Clear Cell Renal Cell Carcinoma in a 60-Year-Old Man Arising From Congenital Left-Sided Ectopic Right Kidney (Crossed Fused Renal Ectopia) With Invasion Into the Contralateral Kidney

Introduction

Embryologically, kidney development begins in week 4 with formation of the nephrogenic cord; however, nephrogenesis is not completed until week 32, when millions of collecting tubules have formed [1]. Rarely, a congenital anomaly occurs during embryologic development in which a kidney not only crosses the midline but also fuses with the contralateral kidney. This rare condition – crossed fused renal ectopia (CFRE) – has an estimated incidence of 1 in 1000 individuals within the general population. Although most cases are asymptomatic and discovered incidentally, CFRE may present with recurrent urinary tract infections, urolithiasis, hydronephrosis, and, in exceptionally rare cases, malignant tumors [2,3]. CFRE itself is benign and typically not associated with life-threatening complications; however, the development of a tumor substantially increases diagnostic and therapeutic complexity. Although this congenital anomaly is uncommon, coexisting renal malignancy results in an even rarer condition. Among renal tumors, renal cell carcinoma (RCC) is the most frequently reported malignancy in CFRE, followed by upper tract urothelial carcinoma and, in pediatric patients, Wilms tumor [4–6]. Globally, with an incidence of approximately 400 000 cases annually (as of 2018), RCC represents 2% of all cancer diagnoses and causes a similar proportion of cancer-related deaths; its incidence is increasing in developed countries [7]. Despite the classic triad of flank pain, palpable abdominal mass, and hematuria, most tumors are detected incidentally on imaging conducted for other indications. Definitive diagnosis requires histopathologic confirmation, either after surgical resection or via percutaneous biopsy [8]. Management mainly depends on patient factors and tumor stage. Most cases of localized RCC are treated via surgical excision, ablation, or active surveillance; immune checkpoint inhibitors are increasingly used in the treatment of metastatic RCC [9]. However, in cases of CFRE, the atypical anatomy and close proximity of the 2 renal moieties pose considerable technical challenges for surgical management. In the few reported cases, most patients have undergone radical nephrectomy of the affected kidney, including nephroureterectomy for urothelial carcinoma; a small number of patients with localized disease have undergone nephron-sparing procedures [4,5]. This report describes a 60-year-old man with clear cell RCC arising in CFRE, with direct invasion into the lower pole of the normally positioned contralateral kidney, highlighting the diagnostic and surgical challenges associated with this rare presentation.

Case Report

PATIENT INFORMATION:

A 60-year-old man presented with a 2-month history of mild left loin pain without associated urinary or systemic symptoms. His medical history was notable for approximately 10 years of hypertension, controlled with amlodipine (10 mg daily) and valsartan (160 mg daily). He had no prior surgical history and was a former smoker. Physical examination was unremarkable, and his Karnofsky performance status was 100.

INVESTIGATIONS:

Baseline laboratory investigations were within normal limits, including a serum creatinine level of 1.2 mg/dL. Abdominal ultrasonography revealed a heterogeneous exophytic mass arising from the lower pole of the left kidney, measuring 95×72 mm, with internal calcified foci. The right kidney was not visualized in its normal anatomical position. Subsequent contrast-enhanced computed tomography demonstrated a normally positioned left kidney with preserved size, parenchymal thickness, and contrast excretion, as shown in Figures 1 and 2. No mass lesions, calculi, or hydronephrosis were identified in the left kidney, and contrast excretion was normal. The right kidney was not identified in its usual location; instead, it was located inferior to the left kidney, consistent with CFRE.

The ectopic right kidney was horizontally oriented as shown in Figure 3, with its pelvicalyceal system directed inferiorly, and was fused to the lower pole of the left kidney. A large heterogeneously enhancing mass (84×68 mm, according to computed tomography measurement) occupied most of the ectopic kidney. Figure 4 highlights the anatomical relationship between the 2 kidneys.

Areas of central necrosis or cystic change were noted within the mass, with involvement of the cortex at the lower pole and exophytic extension from the middle pole. Extension into the medulla was also observed; the upper portion of the mass had invaded the inferior pole of the normally positioned left kidney, as shown in Figures 1 and 2.

To evaluate possible metastasis, the patient underwent an ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography scan, which demonstrated no evidence of abdominopelvic lymphadenopathy or distant metastatic disease.

MANAGEMENT AND TREATMENT:

After discussion and informed consent, the patient underwent surgical intervention. Initially, endoscopic stenting of the right ureter was performed. Subsequently, through a left paramedian incision, the retroperitoneal space was entered without opening the peritoneum. Intraoperatively, the renal pedicle of the ectopic right kidney was ligated, and radical nephrectomy was performed, as shown in Figure 5. Given invasion into the lower pole of the left kidney, partial nephrectomy of the involved segment was performed. The left renal pedicle was identified and secured without clamping of the left renal artery, allowing continuous perfusion during surgery and resulting in zero ischemic time in the normally positioned left kidney. The decision not to clamp the artery was based on preoperative investigations revealing borderline serum creatinine, which increased the risk of renal injury and postoperative renal failure. Both kidneys and ureters were identified; the left ureter was carefully dissected and freed from the overlying mass.

The total operative time was approximately 160 minutes, and the estimated blood loss was 280 mL. After conclusion of the procedure, retrograde pyelography of the left kidney was performed, followed by placement of a double-J stent, as shown in Figure 6.

Diagnosis

FOLLOW-UP:

The patient was monitored postoperatively in the hospital for 5 days and was discharged in good health.

Discussion

This case demonstrates that RCC arising in CFRE can invade the contralateral, normally positioned kidney, creating unique diagnostic and surgical challenges. CFRE is a rare congenital anomaly in which both kidneys are fused on the same side of the body. Although it is usually asymptomatic, CFRE may present with recurrent urinary tract infections or urolithiasis [5,6]. Renal tumors in CFRE are exceedingly rare. To our knowledge, this is the first documented case of RCC arising in right-to-left CFRE with invasion into the normally positioned kidney. Previous reports of malignancy in CFRE, including those by Cakmak et al, Vyas et al, Solanki et al, and Kannan et al, have described renal tumors in ectopic fused kidneys; however, none demonstrated invasion into the contralateral normal kidney [10–13]. As reported by Cakmak et al, patients may present with loin pain and dysuria [10]. In contrast, Vyas et al and Solanki et al described cases detected incidentally on imaging performed for other indications [11,12]. In the present case, the patient presented with mild loin pain without urinary or systemic symptoms. The complex and atypical anatomy associated with CFRE poses substantial technical challenges for surgical management, emphasizing the importance of meticulous preoperative imaging. This consideration is further supported by Bassa et al, who highlighted the critical role of detailed preoperative imaging in the management of renal tumors among patients with CFRE [3]. In our case, preoperative imaging was primarily conducted using contrast-enhanced computed tomography to guide surgical planning. This allowed detailed mapping of the complex anatomy and clarified the tumor’s relationship to the normally positioned left kidney. Because of invasion into the lower pole of the left kidney, the already complex surgical management of CFRE became more challenging and required a tailored approach. The patient underwent combined radical nephrectomy of the ectopic kidney and partial nephrectomy of the normally positioned kidney. In contrast, Cakmak et al and Vyas et al reported cases without invasion of the contralateral kidney; their patients underwent radical nephrectomy of the ectopic kidney alone. Similarly, Tsuboi et al and Bassa et al performed partial nephrectomy of the affected moiety without involving the contralateral kidney [3,4,10,11]. The close proximity of the ectopic kidney to the contralateral normal kidney in the present case further increased technical difficulties in the procedure. Therefore, careful and meticulous dissection was required to prevent injury to the normal renal parenchyma. Given the limited number of reported cases and the successful management of this patient, the present report provides valuable insight into the challenges associated with tumor involvement in CFRE.

Conclusions

This case represents the first reported instance of clear cell RCC arising in CFRE with invasion into the contralateral normal kidney. It emphasizes the importance of comprehensive preoperative imaging, precise anatomic assessment, and individualized surgical planning. Combined radical nephrectomy and partial nephrectomy can be successfully performed to achieve oncologic control while preserving renal function in patients with complex congenital renal anomalies.