CHAPTER 7 Congenital Disorders of the Upper Tracts
What are the features of Potter syndrome?
Compressed facies, low-set ears, and limb contractures.
What is the etiology of Potter syndrome?
Potter syndrome, or Potter sequence, is a series of changes that occur in a fetus secondary to extreme oligohydramnios. This can be from an inability to produce urine such as renal agenesis, bilateral multicystic renal dysplasia, or juvenile polycystic kidneys. Another reason for oligohydramnios is an impaired ability to void such as posterior urethral valves.
What is the embryological basis and the characteristic findings of the Mayer–Rokitansky–Küster–Hauser (MRKH) syndrome and how does it usually present?
Müllerian agenesis, which leads to a congenital absence of the middle and upper third of the vagina with variable uterine and fallopian tube defects. In approximately one-third of these cases, upper tract anomalies can also be found. These include renal agenesis or hypoplasia, renal ectopia, pelvic kidney, and horseshoe kidney. Skeletal abnormalities (usually vertebral) occur in 10% to 20%. There are 2 types of MRKH syndrome. Type A (typical) has symmetric remnant müllerian muscular buds and normal fallopian tubes and Type B (atypical) is associated with asymmetric buds and abnormal fallopian tubes. Although Type B has been deemed “atypical,” it is actually more common than Type A. Renal and skeletal abnormalities occur only in Type B MRKH syndrome. The most common presentation is primary amenorrhea.
Patients found to have a missing vas deferens during an infertility workup should be screened for what abnormality and how?
Ipsilateral renal agenesis that can be confirmed on renal ultrasound.
What is the incidence of unilateral renal agenesis?
Approximately 1:1400 births.
What is the incidence of bilateral renal agenesis?
Approximately 1:4000 with a ratio of male to female of 2.5:1. This is a lethal condition associated with a number of genetic syndromes.
What is the long-term prognosis for a baby born with a solitary kidney?
If there are no other associated anomalies, prognosis is good. However, contralateral reflux is found in one-third of children with renal agenesis and is not uncommon in patients with multicystic dysplastic kidney. Patients with solitary kidneys are at increased risk for developing proteinuria, hypertension, and renal insufficiency over the course of his or her lifetime; however, the patient’s life expectancy is normal.
What is the most common additional urologic abnormality associated with a horseshoe kidney?
The incidence of horseshoe kidney is 1:400 to 1:1800 with a male predominance of 2:1. Up to 35% of patients with a horseshoe kidney have evidence of significant ureteropelvic junction obstruction, more commonly on the left. Patients with a horseshoe kidney are also at a greater risk of vesicoureteral reflux (VUR) with reported rates of 80%.
Is there an increased cancer risk with fused kidneys?
There is a 1.5-fold to 8-fold increased risk of Wilms tumor in these kidneys. It is unclear at this time if there is an increased risk of adult urologic cancers in fused kidneys; however, some studies demonstrate an increased risk of transitional cell carcinoma in these patients.
The cephalad migration of a horseshoe kidney is limited by what structure?
The inferior mesenteric artery.
What is the normal direction of rotation of the human kidney as it ascends out of the pelvis?
The kidney normally rotates 90° ventromedially during ascent. Therefore, the renal pelvis, which was originally directed anteriorly, becomes directed medially.
True/False: Most crossed ectopic kidneys are fused with their mate.
True. Approximately 90% of crossed ectopic kidneys are fused with a normally placed mate.
What is the incidence of antenatal hydronephrosis?
In the United States, more than 600,000 fetal ultrasounds are performed. Of these, 0.2% to 2% will detect antenatal hydronephrosis. Postnatal ultrasound demonstrates that 66% to 75% persist after birth.
What is the most common cause of hydronephrosis in the fetal kidney?
Ureteropelvic junction obstructions are the etiology of 60% to 80% of cases of persistent fetal hydronephrosis. VUR is responsible for 25% to 35% of postnatal hydronephrosis.
True/False: Most cases of prenatally diagnosed ureteropelvic junction obstruction require urgent surgical intervention following delivery.
False. Debate continues surrounding the management of prenatally diagnosed ureteropelvic junction obstructions. Most often surgery is not necessary or can be performed on an elective basis after an appropriate evaluation and period of observation.
In what percent of patients with ureteropelvic junction obstruction does the contralateral kidney demonstrate evidence of ureteropelvic junction obstruction?
In patients found to have ureteropelvic junction obstruction, evidence for bilateral obstruction exists in 10% to 40% of cases.
In what percent of patients with ureteropelvic junction obstruction does vesicoureteral reflux coexist?
Vesicoureteral reflux coexists in 15% of cases.
What is the most common type of renal cystic disease?
Multicystic dysplastic kidney disease. Incidence is 1:3000 to 1:5000 of live births.
A child is discovered to have a multicystic dysplastic kidney. This patient’s contralateral kidney should be screened for what abnormalities?
The contralateral collecting system should been screened for VUR, which is present in 18% to 43% of cases, and for ureteropelvic junction obstruction, which has been demonstrated in 3% to 12% of cases. Duplex system, agenesis, or ectopia can also been seen in the contralateral kidney.
What is the average amount of renal parenchyma drained by the upper pole of a duplicated collecting system?
About one-third of total renal parenchyma is drained by the upper pole of a duplicated collecting system.
A ureteric bud arising on the mesonephric duct in an abnormally low position predisposes to what abnormality?
The ureteric bud will arrive early at the urogenital sinus causing the ureteral orifice to ultimately reside in a more cranial and lateral position within the bladder and be predisposed to VUR.
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