The cart-wheel appearance of the tympanic membrane in ASOM is due to
Perforation of tympanic membrane
Edema of tympanic membrane
Granulation tissue on tympanic membrane
Congested blood vessels along malleus
In the stage of pre suppuration of ASOM, there is congestion of pars tensa. 
A leash of blood vessels appears along the handle of malleus and at the periphery of tympanic membrane imparting it a cart-wheel appearance.