JSUR Journal

Introduction

Renal Cell Carcinoma (RCC) is the most common primary malignancy of the kidney, while liposarcoma is a rare softtissue sarcoma typically arising in the retroperitoneum [1]. The simultaneous occurrence of both neoplasms within the same kidney is exceedingly rare, with a limited number of cases reported in the literature. The pathogenesis of such synchronous tumors remains uncertain and presents significant diagnostic and therapeutic challenges. RCC originates from the renal parenchyma, most commonly as the clear cell subtype arising from the proximal convoluted tubules. It is frequently asymptomatic and often discovered incidentally during imaging for unrelated conditions. When symptoms do occur, they typically include hematuria, flank pain, and a palpable abdominal mass [2]. Recognized risk factors for RCC include cigarette smoking, obesity, hypertension, and hereditary syndromes such as von Hippel–Lindau disease [1]. Diagnostic evaluation is primarily based on Computed Tomography (CT) and Magnetic Resonance Imaging (MRI), followed by histopathological confirmation. Treatment options for localized disease include partial or radical nephrectomy, depending on tumor size, location, and patient comorbidity. In advanced or metastatic stages, targeted therapies and immunotherapy have significantly improved clinical outcomes. Liposarcoma is a malignant mesenchymal neoplasm derived from adipose tissue and accounts for approximately 20% of all adult soft-tissue sarcomas [2,3]. Its occurrence within the kidney is exceedingly rare. The peak incidence is observed in the fifth and sixth decades of life, with a male predominance. Liposarcoma is classified into four subtypes: well-differentiated, dedifferentiated, myxoid, and pleomorphic. The Well-Differentiated Subtype (WDLPS) represents a low-grade malignancy characterized by mature adipocytes with minimal atypia and a relatively indolent course, although it carries a significant risk of local recurrence (20–85%) following surgical excision [3]. It may arise primarily from the renal capsule or renal sinus. The most important prognostic factor for survival is histological grade, which reflects the degree of differentiation and completeness of resection. The principal differential diagnosis includes Angiomyolipoma (AML), as both tumors may appear as large, fat-containing lesions radiographically. Immunohistochemically, WDLPS often expresses S100 and calretinin. The cornerstone of therapy is complete surgical resection with negative margins. Although the prognosis is generally favorable, long-term follow-up is required due to the risk of recurrence [3]. The coexistence of RCC and WDLPS within a single kidney is exceptionally uncommon. The underlying mechanisms remain speculative, with hypotheses including independent tumorigenesis or a shared progenitor cell line. Management is primarily surgical, typically involving radical nephrectomy, as standardized treatment guidelines are lacking due to the rarity of this clinical scenario.

Case Report

A 78-year-old woman presented to a urology clinic with intermittent left flank discomfort persisting for approximately six months. She denied hematuria, dysuria, or a history of urinary tract infection and renal inflammation. Laboratory findings revealed mild anemia (hemoglobin 109 g/L, hematocrit 0.323 L/L) and normal renal function (creatinine 90 µmol/L, urea 7.7 mmol/L). Her medical history was notable for hypertension and well-controlled type 2 diabetes mellitus managed with oral hypoglycemics. On physical examination, a palpable mass was detected in the left flank and hemiabdomen. Abdominal ultrasonography revealed a poorly defined lesion within the left kidney, approximately 90 × 60 mm in size. Contrast-enhanced CT of the thorax, abdomen, and pelvis demonstrated multiple small cystic lesions up to 25 mm in the left kidney, along with two major solid masses of clinical significance. A lobulated mass at the upper pole (67 × 60 mm) exhibited central calcifications and contrast enhancement consistent with RCC (Figure 1). A second, well-circumscribed lipomatous lesion (110 × 100 mm) was identified at the lower pole and renal hilum (Figure 2), causing compression and deformation of the collecting system without invasion, initially interpreted as an angiomyolipoma. The renal vein demonstrated a retroaortic course, a relevant anatomic variation for surgical planning. After multidisciplinary evaluation including urologists, oncologists, abdominal surgeons, and interventional radiologists, preoperative embolization of the left renal artery was recommended, followed by radical nephrectomy.

Figure 1: CT scan demonstrating a left renal mass with radiologic features of clear cell renal carcinoma.

Figure 2: CT image showing a giant liposarcoma occupying the lower pole of the left kidney.

Renal artery embolization was performed under local anesthesia using the Seldinger technique, with complete occlusion confirmed angiographically (Figures 3-4). Six days later, a transabdominal left radical nephrectomy was performed. Intraoperatively, the kidney appeared markedly enlarged and deformed, containing cystic and soft-tissue components but without invasion of adjacent structures (Figures 5-6). The operation was uneventful, with minimal blood loss (approximately 300 mL) and no transfusion requirement. The postoperative course was smooth, and the patient was discharged on postoperative day five in good condition. Histopathological examination revealed that the upper pole lesion corresponded to a low-grade clear cell RCC with focal necrosis (Figures 7-8). The larger lesion was identified as a well-differentiated liposarcoma (Figures 9-10), correcting the initial radiologic misdiagnosis of angiomyolipoma. At the three-month follow-up, the patient remained asymptomatic. Laboratory results indicated mild renal impairment (creatinine 169 µmol/L, urea 9.2 mmol/L) but normal inflammatory markers. Ultrasonography revealed no recurrence or lymphadenopathy. Nephrology follow-up was continued due to reduced renal function. Six months postoperatively, CT imaging of the thorax, abdomen, and pelvis demonstrated no evidence of local recurrence or distant metastasis. Given the absence of standardized surveillance protocols for synchronous RCC and WDLPS, followup was conducted in accordance with conventional RCC and retroperitoneal sarcoma guidelines.

Figure 3: Angiographic visualization of arterial vascularization of the left kidney before embolization.

Figure 4: Post-embolization angiography showing successful

Figure 5:Anterior view of the resected left kidney specimen with tumor dimensions indicated.

Figure 6: Posterior view of the resected kidney specimen