Anatomy, variants and pathologic conditions of the retrocrural space
Transcription
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 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 24 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. Page 2 of 24 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 Page 3 of 24 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: Page 4 of 24 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. Page 5 of 24 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). Page 6 of 24 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). Page 7 of 24 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. Page 8 of 24 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. Page 10 of 24 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. Page 13 of 24 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. Page 15 of 24 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. Page 16 of 24 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. Page 17 of 24 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. Page 19 of 24 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. References • Moore KL, Persaud T. Development of the diaphragm. In: The developing human: clinically oriented embryology. 7th ed. Philadelphia, Pa: Saunders, 2003; 192-197. • 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. Personal Information Page 24 of 24