Type:
Educational Exhibit
Keywords:
Not applicable, Pathology, Diagnostic procedure, MR, CT-High Resolution, Neuroradiology brain, Neuro
Authors:
G. Ilangovan, F. Gomes, H. Balaganesan; Chennai/IN
DOI:
10.26044/ecr2020/C-01389
Background
The facial nerve is a mixed cranial nerve with motor, parasympathetic, and sensory branches.
Course of Facial nerve
The intraaxial segment is located within the brainstem and consists of the motor nucleus, superior salivary nucleus (parasympathetic), and nucleus of tractus solitarius (sensory).
The cisternal segment consists of the motor root and nervus intermedius (nerve of Wrisberg). Both the motor root of the facial nerve and the nervus intermedius(nerve of Wrisberg) leave the brainstem near the dorsal pons at the pontomedullary junction (the cisternal segment of the facial nerve). Within the cerebellopontine angle (CPA), the nerve travels anterolaterally into the porus acousticus of the internal auditory canal (IAC), anterior to the vestibulocochlear nerve. This segment is 24 mm (8). The nervus intermedius either joins the motor root as it emerges from the brainstem or near the meatus of the IAC (7).
The labyrinthine segment courses between the cochlea and vestibule of the inner ear and connects to the geniculate ganglion.The labyrinthine segment runs from the fundus of the IAC to the geniculate ganglion. It is both the narrowest and shortest segment (7)
Arising from the geniculate ganglion are the greater superficial petrosal and lesser petrosal nerves, the greater superficial petrosal nerve (GSPN), exits anteriorly from the geniculate ganglion. The GSPN carries preganglionic parasympathetic fibers from the superior salivatory nucleus, and runs along the anterior surface of the temporal bone into the pterygoid canal (Vidian canal). It synapses at the pterygopalatine ganglion in the pterygopalatine fossa. Postganglionic parasympathetic fibers then join the maxillary nerve to innervate the lacrimal gland and small salivary glands in the nose and palate.(6).Lesser petrosal nerve supply parasympathetic (secretory fibres) to the parotid gland and the external petrosal nerve, which sends sympathetic fibers to the middle meningeal artery.
The tympanic segment courses backward from the geniculate ganglion inferior to the lateral semicircular canal to the second genu before turning downward to become the mastoid segment, with branches to the stapedius and chorda tympani.(9)
The mastoid segment of the facial nerve runs posteromedially along the external auditory canal to its exit from the temporal bone at the stylomastoid foramen (13 mm in adults).(6) Two branches arise from the mastoid segment: the nerve to the stapedius and the chorda tympani. The stylomastoid foramen arises between the styloid process anteriorly and the mastoid process posteriorly. The nerve exits the temporal bone at the stylomastoid foramen, entering the substance of the parotid gland and gives rise to the superior temporozygomatic, inferior cervicofacial, temporal, zygomatic, buccal, mandibular, and cervical branches.(6)