Patient history: 41 year-old woman with three previous deliveries. Her last child had transposition of the great arteries, underwent surgery and is presently healthy. Current pregnancy with twins, in the 36th week. One of the twins was diagnosed with heart malformation and bilaterally enlarged kidneys on ultrasound.

This is a low power micrograph of the diseased kidney.

Question: What are the most striking alterations?

- The large cystic dilatations (to the left), and the central part of the kidney showing immature mesenchyme with some smaller cysts (see arrows).