A 65-year-old woman presents to the physician’s office with a painless mass on the right side of her face that she noticed two weeks ago. Past medical history is significant for hypertension and osteoporosis. Physical examination reveals a palpable mass in the right parotid gland. Cranial nerves are intact, and no lymphadenopathy is noted. An MRI reveals a likely malignant tumor, and she is referred to a head and neck surgeon for further evaluation.
Which of the following nerves is most at risk for injury during a parotidectomy?
- A) Facial nerve
- B) Optic nerve
- C) Trigeminal nerve V2
- D) Trigeminal nerve V3
- E) Trochlear nerve
A) Facial nerve
The facial nerve courses between the superficial and deep layers of the parotid gland and then branches into its five major sensory nerve fibers (temporal, zygomatic, buccal, mandibular, cervical) at the anterior border of the parotid gland.
Answer choice B: Optic nerve, is incorrect. The optic nerve leaves the bony orbit via the optic canal where it unites with the optic nerves from each eye to form the optic chiasm. At the chiasm, fibers from the medial half of each retina cross over t the contralateral optic tract while fibers from the lateral halves remain ipsilateral. Each optic tract travels to its corresponding cerebral hemisphere to reach the lateral geniculate nucleus. Axons then carry visual information via the optic radiation to the visual cortex.
Answer choice C: Trigeminal nerve V2, is incorrect. Trigeminal nerve V2 (maxillary division) exits the cranium via the foramen rotundum and gives rise to 14 terminal branches which innervate the lower eyelid and its conjunctiva; the cheeks and maxillary sinus; the nasal cavity and lateral nose; the upper lip; the upper molar, incisor and canine teeth and the associated gingiva; and the superior palate. It provides parasympathetic supply to the lacrimal gland and nasal glands.
Answer choice D: Trigeminal nerve V3, is incorrect. Trigeminal nerve V3 (mandibular division) exits the cranium via the foramen ovale and provides sensory supply to the mucous membranes and floor of the oral cavity; external ear; lower lip; chin; anterior 2/3 of the tongue; and the lower molar, incisor, and canine teeth and the associated gingiva. It provides motor supply to the muscles of mastication, anterior belly of the digastric muscle and the mylohyoid muscle, the tensor tympani, and tensor veli palatini. It also provides parasympathetic supply to the parotid gland and submandibular and sublingual glands.
Answer choice E: Trochlear nerve, is incorrect. The trochlear nerve moves along the lateral wall of the cavernous sinus before entering the orbit of the eye via the superior orbital fissure.
Key Learning Point
The facial nerve courses between the superficial and deep layers of the parotid gland before branching into its five major sensory nerve fibers at the anterior border of the parotid gland. This puts the facial nerve at risk for injury during surgery on the parotid gland.