Lesions of the Facial Nerve

Case A: CT of the temporal bone demonstrates smooth expansion of the internal auditory canal ( asterisk ), with extension into the labyrinthine segment and geniculate ganglion ( arrow ) of the facial nerve. T1-weighted postcontrast MRI shows a homogeneously enhancing, curvilinear mass ( asterisk ) arising from the cerebellopontine angle and continuing into the intracanalicular, labyrinthine, and geniculate ( arrow ) segments of the facial nerve.

Case B: CT of the temporal bone illustrates irregular bone along the labyrinthine segment, anterior genu, and proximal tympanic ( asterisk ) portions of the facial nerve. Associated expansion, thickening, and sclerosis of the adjacent tegmen tympani and petrous air cells ( arrows ) is noted, producing a “speckled bone” appearance. T1-weighted postcontrast MRI demonstrates corresponding heterogeneous enhancement of the labyrinthine, geniculate, and proximal tympanic segments ( asterisk ) of the facial nerve and the adjacent bone. Increased signal also is present in the tegmen tympani and petrous apex ( arrows ), with adjacent dural thickening and enhancement.

Case C: CT of the temporal bone depicts asymmetric expansion of the distal intracanalicular, labyrinthine ( asterisk ), geniculate, and tympanic segments of the facial nerve. Evidence is seen of bony expansion of the facial hiatus ( arrow ). T1-weighted postcontrast MRI shows corresponding enhancement of the involved facial nerve segments ( asterisk ) and extension to the facial hiatus ( arrow ).