to the degree of eccentricity. Other problems of this unique morphology include the upper level chest wall depression and breast hypoplasia. Unsightly infraclavicular chest depression affects young females for cosmetic and emotional reasons and an associated hypoplastic breast can compound the problem.
In Grand Canyon pectus excavatum repair, the asymmetric bar technique, using an asymmetrically-shaped bar according to degree of eccentricity and depression can elevate a selective point without influencing non depressed areas. For repair of complex morphology, the final bar shape follows the chest wall topography by the ‘terrain contour matching’ (TERCOM) principle [4]. The TERCOM principle designates a different bar shape for each morphological subset. Briefly, a protruded ridge is reflected as a notch in the bar at the corresponding position and to an equivalent degree. Therefore, the finalized bar shape is a mirror image of chest wall undulations. The portion of the bar that matches the excavation is to elevate the depression selectively and the notch that matches the protrusion is to avoid aggravating the protruding ridge. Certain cases with significant protruding ridge (pectus excavatum–carinatum complex) can be effectively managed by crest compression, as previously described [1,4].
Results assessed by new pectus indices, developed by the primary authors (HJP), indicate effective repair. All our results were decreased towards 1. A DI of 1 represents no depression. Likewise, an EI of 1 indicates no residual depression. An AI of 1, a hallmark of post-repair symmetry, reflects correction to symmetry.
In conclusion, the Grand Canyon type of pectus excavatum represents a distinctive morphology, relative female gender preponderance, and association with other skeletal abnormalities and breast hypoplasia. The precise understanding of morphological features and proper repair according to the precise chest wall morphological elements (TERCOM) seems effective in relieving the depression and achieving symmetric configuration.
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Footnotes
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Presented at the 21st Annual Meeting of the European Association for Cardio-thoracic Surgery, Geneva, Switzerland, September 16–19, 2007.
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References
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Abstract
1. Introduction
