Cholesteatoma commonly perforates -
Cholesteatoma has the property to destroy the bone by virtue of the various enzymes released by it.
Structures immediately at the risk of erosion are:

– Long process of incus.Q
– Fallopian canal containing facial nerve. Q
– Horizontal/lateral semicircular canal. Q
Lat. semicircular canal
Sup. semicircular canal
Promontory
Oval window