Table 7.

Surgical challenges in cochlear implantation

Surgical step	Structure on CT	Anomaly	Surgical challenge
Mastoidectomy	Mastoid	Underdeveloped	Reduced access to the middle ear
	Vascular structures	Large emissary vein	Unexpected bleeding
		PSS	Bleeding, reduced mastoid size
	Semicircular canals	Aplasia	Loss of landmark
Post. tympanotomy	Facial nerve	More medial route	Facilitates entrance to the middle ear
Cochleostomy	Ossicles	Dysplasia	Obstructed vision by the incus
	Facial nerve	Aberrant route	Impedes cochleostomy
	Windows	Round window stenosis	Choosing optimal side for cochleostomy
	Jugular bulb	High	Preparing cochleostomy
Insertion	Cochlea	Aplasia	Insertion

Post. posterior, PSS petrosquamosal sinus