Unilateral Multicystic Dysplastic Kidney
A rare form of multicystic dysplastic kidney (MCDK), a congenital anomaly of the kidney and urinary tract (CAKUT), in which one kidney is large, distended by multiple cysts, and non-functional.
Epidemiology
Unilateral MCDK is the most common form of MCDK with a birth prevalence estimated at 1/4,300 live births.
Clinical description
Unilateral MCDK frequently presents antenatally at routine ultrasound scans, with the majority detected around the 20th week of gestation. The large majority of patients are asymptomatic but unilateral MCDK may occasionally present with abdominal obstructive signs (abdominal distention, feeding difficulties, respiratory distress) when the cysts become too large. Patients may also develop hypertension, proteinuria, and renal failure in the long run. The contralateral renal tract has an increased incidence of additional CAKUT such as vesicoureteral reflux and pelvi-ureteric junction obstruction (PUJO). Hypertrophy of the contralateral kidney may occur in 24-46% cases before birth, and in up to 80% in the years after birth.
Etiology
Unilateral MCDK results from disrupted nephrogenesis but the exact pathogenic mechanism is still unknown. Disturbed formation of nephrons could result from impaired fetal urine flow early in development. Mutations in the HNF1B gene (17q12), coding for hepatocyte nuclear transcription factor 1beta, associated with renal cysts and diabetes syndrome, have been detected in cases of unilateral MCDK. MCDK is also linked to gestational diabetes and to the use of some medications during pregnancy, such as anti-epileptic drugs.
Diagnostic methods
Diagnosis is mainly based on prenatal ultrasound showing large hypoechogenic non-communicating cysts within an irregularly outlined kidney with no visible renal pelvis. A tiny remnant kidney can be observed if the cysts have involuted. Complete prenatal involution has been described in 5% of MCDK, with complete involution in 50% during the first decade of life. Histologic examination shows that cysts are surrounded by undifferentiated and metaplastic cells with occasional residual functional renal tissue with recognizable glomeruli and proximal tubules. Renography with technetium-99m-labeled dimercaptosuccinic acid may show little or no renal uptake. As this has no clinical consequences, renography is not routinely indicated.
Differential diagnosis
Differential diagnoses include PUJO, in which the largely dilated calices may appear to be cysts, or in case of involuting MCKD, renal hypoplasia or renal agenesis.
Antenatal diagnosis
Ultrasonographic screening can detect unilateral MCDKs from midway through gestation.
Genetic counseling
Both sporadic and familial cases have been observed. In familial cases, transmission is autosomal dominant with a recurrence risk of 50%.
Management and treatment
Partially based on the supposed increased risk of hypertension and malignancy of which no evidence is found, nephrectomy was performed routinely until recently, whereas nowadays most cases of unilateral MCDK are left in situ and followed with serial ultrasound. However, nephrectomy may be indicated in case of abdominal obstructive complaints when the cysts become too large. Due to an increased risk of hypertension and/or proteinuria, as a sign of glomerular hyperfiltration or renal dysplasia in the solitary functioning kidney, individuals with unilateral MCDK deserve long-term follow-up. Up to 30% of unilateral cases of MCDK may lead to renal failure at the age of 30 years, at which stage renal replacement therapy is indicated.
Prognosis
The prognosis is influenced by the presence of abnormalities in the contralateral kidney.