A Pictorial Essay of the Diaphragmatic Crura and the Retrocrural Space: Normal Appearance, Variants and Pathology Poster No.: C-1939 Congress: ECR 2011 Type: Educational Exhibit Authors: L. Crush, O. J. Flanagan, S. Leong, S. A. Hayes, M. M. Maher; Cork/IE Keywords: Oncology, Veins / Vena cava, Trauma, CT, CT-Angiography, MR, Metastases, Lymphoma DOI: 10.1594/ecr2011/C-1939 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myesr.org Page 1 of 28
Learning objectives The retrocrural space is a small triangular region that serves as a communicating conduit between the thoracic and abdominal cavities Our aim is to facilitate a better understanding and improved recognition of the normal anatomy, variants and disease processes of this easily overlooked region Background Embryology of the diaphragm The diaphragm is formed through the fusion of tissue from four different sources 1. 2. 3. 4. The septum transversum, a thick mass of mesoderm between the primitive heart tube and the developing liver, gives rise to most of the central tendon The paired pleuroperitoneal membranes are sheets of somatic mesoderm that develop from the dorsal and dorsolateral body wall The dorsal mesentery of the oesophagus is invaded by myoblasts and forms the crura of the diaphragm The body wall contributes muscle to the peripheral portions of the definitive diaphragm Figure 1 Page 2 of 28
Fig.: Embryology of the diaphragm References: Restrepo CS, Eraso A, Ocazionez D, Lemon J, Martinez S, Lemons DF. The diaphragmatic crura and retrocrural space: Normal imaging appearance, variants, and pathologic conditions. RadioGraphics 2008; 28:1289-1305. ST - septum transversum ppm - pleuroperitoneal membranes dme - dorsal mesentery of the oesophagus Bw - body wall IVC - inferior vena cava Es - oesophagus Ao - Aorta Anatomy of the diaphragm and crura Page 3 of 28
The diaphragm is a dome-shaped fibromuscular septum which separates the thoracic and abdominal cavities Its peripheral part consists of muscular fibres which take origin from the circumference of the thoracic outlet and converge to be inserted into a central tendon The muscular fibres may be grouped according to their origins into three parts; sternal, costal, and lumbar The sternal part arises by two fleshy slips from the back of the xiphoid process The costal part from the inner surfaces of the cartilages and adjacent portions of the lower six ribs on either side, interdigitating with the transversus abdominis The lumbar part from aponeurotic arches, named the lumbocostal arches, and from the lumbar vertebrae by the two diaphragmatic crura Figure 2 Page 4 of 28
Fig.: Diaphragm from below References: Gray, Henry. Anatomy of the Human Body. Philadelphia: Edinburgh, Scotland: Churchill Livingstone, 2000. The diaphragmatic crura The crura are strong tendons attached to the anterolateral surfaces of the upper lumbar vertebrae and blend with the anterior longitudinal ligament of the vertebral column The right crus, larger and longer than the left, arises from the anterior surfaces of the bodies of the upper three lumbar vertebrae The left crus arises from the corresponding parts of the upper two lumbar vertebrae only Page 5 of 28
Muscle fibres radiate from each crus, diverge and pass superiorly before curving anteriorly into the central tendon Tendinous fibres from the medial edge of each crus unite, anterior to the aorta, at the level of T12 to from the median arcuate ligament Figure 3 Fig.: Axial contrast enhanced CT demonstrating the diaphragmatic crura and retrocrural space Page 6 of 28
The retrocrural space The retrocrural space is bounded by: Anteriorly - the median arcuate ligament Anterolaterally - the right and left crus Posteriorly - vertebral bodies Figure 4 Page 7 of 28
Fig.: Boundaries of the retrocrural space References: www.netterimages.com Normal contents of the retrocrural space The normal retrocrural space contains fatty tissue, the aorta, nerves, veins of the azygos system, lymph nodes, cisterna chyli and the thoracic duct Figure 5 Page 8 of 28
Fig.: Axial contrast enhanced CT outlining the normal anatomy of the retrocrural space and its contents Aorta The aorta is the largest structure within the retrocrural space At the level of the aortic hiatus, the aorta is slightly left of midline Within the retrocrural space, the aorta gives off posterior intercostal and subcostal arterial branches Page 9 of 28
Figures 6 and 7 Fig.: Axial and coronal contrast enhanced CT's showing the normal aorta and its position within the retrocrural space Azygos and hemiazygos veins Azygos vein The azygos vein is usually formed by the union of the ascending lumbar and subcostal veins of the right side It passes through the aortic opening under or through the right crus Hemiazygos vein The hemiazygos vein is formed by the joining of the left ascending lumbar and subcostal veins It passes under cover of or through the left crus Page 10 of 28
Imaging findings OR Procedure details Normal variants of the azygos system Azygos continuation of the IVC Also known as absence of the hepatic segment of the IVC with azygos continuation The causative embryonic event is thought to be failure of formation of the right subcardinal-hepatic anastomosis with atrophy of the right subcardinal vein As a result, blood is shunted from the suprasubcardinal anastomosis through an enlarged retrocrural azygos vein, which is partially derived from the thoracic segment of the right supracardinal vein This was previously thought to be associated with severe congenital heart disease but is now recognized in asymptomatic patients Further variants which result in abnormally enlarged retrocrural azygos and hemiazygos systems include: Duplication of the IVC with azygos and/or hemiazygos continuation Absence of the infrarenal portion of the IVC It is important to be aware of these normal variants to avoid misdiagnosis of an enlarged retrocrural azygos system as adenopathy or a mass Figure 8 Page 11 of 28
Fig.: Axial CT maximum intensity projection with IV contrast showing azygos continuation of the IVC. CT image reveals an abnormally dilated azygos vein (arrow). Figure 9 Page 12 of 28
Fig.: Coronal CT maximum intensity projection with IV contrast showing azygos continuation of the IVC (arrow) Cisterna chyli and thoracic duct Cisterna chyli Page 13 of 28
The cisterna chyli is an elongated sac-like structure formed by the convergence of lymphatic channels It is situated under the right crus, in front of the vertebral bodies of L1 and L2, in between the aorta and azygos vein Thoracic duct The thoracic duct commences at the superior aspect of the cisterna chyli at the level of T12 It is situated between the aorta and the azygos vein Figure 10 Page 14 of 28
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Fig.: Coronal HASTE MRI image shows the thoracic duct (curved arrow) that courses up the right side of the aorta from its origin at the cisterna chyli, which appears as a focal dilatation (arrow) in the retrocrural space. Tubular structure inferior to the lower aspect of the cisterna chyli represents the afferent trunks (arrow head) Pathology of the retrocrural space Diaphragmatic crura Primary malignancies affecting the diaphragmatic crura are rare Metastatic deposits within the crura or retrocrural space occur via cephalic or caudal extension or local invasion from adjacent structure Lung Oesophageal Hepatic Renal Ovarian Lymphoma Figure 11 Page 16 of 28
Fig.: Axial contrast enhanced CT showing a subcentimetre benign lipoma (arrow) in the left crus Figure 12 Page 17 of 28
Fig.: Axial contrast enhanced CT with a large mass (arrows) invading the retrocrural space in a patient with metastatic renal cell carcinoma Metastatic lesions Malignancy is the most common cause of retrocrural lymphadenopathy Figure 13 Page 18 of 28
Fig.: Axial contrast enhanced CT with enlarged lymph nodes (arrow) in the retrocrural space in a patient with metastatic ovarian carcinoma Inflammatory processes Inflammatory conditions can result in a variety of abnormal retrocrural findings Lymphadenopathy Pancreatitis Gastritis Page 19 of 28
Amyloidosis Ascites Aortitis Inflammatory or infectious Retroperitoneal fibrosis (Ormond's disease) Chronic inflammatory condition characterized by the proliferation of fibrous tissue Spondylosis deformans (bone spurs) Characterized by osteophyte formation on the anterolateral aspect of the vertebral bodies Usually right sided as aortic pulsations suppress their formation on the left Figure 14 Page 20 of 28
Fig.: Axial contrast enhanced CT with several small lymph nodes (arrow) in the retrocrural space in a patient with pancreatitis Figure 15 Page 21 of 28
Fig.: Axial contrast enhanced CT showing free fluid (arrow) in the retrocrural space in a patient with large volume ascites Figure 16 Page 22 of 28
Fig.: Axial contrast enhanced CT showing diffuse inflammation of the aorta (arrow) in a patient with giant cell arteritis Figure 17 Page 23 of 28
Fig.: Axial contrast enhanced CT demonstrating spondylosis deformans (arrow) on the right anterolateral aspect of T12 with displacement of the right crus Vascular findings Major aortic findings within the retrocrural space include: Suprarenal aneurysm Pseudoaneurysm Aortic rupture Aortic dissection Aortic haematoma Page 24 of 28
Aortitis Other vascular findings such as entrapment of renal artery by the diaphragmatic crus resulting in renal artery stenosis have been described Figure 18 Fig.: Axial arterial phase CT shows an eccentric suprarenal aortic aneurysm (arrows) with partial thrombosis Page 25 of 28
Trauma related findings Figure 19 Fig.: Axial arterial phase CT in a patient with a peri-aortic haematoma (arrow) at the level of the diaphragmatic crura following a road traffic accident. Similar findings are seen secondary to vertebral body or rib fractures Retrocrural free air Page 26 of 28
This can be a difficult finding to distinguish given the relatively small area the retrocrural space occupies Usually seen in relation to trauma resulting in either pneumo-thorax/mediastinum or pneumoperitoneum Figure 20 Page 27 of 28
Fig.: Axial CT depicting a small focus of retrocrural free air (arrow) following a penetrating thoracic injury Conclusion With such a vast array of variant anatomy and disease processes occurring within this region, a better understanding of the normal and abnormal findings is crucial for the accurate diagnosis of the myriad of both benign and pathological conditions affecting this easily disregarded inter-cavity compartment Personal Information References Moore KL, Persaud T. Development of the diaphragm. In: The developing human: clinically oriented embryology. 7th ed. Philadelphia, Pa: Saunders, 2003; 192-197. Gray, Henry. Anatomy of the Human Body. Philadelphia: Edinburgh, Scotland: Churchill Livingstone, 2000. Shin MS, Berland LL. Computed tomography of retrocrural spaces: normal, anatomic variants, and pathologic conditions. AJR Am J Roentgenol 1985; 145: 81-86. Bass JE, Redwine MD, Kramer LA, Harris JH Jr. Absence of the infrarenal inferior vena cava with preservation of the suprarenal segment as revealed by CT and MR venography. AJR Am J Roentgenol1999; 172: 1610-1612. Restrepo CS, Eraso A, Ocazionez D, Lemon J, Martinez S, Lemons DF. The diaphragmatic crura and retrocrural space: Normal imaging appearance, variants, and pathologic conditions. RadioGraphics 2008; 28:1289-1305. Bass JE, Redwine MD, Kramer LA, Huynh PT, Harris JH Jr. Spectrum of congenital anomalies of the inferior vena cava: cross-sectional imaging findings. RadioGraphics 2000; 20: 639-652. Page 28 of 28