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AJNR - American Journal of Neuroradiology

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Congenital Absence of the Oval Window: Radiologic Diagnosis and Associated Anomalies

Barbara Zeifer^,a, Paul Sabini^a and Jonathan Sonne^a

^a From the Department of Radiology, Beth Israel Medical Center, New York (B.Z.); and the Departments of Radiology (B.Z.) and Otolaryngology (B.Z., P.S., J.S.), The New York Eye & Ear Infirmary, New York.

View larger version (105K): [in a new window]   FIG 1. A and B, Normal anatomy of oval window on coronal (A) and axial (B) CT scans. V indicates vestibule; C, cochlea; S, lateral semicircular canal; single black arrows, margin of the oval window; asterisk, obturator foramen between stapes crura, well delineated on the axial scan; in A, arrowhead indicates horizontal facial nerve canal; cross, incudal body; single white arrow, incudal-stapedial articulation between the lenticular process and capitulum; in B, double black arrow indicates sinus tympani; double white arrow, neck of malleus. Posterior to the malleus lies the long process of the incus cut in cross section. Note that the facial nerve (arrowhead, A) is lateral to an imaginary vertical line drawn through the junction of the lateral and superior semicircular canals

View larger version (92K): [in a new window]   FIG 2. Congenital absence of the oval window, normal facial nerve canal, on coronal CT scan. The oval window is obliterated by a thick bony plate tapering to a central depression. The horizontal facial nerve canal, however, is normal in location (arrowhead), lying lateral to the vertical line drawn through the anterior junction of the lateral and superior semicircular canals.FIG 3. Partial absence of the oval window with a large facial nerve on coronal CT scan. This patient with microtia and external canal stenosis (short arrows) has an unusually large horizontal facial nerve (arrowhead). The bone beneath the lateral semicircular canal is thick. The bony facial nerve canal is not well delineated and the nerve overlies the atretic oval window (long arrow)

View larger version (69K): [in a new window]   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