BACKGROUND: Schwannomas are benign usually encapsulated nerve sheath tumors derived from the Schwann cells, and affecting single or multiple nerves. The tumors commonly arise from the cranial nerves as acoustic neurinomas but they are extremely rare in the pelvis and the retroperitoneal area. Retroperitoneal pelvic schwannomas often present with non-specific symptoms leading to misdiagnosis and prolonged morbidity.
METHODS: We report the case of a 59-year-old woman presenting with a feeling of heaviness in the lower abdomen who was found to have a retroperitoneal pelvic schwannoma originating from the right femoral nerve. She had a history of two resections of peripheral schwannomas at four different sites of limbs. After conducting magnetic resonance imaging, this pelvic schwannoma was misdiagnosed as a gynecological malignancy. The tumor was successfully removed by laparoscopic surgery. Pathological analysis of the mass revealed a benign schwannoma of the femoral nerve sheath with demonstrating strong, diffuse positivity for S-100 protein.
CONCLUSIONS: Although retroperitoneal pelvic schwannoma is rare, it should be considered in the differential diagnosis of pelvic masses, especially in patients with a history of neurogenic mass or the presence of neurogenic mass elsewhere.

A 7-year-old spayed female domestic shorthair cat was presented for evaluation of a large-volume abdominal space-occupying lesion. A computed tomography angiography examination detected a round retroperitoneal mass, in contact with the large abdominal vessels, characterized by an external hyperattenuating capsule and a larger hypoattenuating center. The capsule was soft-tissue attenuating with marked heterogenous contrast enhancement. The center was hypoattenuating pre- and post-contrast administration. The mass displaced both kidneys laterally and the descendent colon ventrally. The mesenteric veins and both phrenicoabdominal veins were markedly increased in diameter. However, the adrenals were not involved. On the excretory phase, no contrast enhancement was observed in either ureter, except for the proximal tract of the right ureter. At laparotomy, both ureters entered the mass that was adherent to the great abdominal vessels. The cytological diagnosis was retroperitoneal extra-adrenal paraganglioma. In cats, retroperitoneal extra-adrenal paragangliomas are very rare. This is the first computed tomography angiography report of a retroperitoneal extra-adrenal paraganglioma in a domestic cat. Key clinical message: This report describes the computed tomography angiography features of a rare case of a retroperitoneal extra-adrenal paraganglioma in a cat. These features could be taken into consideration to direct the diagnosis of a possible neuroendocrine origin for a retroperitoneal mass in a cat.
Caractéristiques de l’angiographie par tomodensitométrie d’un para-gangliome extra-surrénalien rétropéritonéal chez un chatUne chatte domestique à poils courts, âgée de 7 ans, stérilisée, a été présentée pour évaluation d’une lésion abdominale de grand volume occupant de l’espace. Un examen d’angiographie tomodensitométrique a détecté une masse rétropéritonéale ronde, en contact avec les gros vaisseaux abdominaux, caractérisée par une capsule externe hyper-atténuante et un centre hypo-atténuant plus large. La capsule présentait une atténuation des tissus mous avec une prise de contraste hétérogène marquée. Le centre était hypoatténuant avant et après l’administration le milieu de contraste. La masse a déplacé latéralement les deux reins et ventralement le côlon descendant. Le diamètre des veines mésentériques et des deux veines phrénico-abdominales était nettement augmenté. Cependant, les surrénales n’étaient pas impliquées. À la phase excrétrice, aucune augmentation de contraste n’a été observée dans les deux uretères, à l’exception du tractus proximal de l’uretère droit. Lors de la laparotomie, les deux uretères pénétraient dans la masse adhérente aux gros vaisseaux abdominaux. Le diagnostic cytologique était un paragangliome extra-surrénalien rétropéritonéal. Chez le chat, les para-gangliomes extra-surrénaliens rétropéritonéaux sont très rares. Il s’agit du premier rapport d’angiographie par tomodensitométrie d’un para-gangliome extra-surrénalien rétropéritonéal chez un chat domestique.Message clinique clé:Ce rapport décrit les caractéristiques de l’angiographie par tomodensitométrie d’un cas rare de paragangliome extra-surrénalien rétropéritonéal chez un chat. Ces caractéristiques pourraient être prises en considération pour orienter le diagnostic d’une éventuelle origine neuroendocrinienne d’une masse rétropéritonéale chez un chat.(Traduit par Dr Serge Messier).

schwannomas are benign and common soft tissue tumors. They are usually asymptomatic and are discovered for other reasons.
we present the case of an 82-year-old male patient with a recent diagnosis of moderately differentiated adenocarcinoma of the colon and a hypermetabolic periaortic nodule as an incidental finding.
percutaneous biopsy of the periaortic nodule confirmed the diagnosis of schwannoma. At one year of follow-up, growth of the schwannoma has been demonstrated. There are no signs of progression of his oncological disease.
schwannomas are benign tumors, rarely found in the retroperitoneum and can be sources of false-positive positron emission tomography results.
los schwannomas son tumores benignos y frecuentes de las partes blandas. Habitualmente son asintomáticos y son descubiertos por otros motivos.
presentamos el caso de un paciente masculino de 82 años con diagnóstico reciente de adenocarcinoma de colon moderadamente diferenciado y con un nódulo periaórtico hipermetabólico como hallazgo incidental.
la biopsia percutánea del nódulo periaórtico confirmó el diagnóstico de schwannoma. Al año de seguimiento, se ha demostrado crecimiento del schwannoma. No hay signos de progresión de su enfermedad oncológica.
los schwannomas son tumores benignos, infrecuentes en el retroperitoneo y pueden ser fuentes de resultados falsos positivos en tomografía por emisión de positrones.

OBJECTIVE: Anthracycline-based chemotherapies including doxorubicin monotherapy are recommended in major guidelines for patients with advanced or metastatic retroperitoneal sarcoma (RPS); however, few studies have reported the outcomes of doxorubicin monotherapy for these patients. We herein investigated the oncological efficacy and safety of doxorubicin monotherapy for patients with advanced or metastatic RPS in real-world clinical practice.
METHODS: Sixteen patients diagnosed with advanced or metastatic retroperitoneal sarcoma, receiving doxorubicin monotherapy as first-line treatment between February 2017 and March 2023 at our Institution were analyzed. Response rate, progression-free survival (PFS) periods, overall survival (OS) period, and adverse event (AE) profiles were retrospectively investigated.
RESULTS: The median age of patients was 69.5 years. Best responses to doxorubicin were as follows: complete response, 0 patients (0.0%); partial response, 3 (18.8%); stable disease, 9 (56.3%); and progressive disease, 4 (25.0%). The objective response rate and disease control rate were 18.8 and 75.0%, respectively. During the observation period (median, 22 months, range=2-53 months), median PFS and OS periods were 8.0 and 24.0 months, respectively. The following AEs Grade ≥3 occurred: neutropenia in 14 patients (87.5%), febrile neutropenia in 5 (31.3%), leukopenia in 2 (12.5%), thrombocytopenia in 1 (6.3%), and heart failure in 1 (6.3%). Grade ≥3 nausea and vomiting did not occur and there was no treatment-related death.
CONCLUSIONS: The oncological outcomes of doxorubicin monotherapy for RPS in real-world clinical practice were not inferior to those of the EORTC trial. The incidence of hematological AEs was higher; however, severe gastrointestinal AEs were prevented by prophylactic antiemetics and there were no treatment-related deaths. Collectively, doxorubicin monotherapy with appropriate prophylactic agents is a valid option for patients with advanced or metastatic RPS.

OBJECTIVE: There is limited evidence regarding the systemic treatment of retroperitoneal soft-tissue sarcoma, and the current Japanese guidelines fail to make definitive suggestions. Here, we report our experience with combination chemotherapy of mesna, doxorubicin, ifosfamide, and dacarbazine (MAID) in this population.
METHODS: We retrospectively reviewed the records of eight patients (three male and five female) who received MAID for pathologically diagnosed metastatic unresectable retroperitoneal sarcoma (either leiomyosarcoma or pleomorphic sarcoma) between October 2019 and January 2022. Treatment efficacy, tolerability (need for dose reduction), and safety profiles were evaluated and summarized.
RESULTS: At initiation, the median age was 56.0 years, and the body mass index was 20.0 kg/cm2 Six patients had Eastern Cooperative Oncology Group performance status scores of 0. The net clinical benefit was a partial response in three (37.5%) patients, stable disease in four (50.0%), and progressive disease in one (12.5%). During the median 90.8 weeks of follow-up, disease in five patients progressed, resulting in a median progression-free survival of 48.4 weeks, and five deaths occurred, resulting in an overall survival of 95.1 weeks. Commonly observed adverse events were neutropenia (eight patients), anemia (eight patients), and decreased platelet count (seven patients), which led to dose reduction (60-80%) in six patients.
CONCLUSIONS: MAID combination therapy may be an acceptable option for advanced retroperitoneal sarcoma; however, its benefits must be carefully assessed owing to its not insignificant toxicity.

BACKGROUND: Dogs with retroperitoneal hemangiosarcoma (HSA) exhibit variable postoperative median survival times (MST).
OBJECTIVE: To retrospectively evaluate the prognostic value of selected tumour-related factors, such as tumour size, rupture, invasion into adjacent tissue, involvement of lymph node and distant metastasis, they were analysed in dogs with retroperitoneal HSA.
METHODS: Ten dogs with retroperitoneal HSA managed solely with surgical excision were reviewed and compared with spleen (71) and liver (9) HSA. The Kaplan-Meier method and log-rank analysis were used compare MSTs between factors. Multivariable Cox proportional-hazard analysis was used to compare differences between arising sites.
RESULTS: Retroperitoneal HSA showed comparatively longer postoperative MST compared with that of spleen and liver HSA and demonstrated significantly longer MST (p = 0.003) for tumours ≥5 cm (195 days) than <5 cm (70 days). Spleen HSA revealed significantly shorter MSTs in involvement of distant lymph nodes (23 days) and distant metastasis (39 days) than those in negative (83 days, p = 0.002 and 110 days, p < 0.001, respectively). Liver HSA also revealed significantly shorter MST (16.5 days compared with 98 days, p = 0.003) for distant metastasis. Additionally, hazard ratios (HRs) and their forest plot for overall HSA revealed as poor prognostic factors, arising sites (spleen; HR 2.78, p = 0.016 and liver; HR 3.62, p = 0.019), involvement of distant lymph nodes (HR 2.43, p = 0.014), and distant metastasis (HR 2.86, p < 0.001), and as better prognostic factor of tumour size ≥5 cm (HR 0.53, p = 0.037).
CONCLUSIONS: In combination with overall HSA, retroperitoneal HSA shows comparatively longer postoperative MST compared to spleen and liver HSA, associated with tumour size ≥5 cm suggesting better prognostic factor.

Pelvic masses frequently originate from the pelvic cavity and are often associated with uterine, ovarian, or intestinal disorders. This report describes the case of a patient with a pelvic mass diagnosed as a retroperitoneal dermoid cyst at our hospital. We analyzed this case and conducted a literature review, to mitigate the risk of misdiagnosis and enhance the treatment of retroperitoneal masses.

BACKGROUND: Teratomas are germ cell tumors composed of somatic tissues from up to three germ layers. Primary retroperitoneal teratomas usually develop during childhood and are uncommon in adults and in the retroperitoneal space. While there are only a few cases of retroperitoneal thyroid tissue, we report a unique case of a retroperitoneal papillary thyroid carcinoma.
METHODS: A 41-year-old woman presented in our institution due to intermitted unspecific abdominal pain. Magnetic resonance imaging detected a multi-cystic solid retroperitoneal mass ventral to the psoas muscle and the left iliac artery. After surgical removal of the retroperitoneal mass, histology sections of the specimen indicated evidence of papillary thyroid carcinoma cells. A staging computed tomography scan of the body showed no further manifestations. To reduce the risk of recurrence, total thyroidectomy was performed followed by radioiodine therapy with lifelong hormone substitution.
CONCLUSIONS: Primary retroperitoneal teratoma with evidence of papillary thyroid carcinoma is a rare condition. Preoperative diagnosis is difficult due to its non-specific clinical manifestation and lack of specific radiologic findings. Histopathology analysis is necessary for diagnosis. Although surgery is considered the first line treatment, there is still discussion about the extent of resection and the need for total thyroidectomy with adjuvant radioiodine therapy.

OBJECTIVE: We have developed explainable machine learning models to predict the overall survival (OS) of retroperitoneal liposarcoma (RLPS) patients. This approach aims to enhance the explainability and transparency of our modeling results.
METHODS: We collected clinicopathological information of RLPS patients from The Surveillance, Epidemiology, and End Results (SEER) database and allocated them into training and validation sets with a 7:3 ratio. Simultaneously, we obtained an external validation cohort from The First Affiliated Hospital of Naval Medical University (Shanghai, China). We performed LASSO regression and multivariate Cox proportional hazards analysis to identify relevant risk factors, which were then combined to develop six machine learning (ML) models: Cox proportional hazards model (Coxph), random survival forest (RSF), ranger, gradient boosting with component-wise linear models (GBM), decision trees, and boosting trees. The predictive performance of these ML models was evaluated using the concordance index (C-index), the integrated cumulative/dynamic area under the curve (AUC), and the integrated Brier score, as well as the Cox-Snell residual plot. We also used time-dependent variable importance, analysis of partial dependence survival plots, and the generation of aggregated survival SHapley Additive exPlanations (SurvSHAP) plots to provide a global explanation of the optimal model. Additionally, SurvSHAP (t) and survival local interpretable model-agnostic explanations (SurvLIME) plots were used to provide a local explanation of the optimal model.
RESULTS: The final ML models are consisted of six factors: patient\'s age, gender, marital status, surgical history, as well as tumor\'s histopathological classification, histological grade, and SEER stage. Our prognostic model exhibits significant discriminative ability, particularly with the ranger model performing optimally. In the training set, validation set, and external validation set, the AUC for 1, 3, and 5 year OS are all above 0.83, and the integrated Brier scores are consistently below 0.15. The explainability analysis of the ranger model also indicates that histological grade, histopathological classification, and age are the most influential factors in predicting OS.
CONCLUSIONS: The ranger ML prognostic model exhibits optimal performance and can be utilized to predict the OS of RLPS patients, offering valuable and crucial references for clinical physicians to make informed decisions in advance.

BACKGROUND: Benign nerve sheath tumors presenting as solitary retroperitoneal masses (RBNSTs) pose a complex diagnostic challenge for multidisciplinary teams regarding differential diagnosis, staging, and treatment planning. This article reviews the role played by different imaging techniques in assessing RBNSTs and elucidates their typical pathological features with a particular emphasis on the correlation between imaging and histological findings. Furthermore, some examples of retroperitoneal tumors that merit consideration in the process of differential diagnosis based on cross-sectional investigations (CSIs) are reported. The correlation between tissue architecture and appearance on imaging can help increase the accuracy of differential diagnosis with other retroperitoneal neoplasms at CSIs.
UNASSIGNED: This educational review critically examines the correlation between imaging and histological features in solitary retroperitoneal benign nerve sheath tumors, offering valuable insights for improving the accuracy of differential diagnosis in clinical radiology.
CONCLUSIONS: RBNSTs are challenging to diagnose because they lack specific radiological features. Differential diagnosis of RBNSTs from other retroperitoneal neoplasms on imaging is complex. Surgical removal of RBNSTs is recommended for an accurate diagnosis.