Case 24 Answer

WetReadRad -

Answer: Emphysematous Pyelitis from obstructing UPJ stone 

Stone is obvious but note not only the enhancing mucosa (infection, ie pyelitis) but the air (emphysema). But it does not involve the parenchyma currently

Collecting system air - ok

Parenchymal air (emphysematous PYELONEPHRITITS) - BAD!