The Diaphragm and Congenital Diaphragmatic Hernia

The diaphragm is a commonly misunderstood body part. Those who sing appreciate it purely due to their ability to control the diaphragm to enhance their singing. However, its real purpose in the human body is more important than that. The diaphragm plays such a crucial role in everyday life to the extent that one cannot survive without it. In this paper we will consider the role of the diaphragm through its anatomy and physiology. We will then review a congenital birth defect known as Congenital Diaphragmatic Hernia (CDH) and how it changes the anatomy and physiology of the body. We will also look at current research and prognosis of the disease in an effort to gain a better understanding of this often-fatal defect.

The diaphragm is located almost centrally in the body. It is a continuous sheet of muscle that spreads across the bottom of the rib cage creating a divide between the thoracic cavity and the abdominal cavity. As detailed in the text Gray’s Anatomy, the convex upper surface of the diaphragm faces the thorax and forms the bottom of the thoracic cavity. The concave inferior surface is pointed towards the abdomen and is mostly covered in peritoneum forming the superior part of the abdominal cavity. The right side of the diaphragm is superior to the right lobe of the liver, the right kidney, and the right adrenal gland. The left side of the diaphragm lays over the left lobe of the liver, the fundus of the stomach, the spleen, the left kidney, and the left adrenal gland (Gray, 2005).

The diaphragm has three parts, which are based on the regions of attachment of its outer surfaces. They are known as the sternal, the costal and the lumbar. Again, Gray’s Anatomy goes into great detail but in general, the sternal part is formed at the xiphoid process of the sternum. The costal part begins at the internal surfaces of the lower six costal cartilages and their ribs. The lumbar part is connected by the medial and lateral arcuate ligaments and from the lumbar vertebrae by the right and left crura. The muscle fibers of the diaphragm unite more anterior yet still somewhat centrally and form a thin, long aponeurosis called the central tendon. This results in the posterior muscle fibers being longer than the fibers near the xiphoid process. There are three large openings in the diaphragm, which permit the aorta, esophagus, and the inferior vena cava to pass through as well as a number of smaller ones that allow for other structures to pass between the thorax and abdomen. The diaphragm receives its only motor supply from the phrenic nerve, which reaches the diaphragm mainly through the 3rd, 4th and 5th cervical nerve roots. The peripheral portions of the diaphragm send sensory afferents through the intercostal nerves through T5-T11 and sub costal nerves at T12 (Gray, 2005). The overall shape of the diaphragm is influenced by its points of attachment as well as the position of it’s inferior organs in the abdominal cavity. For example, the liver nests beneath the right cupola and the stomach fits right in under the left cupola.

The diaphragm’s main function is respiration. According to Marieb and Hoehn, in its relaxed state the diaphragm is dome shaped. During inhalation the diaphragm muscle contracts by moving downward (via the central tendon) and flattens. The external intercostals muscles are also contracted which lifts the rib cage and pulls the sternum upward. In turn these actions increase the volume of the thoracic cavity. As this happens, the lungs are stretched and the intrapulmonary volume increases as well creating a change in pressure. Air is thus drawn into the lungs through the trachea by suction created by the decrease in pressure. When the diaphragm relaxes and the rib cage descends, air is exhaled by elastic recoil of the lungs. This is due to the thoracic and intrapulmonary volumes, which decrease, compressing the alveoli and raising pulmonary pressure. Air is thus forced out of the lungs following the pressure gradient. The diaphragm also serves other functions such as expelling feces, urine, or a baby from the body. It can also prevent acid reflux by exerting pressure on the esophagus as it passes through the esophageal hiatus (Marieb & Hoehn, 2011). Now that the anatomy and physiology of the diaphragm has been established we can examine what happens in the life-threatening event of a congenital diaphragmatic hernia. Congenital Diaphragmatic Hernia is a birth defect characterized by an opening in the diaphragm resulting from the pleuroperitoneal membrane not developing properly. This causes some of the organs of the abdomen to move up into the chest cavity, which hinders the growth and development of the fetal thoracic organs. According to Skarsgard et al., by the fifth week of gestation, the septum transversum forms an incomplete partition between the thoracic and abdominopelvic cavities by fusing with mesentery of the esophagus. At the same time the pleuroperitoneal membranes fuse with the mesentery of the esophagus and the septum transversum creating the pleuroperitoneal canals. The pleuroperitoneal canals remain open until the end of the sixth week. At about this time, the canals are infiltrated by pleuroperitoneal membrane growth and medial fusion with the septum transversum to form what ultimately becomes a muscularized diaphragm. The pleural cavities continue to expand between the ninth and twelfth weeks, as muscle from the lateral body wall fuses to the diaphragm to form the muscular rim (Skarsgard et al., 1999). So basically a diaphragmatic hernia is created by the failure of one of the pleuroperitoneal membranes to fuse. Skarsgard notes “if the pleuroperitoneal canal remains open when the intestines return to the abdomen from the umbilical cord during the tenth week, the abdominal viscera move freely into the thoracic cavity. If the pleuroperitoneal canal closes but fails to become muscularized, a hernia with a sac results, as is seen in 10% to 15% of patients who have CDH” (Skarsgard & Harrison, 1999).

Congenital diaphragmatic hernias are classified by their position on the diaphragm. There are two types worth mentioning which are the Foramen of Bochdalek and the Foramen of Morgagni. A Bochdalek hernia is a defect in the side or back of the diaphragm (posterolateral) and accounts for up to 90 percent of congenital diaphragmatic hernias. In a Bochdalek hernia the hole in the diaphragm allows for the stomach, liver, and/or intestines to become trapped in the chest cavity. Skarsgard reveals that the Bochdalek defect occurs five times more frequently on the left side than the right. It cites that this is probably because of earlier closure of the right pleuroperitoneal canal (Skarsgard & Harrison, 1999). According to CHOP, babies with the Bochdalek type of diaphragmatic hernia are more likely to have another birth defect such as a congenital heart defect and between 5 to 16 percent have a chromosomal abnormality (CHOP, 2011). A Morgagni hernia is also referred to as a subcostosternal hernia and is a defect involving the anterior part of the diaphragm lateral to the xiphoid process. According to Gray, this type of CDH, accounts for about 2 percent of cases, is often asymptomatic and is less likely to cause severe symptoms at birth (Gray, 2005). There are other types of diaphragmatic hernia, such as those affecting the central region of the diaphragm, or those in which the diaphragm muscle is absent with only a thin membrane in its place, but these are even less common.

As mentioned, in congenital diaphragmatic hernia the abdominal contents herniated, or spill into the thorax and compress the lung. With the heart, lungs and the addition of abdominal organs taking up space in the chest cavity, the lungs do not have enough space to develop properly. The most significant change this leads to is pulmonary hypoplasia, which is the underdevelopment of the lungs and results in a reduced number of alveoli per area of lung tissue. “The severity of congenital diaphragmatic hernia is largely determined by the position of the liver and the lung-to-head circumference ratio (LHR). Outcomes are generally better in cases where the liver remains down in the abdomen and the LHR is higher” (CHOP, 2011). Understandably the larger the amount of herniation there is, the greater the severity of pulmonary hypoplasia. Also, the earlier the occurrence of herniation, the lesser developed the abdominal cavity will be.

As listed on the Children’s Hospital Boston website, once born, it is difficult for a baby with CDH to breathe due to the fact that there are fewer air sacs than normal and the air sacs that are present are only able to partially fill with air. Also, the air sacs deflate easily due to a lack of surfactant. The intestines also may not develop properly, especially if they are not receiving enough blood supply while they are developing (Children’s Hospital Boston, 2011). Observable symptoms with the Bochdalek form include difficulty breathing, fast breathing, fast heart rate, cyanosis, abnormal chest development, and a concave abdomen. “In 5 to 10 percent of affected individuals, signs and symptoms of congenital diaphragmatic hernia appear later in life and may include breathing problems or abdominal pain from protrusion of the intestine into the chest cavity” (Genetics Home Reference, 2011).

Congenital Diaphragmatic Hernia is not one of the common birth defect about which we are used to hearing. As Smith et al. conclude in their study, “Congenital diaphragmatic hernia is a common problem in pediatric surgical practice, with an incidence of 1:2500” (Smith et al., 2002). However, as noted in an evaluation study, “The true incidence of CDH is still difficult to estimate because of the high incidence of hidden mortality of CDH” (Grisaru-Granovsky et al., 2009). So whereas the statistics show a 1:2500 incidence of CHD the numbers are most likely significantly higher due to the high number of fetuses that die before birth due to the severity of the defect. This same study also states that the survival rate for CHD is between 50-70 percent, which varies due to geographic location and whether or not the defect is spotted prenatally or after birth (Grisaru-Granovsky et al., 2009). This study gives a slightly higher survival rate than others, which place it closer to the 50 percent. Whichever the case, more than 50% of cases with CDH are detected prenatally by ultrasound examination. If caught prior to birth, more can be done to help the lungs grow during gestation due to advances in medicine, which can mean the difference between survival and death.

The belief of researchers is that there are many factors involved in diaphragmatic hernia. It is thought that multiple genes from both parents, as well as a number of environmental factors contribute to diaphragmatic hernia. According to Genetics Home Reference, the condition appears as a feature of a syndrome in 10 to 15 percent of affected individuals. Among mentioned syndromes is Donnai-Barrow syndrome, Fryns syndrome, and Pallister-Killian mosaic syndrome. “More than 80 percent of individuals with congenital diaphragmatic hernia have no known genetic syndrome or detectable chromosome abnormality” (Genetics Home Reference, 2011). As reported by CHOP, in cases where it is the only health problem in a baby, the chance for diaphragmatic hernia to happen again in a future pregnancy is two percent (CHOP, 2011).

Congenital Diaphragmatic Hernia is life-threatening due to pulmonary hypoplasia and associated pulmonary hypertension. “Hypoplastic lung development is the leading contributor to its 30-50% mortality rate” (Smith et al., 2002). In cases where the lungs are severely underdeveloped, ECMO is commonly used to help stabilize the baby’s condition. Once stabilized, the diaphragmatic hernia is repaired by surgery. During surgery, the stomach, intestine, and other abdominal organs are moved from the chest cavity back to the abdominal cavity and the hole in the diaphragm is repaired. While the hernia is repaired, the lungs still remain underdeveloped and usually will need to have breathing support after the operation for a period up to a year or more. Other complications include chronic lung disease, gastro esophageal reflux, and failure to thrive as well as developmental delays. “Postnatal intensive respiratory supportive therapy and innovative surgical techniques within specialized tertiary centers has had a major impact on survival of babies with CDH” (Grisaru-Granovsky et al., 2009). Assuming the baby survives the surgery and the lungs are not critically underdeveloped, with the proper care, the lungs will continue to grow in the thoracic cavity. “Children can experience compensatory lung growth until age 8 or 9” (CHOP, 2011).

Prognosis for patients with CDH is variable. As mentioned by Gaxiola et al., early diagnosis and a better understanding of this disease is necessary to improve outcome (Gaxiola et al., 2009). Also, it has been found that transport of CDH patients is associated with increased mortality and an increase in the need for ECMO. The study by Aly et al. supports regionalization of care, and favors maternal transport before delivery of CDH newborns to improve outcomes (Aly et al., 2010). A lot is still unknown about this defect and life expectancy of survivors cannot be determined due to the “newness” of current disease management.

In conclusion, the diaphragm is a muscle that plays an important role in respiration by initiating inspiration. It also serves as a divide between the thoracic and abdominal cavities. Failure of the diaphragm to properly fuse in-utero results in herniation of the abdominal contents into the thoracic cavity. This hinders the growth and development of the fetal lungs leading to hypoplasia and hypertension. There is a high mortality rate for CDH, which is directly correlated to the extent of the underdevelopment of the lungs. It is vital that diagnosis be made as early as possible and that all necessary care be available at the site of birth. With the proper care babies with CDH can survive but will need to be monitored by a physician for life, as they will have significant risk for future complications.

Works Cited
Aly, H., Bianco-Batlles, D., Mohamed, M. A., & Hammad, T. A. (2010). Mortality in infants with congenital diaphragmatic hernia: A study of the United States national database. Journal of Perinatology, 30 (8), 553-557. doi:10.1038/jp.2009.194.
Children's Hospital Boston. (2011, Dec 5). Congenital diaphragmatic hernia. Ret. from Childrens Hospital Boston: http://www.childrenshospital.org/az/Site476/mainpageS476P1.html
Children's Hospital of Philadelphia (CHOP). (2011, Dec.01). Center for fetal diagnosis and treatment. Ret. from Childrens Hospital of Philadelphia: http://www.chop.edu/service/fetal-diagnosiss-and-treatment/fetal-diagnoses/congenital-diaphragmatic-hernia-cdh.html
Gaxiola, A., Varon, J., & Valladolid, G. (2009). Congenital diaphragmatic hernia: An overview of the etiology and current management. Acta Paediatrica , 98 (4), 621-627. doi:10.1111/j.1651-2227.2008.01212.x.
Genetics Home Reference. (2011, January). Congenital diaphragmatic hernia. Ret. Dec 01, 2011, from Genetics Home Reference: http://ghr.nlm.nih.gov/condition/congenital-diaphragmatic-hernia
Gray, Henry. (2005). Grays Anatomy: The Anatomical Basis of Clinical Practice. Susan Standring, (Ed.). (39th ed.). (pp. 1081-1086). Edinburgh, London: Elsevier Churchill Livingston. (Original work published 1859).
Grisaru-Granovsky, S., Rabinowitz, R., Ioscovich, A., Elstein, D., & Schimmel, M. S. (2009). Congenital diaphragmatic hernia: review of the literature in reflection of unresolved dilemmas. Acta Paediatrica , 98 (12), 1874-1881. doi:10.1111/j.1651-2227.2009.01436.x.
Marieb, E. N., & Hoehn, K. (2011). Anatomy and Physiology (4th ed.). (pp. 298, 716-718). Boston, MA: Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
Skarsgard, E. D., & Harrison, M. R. (1999). Congenital diaphragmatic hernia: The surgeon’s perspective. Pediatrics in Review, 20 (10), 71-78. doi:10.1542/pir.20-10-e71.
Smith, N., Jesudason, E., & Losty, P. (2002). Congenital diaphragmatic hernia. Pediatric Respiratory Review , 3, 339-348.