Topics

Topic

design image
Facial Nerve (Cranial nerve VII)

The facial nerve, also known as Cranial Nerve VII (CN VII), is a mixed cranial nerve responsible for the motor innervation of the muscles of facial expression, as well as conveying taste sensations from the anterior two-thirds of the tongue and supplying parasympathetic fibers to several head and neck glands. It arises from the brainstem at the pontomedullary junction and follows a complex course through the internal auditory canal and facial canal within the temporal bone before exiting the skull at the stylomastoid foramen. The facial nerve is essential for facial movements, taste, and secretory functions, and is frequently assessed in clinical practice and visualized in neuroimaging.

Synonyms

  • Cranial Nerve VII (CN VII)

  • Nervus facialis

  • Seventh cranial nerve

Function

  • Motor: Supplies all muscles of facial expression (e.g., orbicularis oculi, orbicularis oris, buccinator, platysma).

  • Sensory: Carries taste sensations from the anterior two-thirds of the tongue via the chorda tympani.

  • Parasympathetic (Secretomotor): Innervates the lacrimal, submandibular, and sublingual glands.

  • General Sensory: Minor sensory supply to the skin of the external ear.

MRI Appearance

  • T1-weighted Imaging:

    • The facial nerve appears as a small, linear, hypointense (dark) structure within the internal auditory canal (IAC) and facial canal.

    • Difficult to distinguish from adjacent nerves unless contrast is used or in cases of pathology (e.g., enhancement in neuritis).

  • 3D T2-weighted Imaging (e.g., CISS or FIESTA):

    • The facial nerve is visualized as a hypointense (dark) linear structure against the hyperintense (bright) background of cerebrospinal fluid (CSF) in the IAC and cisternal segments.

    • 3D T2 sequences provide excellent delineation of the nerve from the vestibulocochlear nerve and adjacent vessels.

CT Appearance

  • Non-contrast CT:

    • The facial nerve itself is not directly visualized; however, its bony canal (facial canal) can be traced through the temporal bone.

    • High-resolution temporal bone CT reveals the labyrinthine, tympanic, and mastoid segments of the facial canal, allowing assessment for bony erosion, fractures, or congenital anomalies.

    • CT is crucial for evaluating bony detail and detecting lesions impinging on the nerve or its canal.

MRI images

Facial nerve (Cranial nerve VII) MRI 3T axial image

MRI images

Facial nerve (Cranial nerve VII) MRI 3T coronal image

MRI images

Facial nerve (Cranial nerve VII) MRI 3T sagittal image 1

MRI images

Facial nerve (Cranial nerve VII) MRI 3T sagittal image