Embryology of diaphragm

diaphragm embryology

The diaphragm is formed by the fusion of the following embryonic structures

1)      Septum transversum

2)      Pleuroperitoneal membranes

3)      Dorsal mesentery of esophagus

4)      Dorsal and dorsolateral body wall

 

The intraembryonic coelom is initially a single space which is later divided into pericardial, peritoneal and pleural space. The diaphragm separates the thoracic cavity from the peritoneal cavity (1). The septum transversum which is a mesodermal layer in the vicinity of the developing liver is established in the 4th week of intrauterine life (2). The septum transversum does not completely separate the thoracic and the abdominal cavities but leaves larges defects called the pleuroperitoneal canals on both sides. The pleuroperitoneal membrane forms over the canals and closes the connection between the thoracic and the abdominal cavities usually around the 8th week (3). Later myoblasts migrate over it to add muscular strength to the diaphragm (4). The right pleuroperitoneal canal closes earlier than the left. Hence hernia is relatively uncommon in the right side. 

During the initial development, which begins at the 4th week of intrauterine life, the diaphragm is at a higher (cervical) level and develops from the 3 to 5th cervical myotomes and is innervated by the phrenic nerve (C3-C5). It starts descending in the 6th week of intrauterine life and the final adult level of L1 is reached by the 8th week of intrauterine life (5). The development of diaphragm continues upto the 3rd month of intrauterine life. Thus the adult diaphragm has its embryologic origin in the cervical level bringing with itself the motor and the sensory innervations from the cervical level through the phrenic nerve (C3-C5).

During the 10th week of the intrauterine life the intestines return from the yolk sac to the abdominal cavity and at 12 weeks they rotate to become fixed (6).  Hence a delay in the closure of the pleuroperitoneal canals or the early return of the intestines to the abdominal cavity is likely to result in congenital diaphragmatic hernia(7). Congenital short esophagus is related to the early return of the intestines to the abdominal cavity and late closure of thepleuroperitoneal canal. The muscle fibres migrate from the 3,4,5th cervical myotomes.  The lack of ingrowth  muscle fibres migrating from the cervical myotomes can occur in eventration of diaphragm.

Traditionally it is believed that the septum transversum becomes the central tendon of the adult diaphragm. The dorsal mesentry becomes the crura of the diaphragm, while the dorsal and dorsolateral wall forms the peripheral portions of the diaphragm. This view has been challenged in a recent study (8). Several aspects regarding the embryology of diaphragm are still poorly understood (9).  

 

References

1.            Dudek RW, Fix JD. Embryology. Lippincott Williams & Wilkins; 2004.

2.            Skarsgard ED, Harrison MR. Congenital Diaphragmatic Hernia: The Surgeon’s Perspective [Internet]. Pediatrics in Review 1999 Oct;20(10):e71 -e78.[cited 2011 Dec 16] Available from: http://pedsinreview.aappublications.org/content/20/10/e71.short

3.            Kluth D, Tander B, Ekesparre M, Tibboel D, Lambrecht W. Congenital diaphragmatic hernia: the impact of embryological studies [Internet]. Pediatric Surgery International 1995 Jan;10(1)[cited 2011 Dec 16] Available from: http://www.springerlink.com/content/uq874225x25r244v/

4.            Parikh D. Pediatric Thoracic Surgery. Springer; 2009.

5.            Shields TW. General Thoracic Surgery. Lippincott Williams & Wilkins; 2009.

6.            Palanivelu C. Operative Manual of Laparoscopic Hernia Surgery. Jaypee Brothers Publishers; [date unknown].

7.            Kluth D, Keijzer R, Hertl M, Tibboel D. Embryology of congenital diaphragmatic hernia [Internet]. Semin. Pediatr. Surg. 1996 Nov;5(4):224-233.[cited 2011 Dec 14] Available from: http://www.ncbi.nlm.nih.gov/pubmed/8936651

8.            Babiuk RP, Zhang W, Clugston R, Allan DW, Greer JJ. Embryological origins and development of the rat diaphragm [Internet]. The Journal of Comparative Neurology 2003 Jan;455(4):477-487.[cited 2011 Dec 14] Available from:http://onlinelibrary.wiley.com/doi/10.1002/cne.10503/abstract

9.            Clugston RD, Greer JJ. Diaphragm development and congenital diaphragmatic hernia [Internet]. Seminars in Pediatric Surgery 2007 May;16(2):94-100.[cited 2011 Dec 14] Available from: http://www.sciencedirect.com/science/article/pii/S1055858607000054

 

 

Date: 
Friday, November 14, 2014