A Pictorial Essay of the Diaphragmatic Crura and the Retrocrural

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
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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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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).
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
Figure 9
Page 12 of 28
Fig.: Coronal CT maximum intensity projection with IV contrast showing azygos
continuation of the IVC (arrow)
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
Page 15 of 28
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)
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
References: L. Crush; Radiology, Cork University Hospital / Mercy University Hospital,
Cork, IRELAND
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
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•
•
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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.
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