Head and neck – Case 56

A : Right Eustachian tube
B : Right external acoustic canal
C : Sphenoid sinus
D : Left carotid canal
E : Left internal acoustic canal

Remarks :
1. Axial CT of head at the level of petrous segment of internal carotid, in bone window. 
2.  Anatomical relationship between Eustachian tube and petrous segment of internal carotid artery :
a) Initial part of Eustachian tube : At the same horizontal plane with ICA in anteromedial manner, but Eustachian tube travels towards more anteriorly located nasopharynx, so it is anterior to petrous segment of internal carotid artery which travels towards cavernous sinus on both side of sella turcica
b) Later part of Eustachian tube : Cannot be seen in the same horizontal cut as it will travels more inferiorly towards the nasopharynx as this horizontal cut is at the level of cranial fossa
3. Petrous part of ICA is located inferior to cochlea, the petrous part of temporal bone is a tented shape at superior surface of skull base, the cochlea is located nearer the ridge between the middle and inferior cranial fossa