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Summary Nephrology 3- usmlerx bricks
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Congenital Disorders ofthe Urinary System
By ScholarRx
Updated July 27, 2021
access_time13 min
Learning Objectives (4)
After completing this brick, you will be able to:
● Describe the bladder development anomalies urachal cysts, fistulas,
and exstrophy.
● 1
● Describe the clinical presentation and radiology findings for
supernumerary kidneys, renal agenesis, pelvic kidney, fused kidney,
crossed renal ectopia, and horseshoe kidney.
● 2
● Describe the developmental events that lead to renal agenesis and
ectopic kidneys.
● 3
● List the congenital anomalies that commonly lead to
oligohydramnios.
● 4
cableCASE CONNECTION
While you are working in the outpatient clinic during your pediatrics
rotation, you are asked to see AM, a 9-month-old baby boy, for his
well-child visit. As you review AM’s record, you notice he has a pelvic
kidney.
,How will you explain this condition to AM’s mother? What
complications can AM develop later in life? Consider your answers as
you read, and we’ll revisit at the end of the brick.
GO TO CONCLUSION arrow_downward
What Are Congenital Disorders of the
Urinary System?
Congenital abnormalities of the urinary system are more common
than you might think; about 10% of people are born with a significant
urinary system malformation. These congenital abnormalities can be
hereditary (a result of genetic mutations passed from parent to child)
or developmental (resulting from a growth defect during gestation). In
this brick, we’ll focus on congenital abnormalities caused by defects
during development.
How Do the Kidney, Collecting
System, and Ureter Normally
Develop?
Before we discuss congenital anomalies of the urinary system, it will
be helpful to briefly review normal embryologic development (Figure
1). Fetal kidneys start to develop around the fourth week of gestation;
in fact, a total of three sets of kidneys are ultimately formed during
this process.
,Figure 1
Credit: ©ScholarRx
The first is the pronephros, which is nonfunctional and disappears
quickly. It is followed by the mesonephros (think of this as the
“embryonic” kidney), which is functional and produces urine. Late in
week 4, the mesonephros drains through a primitive duct, known as
the nephric duct, into the cloaca, a shared opening for the urinary,
genital, and gastrointestinal tracts.
Around the fifth week of gestation, the mesonephric duct forms an
outpouching called the ureteric bud. This grows and begins to interact
with the developing metanephric mesenchyme (think of this as the
, “fetal” kidney), the precursor to the true kidney. The ureteric bud
invades the metanephric mesenchyme and induces differentiation of
the functional unit of the kidney, the nephron.
The ureteric bud itself eventually forms the collecting system, renal
pelvis, and ureter. When this occurs, the mesonephros and
mesonephric duct regress in female fetuses. In male fetuses, the
mesonephric duct (also known as the Wolffian duct) contributes to
reproductive structures such as the epididymis and vas deferens.
Although the metanephros appears around the fifth week, the
permanent kidney continues to develop throughout and even after
birth. The kidney is initially located in the fetal pelvis but later
ascends due to elongation of the fetal torso and rotates medially. The
kidney also undergoes changes in blood supply as it migrates from the
pelvis to the lumbar region. New vessels branch from progressively
higher points on the aorta, while older vessels degenerate.
When the metanephros fails to develop or differentiate, renal agenesis
(a- meaning not, -genesis meaning production) can occur, leading to
the absence of one or both kidneys. For example, if the ureteric bud
fails to form, the metanephric mesenchyme will not be induced.
Abnormalities in migration of the kidneys can also occur and lead to
ectopic (ec- meaning out, -topic meaning place) kidneys. Defective
ureteric buds can again be a culprit, as well as defective metanephric
tissue, regional anatomic abnormalities, or other genetic or maternal
causes. Ectopic kidneys (out of the normal location) are generally
found along the migration pathway between the pelvis and their
normal location (lower thoracic to upper lumbar vertebral levels) but
can also be above in the thorax or across on the contralateral side.
Failed degeneration of vasculature during kidney migration can result
in accessory (extra) renal vessels. These are sometimes end arteries—
meaning the only blood supply—for portions of the kidney and are
therefore vulnerable to ischemia (inadequate blood supply) if
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