Renal dysplasia is a congenital condition where the internal architecture of one or both kidneys fails to develop properly while the fetus is in the womb. This developmental failure results in the formation of abnormal, non-functional tissue that often contains multiple fluid-filled sacs called cysts. The condition is one of the most frequent causes of chronic kidney failure in children. The severity varies widely, ranging from a slightly abnormal kidney to one completely replaced by cysts that cannot function.
How Renal Dysplasia Develops
Renal dysplasia arises from a malfunction during early fetal kidney formation. Normal kidney development depends on a precise interaction between the ureteric bud and the metanephric mesenchyme. When the ureteric bud, which forms the collecting system, fails to properly branch and signal to the metanephric mesenchyme, the essential filtering units of the kidney, known as nephrons, do not mature. This disruption leads to the formation of disorganized tissue and cysts.
The cause is often unknown, occurring as a random, spontaneous event in most cases. However, the condition can sometimes be linked to genetic factors, with changes in certain genes potentially being passed down. Exposure to specific medications during pregnancy, such as certain blood pressure drugs, has also been recognized as a possible cause. Renal dysplasia may occur alone or as part of a larger syndrome, such as congenital abnormalities of the kidney and urinary tract (CAKUT).
The location of the condition is a major factor in its impact and prognosis. Unilateral renal dysplasia means only one kidney is affected, while the other develops and functions normally. This form is often less concerning because the healthy kidney can grow larger and compensate for the non-functional kidney, a process called compensatory hypertrophy. Bilateral renal dysplasia, where both kidneys are affected, is far more serious as it compromises the body’s ability to filter waste and manage fluids.
Recognizing the Signs and Diagnosis
Identification of renal dysplasia often begins before birth during routine prenatal care. The most common diagnostic tool is a fetal ultrasound, which can detect abnormalities in the size, shape, or appearance of the fetal kidneys, such as the presence of cysts. In severe cases, particularly bilateral dysplasia, the ultrasound may show a severely low level of amniotic fluid, known as oligohydramnios. Insufficient amniotic fluid suggests the kidneys are not working well, which can hinder lung development.
Unilateral dysplasia frequently causes no symptoms and may be discovered incidentally later in life during an imaging test for an unrelated issue, such as a urinary tract infection (UTI). When symptoms do occur, they are associated with chronic kidney disease. These symptoms may include fatigue, poor growth, loss of appetite, and high blood pressure. A child may also present with a palpable mass in the abdomen if the dysplastic kidney is large and cystic.
After birth, diagnosis is confirmed using further imaging and laboratory tests. A postnatal ultrasound is performed to assess the size and structure of the kidneys and urinary tract. A Voiding Cystourethrogram (VCUG) may also be used; this specialized X-ray involves filling the bladder with a contrast dye to check for vesicoureteral reflux (the backward flow of urine toward the kidney). Blood tests measuring substances like creatinine and blood urea nitrogen (BUN) are essential for assessing the filtering capacity and function of the remaining healthy kidney tissue.
Management and Long-Term Outlook
The management plan and long-term outlook depend entirely on whether one or both kidneys are involved. For children with unilateral renal dysplasia, the prognosis is favorable, as the single healthy kidney usually takes over the full function of both. Management primarily focuses on monitoring the function of the healthy kidney and preventing complications. This monitoring includes regular blood pressure checks, as hypertension is a known long-term risk.
Periodic follow-up appointments with a pediatric nephrologist are recommended to track kidney function and screen for protein in the urine. The non-functional dysplastic kidney often shrinks over time, a process called involution, and may eventually disappear. Surgical removal of the dysplastic kidney (nephrectomy) is rarely necessary. However, it may be considered if the kidney causes persistently high blood pressure or recurrent, severe infections.
In contrast, bilateral renal dysplasia presents a guarded prognosis, as the child is at high risk for developing chronic kidney disease (CKD) or end-stage renal disease (ESRD). Management involves strategies to slow the progression of CKD, including dietary modifications and medications to control blood pressure and electrolyte imbalances. If kidney function declines severely, the child will require renal replacement therapy, involving either long-term dialysis or a kidney transplant. Early and specialized care is necessary for managing the health challenges associated with bilateral renal dysplasia.