What is the smallest PC case type?

[Pokemon5475]

What's the smallest of the PC case types?

I'm going to say it's one of these:
ATX Mini Tower
HTPC
MicroATX Desktop
MicroATX Mid Tower
MicroATX Mini
MicroATX Slim
Mini ITX Desktop
Mini ITX Test Bench
Mini ITX Tower

Thanks in advanced!

 

[CreepyBobo346]

I would say that the Mini ITX Desktop is, judging from comparing the pictures.

But the HTPC is a close call to the Mini ITX Desktop.