Anatomy, variants and pathologic conditions of the retrocrural space

Anatomy, variants and pathologic conditions of the
retrocrural space
Poster No.:
C-0273
Congress:
ECR 2013
Type:
Educational Exhibit
Authors:
R. Sanchez Oro, A. Llanes Rivada, J. Uchiyamada, M. J. Moreno
Gomez, A. M. Julve Parreño, M. Rausell Félix; Valencia/ES
Keywords:
Abdomen, MR, CT
DOI:
10.1594/ecr2013/C-0273
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Learning objectives
•
Describe the retrocrural space anatomy and its normal variants.
•
Identify the anatomical structures normally found in the retrocrural space.
•
Recognize the imaging findings associated with the wide range of
pathological conditions that can affect the retrocrural space.
Background
The retrocrural space (RCS) can be defined as a triangular region that represents the
lower portion of the posterior mediastinum, with no real boundary with the posteromedial
region of the chest cavity. The space is bound on the front and laterally by the diaphragmic
crura. The posterior limits are the ventral side of the last thoracic and first lumbar vertebra.
The RCS is in contact with the posterior mediastinum and retroperitoneum and is a
potential expansion route between these spaces for various pathologies.
The content of the RCS are fat, vascular structures (aorta and arterial branches, azygos
and hemiazygos veins), neural structures (sympathetic trunk and splanchnic nerves),
nodes (lymph nodes, thoracic duct, cisterna chyli) and other less defined structures (for
example the ascending lumbar venous plexus).
The diaphragm consists of peripheral muscle fibres attached to three different anatomical
regions: the sternum, the lower ribs and lower back. The lumbar portion joins the last rib
arches forming arched ligaments (medial and lateral) and the anterolateral surface of the
lumbar vertebrae bilaterally forming the diaphragmatic cruras.
The right crus is longer and wider than the left, is attached to the ventral surface
of the lumbar vertebral bodies and the intervertebral fibrocartilage of the first three
lumbar vertebrae. The shorter left crus, joins the corresponding structures of the first two
vertebral bodies only (Fig. 2).
Going up the two crura, their medial fibres unite, forming a ventral arch to the aorta just
above the celiac axis. This arch, not visible sometimes, is known as the median arcuate
ligament.
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LYMPH NODES, CISTERNA CHYLI, THORACIC DUCT
Lymph nodes of the RCS are the lymphatic drainage stations for the posterior diaphragm,
posterior mediastinum and lumbar spine. They can be up to 6 mm smaller (Fig. 3).
The cisterna chyli is produced by the convergence of the lymphatic channels at the level
of the first lumbar vertebra. It receives the afferent lymphatic and intestinal lumbar trunks
and finally ascends as the thoracic duct. It is generally to the right of the aorta, but can
also be located to the left or retroaortic. The cisterna chyli has low attenuation on CT,
and the most common morphology is tubular but may also be round, oval plexiform and
fusiform (Fig. 4).
AORTA
At the aortic hiatus level, the aorta is located slightly to the left of the midline. In this
space, major branches such as the posterior intercostal and subcostal arise.
AZYGOS AND HEMIAZYGOS VEINS
The azygos vein is located on the right side, most often arising from the union of the
lumbar azygos veins, right ascending lumbar and subcostal veins. The hemiazygos vein,
located on the left side originates from the union of the left subcostal veins and the left
ascending lumbar vein.
PARAVERTEBRAL VENOUS PLEXUS
It is a network of valveless venous cisterns. If a pressure increase in this plexus, blood
passes into the venous system of the cava. Due to the lack of competent valves free
communication occurs between the veins of the neck, thorax, abdomen and pelvis with
the vertebral venous plexus. The absence of valves is also responsible for it being a route
for the spread of tumours and infections.
ANOMALIES AND VARIANTS OF THE DIAPHRAGMATIC CRURAS
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Compared with other common congenital anomaly such as Bochdalek and Morgagni
hernias, as well as hiatal hernias, anomalies affecting the crura are less symptomatic
and are usually detected incidentally.
The partial duplication of the diaphragm may include the crura (Fig. 5). This is associated
with cardiovascular malformations and ipsilateral lung development disorders. The
duplicated accessory diaphragm extends obliquely upward and backward to attach itself
to the posterior third of the seventh rib. This anomaly is more frequent on the right side.
The discontinuity between the crura of the diaphragm and the lateral arcuate ligament
is a normal variation, present in up to 11% of patients and should not be confused with
diaphragm rupture. Its association with age suggests that atrophy may be related to the
loss of integrity of the diaphragm muscle (Fig. 6).
CONGENITAL ANOMALIES OF THE INFERIOR VENA CAVA
Several anomalies vena cava inferior are associated with variations of the azygous and
hemiazygos in the RCS (Fig. 7, 8 and 9).
The absence of the hepatic segment of the inferior vena cava continuing into the azygous
vein is probably the most studied anomaly. It can be present in both asymptomatic
patients, as well as being associated with cardiovascular abnormalities, asplenia and
polysplenia syndromes. The azygos-hemiazygos system receives blood from the lower
limbs, pelvis, lower abdomen and renal veins, and via the RCS pass into the chest to
drain into the superior vena cava. In CT and MR, the enlarged azygos vein is recognized
as a well-defined tubular structure, parallel to the aorta behind the crural diaphragm and
extending cranially to contact the azygos arch.
Images for this section:
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Fig. 1: Fig. 2: Thoracoabdominal CT. Successive coronal cuts in a posterioanterior
direction showing the attachment points of the diaphragmatic crura.
Fig. 2: Fig 3: abdominal CT axial section showing a lymph node (white arrow) with a
diameter less than 6 mm.
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Fig. 3: Fig 4: Abdominal CT in axial section after the administration of IVC showing a
structure of oval morphology, low attenuation, to the right of the aorta, corresponding to
the cisterna chyli (white arrow).
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Fig. 4: Fig 5: CT after the administration of IVC. Axial cut showing a right hemidiaphragm
duplication (black arrow).
Fig. 5: Fig. 6: Abdominal CT after the administration of IVC, axial slices showing an
incomplete right hemidiaphragm (white arrow).
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Fig. 6: Fig. 7: Thoracoabdominal the administration of IVC. A: axial at the level of the
retrocrural space showing the dilated azygous vein (red arrow) to the right of the aorta,
absence of the hepatic segment of the inferior vena cava continuing into the azygous vein.
B: axial cut at the level of the azygos arch (blue arrow), dilated azygos vein emptying into
the superior vena cava. C: coronal reconstruction showing the azygos vein (red arrow)
dilated to the right of the aorta, and leading into the superior vena cava.
Fig. 7: Fig 8: Abdominal CT after the administration of IVC. Axial cut showing the dilated
hemiazygos vein (red arrow) to the left and posterior to the aorta, absence of the hepatic
segment of the inferior vena cava continuing into the hemiazygos vein.
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Fig. 8: Fig. 9: Thoracoabdominal CT after the administration of IVC. Axial cut of a patient
with situs showing agenesis of the hepatic segment of the inferior vena cava continuing
into the azygous vein, located to the left of the aorta.
Page 9 of 24
Imaging findings OR Procedure details
CRURAL ANOMALIES
Primary neoplasms of the crurals of the diaphragm are rare. Lipomas, desmoid tumours
and muscle tumours such as leiomyosarcomas and rhabdomyosarcomas have been
described. Malignant neoplasms of the crurals of the diaphragm are produced by
local dissemination or by blood. They can also be produced by anatomical proximity,
the extension of intrathoracic malignancies such as pleural mesothelioma, pulmonary
neoplasms or oesophageal tumours, and taking in the crurals of the diaphragm
in its expansion. Similarly, the abdominal neoplasis malignancies, especially in the
retroperitoneum, can extend through the paravertebral space and the RCS with the
consequent invasion of the crural diaphragm.
Other non-neoplastic conditions that may involve the crurals of the diaphragm are
traumatic ruptures and infectious processes such as intracrural abscesses. The
thickening of the crurals has been described as an indicator diaphragmatic injury in the
context of trauma. However, normal thickness variations related to respiration or patient
age limits the use of this parameter as an indicator of traumatic injury to the diaphragm.
RETROCRURAL SPACE ANOMALIES
Lymphadenopathy
The lymph nodes dorsal to the crura of the diaphragm drain the posterior mediastinum,
diaphragm and lower back. The detection of ganglia larger than 6mm should be
considered suspect.
An increase in the size of retrocrural lymph nodes may occur as a result of inflammatory
diseases, infections and, most frequently, genitourinary (Fig. 10), gastrointestinal (Fig.
11), lung or oesophagus cancer metastases. Furthermore, lymphomas, both Hodgkin
as well as non-Hodgkin, is a common malignant cause of enlarged lymph nodes and of
lymphadenopathy/granulomas.
Inflammatory diseases which manifest themselves as enlarged lymph nodes, as is
the case of sarcoidosis, lymphangioleiomyomatosis and amyloidosis, can occasionally
appear so in the RCS. Lymph nodes affected by mycobacteria and those of
lymphangioleiomyomatosis generally have lower attenuation values in the CT.
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Regarding infectious causes, disseminated TB (Fig. 12 and 13), mycobacterium aviumintracellulare complex, AIDS and lymphadenopathy stand out. It is unusual that these
produce lymph nodes with a diameter greater than 15mm.
RETROCRURA LNEOPLASMS
SRC primary neoplasms can be classified according to the cell of origin in neurogenic,
mesenchymal, lymphoid and germ cell tumours.
Retrocrurales neurogenic tumours can be divided into three categories: ganglion cell
tumours, tumours of the nerve and nerve sheath, and paragangliomas.
Tumours arising from ganglion cells such as neuroblastoma, ganglioneuroblastoma and
ganglioneuroma are most common in early childhood.
Tumours of the nerve sheath, such as neurofibroma and schwannoma are usually benign.
They are more common in patients with neurofibromatosis. Neurofibromas (Fig. 14) are
generally rounded, with low attenuation on CT without the administration of intravenous
contrast and with homogeneous enhancement after contrast administration in T1. 10%
of tumours of the sheath have an intraspinal extension, producing intraspinal foramina.
The RCS parangliomas are much less frequent. They affect patients typically between
10 and 20 years of age.
Extramedullary hematopoiesis is a rare benign neoplasm that can manifest itself as soft
tissue masses in the RCS. It is more common in patients with thalassemia, but can also
occur in patients with sickle cell anaemia, hereditary spherocytosis, myelosclerosis and
in other causes of anaemia and myeloproliferative disorders. In TC (Fig. 15) they show
up as lobulated, well-defined, multi-levelled soft tissue masses, along the distal thoracic
paravertebral region, which may have areas with attenuation of fat.
MR images in which the characteristics of extramedullary hematopoiesis depend on the
level of activity of the haematopoietic injury. In hematopoietically active lesions, there is
intermediate signal intensity on T1 and high intensity on T2-weighted images regarding
muscles, with a slight increase after the administration of gadolinium. Old and inactive
lesions showed low intensity on both T1 and T2 for iron deposition, while if there is fatty
infiltration, it is hyperintense.
Page 11 of 24
FOREGUT MALFORMATIONS
Although usually found in the middle mediastinum in the paratracheal or subcarinal
region, there have been reports of pulmonary sequestration with oesophageal duplication
cysts in gastric and RCS. Surgical resection of these lesions to avoid complications such
as infection and malignant transformation was chosen.
VASCULAR DISORDERS
The aorta is the largest anatomical structure within the RCS. Pathologies such as
aneurysms, pseudoaneurysms, traumatic ruptures, aortic dissections (Fig. 16) and
inflammations such as aortitis may occur in the RCS.
A periaortic hematoma in the RCS may develop after a traumatic lesion to the aorta
or rupture of an aneurysm. In the context of a trauma, the periaortic hematoma in
the retrocrural region may also be present secondary to the posterior rupture of the
diaphragm or to fractures of vertebra or ribs.
Portal hypertension, occlusion of the vena cava and other central venous occlusions
can alter the normal venous drainage, altering the flow in theacigo-hemiazygos venous
system.
The central obstructive venouo sand portal hypertension can also manifest themselves
as varicosities of the intercostal and ascending lumbar veins and of the paravertebral
venous plexus.
INFLAMMATORY PATHOLOGIES
Retroperitoneal fibrosis is a rare chronic inflammatory disease of unknown pathogenesis
characterized by the substitution of retroperitoneal tissues, especially fat by fibrous tissue.
Although it usually affects the retroperitoneum between the kidneys, retroperitoneal
fibrosis can occur again or extend beyond the crura of the diaphragm in the posterior
mediastinum and mediastinal fibrosis.
Page 12 of 24
It has a similar behaviour to when it occurs at the level of the kidneys, trapping without
displacing adjacent structures such as the aorta (Fig. 17). Fibrosis in the RCS can be
confused with lymphadenopathy.
Steroid-induced retrocrural lipomatosis may also develop. The CT showed the low
attenuation values characteristic of fat. It can also occur as a result of antiretroviral agents
for the treatment of HIV
Spondylitis deformans is a very common degenerative spine disease manifested by
osteophyte formation along the anterolateral aspect of the vertebral bodies. Osteophytes
in the thoracic spine are more frequent along the right anterolateral face (Fig. 18),
presumably because pulsation of the descending aorta to the left inhibits the production
of bone.
The pancreatic pseudocysts are encapsulated collections containing the remains of
blood, pancreatic secretions and blood degradation products that originated in the
pancreas after pancreatitis. Retroperitoneal and transhiatal extension of the inflammation
of the pancreas explains the unusual presentation of pancreatic pseudocysts in the
retrocrural region (Fig. 19) and posterior mediastinum. Pancreatic pseudocysts in the
ERC may be suspected when there is rapid development of fluid in this region in a patient
with a clinical diagnosis of pancreatitis. The CT and MRI demonstrate the cystic nature
of the lesion and its communication with an intraabdominal pancreatic pseudocyst.
INFECTIONS
Distal spine and dorsal lumbar spine infections may extend proximal the prevertebral
and paravertebral soft tissues to the RCS. Paravertebral abscesses are associated with
pyogenic spondylitis (especially staphylococcus) and tuberculous spondylitis. Diabetes,
immunosuppression, addiction to peritoneally administered drugs and sickle cell anaemia
are risk factors.
Infectious spondylitis (Fig. 20) appears as the destruction of the endplates of the vertebral
bodies and the intervertebral disc. Once the vertebral body is involved, subligamentous
and preverterbral tissue fistula extensions of the infection can occur.
The walls of the abscesses are hypervascular. The use of contrast increases the
sensitivity for the detection of spondylodiscitis and paravertebral abscesses.
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Tuberculous spondylitis most often involves the last lumbar dorsal vertebrae and the first
lumbar vertebrae, therefore, the presence of a retrocrural abscess along with spondylitis
favours the diagnosis of tuberculosis.
OTHER ANOMALIES
Pneumomediastinum can be recognized by the presence of gas within the RCS. It was
initially described in patients with distal oesophageal perforation, however, this is not
specific.
Pleural effusion (Fig. 21) is probably the most frequently detected anomaly in the RCS.
Traumatic fractures of the proximal and distal lumbar vertebrae may be associated with
paraspinal hematomas that can occupy the RCS. These fractures (Fig. 22) are usually
related to high-energy traumas.
Images for this section:
Fig. 9: Fig 10: Abdominopelvic CT after the administration of IVC. Axial slices in
which there is a retrocrural adenopathy (black arrow) of metastatic origin (clear cell
renal carcinoma). The right renal tumor (red arrow), a lymphadenopathy/granuloma
encompassing the cava (blue arrow) and peritoneal carcinomatosis (white arrow) can
also be seen.
Page 14 of 24
Fig. 10: Fig. 11: Abdominopelvic CT after the administration of IVC, axial cut which shows
a right retrocrural adenopathy (red arrow) of low attenuation and of metastatic origin,
along with multiple hepatic and splenic metastases of low attenuation. The primary tumor
was a mucinous carcinoma in the ascending colon.
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Fig. 11: Figure 12: Figures 12 and 13. Thoracoabdominal CT after administration of
IVC. Axial cuts, HIV+ patient, presenting with left retrocrural adenopathy and multiple
mediastinal lymph nodes in the left internal mammary chain and hilar, all with low
attenuation and all caused by the TB.
Fig. 12: Figure 12: Figures 12 and 13. Thoracoabdominal CT after administration of
IVC. Axial cuts, HIV+ patient, presenting with left retrocrural adenopathy and multiple
mediastinal lymph nodes in the left internal mammary chain and hilar, all with low
attenuation and all caused by the TB.
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Fig. 13: Fig 14: Abdominal CT afterthe administration of IVC. Axial cut in which there
is a nodular lesion, with low attenuation, in the left retrocrural space adjacent to the
conjunction hole corresponding to the neurogenic tumor.
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Fig. 14: Fig. 15:Thoracoabdominal after the administration of IVC, lower thoracic and
upper abdominal axial cuts showing lobulated, well-demarcated soft tissue masses
at different levels along the left distal thoracic paravertebral region, corresponding
to extramedullary hematopoiesis. Bilateral pleural effusion with passive atelectasis of
adjacent lung parenchyma. Sparse pericardial effusion.
Fig. 15: Fig. 16: CT thoracoabdominal after the administration of IVC. Axial cut and
coronal reconstruction showing a type A aortic dissection, true light (red arrow) of smaller
size and greater attenuation, andartificiallight (blue arrow) of greater size and lesser
attenuation.
Page 18 of 24
Fig. 16: Fig 17: Abdominal CT after administration of IVC. Axial cut showing the fibrous
tissue trapping, without shifting, the abdominal aorta (black arrow), correspondent to
retroperitoneal fibrosis.
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Fig. 17: Fig. 18: Abdominal CT. Axial cut showing a large right anterolateral osteophyte.
Page 20 of 24
Fig. 18: Figure 19: Thoracoabdominal TC after the administration of IVC. In a patient with
a history of pancreatitis, it is showed encapsulated collections in the retrocrural space
(black asterisk), adjacent to the uncinate process (white asterisk) and posterior pararenal
space (red asterisk), corresponding to pseudocysts. Splenic hydatid cyst (blue asterisk).
Fig. 19: Figure 20a: Sagittal T1-weighted image. There is a low abnormal signal T12/ L1.
End plates show signs of destruction, and there is a decrease in disc height. 20b: Axial
T2-weighted image. High signal in the intervertebral disc. Spondylodiscitis by S. aureus.
Page 21 of 24
Fig. 20: Fig 21: Abdominal CT after the administración IVC. Axial cut showing the left
pleural effusion. Liver cyst.
Page 22 of 24
Fig. 21: Fig 22: Thoracoabdominal CT. Axial cut showing fracture of the L1 in a
precipitate.
Page 23 of 24
Conclusion
The normal content of the retrocrural space includes vascular, nerve and lymph structures
as well as fat. With such a wide variety of anatomical and pathological processes that
occur in this region, a better understanding of normal and abnormal findings in this
anatomical compartment is crucial to the making of a correct diagnosis.
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Personal Information
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