Facial Nerve

The vertical portion of the mastoid segment of the facial nerve in the fallopian canal, a critical structure in surgical approaches to the jugular bulb, is separated from the lateral wall of the jugular bulb by the retrofacial and infralabyrinthine air cells. The relationship between the mastoid segment of the facial nerve and the jugular bulb is variable.15 In approximately 60% of specimens at least one-half of the jugular bulb lies anterior to the facial nerve, and in the remaining 40% only one-third of the jugular bulb lies anterior to the facial nerve.15 The facial nerve exits the stylomastoid foramen about 5 mm lateral to the lateral margin of the jugular foramen or approximately midway between the styloid process and the anterior part of the digastric groove.

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