111 2 3 4 4 5 6 The Anatomy and Physiology of 7 8 the Diaphragm 9 1011 George R. Harrison 1 2 3 4 5 6 7 8 9 2011 laterally, the ventral ends and costal cartilages 1 Aims of the seventh to twelfth ribs, the transverse 2 processes of the first lumbar vertebra, and the 3 To describe development, anatomy and bodies and symphyses of the first three lumbar 4 physiology of the diaphragm. vertebrae. As the periphery of the diaphragm is 5 attached to the thoracic outlet anteriorly and 6 laterally, and beyond it posteriorly, it will follow 7 Anatomy that the anterior portion of the diaphragm will 8 be shorter than the lateral and posterior parts. 9 The Shape of the Diaphragm The presence of the viscera in the thorax and 3011 abdomen causes the part of the diaphragm sep- 1 The diaphragm is a musculo-fibrous sheet sep- arating them to be roughly horizontal, but will 2 arating the thorax and the abdomen. It takes the determine the shape of the unstressed dome. 3 shape of an elliptical cylindroid capped with a This may be considered as a separate zone from 4 dome [1]. This short description of the shape of the other part of the diaphragm, and will be 5 the diaphragm is not adequate to explain the referred to as the diaphragmatic zone. The other 6 way in which the structure and function are part of the diaphragm will be referred to as the 7 related, and a further expansion of this descrip- apposition zone, because it assumes a roughly 8 tion is necessary. The use of the word dome in vertical direction. It is also the area through 9 itself introduces a degree of inaccuracy, as it which the rib cage is apposed to the abdominal 4011 gives the impression that there is a curved struc- contents and thus exposed to abdominal pres- 1 ture rising equally from the sides to a central sure (see below). 2 point, whereas a more accurate description is of 3 a pair of cupolas either side of a central plateau. Diaphragmatic Attachments 4 This elliptical shape is determined by the 5 thoracic outlet, which will also have an influence The sternal part is attached by two slips to the 6 upon the function of the diaphragm, as it will back of the xiphoid process, although these slips 7 determine the anatomical structure of it. This is may be absent (Figure 4.1). The costal part is 8 because the thoracic outlet is set obliquely to the attached to the internal surfaces of the lower 9 coronal plane, being superior anteriorly and six costal cartilages and their adjoining ribs, 5011 inferior posteriorly. the vertical fibres of the diaphragm interdigitat- 1 The skeletal attachments of the diaphragm ing with the horizontal fibres from the trans- 2 to the thoracic outlet commence at the xiphoid versi abdominis. The lumbar part is attached 311 process and symphysis centrally, and, moving to the aponeurotic medial and lateral arcuate 45 46 4 · UPPER GASTROINTESTINAL SURGERY parts of the upper two. As with the anterior lon- 1111 gitudinal ligament, the main area of attachment 2 is at the level of the intervertebral discs and 3 the adjacent margins of the vertebral bodies. 4 Between these attachments the upper lumbar 5 arteries separate the fibres from the bodies of 6 the vertebrae. The fibres ascend and run anteri- 7 orly to cross the aorta in a median arch, where 8 the tendinous margins converge to form the 9 median arcuate ligament. This ligament is often 1011 poorly defined, but when it occurs it is at the 1 level of the thoracolumbar disc. 2 The fibres of the crura continue in their 3 passage anteriorly and superiorly, but divide 4 Figure 4.1. The inner anterior surface of the diaphragm. into medial and lateral bundles. The lateral 5 (Reproduced with permission from Gluzel P, Similowski T, fibres continue laterally to reach the central 6 Chartrand-Lefebvre C et al. Diaphragm and chest wall: assess- ment of the inspiratory pump with MR imaging – preliminary tendon. The medial fibres from the right crus 7 observations. Radiology 2000;215:574–83. Copyright Radio- ascend to the left of the oesophageal opening. 8 logical Sciety of North America.) Sometimes a muscular fasciculus from the 9 medial side of the left crus crosses the aorta and 2011 runs obliquely through the fibres of the right 1 ligaments (lumbocostal arches) and to the crus towards the vena caval opening but does 2 upper three lumbar vertebrae by crura. The ster- not approach the oesophageal opening. The 3 nocostal and lumbar portions are distinct devel- right margin of the oesophageal opening is 4 opmentally and in 80% of the population are covered by the deeper medial right crural fibres. 5 separated by a hiatus in the muscular sheet – the From part of the right crus near the oesophageal 6 vertebrocostal trigone. This gap lies above the opening originates the suspensory muscle of the 7 twelfth rib so that the upper pole of the kidney duodenum, which goes to connective tissue near 8 is separated from the pleura by loose areolar the coeliac artery. Here it joins with a fibro- 9 tissue only. muscular band of non-striated muscle originat- 3011 The lateral arcuate ligament is a thickened ing along the third and fourth parts of the 1 band in the fascia of quadratus lumborum, duodenum and the duodenojejunal flexure. The 2 which arches across the muscle and is attached exact nature and function of this muscle has 3 medially to the front of the first transverse been the subject of discussion over many years, 4 process and laterally to the inferior margin of and will not be considered here. 5 the twelfth near its midpoint. 6 The medial arcuate ligament is a thickened The Central Tendon of the 7 band in the fascia covering psoas major. 8 Medially it blends with the lateral tendinous Diaphragm 9 margin of the corresponding crus and is thus All the muscular fibres converge upon the 4011 attached to the side of the first or second lumbar central tendon of the diaphragm (Figure 4.2). 1 vertebrae. Laterally it is attached to the front The central tendon is a thin, strong aponeuro- 2 of the first lumbar transverse process at the sis of interwoven collagen fibres, with its ante- 3 lateral margin of psoas. The arcuate ligaments rior margin closer to the front of the diaphragm. 4 allow the contraction of quadratus lumborum This results in the longer fibres being lateral and 5 and psoas to occur without interfering with posterior. The longest fibres of the diaphragm 6 diaphragmatic activity. arise from the ninth costal cartilage. 7 The crura are tendinous at their attachments, 8 blending with the anterior longitudinal verte- 9 bral ligament. The right crus is broader and Embryology 5011 longer and arises from the anterolateral aspect 1 of the bodies and discs of the first three lumbar The diaphragm develops from four main struc- 2 vertebrae, the left crus from the corresponding tures, the septum transversum, the pleuroperi- 311 46 47 THE ANATOMY AND PHYSIOLOGY OF THE DIAPHRAGM 111 mass of tissue which then extends dorsally and 2 medially towards the dorsal body wall, to meet 3 the dorsal mesentery of the foregut. As it grows 4 it leaves two dorsolateral gaps, which are the 5 orifices of the pleuroperitoneal canals. 6 The pleuroperitoneal membranes are a pair 7 of membranes which gradually separate the 8 pleural and peritoneal cavities. They are 9 attached dorsolaterally to the body wall with 1011 their free edge projecting into the caudal end 1 of the pericardioperitoneal canals. At about the 2 sixth week of gestation they grow medially and 3 ventrally away from the body wall towards the 4 septum transversum. By the end of that week 5 they have come to fuse with the dorsal mesen- 6 tery of the oesophagus and the septum trans- 7 versum to separate the pleural and peritoneal 8 cavities. The closure of the openings is further 9 Figure 4.2. Inner posterior aspect of the diaphragm. 1, The enhanced by the growth of the liver and muscle 2011 central tendon. 2, Attachment of lateral arcuate ligament to end tissue extension into the membranes. The right 1 of the twelfth rib. 3, Lateral arcuate ligament. 4, Medial arcuate pleuroperitoneal canal closes before the left one, 2 ligament. 5, Transverse process first lumbar vertebra. the latter being the more common site of per- 3 (Reproduced with permission from Gluzel P, Similowski T, sistent communication between the pleural and Chartrand-Lefebvre C et al. Diaphragm and chest wall: assess- 4 ment of the inspiratory pump with MR imaging – preliminary peritoneal cavities. The pleuroperitoneal mem- 5 observations. Radiology 2000;215:574–83. Copyright Radio- branes are believed only to produce a small 6 logical Sciety of North America.) dorsolateral part of the diaphragm in adult life. 7 The dorsal mesentery of the oesophagus fuses 8 with both the septum transversum and the pleu- 9 toneal membranes, the dorsal oesophageal roperitoneal membranes. This mesentery forms 3011 mesentery and the body wall. the medial portion of the diaphragm. The crura 1 The septum transversum forms the bulk of of the diaphragm develop from muscle fibres 2 the diaphragm, namely the central tendon and that grow into the oesophageal mesentery. 3 the majority of centrally placed muscle. It starts The contribution of the muscular body 4 off as a plate of mesoderm developing at the end wall to the diaphragm is the result of the expan- 5 of the fourth week of gestation in a position sion of the pleural cavities between the ninth 6 between the heart and the yolk sac.