Which condition is characterized by congenital dysplastic cystic dilatation of the medullary pyramids?

Medullary sponge kidney is characterized by the congenital dysplastic cystic dilatation of the medullary pyramids. In this condition, there are cystic dilatations that form within the renal collecting ducts, leading to a sponge-like appearance of the renal medulla on imaging. This can predispose individuals to various complications, such as urinary tract infections and kidney stones, due to the disrupted normal drainage of urine.

This condition is distinct from multicystic dysplastic kidney, which involves multiple cysts in a more complex formation and usually affects kidney development on a larger scale, often resulting in non-functional renal tissue. Von Hippel-Lindau disease is a hereditary condition associated with the development of various tumors and cysts, rather than being characterized specifically by dilatation of medullary pyramids. Angiomyolipoma is a benign tumor made up of blood vessels, smooth muscle, and fat within the kidney, which does not involve cystic dilation of the pyramids.

Therefore, the unique feature of congenital cystic dilatation of the renal medullary pyramids is what specifically defines medullary sponge kidney.