Which nerve is involved in loss of taste on one side of the tongue and the ipsilateral cheek?

The Facial Nerve (CN VII) is Involved

Loss of taste on one half of the tongue combined with ipsilateral cheek sensation loss indicates facial nerve (CN VII) pathology, as this nerve provides special sensory (taste) innervation to the anterior two-thirds of the tongue and can be associated with general sensory disturbances in the facial region.

Anatomical Basis

The facial nerve (CN VII) is one of the most complex cranial nerves, carrying multiple functional components 1, 2, 1:

• Special sensory function: Taste to the anterior two-thirds of the tongue
• Branchial motor function: Innervation to muscles of facial expression
• Visceral motor function: Parasympathetic innervation to lacrimal and salivary glands
• General sensory function: Surface innervation to portions of the external ear and tympanic membrane

The nerve originates in the pons, traverses the cerebellopontine angle, enters the internal auditory canal, courses through the temporal bone (including the geniculate ganglion where taste fibers are located), and exits at the stylomastoid foramen 1.

Clinical Presentation Pattern

Facial nerve pathology characteristically presents with 1:

• Reduced or absent taste on the ipsilateral anterior two-thirds of tongue
• Facial droop (if motor fibers involved)
• Pain around the jaw or ear
• Decreased lacrimation or salivation
• Hyperacusis (if stapedius muscle involvement)

The combination of taste loss with ipsilateral facial sensory changes points specifically to CN VII rather than other cranial nerves. The trigeminal nerve (CN V) provides general sensation to the face and tongue but does not carry taste fibers 1.

Common Etiologies to Consider

Lesions can occur anywhere along the facial nerve pathway 1:

• Bell's palsy: Most common cause of acute peripheral facial nerve palsy, attributed to inflammation (possibly herpes simplex virus-related)
• Intracranial lesions: Schwannomas, meningiomas, vascular lesions, cholesteatomas, paragangliomas
• Temporal bone pathology: Trauma, infection, inflammatory disease
• Extracranial causes: Parotid tumors, skull base pathology, perineural tumor spread

Critical Diagnostic Approach

Imaging is not routinely required for typical Bell's palsy presentations unless symptoms are atypical, recurrent, or persist beyond 2-4 months 1, 3.

When imaging is indicated:

• MRI is the primary modality for evaluating both intracranial and extracranial facial nerve segments 2
• High-resolution temporal bone CT provides complementary information about osseous integrity, fractures, and bony canal involvement 1
• Enhancement may be seen in various nerve segments with neuritis, though geniculate, tympanic, and mastoid portions can enhance normally 2

Important Clinical Pitfall

Do not confuse this with lingual nerve pathology. The lingual nerve (a branch of CN V3) provides general sensation and taste to the anterior two-thirds of the tongue but does not typically cause the combination of taste loss with broader ipsilateral facial/cheek sensory changes 4. The pattern described in the question—taste loss on one half of the tongue plus ipsilateral cheek involvement—is characteristic of CN VII pathology, not isolated lingual nerve dysfunction.