fig 4.

A and B, Congenital absence of the oval window on coronal (A) and axial (B) CT scans. The oval window is completely obliterated. In A, the horizontal facial nerve canal is intact (arrowhead) but is low in position, directly lateral to the oval window. The canal lies medial to the vertical line drawn through the anterior junction of the lateral and superior semicircular canals. The bone below the lateral semicircular canal (S) is extremely thick. Note the myringotomy tube placed for serous otitis media that had no effect on the patient's maximal conductive hearing loss. In B, there is posterior and inferior displacement of a well-formed stapes arch, now located at the level of the round window (arrow), straddling the sinus tympani. O indicates the obturator foramen between the stapes crura.fig 5. Congenital absence of the oval window with a dysplastic stapes on coronal CT scan. The oval window is completely obliterated. The bone below the lateral semicircular canal is intact and solid, lacking the facial nerve canal. The nerve is aberrant, found along the lower border of the oval window (arrowhead) and could be followed anteriorly to the geniculate ganglion (not shown). The stapes is dysplastic and one crus extends onto the facial nerve. Note that the nerve is medial in location