Polycystic kidney disease in neonates and infants. Clinical diagnosis and histopathological correlation.

A significant cause of end-stage renal disease in infants (40% to 50% of cases) is represented by the group of renal cystic diseases. Actually, the fourth cause of renal failure in young adults is the autosomal dominant polycystic kidney disease (ADPKD). Moreover, the most common genetically inherited kidney disease was proved to be ADPKD, affecting 1-5 per 10 000 individuals. The study was conducted over a period of three years (July 26, 2015-October 30, 2018) on 22 patients aged between two days and 36 months, diagnosed with polycystic kidneys that presented multiple hospital admissions in the Department of Nephrology, "Maria Skłodowska Curie" Emergency Children's Hospital, Bucharest, Romania. The nephrectomy sections were obtained from the material of the Department of Pathology of the same Hospital. Prenatal ultrasonography results were correlated with positive family history of polycystic kidney disease (PKD), fetal enlarged kidneys and oligohydramnios. Neonatal diagnosis of PKD was considered when some of the neonates presented palpable flank masses that caused fetal dystocia. On the other hand, the pediatric clinical examination of older infants revealed abdominal distention secondary to renal masses. After surgical resection, the overall aspect of the kidneys showed that the normal parenchyma had been mostly replaced by cysts with thin, translucent walls that contained a clear fluid. Microscopy confirmed that the parenchyma was mostly replaced by dilated cysts delineated by simple cuboidal or simple flattened epithelium, with areas of remnant fetal kidney parenchyma separated by an enriched stroma. Immunohistochemistry for blood vessels (CD34) revealed normal fine walled blood vessel arcades in the control kidneys, while in most areas from polycystic disease, the blood vessels exhibited enlarged, thickened endothelium, and less collapsed lumens. Regarding the proliferative capacity of the tissues, our Ki67 immunostaining revealed that the less formed, younger tubules in the pathological state had a higher proliferative index compared to control tissue. There seemed to be less albumin immunostaining in the epithelia of the distal contort tubules but that distinction was present also in our pathology. The overall expression level was reduced in polycystic cases (p<0.05), and it could be that this expression decrease might be related to the reduced function of these kidneys. According to what literature states, we have emphasized in our study that aquaporin 1 (AQP1) showed overall decreased reactivity in PKD along with its expression in proximal tubule epithelia.