Itachi *max power* VS. Aizen

Itachi VS. Aizen

Itachi: He could easily tell which aizen is real and where he is with his mangekyo while at the same time putting him under a genjutsu
However aizen can change anything related to the five senses so he could probably get out of even tsukiyoshimi with little to no difficulties

In Susano'o Itachi had that sealing sword which casts a powerful genjutsu on whoever is struck with it leaving even the immortal Aizen hougyoku utterly defeated

Keep in mind Itachi has never shown its full strength in any battle, mainly because he was not evil and never wanted to actually kill. With that said his susano o has a special sword (Tetsuka) who drains all the chakra(reiatsu) of a specific type when it touches an entity. So if aizen ever touched itachi's sword, the hougyoku would be drained together with the power that came with it. GF aizen

Nope. I Think Aizen Has This For A Couple Of Reasons...
First Of All
#1: Aizen Got Hit By Ichigos Mugetsu And Is Chilling In Jail Like Nothing Even Happen With His Fast Regeneration So He Can Probably Heal Faster Than He Takes Damage (Hes Kinda Immortal Now)
#2: Ninjas Run On Their Feet... While Shinigami Flash Step So Hes 10 Times Faster Than Itachi  So IF Its A Fight To See Who Can Trap The Other In The Others Gen/Illusions First Aizen Has The Upper Hand.
#3:I Got This From Bleach Wiki : "Aizen's Reiatsu is powerful enough to nullify abilities, such as when he negated Suì-Fēng's Nigeki Kessatsu technique."
GG

Indeed

susano'o's thingy is a sealing technique tho