Congenital Bifurcation of the Intratemporal Facial Nerve
Christine M. Glastonburya,
Nancy J. Fischbeina,
H. Ric Harnsbergerb,
William P. Dillona and
Thomas R. Kerteszc
a Department of Radiology, Section of Neuroradiology, University of California, San Francisco, CA
b Department of Neuroradiology, University of Utah Health Sciences Center, Salt Lake City, UT
c Department of Otolaryngology, University of Utah Health Sciences Center, Salt Lake City, UT
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FIG 1 Case 1, 6-year-old girl evaluated for mixed hearing loss, worse on the left side. Axial 1-mm section at the superior aspect of the left internal auditory canal (IAC) showns two canals coursing anteriorly in the expected location of the labyrinthine segment of the facial nerve (arrow). Note also the dilated posterior semicircular canal (curved arrow).
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FIG 2 Case 2, 12-year-old boy with right-side mixed HL. Axial 1-mm CT sections through the level of the cochlear modiolus and the malleo-incudal joint (A) demonstrate a thickened tympanic CN7 (black arrow). The more inferior axial section at the level of the round window (B) shows two separate proximal mastoid segment nerves. The stapedius tendon is distinctly seen separate from these nerve elements (white arrow). The coronal images confirm a thickened proximal tympanic nerve (C, black arrow) and two segments more posteriorly at the level of the oval window (D). The more inferior of the bifid segments courses lateral to a stenotic oval window (arrow). T = tensor tympani tendon.
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FIG 3 Case 3, 40-year-old woman with branchio-oto-renal syndrome and bilateral congenital HL. Axial (A) and coronal (B) images of the right side demonstrate two distinct symmetric mastoid segments of CN7 (arrows) that exit via separate stylomastoid foramina. On the left side, bifid mastoid CN7 segments are also seen (arrows, axial image C), with the smaller, medial segment exiting into the lateral wall of the jugular foramen (smaller arrow, coronal image D). Additional axial (E) image of the labyrinthine portion of CN7 on the left side shows a looplike anterior course separate to the internal auditory canal (arrow). This anomalous CN7 course was seen bilaterally, and there was bilateral severe cochleo-vestibular dysplasia.
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