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Figure 15a. Normal anatomy of the facial nerve canal. Three-dimensional VR CT images (posterior [a], superior [b], and lateral [c] views) show the course of the facial nerve through its bony canal as it exits the anterosuperior aspect of the fundus of the internal auditory canal (IAC). The labyrinthine segment of the facial nerve courses through the fallopian canal (fc) to the geniculate ganglion, where the nerve makes a hairpin turn known as the anterior genu (ag). The tympanic segment (ts) of the facial nerve canal runs below the lateral semicircular canal (LSCC) and above the oval window (OW) along the medial wall of the tympanic cavity. It then makes a gentle curve (the posterior genu [pg]) and heads vertically downward as the mastoid segment (ms) to exit the temporal bone at the stylomastoid foramen. The chorda tympani arises from the lateral aspect of the mastoid segment approximately 5 mm proximal to the stylomastoid foramen and courses superiorly within its own bony canal, the canaliculus chorda tympani (cct). Co = cochlea, In = incus, M = malleus.
