Diagnosing liposarcoma on (peri)-renal mass biopsy: A clinicopathological study of 30 cases.

AIMS: Classification of renal neoplasms on small tissue biopsies is in increasing demand, and maintaining broad differential diagnostic considerations in this setting is necessary. When evaluating a renal or perirenal tumour biopsy with sarcomatoid morphology, together with sarcomatoid renal cell carcinoma and sarcomatoid urothelial carcinoma as top diagnostic considerations, it is vital to additionally consider the possibility of well-differentiated and de-differentiated liposarcoma. METHODS AND RESULTS: This study reports a series of 30 biopsy samples from sites in or around the kidney collected from four institutions in which the correct diagnosis was either well-differentiated or de-differentiated liposarcoma. The majority (26 of 30, 87%) of lesions were accurately diagnosed on biopsy sampling, all of which incorporated testing for MDM2 by immunohistochemistry (IHC), fluorescence in-situ hybridisation (FISH) or a combination of the two as part of the diagnostic work-up. Tumour expression of MDM2 by IHC without confirmatory FISH analysis was sometimes (30%) sufficient to reach a diagnosis, but demonstration of MDM2 amplification by FISH was ascertained in the majority (57%) of biopsy samples. A diagnosis of de-differentiated liposarcoma was not definitively established until resection in four (13%) patients, as no MDM2 testing was performed on the corresponding pre-operative biopsies. CONCLUSIONS: When a retroperitoneal tumour is not clinically suspected, histological consideration of a liposarcoma diagnosis may be overlooked. Implementation of ancillary immunohistochemical and cytogenetic testing can ultimately lead to a definitive diagnosis in this potentially misleading anatomical location.

Optimizing surgical strategies for retroperitoneal liposarcoma: a comprehensive evaluation of standardized aggressive surgical policies.

BACKGROUND: Retroperitoneal liposarcoma (RLPS) constitutes the majority of retroperitoneal sarcomas. While surgical resection remains the sole curative approach, determining the optimal surgical strategy for RLPS remains elusive. This study addresses the ongoing debate surrounding the optimal surgical strategy for RLPS. METHODS: We recruited 77 patients with RLPS who underwent aggressive surgical policies. Patients were categorized into three surgical subtypes: suprapancreatic RLPS, pancreatic RLPS, and subpancreatic RLPS. Our standardized surgical strategy involved resecting macroscopically uninvolved adjacent organs according to surgical subtypes. We collected clinical, pathological and prognostic data for analyses. RESULTS: The median follow-up was 45.5 months. Overall survival (OS) and recurrence-free survival (RFS) were significantly correlated with multifocal RLPS, pathological subtype, recurrent RLPS and histological grade (P for OS = 0.011, 0.004, 0.010, and < 0.001, P for RFS = 0.004, 0.001, < 0.001, and < 0.001, respectively). The 5-Year Estimate OS of well-differentiated liposarcoma (WDLPS), G1 RLPS, de novo RLPS and unifocal RLPS were 100%, 89.4%, 75.3% and 69.1%, respectively. The distant metastasis rate was 1.4%. The morbidity rates (≥ grade III) for suprapancreatic, pancreatic, and subpancreatic RLPS were 26.7%, 15.6%, and 13.3%, respectively. The perioperative mortality rate is 2.6%. CONCLUSIONS: Standardized aggressive surgical policies demonstrated prognostic benefits for RLPS, particularly for G1 RLPS, WDLPS, unifocal RLPS, and de novo RLPS. This approach effectively balanced considerations of adequate exposure, surgical safety, and thorough removal of all fat tissue. G1 RLPS, WDLPS, unifocal RLPS, and de novo RLPS could be potential indications for aggressive surgical policies.

Clinicopathological and molecular genetic analysis of 13 cases of primary retroperitoneal Ewing sarcoma.

Retroperitoneal Ewing sarcomas (RES) are very rare and mostly described in case reports. The purpose of this study was to retrospectively analyze the clinicopathology, molecular characteristics, biological behavior, and therapeutic information of 13 cases of primary RES with immunohistochemical staining, fluorescence in situ hybridization, RT-PCR and NGS sequencing detection techniques. The thirteen patients included eight males and five females with a mean age of 34 years. Morphologically, the tumors were comprised of small round or epithelial-like cells with vacuolated cytoplasm (6/13,46 %) arranged in diffuse, nested (8/13,62 %) and perivascular (7/13,54 %) patterns. Unusual morphologic patterns, such as meningioma-like swirling structures and sieve-like structures were relatively novel findings. Immunohistochemical studies showed CD99 (12/13; 92 %), CD56 (11/13; 85 %), NKX2.2 (9/13; 69 %), PAX7 (10/11;91 %) and CD117(6/9;67 %) to be positive.12 cases (92 %) demonstrated EWSR1 rearrangement and 3 cases displayed EWSR1::FLI1 fusion by FISH. ERCC4 splice-site variant, a novel pathogenic variant, was discovered for the first time via RNA sequencing. With a median follow-up duration of 14 months (6 to 79 months), 8/13 (62 %) patients died, while 5/13(38 %) survived. Three cases recurred, and five patients developed metastasis to the liver (2 cases), lung (2 cases) and bone (1 case). RES is an aggressive, high-grade tumor, prone to multiple recurrences and metastases, with distinctive morphologic, immunohistochemical, and molecular genetic features. ERCC4 splicing mutation, which is a novel pathogenic variant discovered for the first time, with possible significance for understanding the disease, as well as the development of targeted drugs.

An unusual case of retroperitoneal synovial sarcoma with CT, MRI, and F-18 FDG PET/CT findings.

Synovial sarcoma, predominantly found in the extremities, rarely occurs in the retroperitoneum. Tumors can often grow to a considerable size before diagnosis, which warrant the critical importance of early detection to minimize morbidity and mortality. While the final diagnosis relies on pathologic examination, imaging plays a crucial role in early detection.

Computed tomography features and prevalence of focal diaphragmatic mineralization in 300 dogs.

A focal area of mineral attenuation is commonly observed in the diaphragmatic crura of canine patients undergoing a thoracic CT. There is no mention of this finding in either the human or veterinary medicine literature. This retrospective study evaluates 300 canine thoracic CT studies with the aim of describing the CT appearance of this finding and establishing a prevalence in a large cohort of dogs. The presence of the mineral focus and its CT characteristics, including length, attenuation, and appearance, were recorded and correlated with the patient's signalments and anamnesis. The focus was observed in 43 of 300 studies (14.3%). The most common appearance was a thin, millimetric, toothpick-like mineral attenuating structure in the confluence of the diaphragmatic crura, just ventral to the aorta. There was no association with adjacent potentially pathological changes. A significant correlation was found between the presence of the focus and the patient's body weight (P = .03), as well as with a brachycephalic conformation (P = .03). This focus of mineralization represents a relatively common incidental finding in the canine diaphragm and has no evident association with pathology.

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.

Unicentric Portocaval Castleman Disease in an Adolescent: Challenges in Diagnosis and Management.

Castleman disease is an unusual, benign disorder of unknown etiology, characterized by the proliferation of the lymphoid tissue. It can have a unicentric or multicentric presentation, depending on the number of lymph nodes involved. On clinical examination and imaging, it can imitate a malignancy and the diagnosis can only be confirmed on histopathological examination. Retroperitoneal location and presentation in the pediatric age group are extremely rare. We report a case of an adolescent girl with a unicentric lymph nodal mass in the portocaval space which was completely excised.

Use of the right retroperitoneum as an alternative approach to the abdominal aorta.

OBJECTIVE: The left retroperitoneal approach to the aorta is a well-established technique for aortic exposure. The right retroperitoneal approach to the aorta is performed less commonly, and the outcomes remain unknown. This study aimed to evaluate the outcomes of right retroperitoneal aortic-based procedures and to determine its utility in aortic reconstruction when faced with hostile anatomy or infection in the abdomen or left flank. METHODS: A retrospective query of a vascular surgery database from a tertiary referral center was performed for all retroperitoneal aortic procedures. Individual patient charts were reviewed, and data were collected. Demographics, indications, intraoperative details, and outcomes were tabulated. RESULTS: From 1984 through 2020, there have been 7454 open aortic procedures; 6076 were retroperitoneal-based, and 219 of which were performed from the right retroperitoneal approach (Rrp). Aneurysmal disease was the most common indication (48.9%), and graft occlusion was the most common postoperative complication (11.4%). The average aneurysm size was 5.5 cm, and the most common reconstruction was with a bifurcated graft (77.6%). Average intraoperative blood loss was 923.8 mL (range, 50-6800 mL; median, 600 mL). Perioperative complications occurred in 56 patients (25.6%) for a total of 70 complications. Perioperative mortality occurred in two patients (0.91%). The 219 patients treated with Rrp required 66 subsequent procedures in 31 patients. These included 29 extra-anatomic bypasses, 19 thrombectomies/embolectomies, 10 bypass revisions, 5 infected graft excisions, and 3 aneurysm revisions. Eight Rrp eventually underwent a left retroperitoneal approach for aortic reconstruction. Fourteen patients with a left-sided aortic procedure required a Rrp. CONCLUSIONS: The right retroperitoneal approach to the aorta is a useful technique in the setting of prior surgery, anatomic abnormality, or infection that complicates the use of other more frequently employed approaches. This review demonstrates comparable outcomes and the technical feasibility of this approach. The right retroperitoneal approach to aortic surgery should be considered a viable alternative to left retroperitoneal and transperitoneal access in patients with complex anatomy or prohibitive pathology for more traditional exposure.

Prospective Cohort Study Quantifying the Effect of the LevaLap 1.0 on the Distance between the Abdominal Wall and Intra-abdominal Viscera.

STUDY OBJECTIVE: More than 13 million laparoscopic procedures are performed globally every year. The LevaLap 1.0 device may facilitate safe abdominal access when using the Veress needle for initial abdominal insufflation during laparoscopic surgery. We undertook this study to test the hypothesis that use of the LevaLap 1.0 would increase the distance from the abdominal wall to underlying viscera and the retroperitoneum, including from major vessels. DESIGN: Prospective cohort study. SETTING: Referral center. PATIENTS: Eighteen patients scheduled to undergo an interventional radiology procedure under general anesthesia and muscle relaxation. INTERVENTIONS: Application of the LevaLap 1.0 device on the umbilicus and on Palmer's point, during computed tomography scanning. MEASUREMENTS: Distance from the abdominal wall to the underlying bowel and to retroperitoneal blood vessels and more distant intra-abdominal organs before and after vacuum was applied to the LevaLap 1.0. MAIN RESULTS: The device did not significantly increase the distance from the abdominal wall to the immediate underlying bowel. Alternatively, the LevaLap 1.0 created a significant increase in the distance between the abdominal wall at the access point and more distant intra-abdominal organs at the umbilicus and at Palmer's point (mean ± SD: +3.91 ± 2.32 cm, p = .001, and +3.41 ± 3.12 cm, p = .001, respectively). At the umbilicus, the device increased the distance between the abdominal wall and the anterior wall of the vena cava by +5.32 ± 1.22 cm (p = .004) or the anterior wall of the aorta by 5.49 ± 1.40 cm (p = .004). At Palmer's point, the device increased the distance between the anterior abdominal wall and the colon and/or small bowel by 2.13 ± 1.81 cm (p = .023). No adverse events were reported. CONCLUSIONS: The LevaLap 1.0 increased the distance between abdominal wall and major retroperitoneal blood vessels by >5 cm, promoting safer access during Veress needle insufflation when performing laparoscopic surgery.

A case of cystic lymphangioma arising from the parauterine tissue.

A 57-year-old woman, gravida 3, para 3, with no complaints visited our hospital for right-sided adnexal tumor found incidentally in cancer screening. She had no medical history, surgical history, or gynecological disease. Imaging studies showed a 5-cm lobular cystic tumor on the right side of uterus. We suspected right hydrosalpinx and decided to perform diagnostic laparoscopy. During laparoscopy, the right adnexa was found to be atrophic, and the tumor was located in the broad ligament. The tumor was observed to be a multilocular cyst containing yellow fluid that developed from the right parauterine tissue. The tumor was resected from the surrounding tissue. Histological examination revealed that the multilocular cyst contained a vascular component surrounding the lymphatic endothelium and was decided to be a cystic lymphangioma. The patient was followed up and there was no evidence of recurrence at postoperative 7 months. We experienced a very rare case of lymphangioma arising from the parauterine tissue. The laparoscopic approach can assist with both diagnosis and treatment.

Progressive abdominal pain with acute exacerbation due to retroperitoneal follicular dendritic cell sarcoma: a case report with targeted genomic sequencing analysis.

BACKGROUND: Follicular dendritic cell sarcoma (FDCS) is a rare malignancy that arises from follicular dendritic cells and typically presents as a slow-growing painless mass without specific symptoms. Here we report an unusual case of a 55-year-old female with retroperitoneal FDCS who presented with progressive abdominal pain onset and acute exacerbation. METHODS: On CTA, a middle-upper abdominal mass (58*40 mm) was shown with multiple enlarged lymph nodes. After en-bloc resection of the tumor, the patient recovered completely from her symptoms and was discharged without complication. One month later, the patient returned for follow-up and the relevant tests were completed. RESULTS: In this case, CA724 elevated significantly and seemed to be associated with tumor progression. The results of positron emission tomography/computed tomography (PET/CT) and radiological examinations, including magnetic resonance imaging (MRI) and computed tomography angiography (CTA), were discussed to improve our understanding of diagnostic tools on FDCS. Targeted genomic sequencing analysis revealed three novel gene mutations, EPHA3 (nonsense mutation), DDR2 (SNV), and BIRC3 (InDel). CONCLUSION: We reported an unusual case of retroperitoneal FDCS with acute exacerbated abdominal pain. The interpretations of CA724, PET/CT, as well as imaging results deserve further investigation in FDCS. Genomic sequencing revealed three novel gene mutations in FDCS, including EPHA3 (nonsense mutation), DDR2 (SNV), and BIRC3 (InDel).

Twin Fetus-in-Fetu: The Story of an Encaged Twin.

Background: Fetus-in-fetu (FIF) features a monozygotic, diamniotic, parasitic twin enclosed within its host twin. Case report: An 11-month baby girl presented with an antenatal diagnosis of a retroperitoneal mass. Radiological findings suggested it to be a teratoma. The mass was excised in-toto, histological findings were consistent with fetus-in-fetu. Conclusions: FIF may not have identifiable vertebral bodies and limbs upon imaging. Organized organ systems help differentiate this from a teratoma.

Single-port retroperitoneoscopic partial nephrectomy: Initial description and standardisation of technique.

Introduction: Minimally invasive surgery has been established as the gold standard for the treatment of localised renal tumours. A retroperitoneal approach is a feasible option with advantages in posterior tumours and patients with previous abdominal surgeries. In this context, single-port retroperitoneoscopic partial nephrectomy (SPOR-PN) has not been widely explored and developed. We present this technique's description and our first results. Methods: We present a case series of nine patients undergoing SPOR-PN in a single institution. We used a multi-channel single-port access dispositive through a 35 mm incision below the 12th rib, a 30° two-dimensional laparoscope, curved graspers and needle drivers on the left hand and standard rigid material in the right hand. In all surgeries, we performed a complete renorrhaphy with the sliding-clip technique. The pain was evaluated through visual analogue scale (VAS) the day after surgery. Results: Patients' age ranged from 44 to 78 years. The median RENAL score was 5p, and the mean surgical time was 134 min. We performed an 'off-clamp' procedure on three patients. Among the patients who had renal artery clamped, the median ischaemia time was 18 min. The median in-hospital stay time was 48 h. Median VAS the day after surgery was 2. None of the anatomical pieces had positive borders. Only one complication was reported (Clavien IIIa). Conclusions: SPOR-PN is a feasible minimally invasive and nephron-sparing technique. The advantages of this procedure may not be only a better cosmetic appearance but also less post-operative pain. Further development and larger studies are needed.

Retroperitoneal abscess after urgent resection of the stomach in a geriatric patient treated with a surgical extraperitoneal approach - case report.

Retroperitoneal abscess after abdominal and retroperitoneal surgery is a relatively rare but serious complication that most often occurs as a result of a healing disorder in the postoperative period. The incidence is not high, in the literature the cases are mostly reported as case reports with a serious clinical course, high morbidity and mortality. The most important factor of effective treatment, after successful diagnosis by CT examination is rapid evacuation of the abscess and retroperitoneal drainage, in which mini-invasive surgical or radiological drainage dominate as methods of choice. Surgical drainage, burdened by higher morbidity and mortality is considered the last resort after failure of mini-invasive methods. In our case report, we present a case of retroperitoneal abscess, arising as a complication after gastric resection, which was evacuated and drained primarily surgically due to unsuitability for radiological intervention.

Post-Systemic Chemotherapy Prognoses of Recurrent/Metastatic Soft Tissue Sarcoma Patients with Retroperitoneal/Intra-Abdominal Origin versus Those with Extremities/Trunk Origin.

BACKGROUND: The clinical benefit of systemic chemotherapy for recurrent/metastatic retroperitoneal/intra-abdominal soft tissue sarcoma (STS) compared to its benefits for other primary lesions has not been known or sufficiently evaluated. METHODS AND PATIENTS: We retrospectively reviewed the cases of the STS patients who consulted a department of medical oncology in Tokyo between June 2011 and March 2018, and we extracted the cases of patients with primary sites at the retroperitoneum/intra-abdomen (cohort R) or extremities/trunk (cohort E) who received systemic chemotherapy in a recurrent/metastatic setting, comparing the cohorts' characteristics, chemotherapy details, and prognoses. RESULTS: Of all 337 STS patients, we enrolled 49 patients in cohort R and 75 patients in cohort E. Liposarcoma was more frequently observed in cohort R (51.0%) than cohort E (22.7%). The median chemotherapy treatment line was two lines (range: 1-6) in cohort R and three lines (range: 1-9) in cohort E. The doxorubicin usage rates differed in recurrent/metastatic settings (90.0% in cohort R and 55.0% in cohort E), due mainly to the higher rate of a perioperative chemotherapy treatment history in cohort E (52.0% vs. 6.1% in cohort R). The median overall survival from the start of salvage chemotherapy was 31.9 months (cohort R; 95% CI: 20.9-42.8) and 27.1 months (cohort E; 95% CI: 21.6-32.5) (p = 0.549). CONCLUSION: There were differences in the distributions of pathology and antitumor drugs used in a salvage setting between retroperitoneal/intra-abdominal and extremities/trunk STS patients in recurrent/metastatic settings, but the prognoses with salvage chemotherapy were similar in the two cohorts.

How I Treat Localized Soft Tissue Sarcomas: Update on Diagnosis, Risk Stratification, and Treatment.

BACKGROUND: Adult-type soft tissue sarcomas (STSs) are rare tumors representing about 1% of all adult malignant tumors. Their extreme histological heterogeneity places them among the most challenging fields of diagnostic pathology. The variability of clinical and prognostic presentation between the various histotypes reflects the different management that should be followed on a case-by-case basis. These features make STSs the case in point of how important it is a centralized and multidisciplinary approach. SUMMARY: Surgery represents the mainstay in the treatment of localized STSs. Recently, more and more studies are making efforts to understand what the contribution of chemotherapy and radiotherapy with neoadjuvant and adjuvant intent may be both in unselected and selected histological subgroups. In fact, despite the improvement in overall survival seen in the past few years thanks to the adoption of a more radical surgical approach, mortality remains relatively high and the 5-year overall survival is around 65%. KEY MESSAGES: In this review, we comment upon the treatment of localized STSs of the extremity, trunk wall, and retroperitoneum and how surgery, radiotherapy, and chemotherapy can be integrated with each other and individually tailored. Nomograms can assist clinicians in this complex therapeutic decision-making process, through the identification of patients at higher risk of death or disease relapse.

Diagnostic yield and safety of percutaneous CT-guided biopsy of retroperitoneal lesions and analysis of imaging features.

BACKGROUND: Computed tomography (CT)-guided biopsy is emerging as a preferred method for obtaining tissue samples from retroperitoneal lesions due to clear visualization of needle and vessels. PURPOSE: To assess diagnostic yield and safety of CT-guided biopsy of retroperitoneal lesions and compare CT findings in different disease categories. MATERIAL AND METHODS: This retrospective analytical study included 86 patients with retroperitoneal lesions who underwent CT-guided biopsy from December 2010 to March 2020. All procedures were performed with co-axial technique and multiple cores were obtained and subjected to histopathology. Additional tests like immunohistochemistry or microbiological analysis were done depending on clinical suspicion. Diagnostic yield calculation and comparison of imaging findings was done by one-way ANOVA, chi-square, and Fisher's exact tests. RESULTS: CT-guided biopsy was technically successful in all cases with a diagnostic yield of 91.9%. Minor complications in the form of small hematomas were seen in two patients. Major disease categories on final diagnosis were lymphoma, tuberculosis, and metastases. A variety of malignant and benign soft-tissue neoplasms were also noted less commonly. With help of immunohistochemistry, lymphoma subtype was established in 88.8% of cases. Addition of microbiological tests like the GeneXpert assay helped in the diagnosis of tuberculosis in some cases. A mass-like appearance and vascular encasement was common in metastatic group and lymphoma. CONCLUSION: Percutaneous CT-guided biopsy is a safe method for the sampling of retroperitoneal lesions with high diagnostic yield. Imaging findings are mostly overlapping; however, some features are more common in a particular disease condition.

Myxoid liposarcoma originating in the retroperitoneum with metastasis to the calcaneus: a rare case report and review of literature.

Myxoid liposarcoma (MLPS) is known to have a variety of metastatic manifestations. We report a MLPS originating in the pelvis with metastasis to the calcaneus. The patient was a 72-year-old man who developed lumbar pain and right lower extremity pain 2 years ago. He visited a nearby clinic and underwent a radiographic examination. Computed tomography (CT) revealed a tumor in the right retroperitoneum. A CT-guided needle biopsy was performed, and pathological examination revealed myxoid liposarcoma. Wide surgical resection was not performed due to the patients' wishes, technical difficulties, and magnitude of the invasion, and the patient received heavy particle radiation therapy (HPRT) of 70.4 Gy. After HPRT, the tumor mass was slightly reduced. However, 11 months after HPRT, a recurrent lesion in the liver was observed. Although HPRT was performed again for the metastatic liver lesion (70.4 Gy), the tumor increased in size. Furthermore, 1 month later, the patient complained of pain in the left foot, and CT and magnetic resonance imaging revealed an osteolytic lesion in the calcaneus. A biopsy was performed, and pathological examination showed a metastatic lesion of myxoid-type liposarcoma. The patient wore a short lower limb orthosis and was able to walk but died 1 month later. Oncologists should note that MLPS can metastasize to the calcaneus.

Perirenal perivascular epithelioid cell tumor (PEComa).

A 52-year-old woman, who is a carrier of MLH-1 mutation (HNPCC-type Lynch syndrome) with a history of colon adenocarcinoma, was diagnosed with a 26 mm lobulated contrast-capturing mass located caudally of the pancreas tail, anteromedial of the spleen and medial of the splenic colon angle. She underwent an exploratory laparotomy with resection of the tumor. Initially, this mass was presumed to be metastasis in a patient with a history of colon adenocarcinoma. However, after further histopathological and immunohistochemical examination, the mass appeared to be a rare PEComa. Only a few cases of a PEComa in this retroperitoneal perirenal location have been described.

Retroperitoneum ganglioneuroma: imaging features and surgical outcomes of 35 cases at a Chinese Institution.

BACKGROUND: The preoperative evaluation is crucial for diagnosis and surgical plan of retroperitoneum ganglioneuroma (GN). In this study, we reviewed a relatively large series of histopathological proved retroperitoneum GN cases, summarized the imaging features and further depicted risk factors of increased surgical blood loss. METHODS: A total of 35 (18 male, 17 female) patients were retrospectively enrolled from January 2012 to June 2019 at our institution. Among them, 24 patients had undergone CT scans and 19 patients had undergone MR examination before treatment. The clinical and radiological features were analyzed and the relationships between image features and surgical blood loss were evaluated. RESULTS: The media age of the involved 35 patients was 40 years (range, 14-66 years). The histological tumor size was 10.12 ± 4.56 cm for average. Retroperitoneum GN was relatively low density on unenhanced CT images and showed delayed progressive enhancement on enhanced CT and MR images. The whorled sign could be seen in 14 patients. The vessel encasement sign could be found in 17 patients. Univariate analysis revealed maximal tumor size measured on axial image, maximal tumor size measured on coronal image, encasing one or both renal pedicles, encasing the aorta and/or vena cava and whorled sign on MRI showed significant difference between the blood loss ≥ 400 ml and blood loss < 400 ml group. Logistic regression further detected that maximal tumor size measured on axial images (OR: 1.12; 95% CI: 1.02-1.24; P = 0.023) and encasing one or both renal pedicles (OR: 22.39; 95% CI: 1.35-372.99; P = 0.030) were independently correlated with surgical blood loss. CONCLUSIONS: Preoperative CT and MR imaging analysis was valuable for both diagnosis and surgical risk prediction of retroperitoneum GN.