Itachi and Madara's relationship:

[Everlasting Hebi King]

When Madara said he wondered what Sasuke and his relationship were due to their similar eyes.. He was talking about Itachi.. since Sasuke took Itachi's eyes. What was their relationship?

 

[Yokaze Sama]

He obviously talked about their spiritual connection which is Indras spirit.

 

[Lord Tywin]

Madara was Itachi's superior. That's the relationship

 

[IchaIchaSage]

They both loved there brothers and turned on their clans for the greater good.
They both are very, very strong also....
Personality wise they both hide it well but deep down we know how they really feel.
Don't pin me for this its just a blind guess...

 

[Mahesvara]

They don't have one, Madara probably never even knew of Itachi's existence.

 

[Flakez]

Madara talked how his and Sasuke's eyes both have straight tomoe. Itachi doesn't have straight tomoe.

 

[Melanin]

Their both reincarnations of the same person so Madara acknowledged that in a sense..

 

[khaoz]

they both took there eyes from there brother but the main relationship he was refering to was that they shared indra spirit