Retroperitoneum revisited: a review of radiological literature and updated concept of retroperitoneal fascial anatomy with imaging features and correlating anatomy.

PURPOSE: Spread of disease in the retroperitoneum is dictated by the complex anatomy of retroperitoneal fasciae and is still incompletely understood. Conflicting reports have led to insufficient and incorrect anatomical concepts in radiological literature. METHODS: This review will discuss previous concepts prevalent in radiological literature and their shortcomings will be highlighted. New insights from recent anatomical and embryological research, together with imaging examples, will be used to clarify patterns of disease spread in the retroperitoneum that remain unexplained by these concepts. RESULTS: The fusion fascia and the renal fascia in particular give rise to planes and spaces that act as vectors for spread of disease in the retroperitoneum. Some of these planes and structures, such as the caudal extension of the renal fascia, have previously not been described in radiological literature. CONCLUSION: New insights, including the various fasciae, potential spaces and planes, are incorporated into an updated combined retroperitoneal fascial concept.

A Morphometric Study of Cadavers for the Anterior Approach to the Lower Lumbar Spine.

AIM: To explore the relationship between the retroperitoneal vasculature and anterior surface of the lower spine, and to establish values for aiding in prediction of the pertinence of anterior approach at the L4-L5 and L5-S1 intervertebral discs. MATERIAL AND METHODS: The study included 13 fresh human cadavers. After exploration of the abdominal cavity and removal of the visceral organs, the vasculature, and anterior spinal surface were revealed beneath the lower extension of the perirenal fascia. Morphometric measurements of the great vessels and the intervertebral discs were obtained. All measurements were analyzed and presented as mean and standard deviation. Differences in the values between sexes were assessed. RESULTS: The anterior height of the L4-L5 and L5-S1 intervertebral disc was 6.8 ± 0.81 mm and 6.7 ± 0.99 mm, respectively. The widths of the aorta, inferior vena cava, right and left common iliac arteries, and right, and left common iliac veins were 16.4 ± 3.58, 20.6 ± 3.36, 11.5 ± 2.32, 11.5 ± 2.43, 14.7 ± 3.13, and 15.5 ± 3.27 mm, respectively. The mean aortic bifurcation angle was 45.5°. The aortic bifurcation was located above the lower endplate of the L4 vertebrae in 53.8% of the cadavers. The area of the interarterial and interiliac trigones was 14.6 ± 5.33 cm < sup > 2 < /sup > and 7.1 ± 4.35 cm2, respectively. No statistically significant differences were noted between the sexes. CONCLUSION: An elaborate radiological examination of the vasculature should be performed prior to surgery to avoid unwanted vascular complications during the anterior approach. Knowing the area of the interarterial and interiliac triangles and the aortic bifurcation location could be aid in assessing the safe working zone.

Retroperitoneal fasciae as barriers for nerve and arterial passages connecting the retroperitoneal region to the peritoneal organs.

The fascia of the pancreatic head is referred to as the retropancreatic fascia of Treitz, and that of the body and tail of the pancreas is named the retropancreatic fascia of Toldt. However, the spatial relationship between the nerves, fascia, and the distribution of the fascia on the dorsal side of the pancreas remains unclear. Therefore, this study aimed to explore the distribution of these fasciae and elucidate the spatial relationship between the nerves and arteries connecting the retroperitoneal space and the peritoneal organs by studying eight cadavers using macroscopic anatomical examination, wide-range serial sectioning, and three-dimensional reconstruction. The fasciae of Treitz and Toldt converge caudally to the root of the superior mesenteric artery (SMA), forming a narrower gap around the roots of the celiac trunk and SMA than in the celiac plexus. The fasciae eventually get closer to each other, and the boundary between them becomes obscured, providing coverage to the anterior surface of the aorta between the SMA and the inferior mesenteric artery. The celiac plexus does not penetrate the fascia but converges before spreading into the pancreas. Similarly, the arteries pass through this gap in the fasciae. Our findings suggest that the retroperitoneal space and peritoneal organs are connected through a narrow no-fascia area, with the distribution of the fascia relating to nervous and vascular pathways. Our findings reveal that the distribution of the avascular plane may provide a crucial anatomical foundation for abdominal digestive organ surgery by reducing bleeding volume and determining the dissection region.

Carl Toldt Centennial, Surgeon and Anatomist.

Carl Florian Toldt was an Austrian anatomist who made meaningful contributions worldwide and defined what is one of the most important surgical landmarks in abdominal surgery. Through his research studies, the embryologic dissection plane known as the "White Line of Toldt" represents an important anatomical landmark that helps to mobilize either the ascending or descending colon. His career spanned over 45 years, beginning in Verona and continuing to Prague and Vienna. He was an author of several innovative books and scientific articles regarding micro- and macroscopic anatomy. In addition, he received numerous recognitions and prizes for his work, making him an essential figure in the medical scientific community. Even a street in Vienna, Karl-Toldt-Weg, is named in his honor. The purpose of this historical article is to celebrate and honor Toldt 100 years following his death, remembering his scientific contributions to the medical and surgical fields and giving thanks for his numerous accomplishments. This article brings light to the man behind the eponym.

Ligament of Treitz: Anatomy, Relevance of Radiologic Findings, and Radiologic-Pathologic Correlation.

OBJECTIVE. The objective of this article is to discuss the anatomy, embryonic origin, normal variants, and various attachments of the ligament of Treitz. We also describe the pathologic processes that develop along the ligament of Treitz and the role of cross-sectional imaging in identifying these conditions. CONCLUSION. The ligament of Treitz, also known as the suspensory ligament of the duodenum, is an important anatomic landmark in the abdomen. It is essential that radiologists understand the anatomic attachments, normal variants, and various pathologic conditions involving the ligament of Treitz as well as the role of cross-sectional imaging in the assessment of these conditions.

There are no three physiological narrowings in the upper urinary tract: a new concept of the retroperitoneal anatomy around the ureter.

The widely held dogma of three physiological narrowings in the upper urinary tract has proven incorrect by recent several studies using computed tomography images. There are only two common obstruction sites: the upper ureter and the ureterovesical junction. The second narrowing, where the ureter crosses the iliac vessels, cannot be regarded anymore as a common obstruction site. The mechanism by which stones lodge in the upper ureter is explained anatomically by the change in ureteral mobility and compliance at the level where the ureter exits the perirenal space. This level can be identified radiologically as the point where the ureter crosses under the ipsilateral gonadal veins, termed the "crossing point". Kinking of the upper ureter is another manifestation of this anatomical phenomenon, visible in radiological images. It is caused by loosening of the ureter at or above the crossing point (within the perirenal space), corresponding with renal descent such as during the inspiratory phase. This new anatomical discovery in the retroperitoneum will not only bring about a paradigm shift in terms of the physiological narrowings in the upper urinary tract, but may also lead to the development of new surgical concepts and approaches in the area.

Useful Pelvic Retroperitoneal Neuroanatomy for Benign Gynecologic Surgery: A Cadaveric Dissection.

OBJECTIVE: Knowledge of the retroperitoneal anatomy is particularly important to facilitate surgical procedure and reduce the number of complications. The objective of this video is to demonstrate pelvic neuroanatomic structures and their relationships in the pelvic sidewall and the presacral space in a laparoscopic cadaveric dissection. DESIGN: Case report (anatomic study). SETTING: Medical training center (AdventHealth Nicholson Center, Orlando, FL). INTERVENTIONS: The dissection started with the mobilization of the iliac vessels from the pelvic sidewall to identify the obturator nerve. The peritoneum of the ovarian fossa was opened, and the ureter was dissected up to the level of the uterine artery. The hypogastric nerve was identified. The close relationship between the ovarian fossa and the obturator nerve could be demonstrated. The deep dissection of the obturator fossa allowed for the identification of the lumbosacral trunk, S1, the sciatic nerve, S2, S3, S4, and the splanchnic nerves. Then, the ischial spine and the sacrospinous ligament were identified. The pudendal nerve and vessels could be observed passing below the sacrospinous ligament, entering the pudendal canal (Alcock's canal). The presacral space was dissected, and the hypogastric fascia was opened. S1 to S4 were identified coming from the sacral foramens. The laparoscopic dissection, using the cadaveric model, allowed for the development of the entire retroperitoneal anatomy, focusing on the dissection of the pelvic innervation. Anatomic relationships among the ureter, the hypogastric nerve, the uterosacral ligament, the splanchnic nerves, the inferior hypogastric plexus, and the organs (bowel, vagina, uterus, and bladder) could be demonstrated. CONCLUSION: A laparoscopic cadaveric dissection can be used as a resource to demonstrate and educate surgeons about the neurologic retroperitoneal structures and their relationships.

Horseshoe kidney: is there still a debate?

Horseshoe kidneys (HSK) represent an interesting surprise during anatomical dissections directed towards teaching of the urinary system. Clinically, the HSK limits access into the retroperitoneal space due to its location, orientation, and positioning of the ureters. In addition, its highly variable arterial and venous patterns provide great difficulties for surgeons during aortic aneurysm correction, and more recently, HSK transplantation. This case is a morphological study of a noticeably different HSK from the perspective of location, arterial blood supply, and venous drainage, which is further solidified by an embryological review. The debate is opened for further exploration into the theories associated with HSK ascent, its vasculature patterns, and the need for precise diagnostic imaging to serve preoperative planning

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Anatomy of the retro-crural space (RCS): a potential conduit of infection and metastasis

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The Anatomic Characteristics of the Retroperitoneal Oblique Corridor to the L1-S1 Intervertebral Disc Spaces.

STUDY DESIGN: This is a cross-sectional study. OBJECTIVE: To investigate the oblique corridor to the L1-S1 intervertebral disc space between the psoas muscle and the great vessels in cadaveric specimens bilaterally and the location of genitofemoral nerve and the diaphragmatic crura relative to the oblique corridor. SUMMARY OF BACKGROUND DATA: Although use of oblique lumbar interbody fusion is rapidly expanding, the morphometric data related to the procedure are limited. METHODS: Twelve fresh-frozen full-torso cadaveric specimens were dissected to examine the oblique corridor to access the L1-S1 space in a static state and with mild retraction of the psoas. The level at which the genitofemoral nerve pierces from the psoas major and the diaphragmatic crura originate from the lumbar vertebral body was also investigated. RESULTS: The mean width of oblique corridor in the static state and with mild psoas retraction, respectively, were as follows: on the right side: (L1-2) 13.33 and 16.75 mm; (L2-3) 15.42 and 21.42 mm; (L3-4) 16.58 and 22.67 mm; (L4-5) 12.75 and 21.17 mm; (L5-S1) 5.92 and 12.00 mm; on the left side: (L1-2) 16.75 and 19.67 mm; (L2-3) 18.50 and 25.33 mm; (L3-4) 20.58 and 28.00 mm; (L4-5) 18.17 and 26.08 mm; and (L5-S1) 5.83 and 12.00 mm. The level at which the genitofemoral nerve pierces from the psoas major was between L2 and L4. The diaphragmatic crura originates from L1 to L3. CONCLUSION: The oblique corridor allows access to the L1-L5 discs from both sides, but it is larger on the left side. The corridor between the iliac vessels and the psoas for L5-S1 is difficult to be applied clinically. Mild psoas retraction can moderately enlarge the oblique corridor. The genitofemoral nerve and diaphragmatic crura may be encountered in this approach and should be carefully observed. LEVEL OF EVIDENCE: 5.

Anatomic evaluation of retroperitoneal organs for lateral approach surgery: a prospective imaging study using computed tomography in the lateral decubitus position.

PURPOSE: The aim of this study is to investigate retroperitoneal organ distribution with the retroperitoneal approach in the lateral decubitus position. METHODS: We enrolled 100 patients scheduled for lateral approach surgery, including LIF and lateral corpectomy. We performed computed tomography with lateral decubitus positioning (L-CT) to assess the position of the organs, including abdominal aorta, kidney, descending colon, ureter, and gonadal artery. Anteroposterior organ positions were divided into four zones: A, anterior to the anterior margin of the vertebral body; AL, anterior margin to the middle line of the vertebral body; PL, middle line to the posterior margin of the vertebral body; and P, posterior to the posterior margin of the vertebral body. We defined zone PL-P as the "approach zone." Measurements obtained using L-CT were compared with those obtained in the conventional supine position (S-CT). RESULTS: Retroperitoneal organs in the approach zone significantly decreased in lateral positioning. Eighty-three percent of kidney and 20% of descending colon remain in the approach zone in L-CT. Sixty-six percent of disk levels recorded for the descending colon in zone P in S-CT remained in the approach zone even in L-CT. CONCLUSIONS: We observed anterior migration in L-CT in all retroperitoneal organs. However, a considerable percentage of kidney and that of descending colon remain obstruent while performing LIF. We discuss that the preoperative imaging evaluation is beneficial, and gentle and meticulous surgical detachment is essential for safe and reliable lateral approach surgery, especially in the case that the descending colon extends outside zone P in S-CT. These slides can be retrieved under electronic supplementary material.

Non-traumatic causes of fluid in the retropharyngeal space.

There are multiple reasons for imaging the soft tissues of the neck in the emergency setting, in particular when symptoms are vague or if there is worry for complications from a certain clinical diagnosis. When fluid is seen in the retropharyngeal space, it is important to pay attention to history and look at key structures in the neck. This article will discuss anatomy of the retropharyngeal space, followed by four causes of fluid within the space that the radiologist is likely to encounter in the emergency setting: tonsillitis/pharyngitis, acute calcific tendinitis of the longus colli muscles, internal jugular vein thrombosis, and post-radiation changes. It is important to recognize these entities because each has different clinical implications and management.

The anatomy of the infrarenal lumbar splanchnic nerves in human cadavers: implications for retroperitoneal nerve-sparing surgery.

Injury to the nerves of the aortic- and superior hypogastric plexuses during retroperitoneal surgery often results in significant post-operative complications, including retrograde ejaculation and/or loss of seminal emission in males. Although previous characterizations of these plexuses have done well to provide a basis for understanding the typical anatomy, additional research into the common variations of these plexuses could further optimize nerve-sparing techniques for retroperitoneal surgery. To achieve this, the present study aimed to document the prevalence and positional variability of the infrarenal lumbar splanchnic nerves (LSNs) through gross dissection of 26 human cadavers. In almost all cases, two LSNs were observed joining each side of the aortic plexus, with 48% (left) and 33% (right) of specimens also exhibiting a third joining inferior to the left renal vein. As expected, the position of the LSNs varied greatly between specimens. That said, the vast majority (98%) of LSNs joining the aortic plexus were found to originate from the lumbar sympathetic trunk above the level of the inferior mesenteric artery. It was also found that, within specimens, adjacent LSNs often coursed in parallel. In addition to these nerves, 85% of specimens also demonstrated retroaortic LSN(s) that were angled more inferior compared with the other LSNs (P < 0.05), and exhibited a unique course between the aorta/common iliac arteries and the left common iliac vein before joining the superior hypogastric plexus below the aortic bifurcation. These findings may have significant implications for surgeons attempting nerve-sparing procedures of the sympathetic nerves in the infrarenal retroperitoneum such as retroperitoneal lymphadenectomies. We anticipate that the collective findings of the current study will help improve such retroperitoneal nerve-sparing surgical procedures, which may assist in preserving male ejaculatory function post-operatively.

Retroperitoneal Laparoscopy in Dogs: Access Technique, Working Space, and Surgical Anatomy.

OBJECTIVE: To develop and describe a laparoscopic retroperitoneal access technique, investigate working space establishment, and describe the surgical anatomy in the retroperitoneal space as an initial step for clinical application of retroperitoneal laparoscopy in dogs. STUDY DESIGN: Cadaveric and experimental study. ANIMALS: Cadaveric (n=8) and healthy (n=6) adult dogs. METHODS: The retroperitoneal access technique was developed in 3 cadavers based on the human technique and transperitoneal observation. Its application and working space establishment with carbon dioxide (CO2 ) insufflation alone was evaluated in 5 cadavers by observing with a transperitoneal telescope and in 6 live dogs by repeated computed tomography (CT) scans at pressure of 0, 5, 10, and 15 mmHg. Recordings of retroperitoneoscopy as well as working space volume and linear dimensions measured on CT images were analyzed. RESULTS: Retroperitoneal access and working space establishment with CO2 insufflation alone were successfully performed in all 6 live dogs. The only complication observed was in 1 dog that developed subclinical pneumomediastinum. As pressure increased, working space was established from the ipsilateral to the contralateral side, and peritoneal tearing eventually developed. Working space volume increased significantly from 5 mmHg and linear dimensions increased significantly from 0 to 10 mmHg. With pneumo-retroperitoneum above 5 mmHg, retroperitoneal organs, including kidneys and adrenal glands, were easily visualized. CONCLUSION: The retroperitoneal access technique and working space establishment with CO2 insufflation starting with 5 mmHg and increasing to 10 mmHg provided adequate working space and visualization of retroperitoneal organs, which may allow direct access for retroperitoneal laparoscopy in dogs.

Retroperitoneal course of iliohypogastric, ilioinguinal, and genitofemoral nerves: A study to improve identification and excision during triple neurectomy.

Triple neurectomy of the iliohypogastric (IHN), ilioinguinal (IIN), and genitofemoral (GFN) nerves is an available treatment option for chronic groin pain when conservative measures are ineffective. This research study attempted to define the variability of IHN, IIN, and GFN by categorizing variation and establishing a relationship to clinically significant landmarks. 22 cadavers (43 specimens) were dissected. Age, gender, ethnicity, BMI, and pertinent medical history were recorded for each specimen. Nerve emergence, insertion, and split points were measured in relation to clinically significant landmarks. Retroperitoneal trajectories of IHN, IIN, and GFN were analyzed and categorized based on nerve branching patterns. IIN and IHN had three branching patterns - type A (47%) in which the IIH and IIN exit as separate branches; type B (26%) in which the IIH and IIN exit as a single bundle and split; and type C (28%) in which the IIH and IIN exit and do not split. The GFN had three branching patterns--type 1 (50%) in which the GFN exited from the psoas major and then split into the genital and femoral branches; type 2 (30%) in which the GFN exited and did not split; and type 3 (20%) in which the GFN exited the psoas major already split into the genital and femoral branches. Variations in the IHN, IIN, and GFN nerves outlined in this study will provide surgeons with clinically useful information aiding in successful and efficient localization of these nerves during retroperitoneal procedures, including laparoscopic triple neurectomy.

Supraumbilical primary trocar insertion for laparoscopic access: the relationship between points of entry and retroperitoneal vital vasculature by imaging.

OBJECTIVES: Advances in laparoscopy have demonstrated that supraumbilical primary ports can be desirable in complex cases with large masses. This study evaluated distances to vital retroperitoneal vasculature that were encountered with 45- and 90-degree angle entry from the umbilicus and 2 commonly described supraumbilical entry points at 3 and 5 cm cephalad from the umbilicus. STUDY DESIGN: Retrospective analysis of computed tomography scans of the abdomen and pelvis from 100 randomly selected women who were 18-50 years old with normal anatomy was performed. Three-dimensional models of sagittal sections were generated using IMPAX software. Measurements from the abdominal wall at the umbilicus and 3 and 5 cm cephalad with 45- and 90-degree angles to retroperitoneal structures were performed. RESULTS: With 90-degree angle entry, the abdominal wall thickness (AWT) was thinnest at the umbilicus; however, the thickness at 3 and 5 cm was similar. AWT increased at all sites with 45-degree angle entry, and the same pattern was observed. AWT and intraperitoneal distance positively correlated with body mass index and supraumbilical entry points. With 90-degree angle entry, the aorta was 1.9 cm (95% confidence interval [CI], 1.4-2.4) and 2.5 cm (95% CI, 2.0-2.9) farther away at 3 and 5 cm cephalad compared with umbilical entry. In one-third of the cases, regardless of port placement, a vascular structure other than the aorta was the most anterior vessel. With 45-degree angle entry at the umbilicus, no vessels were encountered. With 45-degree angle entry at 3 and 5 cm cephalad, the aorta was the most anterior vessel in 1% and 2% of cases, respectively, and was noted to be 1.0 cm (95% CI, 1.0-1.0) and 2.3 cm (95% CI, 1.2-3.3) farther away than with 90-degree angle entry. A vessel other than the aorta was encountered in 4% and 7% of cases at 3 and 5 cm, respectively. CONCLUSION: According to theoretic modeling, supraumbilical primary port placement can be implemented safely in laparoscopy. With supraumbilical entry, the distance to retroperitoneal vessels was greater than at the umbilicus. Compared with a 90-degree angle, with a 45-degree angle entry, it was uncommon to encounter vasculature, and all measured distances were greater.

Retroperitoneal anatomy of the iliohypogastric, ilioinguinal, genitofemoral, and lateral femoral cutaneous nerve: consequences for prevention and treatment of chronic inguinodynia.

PURPOSE: Chronic inguinodynia is one of the most frequent complications after groin herniorrhaphy. We investigated the retroperitoneal anatomy of the iliohypogastric, ilioinguinal, genitofemoral, and lateral femoral cutaneous nerve to prevent direct nerve injury during hernia repairs and to find the most advantageous approach for posterior triple neurectomy. METHODS: We dissected the inguinal nerves in 30 human anatomic specimens bilaterally. The distances from each nerve and their entry points in the abdominal wall were measured in relation to the posterior superior iliac spine, anterior superior iliac spine, and the midpoint between the two iliac spines on the iliac crest. We evaluated our findings by creating high-resolution summation images. RESULTS: The courses of the iliohypogastric and ilioinguinal nerve are most consistent on the anterior surface of the quadratus lumborum muscle. The genitofemoral nerve always runs on the psoas muscle. The entry points of the nerves in the abdominal wall are located as follows: the iliohypogastric nerve is above the iliac crest and lateral from the anterior superior iliac spine, the ilioinguinal nerve is with great variability, either above or below the iliac crest and lateral from the anterior superior iliac spine, the genital branch is around the internal inguinal ring, the femoral branch is either cranial or caudal to the iliopubic tract, and the lateral femoral cutaneous nerve is either medial or lateral to the anterior superior iliac spine. CONCLUSION: Nerve injury during inguinal hernia repairs can be avoided by taking the topographic anatomy of the inguinal nerves into consideration. The most advantageous plane to look for the iliohypogastric and ilioinguinal nerve during posterior neurectomy is on the anterior surface of the quadratus lumborum muscle. For the surgical treatment of severe chronic inguinodynia, especially after posterior open or endoscopic mesh repair (TAPP/TEP), the retroperitoneoscopic or open retroperitoneal approach for posterior triple neurectomy can be considered.

Lesiones duodenales secundarias a traumatismo: revisión de la literatura / Duodenal injuries due to trauma: Review of the literature

Las lesiones duodenales, debido a su localización retroperitoneal, constituyen un reto diagnóstico para el cirujano, de forma que son identificadas tardíamente y, en consecuencia, se asocian a un aumento de la morbimortalidad. En las mejores estimaciones las lesiones duodenales ocurren en un 4,3% de todos los pacientes con lesiones abdominales, en un rango de 3,7% a 5% y, además, debido a su proximidad anatómica con otros órganos sus lesiones raramente se presentan de forma aislada. El objetivo de este trabajo es presentar una descripción concisa de la anatomía, diagnóstico, manejo quirúrgico y tratamiento de las complicaciones del traumatismo duodenal, y realizar un análisis de las complicaciones y de la mortalidad de las lesiones del duodeno en función de una revisión de la literatura de los últimos 46 años

Duodenal injuries constitute a challenge to the Trauma Surgeon, mainly due to their retroperitoneal location. When identified, they present associated with other abdominal injuries. Consequently, they have an increased morbidity and mortality. At best estimates, duodenal lesions occur in 4.3% of all patients with abdominal injuries, ranging from 3.7% to 5%, and because of their anatomical proximity to other organs, they are rarely an isolated injury. The aim of this paper is to present a concise description of the anatomy, diagnosis, surgical management and treatment of complications of duodenal trauma, and an analysis of complications and mortality rates of duodenal injuries based on a 46-year review of the literature

Primary retroperitoneal masses: what is the differential diagnosis?

Primary retroperitoneal masses include a diverse, and often rare, group of neoplastic and non-neoplastic entities that arise within the retroperitoneum but do not originate from any retroperitoneal organ. Their overlapping appearances on cross-sectional imaging may pose a diagnostic challenge to the radiologist; familiarity with characteristic imaging features, together with relevant clinical information, helps to narrow the differential diagnosis. In this article, a systematic approach to identifying and classifying primary retroperitoneal masses is described. The normal anatomy of the retroperitoneum is reviewed with an emphasis on fascial planes, retroperitoneal compartments, and their contents using cross-sectional imaging. Specific radiologic signs to accurately identify an intra-abdominal mass as primary retroperitoneal are presented, first by confirming the location as retroperitoneal and secondly by excluding an organ of origin. A differential diagnosis based on a predominantly solid or cystic appearance, including neoplastic and non-neoplastic entities, is elaborated. Finally, key diagnostic clues based on characteristic imaging findings are described, which help to narrow the differential diagnosis. This article provides a comprehensive overview of the cross-sectional imaging features of primary retroperitoneal masses, including normal retroperitoneal anatomy, radiologic signs of retroperitoneal masses and the differential diagnosis of solid and cystic, neoplastic and non-neoplastic retroperitoneal masses, with a view to assist the radiologist in narrowing the differential diagnosis.

Radioanatomy of the retroperitoneal space.

The retroperitoneum is a space situated behind the parietal peritoneum and in front of the transversalis fascia. It contains further spaces that are separated by the fasciae, between which communication is possible with both the peritoneal cavity and the pelvis, according to the theory of interfascial spread. The perirenal space has the shape of an inverted cone and contains the kidneys, adrenal glands, and related vasculature. It is delineated by the anterior 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.