Upper tract urothelial carcinoma arising in a horseshoe kidney with ureteropelvic junction obstruction: a case report

Abstract

Horseshoe kidney (HSK) is frequently associated with ureteropelvic junction obstruction (UPJO), but the occurrence of upper tract urothelial carcinoma (UTUC) in this setting is exceptionally rare. We report a 66-year-old man presenting with left flank pain and a giant hydronephrotic moiety of an HSK caused by longstanding UPJO. Computed tomography revealed massive hydronephrosis (50 × 46 × 28 cm) with enhancing urothelial wall thickening suspicious for UTUC. The patient underwent open heminephroureterectomy. Histopathology confirmed UTUC. This case highlights the need to suspect malignancy in chronically obstructed horseshoe kidneys and emphasizes the importance of meticulous preoperative imaging and surgical planning.

1. Introduction

Congenital anomalies of the kidney and urinary tract (CAKUT) comprise a heterogeneous group of developmental abnormalities affecting the kidneys, ureters, bladder, and urethra. Among these anomalies, horseshoe kidney (HSK) is the most common renal fusion defect, occurring in approximately 1 in 400 to 500 individuals.^1,2

HSK results from fusion of the lower poles of the kidneys during embryogenesis and is frequently associated with various urological abnormalities, including ureteropelvic junction obstruction (UPJO), vesicoureteral reflux, urinary tract infection, and nephrolithiasis. UPJO is one of the most commonly encountered anomalies in patients with HSK and may lead to progressive hydronephrosis, recurrent infections, and deterioration of renal function when left untreated.²

Upper tract urothelial carcinoma (UTUC) is an uncommon malignancy, accounting for 5-10% of all urothelial tumors. Although HSK itself is not considered a premalignant condition, the associated urinary stasis, chronic inflammation, recurrent infections, and prolonged exposure of the urothelium to carcinogens may contribute to an increased risk of urothelial malignancies in selected patients.³

The coexistence of HSK, UPJO, and UTUC is exceptionally rare. We report a case of UTUC arising in a giant hydronephrotic moiety of a horseshoe kidney secondary to UPJO. This case highlights the diagnostic and surgical challenges posed by this unusual association and underscores the importance of meticulous preoperative assessment and individualized management.

2. Case presentation

A 66-year-old man with a history of heavy tobacco use presented to our urology department with a 6-month history of isolated left flank pain. He denied gross hematuria, lower urinary tract symptoms, fever, weight loss, or other constitutional symptoms. No clinical signs suggestive of a paraneoplastic syndrome were noted.

Physical examination revealed a large, firm abdominal mass occupying the left hemiabdomen, extending from the left costal margin to the lower abdomen. Laboratory investigations, including complete blood count, serum creatinine, and routine biochemical tests, were within normal ranges.

Contrast-enhanced computed tomography (CT) of the abdomen demonstrated a horseshoe kidney associated with left-sided ureteropelvic junction obstruction (UPJO), resulting in massive hydronephrosis measuring 50 × 46 × 28 cm (Fig. 1). Irregular thickening of the renal pelvis and upper urinary tract with focal contrast enhancement was identified within the affected moiety, with attenuation values increasing from 44 to 84 Hounsfield units following contrast administration, raising suspicion for upper tract urothelial carcinoma (UTUC) (Fig. 2).

Fig. 1.

Abdominal CT scan showing a horseshoe kidney (A) with left ureteropelvic junction obstruction and severe hydronephrosis (B).

Fig. 2.

Abdominal CT scan highlighting thickening of the upper urinary tract with focal enhancement in the left kidney, suggestive of upper tract urothelial carcinoma.

CT angiography revealed a complex vascular anatomy. Each renal moiety was supplied by a single renal artery. The artery supplying the right moiety originated from its usual anatomical position, whereas the artery supplying the left moiety arose lower, just above the aortic bifurcation (Fig. 3). The contralateral moiety appeared normal, and no enlarged lymph nodes or distant metastases were detected.

Fig. 3.

CT angiography revealed a right renal artery supplied upper right renal moiety (A), whereas the artery supplying the moiety arose lower, just above the aortic bifurcation.

Diagnostic ureteroscopy and urine cytology were not performed preoperatively. Based on the radiological findings, a diagnosis of suspected UTUC arising in a giant hydronephrotic horseshoe kidney was made. After multidisciplinary discussion, a left heminephroureterectomy was indicated. Given the massive size of the kidney and the anticipated vascular complexity, an open surgical approach was selected.

The patient was placed in the supine position, and a midline xiphopubic laparotomy was performed. Following mobilization of the transverse and descending colon, a giant retroperitoneal mass extending throughout the left abdomen was exposed (Fig. 4). Careful dissection allowed identification and division of the isthmus. Surgical management was technically challenging because of the abnormal vascular anatomy and difficult hilar exposure. After meticulous isolation and ligation of the vascular pedicle, the specimen was completely removed. The resected kidney weighed approximately 5000 g.

Fig. 4.

Intraoperative image of the tumoral horseshoe kidney.

Estimated intraoperative blood loss was 400 mL. Postoperatively, the hemoglobin level decreased from 12.3 g/dL to 10.9 g/dL, and one unit of packed red blood cells was transfused. The postoperative course was uneventful, and the patient was discharged on postoperative day 5.

Histopathological examination confirmed a high-grade infiltrating urothelial carcinoma of the upper urinary tract. Microscopic examination demonstrated sheets and cords of malignant urothelial cells infiltrating the muscularis propria of the renal pelvis (Fig. 5). The tumor exhibited a complex papillary architecture with marked nuclear pleomorphism, hyperchromasia, prominent nucleoli, and numerous atypical mitotic figures. Extensive invasion of the renal parenchyma was present within a desmoplastic fibrous stroma, and areas of tumor necrosis accounted for approximately 30% of the lesion.

Fig. 5.

Histological section stained with hematoxylin and eosin demonstrating sheets and cords of malignant urothelial cells infiltrating the muscularis propria of the renal pelvis (magnification ×100, panels A and B).

At the latest follow-up, the patient remained asymptomatic, with complete resolution of flank pain and no radiological evidence of local recurrence, contralateral upper tract disease, or bladder recurrence.

3. Discussion

Horseshoe kidney (HSK) is the most common congenital renal fusion anomaly, accounting for the majority of fusion defects involving the kidneys.^1,2 It results from abnormal fusion of the metanephric blastemas during embryogenesis, leading to fusion of the lower poles and the formation of an isthmus composed of either fibrous or functional renal parenchyma.⁴ Although many patients remain asymptomatic, HSK is associated with a higher incidence of urological complications, including ureteropelvic junction obstruction (UPJO), urinary tract infection, nephrolithiasis, vesicoureteral reflux, and hydronephrosis.^2,4

UPJO is one of the most frequently reported abnormalities associated with HSK and is thought to result from anomalous ureteral insertion, high ureteral origin, aberrant vessels, or mechanical compression by the renal isthmus.⁴ Chronic urinary obstruction may lead to progressive hydronephrosis, recurrent infections, and prolonged urinary stasis. These conditions create a favorable environment for chronic urothelial irritation and inflammation, which may contribute to carcinogenesis.^3,5

Upper tract urothelial carcinoma (UTUC) accounts for approximately 5-10% of all urothelial malignancies.⁶ Cigarette smoking remains the most important recognized risk factor, increasing the risk of UTUC through prolonged exposure of the urothelium to carcinogenic metabolites excreted in the urine.⁶ Although HSK itself is not considered a premalignant condition, the combination of urinary stasis, recurrent inflammation, and exposure to carcinogens may increase the likelihood of urothelial tumor development.³ Sastry et al. reported that urothelial carcinoma occurring in HSK remains extremely uncommon, with only a limited number of cases described in the literature.³ In the present case, the coexistence of longstanding UPJO and heavy tobacco consumption likely played a synergistic role in tumor development.

The diagnosis of UTUC in a horseshoe kidney may be challenging because of the distorted anatomy and the presence of associated abnormalities. Cross-sectional imaging is therefore essential for both diagnosis and surgical planning. CT urography is currently considered the imaging modality of choice for evaluating suspected UTUC, providing excellent assessment of the collecting system, tumor characteristics, local extension, and renal vascular anatomy.⁷ In our patient, CT imaging identified not only the giant hydronephrotic horseshoe kidney but also an enhancing lesion of the renal pelvis highly suggestive of urothelial carcinoma. Furthermore, CT angiography accurately demonstrated the vascular variations, which proved crucial for operative planning.

Surgical treatment of UTUC arising in HSK presents unique technical challenges. The vascular anatomy of HSK is highly variable and often includes aberrant or accessory arteries arising from the aorta or iliac vessels.^3,4 Careful preoperative mapping of the renal vasculature is therefore essential to minimize intraoperative complications. In our case, preoperative CT angiography enabled precise identification of the arterial supply and facilitated safe surgical dissection.

Radical nephroureterectomy remains the standard treatment for high-risk UTUC.⁸ Although minimally invasive approaches have gained popularity in selected patients, open surgery continues to play an important role in cases involving large tumors, distorted anatomy, or complex vascular variations.^9,10 In the present case, the exceptional size of the hydronephrotic kidney, weighing approximately 5 kg, combined with the anatomical complexity of the horseshoe kidney, made an open heminephroureterectomy the most appropriate and safest surgical approach. The procedure allowed adequate exposure of the isthmus and vascular pedicle, resulting in complete tumor excision with favorable postoperative outcomes.

This case illustrates the rare coexistence of HSK, UPJO, and UTUC. It emphasizes the importance of maintaining a high index of suspicion for malignancy in chronically obstructed collecting systems, particularly in high-risk patients such as smokers. Comprehensive preoperative imaging and meticulous surgical planning are essential for successful management of these challenging cases.

4. Conclusion

The coexistence of horseshoe kidney, ureteropelvic junction obstruction, and upper tract urothelial carcinoma is exceptionally rare. Chronic urinary stasis secondary to UPJO, combined with tobacco exposure, may contribute to urothelial carcinogenesis. This case highlights the crucial role of CT urography and vascular mapping in establishing the diagnosis and planning treatment. Open heminephroureterectomy remains a valuable option for patients with giant hydronephrotic tumors and complex renal vascular anatomy. Long-term surveillance is mandatory because of the risk of recurrence in the remaining upper urinary tract and bladder.

CRediT authorship contribution statement

Ahmed Chaabouni: Writing – original draft, Validation, Conceptualization. Wafa Elleuch: Writing – original draft, Visualization, Conceptualization. Kays Chaker: Writing – original draft, Validation, Conceptualization. Houcine Bouchaala: Validation, Investigation. Yassine Nouira: Visualization, Investigation. Mourad Hadj Slimen: Validation, Investigation, Conceptualization.

Consent for publication

An informed consent was obtained from the patient to use the necessary data for publication.

Availability of data and materials

The data used and/or analysed during the current study are available from the corresponding author on reasonable request.

Clinical trial number

Not applicable.

Ethics approval and consent to participate

An informed consent was obtained from the patient.

Financial disclosure

The authors declare that they have no relevant financial interests.

Competing interests

The authors declare that they have no competing interests.