Fig. 4

Sinus tympani (ST) (STR) measurements and types. a Axial CT images showing the right and left Sinus tympani (ST) (red arrows). b Measurement of right ST length and width (ST-L & ST-W) in axial CT image. c–e Different types of ST; yellow arrow points to ST and red arrow points to the facial nerve. The green lines passing through the floor of the ST and the outer wall of the facial nerve canal demonstrate the relation between ST and facial nerve. c Type A ST: small sinus tympani without medial or posterior extension in relation to the facial nerve. d Type B ST: deep sinus tympani with medial extension but without posterior extension in relation to the facial nerve. e Type C ST: large and deep sinus tympani with medial and posterior extension in relation to the facial nerve