Horseshoe kidney presenting with features of left ureteropelvic junction obstruction—insights into management: a case report and review of the literature

Abstract

Background

Horseshoe kidney is the most common renal fusion anomaly, occurring in approximately 1 in 500 individuals worldwide. It is characterized by abnormalities in kidney position, rotation, and vascular supply. While often asymptomatic, horseshoe kidneys can lead to urological complications, primarily due to ureteric obstruction and impaired urinary drainage.Although ureteropelvic junction obstruction (UPJO) is uncommon in horseshoe kidneys, its occurrence presents unique diagnostic and management challenges. This case explores the etiology, clinical presentation, and surgical management of UPJO in a patient with a horseshoe kidney, highlighting the critical role of urologists in addressing these anatomical and functional complexities.

Case presentation

We report the case of a 3-month-old African male infant who presented with a two-month history of excessive crying and symmetrical abdominal distension. Radiological evaluation revealed a horseshoe kidney with decreased parenchymal thickness in the left kidney and marked hydronephrosis of the pelvis and calyces, with abrupt cessation at the left ureteropelvic junction. Surgical correction of the obstruction was performed successfully. The patient was followed for six months, during which he remained symptom-free with normal renal function tests.

Conclusion

Ureteropelvic junction obstruction in a horseshoe kidney presents unique anatomical challenges. Symptomatic cases require thorough imaging for diagnosis and surgical planning. Pyeloplasty is the typical surgical intervention, meticulously planned to address these complexities. This ensures effective relief of obstructions and proper urinary drainage.

Introduction

Horseshoe kidney is commonly associated with other congenital anomalies, though its association with ureteropelvic junction obstruction (UPJO) is rare. This renal fusion anomaly is characterized by renal malrotation, variable blood supply, and a high insertion of the ureter, contributing to a predisposition for UPJO in up to one third of cases. However, there remains no consensus on the optimal management of UPJO in children [1].

In more than 90% of cases, fusion occurs at the lower poles; as a result, two separate excretory renal units and ureters are maintained. Fusion is thought to occur before the kidneys ascend from the pelvis to their normal dorsal lumbar position. This is usually between the fifth and ninth weeks of gestation. The majority of horseshoe kidneys with a parenchymal isthmus result from abnormal migration of the posterior nephrogenic area, which generally occurs before the fifth week of gestation [2, 3]. Horseshoe kidneys with a fibrous isthmus arise from fusion after the fifth week of gestation, before renal ascent. If large portions of the renal parenchyma fuse, the fusion anomaly loses its horseshoe appearance and appears as a flattened disc or lumpy kidney. Since horseshoe kidneys are frequently asymptomatic, they are frequently discovered incidentally. Otherwise, the presentation may be nonspecific; one study found that abdominal pain and urinary tract infection symptoms are the two most prevalent complaints made by kids with horseshoe kidneys [4].

A variety of clinical symptoms may be present with ureteropelvic junction obstruction of the kidney, which frequently requires surgical intervention. Only approximately one third of affected children will need surgical correction.

Ureteropelvic junction obstruction (UPJO) and other congenital abnormalities are commonly linked to horseshoe kidneys [5].

Anomalous vascular supply to the kidney, elevated ureteric insertion into the renal pelvis, an aberrant ureteric course over the isthmus and intrinsic pathophysiology are all potential causes of UPJO in horseshoe kidneys [5]. Abdominal pelvic computed tomography (CT) or ultrasound scans are most frequently used to diagnose horseshoe kidney. The best imaging modalities for revealing the architecture and identifying the surrounding structures and accessory vasculature are CT and magnetic resonance imaging (MRI) [6].

Open surgery is used in the management of pelvic ureteric junction obstruction; however, other minimally invasive modalities yield similar surgical outcomes. The Hynes–Anderson dismembered pyeloplasty technique is the gold standard and the operation of choice, regardless of access. In our patient, we used the dismembered technique for surgical correction of pelvic ureteric junction obstruction and achieved good surgical outcomes.

Case presentation

We report the case of a 3-month-old African male infant who presented with a 2-month history of excessive crying while urinating, which was associated with a tendency to roll around his bed and episodes of restlessness and occasional vomiting. His caregiver reported that the baby had normal voiding with no evidence of reduced urine output or hematuria; however, he had a history of blood-stained stool episodes.

Physical examination revealed pallor in the conjunctiva. Abdominal examination revealed a slightly distended abdomen with tenderness in the left lumbar region and no organomegaly, and there was no palpable renal angle mass.

Full blood counts revealed a hemoglobin level of 9.2 g/dl with normal leukocyte and platelet counts. Renal function tests, coagulation profiles, and serum electrolytes were all within the normal range.

Abdominal ultrasound revealed a thick-walled urinary bladder with irregular outlines and a dilated pelvicalyceal system with features of left hydronephrosis and moderate corticomedullary differentiation. Abdominal CT revealed features of a horseshoe kidney with a slightly enlarged left kidney half compared to the right kidney, decreased parenchymal thickness and marked hydronephrosis with abrupt termination at the ureteropelvic junction; moreover, no intraluminal or mural cause for the obstruction was detected (Fig. 1).

Fig. 1

A Axial abdominal pelvic contrasted computed tomography (CT) image showing a horseshoe kidney appearance (white arrow) with left dilated renal calyces (indicated by the black arrow). B Coronal abdominal pelvic contrasted CT image displaying a grossly dilated left kidney segment with severe hydronephrosis and delayed excretions of the left kidney (highlighted by the white arrow). C Volumetric rendering CT scan image illustrating left dilated renal calyces with severe hydronephrosis (pointed out by the white arrow). D Volumetric rendering image showing the horseshoe kidney morphology (indicated by the white arrow)

Through a supraumbilical transverse incision via a transperitoneal approach, we found a small accessory spleen that was seen above the normal spleen; to achieve adequate space, the splenorenal ligament and nephrocolic ligaments were incised. A dilated renal pelvis with high insertion of the left ureter was observed with constriction at the ureteropelvic junction (Fig. 2).

Fig. 2

A, B Shows an enlarged renal pelvis (white arrow) with high insertion of the left ureter, and constriction at the pelvic ureteric junction (black arrow)

An accessory renal vein that was not obstructed passed over the dilated pelvis. The lower renal pole was connected to the right renal pole passing anterior to the abdominal aorta.

A stay suture was placed in the pelvis proximal to the anticipated line of dismemberment, and another stay suture was placed in the ureter distal to the level of the stenosis. A tensely dilated pelvis was decompressed with a 21-gauge needle before dismembering to avoid excessive pelvic reduction. The UPJ was dismembered, and the excess pelvis was excised. The ureter was then spatulated along its lateral border beyond the dysplastic stenotic segment and carried through adequately into healthy ureteral tissue (Fig. 3). At this stage, the stenotic part of the ureter was not removed, as it served as a handle to minimize ureteral tissue manipulation while performing the anastomosis to reduce the risk for mucosal edema.

Fig. 3

A, B Showing the ureteropelvic anastomosis performed using the Hynes–Anderson technique. A tensely dilated pelvis was decompressed with a 21-gauge needle before the dismembering procedure to avoid excessive reduction of the pelvic size. The ureter was then spatulated along its lateral border beyond the dysplastic stenotic segment and carefully anastomosed into healthy ureteral tissue

The stenotic part of the ureter was then removed, and the pelvis was irrigated with saline to avoid blood clots obstructing the ureter. A double J (DJ) stent was inserted before closure of the anastomosis; the anastomosis was completed with continuous suturing by using 5–0 absorbable monofilaments in a tension-free manner before completing the anastomosis. The patient was followed for 6 months, during which significant clinical improvement was observed, and no episodes of excessive crying were noted.

Discussion

A horseshoe kidney is identified as having functioning renal units present on both sides of the vertebral column fused together with ureters that remain uncrossed from the renal hilum to the urinary bladder. The isthmus connecting the two renal units may be positioned in the midline or laterally, resulting in an asymmetric horseshoe kidney, 70% of which is left dominant [7].

A horseshoe kidney results from the fusion of metanephric buds between 4 and 8 weeks of embryogenesis, which hampers cephalic migration and normal rotation. The renal pelvis and ureters in the horseshoe kidney are anteriorly placed, with the ureters lying anterior to the isthmus with a tendency to kink, often resulting in hydronephrosis [7, 8]. In more than 90% of cases, fusion occurs at the lower pole, although in a small minority of cases fusion may occur at the upper pole [6, 9]. In the presented case, the fusion involved the lower pole of the kidneys, as seen in the majority of cases.

Normally, the kidneys are situated in the retroperitoneum, with the left kidney being slightly more superior than the right, between the transverse processes of T12 and L3. In relation to the lower poles, the higher poles are often positioned somewhat medially and posteriorly [10]. Three primary differences exist between horseshoe kidneys: their location, orientation, and vasculature [11]. In the general population, the incidence of horseshoe kidney is ~ 1:500, with a 2:1 male preponderance [1, 6]. In our case, the patient was a 3-month-old male.

Early fusion also causes abnormal rotation of the developing kidney. As a result, the axis of each kidney is shifted so that the renal pelvis lies anteriorly, and the ureters either traverse over the isthmus of the horseshoe kidney or the anterior surface of the fused kidney. Fusion anomalies seldom ascend to the dorsolumbar position of normal kidneys and are typically found in the pelvis or at the lower lumbar vertebral level (L4 or L5). The blood supply of the fused kidney is variable and may come from the iliac arteries, aorta, and, at times, the hypogastric and middle sacral arteries [12].

A number of etiological variables may contribute to the development of horseshoe kidneys, but no specific genetic etiology has been identified, despite reports of familial clustering [13]. In our case, it was an incidental finding, with no symptom that suggesting a horseshoe kidney.

UPJ obstruction in horseshoe kidneys is postulated to develop secondary to congenital stricture at the UPJ, high ureteral insertion, abnormal ureteral course over the isthmus, crossing vessels supplying the isthmus, or abnormal motility of the UPJ segment. Hydronephrosis from UPJO occurs in approximately 14–35% of horseshoe kidney patients. The anomaly is generally detected incidentally. Symptoms are related to hydronephrosis, infection, or calculus formation. The most common symptom is vague abdominal pain radiating to the lower lumbar region [2, 6, 14]. The reported patient presented with symptoms related to UPJO, and the congenital anomaly of horseshoe kidneys was an incidental finding. The obstruction, found intraoperatively, was due to high insertion of the ureter and UPJ stenosis.

The inferior mesenteric artery at L3 level is frequently cited as preventing the horseshoe kidney from ascending; however, the kidney can also be located lower in the belly and pelvis. Renal ascent and 90° medial rotation occur in weeks 6 through 8 of development. Nevertheless, the isthmus causes the horseshoe kidneys to malrotate. As a result, the ureters must either travel across the isthmus or down the anterior surface of the kidneys, which can lead to stasis and issues with urine drainage [15, 16]. Additionally, the origin and number of renal arteries and veins vary more in horseshoe kidneys [6, 7]. In our patient, intraoperatively, we found a dilated renal pelvis with high insertion of the left ureter and constriction at the ureteropelvic junction, and the ureters crossed the anterior surface of the kidney.

The primary technical challenges of pyeloplasty in this population are related to aberrant lower pole vessels, an unfamiliar caudal position of the kidney, and the renal isthmus [5]. Despite these anatomical challenges to optimize success, anatomic complexities can be anticipated with appropriate preoperative imaging. On imaging, the classic findings include low-lying kidneys close to the vertebral column, a collecting system directly posterior to each renal pelvis, a lowermost calyx pointing medially, and high insertion of the ureter into the pelvis [16]. Ultrasound and renal dynamic scans are usually sufficient for the diagnosis, management and follow-up of patients with horseshoe kidney with UPJO. Ultrasound is very accurate and sensitive in these patients, which reduces the need for cross-sectional imaging in most cases. A CT angiogram can accurately delineate the vasculature and collecting system. Magnetic resonance urography (MRU) can also be utilized for simultaneous evaluation of renal function and anatomy [6].

Surgical treatment can include either the open flank approach (extraperitoneal for unilateral and transperitoneal for bilateral involvement) or laparoscopy or robotic surgery. Surgical management in the form of excision of stenotic ureteropelvic segments, trimming of a redundant pelvis, transposition of any aberrant vessels, and ureteropelvic anastomosis are the basic principles of management. The incision and approach (transperitoneal) used in our patient took into consideration the associated abnormality (horseshoe kidneys) and the patient’s age. Horseshoe UPJ obstruction caused by intrinsic stenosis, high ureteral insertion, or an abnormal course of the ureter across the isthmus can be appropriately addressed by dismembered pyeloplasty [14].

Conclusion

Ureteric pelvic junction obstruction on a horseshoe kidney present unique anatomical challenge due to the abnormal rotation, anterior placement of the renal pelvis and ureters, and variable blood supply. Although many cases are asymptomatic and discovered incidentally, symptomatic cases necessitate thorough diagnostic evaluation using imaging techniques for diagnosis and proper surgical preparation. Surgical intervention, typically pyeloplasty, must be meticulously planned to address these anatomical complexities, ensuring effective relief of obstructions and proper urinary drainage.