Diagnostic and Interventional Imaging (2015) 96, 171—186 PICTORIAL REVIEW / Gastrointestinal imaging Radioanatomy of the retroperitoneal space ∗ A. Coffin , I. Boulay-Coletta, D. Sebbag-Sfez, M. Zins Radiology department, Paris Saint-Joseph Hospitals, 185, rue Raymond-Losserand, 75014 Paris, France KEYWORDS Abstract The retroperitoneum is a space situated behind the parietal peritoneum and in front Retroperitoneal of the transversalis fascia. It contains further spaces that are separated by the fasciae, between space; which communication is possible with both the peritoneal cavity and the pelvis, according to Kidneys; the theory of interfascial spread. The perirenal space has the shape of an inverted cone and Cross-sectional contains the kidneys, adrenal glands, and related vasculature. It is delineated by the anterior anatomy and posterior renal fasciae, which surround the ureter and allow communication towards the pelvis. At the upper right pole, the perirenal space connects to the retrohepatic space at the bare area of the liver. There is communication between these two spaces through the Kneeland channel. The anterior pararenal space contains the duodenum, pancreas, and the ascending and descending colon. There is free communication within this space, and towards the mesenteries along the vessels. The posterior pararenal space, which contains fat, communicates with the preperitoneal space at the anterior surface of the abdomen between the peritoneum and the transversalis fascia, and allows communication with the contralateral posterior pararenal space. This space follows the length of the ureter to the pelvis, which explains the communication between these areas and the length of the pelvic fasciae. © 2014 Éditions franc¸aises de radiologie. Published by Elsevier Masson SAS. All rights reserved. An accurate understanding of the anatomy of the retroperitoneum is essential in order to understand most of the pathological phenomena that occur in this space and how they spread within the various retroperitoneal compartments. As well as knowledge of the retroperitoneal compartments, an accurate understanding of the interconnections between the retroperitoneum, peritoneal cavity, and other extra-peritoneal spaces is cru- cial in order to understand the spread of inflammatory pathological processes or tumours. Abbreviations: APR, Anterior Pararenal Space; PPR, Posterior Pararenal Space; ARf, Anterior Renal Fascia; PRf, Posterior Renal Fascia. ∗ Corresponding author. E-mail address: alex [email protected] (A. Coffin). http://dx.doi.org/10.1016/j.diii.2014.06.015 2211-5684/© 2014 Éditions franc¸aises de radiologie. Published by Elsevier Masson SAS. All rights reserved. 172 A. Coffin et al. This review based on a description and interpretation of The mesenchyme is the posterior part of the embryo, imaging findings aims to review the radiological anatomy and it develops into the elements of the body wall [1]. It of the retroperitoneum, with emphasis on the theory of is covered by the transversalis fascia, a lamina of contin- interfascial spread to explain the various communications uous connective tissue that separates its components from between this space and the peritoneal cavity. the abdominal cavity. Fig. 2a summarizes the embryological organization of the retroperitoneal space. The intermedi- ary mesoderm forms the primordium of the genitourinary Review of anatomy system, and it is shown in Fig. 2b and c. The metanephros develops into the secretory urinary apparatus, and from here The retroperitoneal space is an anatomical structure delin- the initially caudal renal primordia will ascend in a posterior eated by the parietal peritoneum and the transversalis and caudo-rostral direction, in parallel with the descent of fascia. It is divided into five compartments (Fig. 1). a) the excretory urinary apparatus and gonads. The lateral compartments: these are an asymmetrical pair Fig. 3 summarizes the organization of the retroperi- containing the kidneys and other organs. Each lateral com- toneum after the ascension of the renal primordia. partment is divided by the fasciae into three separate This is a key moment in the formation of the retroperi- spaces: the anterior pararenal (APR), perirenal, and pos- toneum, delineating a fat-containing space into different terior pararenal (PPR) spaces. The APR space contains part spaces bordered by fasciae. The fasciae are lamina of con- of the ascending colon, descending colon, and the duode- nective tissue approximately 2 mm thick that will make up num and pancreas. The perirenal spaces contain the kidneys, the partitions between the various compartments of the adrenal glands, ureters, blood vessels and lymphatics. The retroperitoneum [1]. PPR space only contains fat. b) A central vascular compart- ment, extending from D12 to L4-L5, located between the two perirenal spaces, behind the anterior perirenal space, Perirenal space and in front of the spine. This contains the abdominal aorta and its branches, the inferior vena cava and its afferent The fasciae vasculature, lymphatic chains and the abdominal sympa- thetic trunk. c) Tw o symmetrical posterior compartments, The perirenal space has the shape of an inverted cone with containing the psoas major, which joins the iliacus muscle the point directed at the pelvis, and the base resting on the and sometimes the psoas minor, terminating at the arch of diaphragm [5]. Fig. 4 summarizes the borders of the perire- the hip bone. The psoas major extends from T12 to the nal space. The PRf is in fact made up of two apposed lamina, lesser trochanter, and it is covered with transversalis fas- one superficial and one deep, which explains why it is more cia, which is known as iliac fascia in this area. The iliopsoas easily visible on imaging [1]. The superficial lamina of the compartment is generally considered to be retroperitoneal PRf is made up of the lateroconal fascia, which extends in even though it is behind the transversalis fascia because it is front and attaches to the peritoneum. Fig. 5 summarizes frequently involved in processes that begin in the retroperi- the anatomy of the PRf. Fig. 6 shows invasion of the renal toneum. fasciae secondary to acute pancreatitis. Superior border of the perirenal space Review of embryology The right perirenal space has an unusual feature. Here, the It is necessary to review the embryology in order to under- perirenal space is in direct contact with the posterior sur- stand the formation of the perirenal compartment and to face of the right kidney, and has no peritoneal covering: this introduce the theory of planes of interfascial spread. is the bare area of the liver. This feature is explained by the Figure 1. Mapping the retroperitoneum. a): view of the retroperitoneal space on an axial CT cross-section passing through both kidneys: the retroperitoneal space (in red) is located between the parietal peritoneum (in green) and the transversalis fascia (in brown). b): the five retroperitoneal compartments: Lateral retroperitoneal compartments (in blue), median ‘‘vascular’’ retroperitoneal compartment (in red), posterior ‘‘iliospsoas’’ retroperitoneal compartments (in orange). c): three spaces of the lateral compartment: APR (in blue), perirenal (in yellow), PPR (in purple). Radioanatomy of the retroperitoneal space 173 Figure 2. Diagram of the embryological origins of the components of the retroperitoneum. a: axial view. The mesenchyme will form the vertebral bodies (in blue) and the muscular components of the abdominal wall, which are the paraspinal, psoas, and transverse abdominal muscles (in orange) [1]. Isolated between the transversalis fascia (in brown) and the parietal peritoneum (in green), fatty tissue is found at the dorsal side of the embryo (in yellow), which will become the posterior pararenal space. This fatty space will contain the renal primordia, which originates from the intermediary mesoderm. b: sagittal cross-sectional diagram of an embryo showing the intermediary mesoderm. It is divided into three parts organized rostro-caudally: the pronephros (in blue), which is most cranial, the mesonephros (in orange), and the metanephros (in green), the most caudal. The pronephros eventually atrophies. The mesonephros will develop into the excretory urinary apparatus and the genital organs. The mesonephric or Wolffian duct develops in males into the vas deferens, the ejaculatory duct, and the ureteric bud. The paramesonephric or Müllerian ducts develop into the components of the female genital system. c: organization of the mesonephros. Wolffian duct (in blue), Müllerian duct (in pink), primitive gonads (in red). Primitive gut in front (in yellow), parietal and visceral peritoneum (in light green), posterior vertebral primordium (white star). formation of peritoneal folds at the posterior part of the We have used the results of a number of cadaver studies liver, creating the falciform, coronary, right triangular and [1—4], as well as the embryology of the renal and urinary left triangular ligaments, and it directly exposes the liver system, with the metanephros (renal primordium) attaching to the retroperitoneal space behind. Fig. 7 summarizes the to the ureteric bud that forms the ureter, and both ascend- anatomy of the bare area of the liver. On the left, the ARf ing towards the lumbar fossae surrounded by their fasciae, fuses with the diaphragm leaving a free space above the to explain the anatomical relationships in the inferior part of adrenal gland, which is in fact part of the perirenal space the perirenal