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|Classification and external resources|
An example of a severe case.
|Classification and external resources|
An example of a severe case.
Pectus excavatum (a Latin term meaning hollowed chest) is the most common congenital deformity of the anterior wall of the chest, in which several ribs and the sternum grow abnormally. This produces a caved-in or sunken appearance of the chest. It can either be present at birth or not develop until puberty.
Pectus excavatum is sometimes considered to be cosmetic; however, depending on the severity, it can impair cardiac and respiratory function and cause pain in the chest and back. People with the condition may experience negative psychosocial effects, and avoid activities that expose the chest.
Researchers are currently unsure as to the actual cause of pectus excavatum but hypothesize genetic defect. Approximately 37% of individuals with pectus excavatum have a first degree family member with the condition. Physiologically, increased pressure in utero, rickets and increased traction on the sternum due to abnormalities of the diaphragm have been postulated as specific mechanisms. Pectus excavatum is also a relatively common symptom of Marfan syndrome. Many children with spinal muscular atrophy develop pectus excavatum due to the diaphragmatic breathing that is common with the disease. Pectus excavatum also occurs in about 1% of persons diagnosed with Celiac disease for unknown reasons.
Because the heart is located behind the sternum, and because individuals with pectus excavatum have been shown to have visible deformities of the heart (seen both on radiological imaging and after autopsies), it has been hypothesized that there is impairment of function of the cardiovascular system in individuals with pectus excavatum. While some studies have demonstrated decreased cardiovascular function in pectus excavatum, there has been no consensus reached based on newer physiological tests (such as echocardiography) of the presence or degree of impairment in cardiovascular function in people with pectus excavatum. Similarly, there is no consensus on the degree of functional improvement after corrective surgery.
Pectus excavatum is initially suspected from visual examination of the anterior chest. Auscultation of the chest can reveal displaced heart beat and valve prolapse. There can be a heart murmur occurring during systole caused by proximity between the sternum and the pulmonary artery. Lung sounds are usually clear yet diminished due to decreased base lung capacity.
Many scales have been developed to determine the degree of deformity in the chest wall. Most of these are variants on the distance between the sternum and the spine. One such index is the Backer ratio which grades severity of deformity based on the ratio between the diameter of the vertebral body nearest to xiphosternal junction and the distance between the xiphosternal junction and the nearest vertebral body. More recently the Haller index has been used based on CT scan measurements. An index over 3.25 is often defined as severe. The Haller index is the ratio between the horizontal distance of the inside of the ribcage and the shortest distance between the vertebrae and sternum.
Chest x-rays are also useful in the diagnosis. The chest x-ray in pectus excavatum can show an opacity in the right lung area that can be mistaken for an infiltrate (such as that seen with pneumonia). Some studies also suggest that the Haller index can be calculated based on chest x-ray as opposed to CT scanning in individuals who have no limitation in their function.
Pectus excavatum is differentiated from other disorders by a series of elimination of signs and symptoms. Pectus carinatum is excluded by the simple observation of a collapsing of the sternum rather than a protrusion. Kyphoscoliosis is excluded by diagnostic imaging of the spine, where in pectus excavatum the spine usually appears normal in structure.
Treatment for pectus excavatum can involve either invasive or non-invasive techniques or a combination of both. Before an operation proceeds several tests are usually to be performed. These include, but are not limited to, a CT scan, pulmonary function tests, and cardiology exams (such as auscultation and ECGs). After a CT scan is taken the Haller index is measured. The patient's Haller is calculated by obtaining the ratio of the transverse diameter (the horizontal distance of the inside of the ribcage) and the anteroposterior diameter (the shortest distance between the vertebrae and sternum). A Haller Index of greater than 3.25 is generally considered severe, while normal chest has an index of 2.5. The cardiopulmonary tests are used to determine the lung capacity and to check for heart murmurs.
Surgical correction has been shown to repair any functional symptoms that may occur in the condition, such as respiratory problems or heart murmurs, provided that permanent damage has not already arisen from an extremely severe case.
The Ravitch technique is an invasive surgery that was introduced in 1949, and developed in the 1950s to treat the condition. This procedure involves creating an incision along the chest through which the cartilage is removed and the sternum detached. A small bar is then inserted underneath the sternum to hold it up in the desired position. The bar is left implanted until the cartilage grows back, typically about 6 months. The bar is subsequently removed in a simple out-patient procedure. The Ravitch technique is not widely practiced because it is so invasive. It is often used in older patients, where the sternum has calcified, when the deformity is asymmetrical, or when the less invasive Nuss procedure has proven unsuccessful.
Since then, Dr. Donald Nuss, based at Children's Hospital of The King's Daughters (CHKD) in Norfolk, Virginia, has developed a technique that is minimally invasive. The Nuss procedure involves slipping in one or more concave steel bars into the chest, underneath the sternum. The bar is flipped to a convex position so as to push outward on the sternum, correcting the deformity. The bar usually stays in the body for about two years, although many surgeons are now moving toward leaving them in for up to five years. When the bones have solidified into place, the bar is removed through outpatient surgery.
A relatively new alternative to surgery is the vacuum bell. It consists of a bowl shaped device which fits over the caved-in area; the air is then removed by the use of a hand pump. The vacuum created by this lifts the sternum upwards, lessening the severity of the deformity. As it is such a recent device there is currently no information as to whether it is effective in the long term.
The cosmetic appearance of pectus excavatum can be treated with a dermal filler called Bio-Alcamid. However, as this does nothing to alleviate the actual deformity it will not prevent any physiological symptoms caused by the condition.
There are also prosthetic implants available to fill the depressed area. Solid silicone implants have been successfully used for many years with acceptable results in some cases. More recently a porex implant has been used which is a similar material used to replace skull in brain surgery and severe head injuries.
The magnetic mini-mover procedure (3MP) is a technique used to correct pectus excavatum by using two magnets to realign the sternum with the rest of the chest and ribcage. One magnet is inserted 1 cm into the patients body on the lower end of the sternum, the other is placed externally onto a custom fitted brace. These two magnets generate around 0.04 tesla (T) in order to slowly move the sternum outwards over a number of years. The maximum magnetic field that can be applied to the body safely is around 4 T, making this technique safe from a magnetic viewpoint. The 3MP technique's main advantages are that it is more cost-effective than major surgical approaches such as the Nuss procedure and it is considerably less painful postoperatively. One potential adverse effect of 3MP is inactivation of implanted devices such as an artificial pacemaker. Since the 3MP is still in a trial period it is unknown whether long term wearing of the magnet will affect the skin or other vital organs.
Pectus excavatum occurs in an estimated 1 in 150-1000 births, with male predominance (male-to-female ratio of 3:1). Occurrences of the condition in family members have been reported in 35% to 45% of cases.
Pectus excavatum is also known to occur in animals, e.g. the Munchkin breed of cat. Some procedures used to treat the condition in animals have not been used in humans, such as the use of a cast with sutures wrapped around the sternum and the use of internal and external splints. These techniques are generally used in immature animals with flexible cartilage.
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