Pectus Excavatum

Etiology

Several hypotheses exists regarding the underlying etiology that results in pectus excavatum.  The funnel - formed chest has been attributed to a weakness and abnormal flexibility of the sternum, overgrowth of the ribs, and developmental failure of the bony thorax.[4]  Regardless of the mechanism, the result is depression and dorsal deviation of the sternum and adjacent ribs or costal cartilages of varying degrees. Although a specific genetic defect has not been identified, a genetic predisposition is supported by the presence of a positive family history in more than 40% of cases.  

Epidemiology

Reported prevalence has been 1/300 to 1/1000 live births; with a 5:1male to female ratio.[5] Pectus excavatum constitutes 90% of all chest wall deformities.  Most defects are appreciated within the first year of life, with severe deformities present at birth.  The funnel - formed chest tends to become more pronounced during the pubertal growth spurt.[6]  Pectus excavatum may present as an isolated anomaly or as a part of a multitude of congenital disorders. Amongst these clinical syndromes, connective tissue disorders are rarely (less than 1%) associated with pectus excavatum.[7]

History and Physical

The presenting patient is commonly a thin, tall male that appears to be slouching, and thoracic scoliosis may also be appreciated.  Sternal depression and rotation may depress the heart, causing a slew of cardiopulmonary signs and symptoms, including exercise intolerance. An audible murmur can be attributed to a defective mitral valve (i.e., prolapse, regurgitation).  Exercise intolerance, though its exact cause is unclear, is one of the most common presenting complaints. Additionally, the psychological impact on patients can be significant, especially during the adolescent period. 

Evaluation

The lateral view of the chest radiograph clearly demonstrates the sternal defect.  Additional imaging studies may reveal displaced vertebral bodies and varying degrees of scoliosis.  Patients with mild pectus excavatum may have minimal or no symptoms; however, cardiopulmonary evaluation to establish a baseline as well as assess for progression is warranted every one to two years.[3][8][9][4][5]  Complete evaluation includes chest radiograph, pulmonary function testing (spirometry, plethysmography, respiratory muscle strength assessment), electrocardiogram, and echocardiogram to assess for the secondary or associated anomalies of a clinical syndrome. Pulmonary function testing may reveal obstructive or restrictive lung disease in older patients, as well as air trapping with increase in residual volume (RV). The air trapping may be caused by a mechanical disadvantage impairing respiratory muscle function. The presence of axis deviation on electrocardiogram (EKG) suggests leftward cardiac deviation.  Arrhythmias in the form of first-degree heart block, right bundle branch block, and Wolff–Parkinson–White occur in 16% in this patient cohort.  Cardiopulmonary exercise testing may reveal cardiopulmonary limitation not appreciated in a resting state.  Echocardiography should be performed to assess for cardiac compression, valvular defects, and myocardial function.  Patient with pectus excavatum may have a cardiac deviation to the left and conduction defects.[4]

The Haller index (HI) is the standard upon which to quantify the severity of a pectus excavatum deformity.  It is defined as the ratio of the transverse diameter and anteroposterior diameter.  The measurements are obtained from computed tomography (CT) scan; normal value is 2.5 or less.  Measurement above 3.2 are considered severe.[5]  Patients with a Haller Index of greater than 7 are four times more likely to have a restrictive pattern on pulmonary function testing. [10] MRI including breath-hold MRI has been used for the morphologic assessment of thoracic deformities for the preoperative assessment of pectus excavatum. A better insight in the functioning of lungs of the patients with pectus excavatum deformity may be obtained using recently introduced techniques such as oculo-electronic plethysmography (OEP),which can show that the depressed portion of the sternum and adjacent chest wall do not move with respiration and there is a reduction in lung volume.[11]

Treatment / Management

Early surgical correction of pectus excavatum was based on the aggressive resection and chest wall reconstruction performed for asphyxiating thoracic dystrophy (Jeune's syndrome). The current trend is to delay the repair until pubertal growth, and the technique is modified to perform limited cartilage resection. Impaired cardiopulmonary function, not cosmesis, is the most common indication for surgical correction.  It is pertinent that surgical repair occur after the child's pubertal growth spurt.[12][13][14]

The first documented surgical repair of pectus excavatum was performed by Ravitch in 1949.  Based on the aggressive chest wall resection used to manage asphyxiating thoracic dystrophy (Jeune's syndrome), Ravitch performed a subperichondrial resection of all deformed costal cartilages and the xiphoid process, along with a transverse sternotomy.[15]  Rehbein and Wernicke modified the procedure six years later, implanting a variety of metallic bars  longitudinally and/or transversely to stabilize the sternum.[16]  This repair can be approached via a median longitudinal incision long the sternum or a submammary skin incision, which is preferable in female patients.  Patients return one year later for removal of the implanted bars.  Modernization of the Ravitch procedure utilizes orthopedic metal plates and screws. These devices can be modelled specifically to the patient's defect, and don't require a second operative procedure for hardware removal.  

The minimally invasive technique described by Nuss and Kelly involves inserting a metal bar under the sternum at the most depressed zone and most everted costal line on both sides of the chest.[17]  The retrosternal bar in placed thoracoscopically, via approximately 3cm incisions along the mid-axillary lines.  Skin flaps are raised and tennelled up to the previously identified most-everted intercostal spaces.  A metal introducer is guided under thoracoscopic guidance to dissect a retrosternal plane between the anterior pericardium and the posterior sternal table.  The guide is exteriorized through the left sided incision, in order to be tied to titanium rod and subsequently withdrawn.  The retrosternal curve var is rotated such that the concave side is directed backwards, thus pushing the sternum ventrally.  Metallic stabilizers and/or subperiostal cable wires are used to prevent migration of the bar.  The initial stabilization period was 2 years; however, it is now more common to leave the bar in situ for 3 years.(B3)

Additional modifications to both the Ravitch and Nuss procedures have been described.  The Leonard modification to Ravitch's procedure entails excision of the lower costal cartilage, leaving the perichondirum in place, after mobilization of the pectoralis muscles.[18]  Robicsek describes posterior stabilization of the sternum after the transverse osteotomy with fixation of a piece of Marlex mesh to the remnants of costal cartilage.[19] Minimal cartilage resection defines Erlangen's adaptation of the Nuss procedure,[20] with transternal implantation of an elastic metal bar through stitch incisions.  Intraoperative tensiometry is utilized to minimize the cartilage excision.  The magnetic mini-procedure employs magnetic forces between a sternal magnet and another on a prescribed brace worn by the patient to pull the sternum anteriorly.[21] This modification described by Lacquet is the only technique that avoids the use of prosthetic material, correcting the defect with a sternochondroplasty.  This procedure appears to offer results superior to the Nuss procedure for asymmetric defects.  (B3)

The application of negative pressure to the thorax offers a non-surgical alternative to pectus excavatum.[22]  A vacuum bell is applied to the chest wall defect and negative pressure applied by the patient via a handpump.  While long term results are lacking, this may be a viable option for the management of less severe defects in the future.  Additionally, this therapy would be applicable in younger symptomatic patients, in which prepubertal surgical correction is not desired.

Differential Diagnosis

• Ehlers-Danlos syndrome

• Marfan syndrome

• Noonan syndrome

• Scoliosis

Complications

Minor pectus excavatum defects are usually asymptomatic, thus without complications.  More severe defects can, however, negatively impact cardiopulmonary function, presenting with variety of symptoms:

• chest pain
• fatigue
• exertional dyspnea
• recurrent respiratory tract infections
• asthma
• palpitations
• heart murmur (mitral regurgitation)
• arrythmia
• syncope

Complications are more commonly appreciated in patients who undergo surgical correction of the defect: 

• migration of the sternal bar
• infection
• pneumothorax
• bleeding
• cardiac laceration
• chronic pain
• recurrence

Overall morbidity and length of stay are comparable for Ravitch and Nuss procedures, according to a recent meta-analysis.[23] However, the incidence of postoperative hemothorax, pneumothorax, and return to OR rates are higher with the Nuss procedure.  The comparison done by Antonoff et al included the Ravitch, Nuss, and Leonard procedures.  The analysis clearly demontrated increased LOS, costs, narcotic use, and complications with the Nuss cohort.[24]  Subjectively, the Nuss and Ravitch procedures appear to be comparable, based on similar health-related quality-of-life (HRQL) outcomes.[25]