Most retroperitoneal tumors are malignant and account for one-third of soft tissue sarcomas. They usually present as large masses at primary diagnosis. Patients will be asymptomatic until the mass is large enough to compress or invade contagious structures. Patients may have nonspecific abdominal symptoms such as abdominal discomfort, distention, nausea, and vomiting [15, 16]. The family of ES and related tumors is characterized by small round blue cell tumors associated with a nonrandom t(11:22)(q24:q12) chromosome rearrangement [4, 17]. ESs and PNETs are well-known tumors in this family. They are malignant small blue round cell tumors with variable degrees of neuroectodermal differentiation [18]. Since the most common site of ES is the bone, most pediatric patients have so-called skeletal ESs, while ESS is very rare. Unlike children, more than 50% of ESs in adults are ESS, which can develop in the trunk, intraabdominal tissues, retroperitoneum, and viscera [18,19,20]. These tumors often present with rapid growth and widespread metastasis, leading to poor prognoses [21].

Imaging studies are essential for diagnosing such retroperitoneal lesions. MRI is the preferred tool for delineating the tumor’s extent and relationship with adjacent tissues or blood supplies [16]. However, while imaging studies are necessary, they cannot make a definite diagnosis due to other equivalent tumors having the same imaging characteristics [18]. Tissue confirmation of such tumors is always required. Specific stains are helpful for diagnosis, including those for the CD99 molecule (Xg blood group), micrometastases, vimentin, nonspecific esterase, S100 calcium-binding proteins, desmin, and cytokeratins [20,21,22,23]. Multimodal treatment consisting of surgical resection, chemotherapy, and high-dose radiotherapy (if indicated) has been recommended [24]. Prognostic factors are similar for ESS and ES, such as the presence or absence of metastasis, tumor size, extent of necrosis, and response to chemotherapy [25]. The quality of the primary excision is also important for local and distant recurrence, and wider resection margins are required [26]. Furthermore, combining surgery with chemotherapy and/or radiotherapy is recommended based on the location, respectability, and tumor stage [27]. The patients should undergo radiotherapy when negative surgical margins cannot be achieved [8]. In patients with distant metastasis, chemotherapy remains an option after primary tumor excision, providing better progression-free survival [28]. In some reports, targeted therapy and immunotherapy also play a role in ES treatment [29, 30]. To our knowledge, this is the first case report of ESS presenting with renal artery invasion but a normal kidney. In our case, the patient had nonmetastatic disease. She received a tumor resection with negative surgical margins after renal artery embolization. She underwent chemotherapy and radiotherapy to avoid local and distant metastasis. Continuous follow-up is necessary for treatment outcome evaluations.

In conclusion, retroperitoneal malignancies are rare but usually severe conditions. Their clinical symptoms are usually nonspecific. Imaging studies are required for primary diagnosis, but a definite diagnosis still depends on histopathology. EES is one of the differential diagnoses of retroperitoneal malignancy, characterized by small blue round cells. Multimodality treatment comprising surgical resection, chemotherapy, and radiotherapy is recommended for better outcomes. Our case report shows that retroperitoneal EESs with renal artery invasion can be treated safely with transarterial embolization and surgery.