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Q1: Name the congenital renal anomaly identified in fig 1 (see p355)
Horseshoe kidney. The lower poles of the kidney being displaced towards the midline, joined by either functioning renal tissue or a fibrous band.
Q2: What is the incidence and sex ratio of this anomaly?
Incidence is one in 400. It is more commonly found in males at a ratio of 2:1.
Q3: What complications occur with this condition?
Thirty percent of cases are asymptomatic and are identified incidentally. Stasis of urine due to the malrotation of the kidneys, and impaired ureteric drainage result in infection and stone formation.
Q4: Name three other genitourinary anomalies that can be associated with this condition
These are: (1) hypospadiasis; (2) undescended testis; (3) ureteral duplication. Vaginal septation and bicornuate uterus can also be associated with this condition.
Horseshoe kidney was first recognised during a necropsy by DeCarpi in 1521, but Botallo in 1564 provided the first description and illustration of a horseshoe kidney.1 Horseshoe kidneys are believed to result from the median fusion of metanephric tissue due to mechanical forces. However studies have suggested that abnormal fusion of tissue associated with the parenchymatous isthmus of horseshoe kidney is the result of a teratogenic event involving the abnormal migration of posterior nephrogenic cells.
In most cases the kidneys are linked at the lower poles by a parenchymatous or fibrous isthmus that crosses the midline of the body. In general isthmus lies anterior to aorta and vena cava. Because kidneys fail to rotate, the calyces point posteriorly. The ureter inserts higher on the renal pelvis and lies laterally and crosses over and anterior to isthmus. The blood supply can be quite variable.1
The horseshoe kidney is frequently found in other congenital anomalies, some of which are incompatible with long term survival. Most common congenital anomalies involved include skeletal, cardiovascular, and central nervous systems. There is increased occurrence of other genitourinary anomalies. Females with Turner’s syndrome have a high incidence of horseshoe kidney. Horseshoe kidney with situs inversus is a rare and interesting association.2
One third of all patients remain asymptomatic. Others present with vague abdominal pain resulting from hydronephrosis, infection, or calculus formation. Horseshoe kidney is associated with an increased relative risk of Wilms’ tumour, transitional cell carcinoma, and renal carcinoid.3
Ultrasound or an excretory urogram readily makes the diagnosis. Ultrasound diagnosis depends on the demonstration of an isthmus or band of renal tissue across the midline. In a number of cases the band of renal tissue may evade ultrasonic detection.4 Computed tomography may be necessary to confirm the diagnosis.
Intervention is required because of obstruction or calculi. The combination of horseshoe kidney with an aortic aneurysm presents a diagnostic and therapeutic challenge to the vascular surgeon.5
Horseshoe kidney with situs inversus.