Facial Nerve Injury 2_0613 Derm Dx
Facial Nerve Injury 1_0613 Derm Dx
A 66-year-old male presents for post-operative evaluation three-weeks after excision of a large highly invasive squamous cell carcinoma. Intraoperative frozen sections of the excised tissue demonstrated nerve invasion. Therefore, the nerve was transected during surgery.
The patient’s surgical site on the left side of his scalp is clean, dry and intact on examination. At rest, his left eyebrow appears to droop significantly. He is unable to raise the left eyebrow. “At least the left side of my forehead doesn’t have wrinkles anymore,” he jokes.
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The facial nerve, also known as ‘cranial nerve VII,’ is responsible for innervating the muscles of facial expression. These include the frontalis muscle, which is the forehead muscle responsible for raising the eyebrows and causing forehead wrinkles.
The temporal branch of the facial nerve innervates the frontalis muscle. Since this nerve was injured during the surgical procedure, the patient cannot raise his eyebrow. Additionally, he no longer has wrinkles on the affected side.
The facial nerve exits the skull through the stylomastoid foramen and enters the parotid gland. The facial nerve branches within the parotid gland, and the branches course in an upward pathway out of the parotid gland and into the muscles of facial expression.
The five branches of the facial nerve are the temporal, zygomatic, buccal, marginal mandibular and cervical. The temporal branch innervates the muscles of the forehead and brow that both raise and depress the brow.
The zygomatic branch innervates the muscle that squeezes the eye shut and several of the major lip elevators that produce a smile. The buccal branch also innervates muscles that produce a smile, whereas the marginal mandibular branch innervates muscles that produce a frown.
The transverse cervical branch innervates the platysma muscle, which functions as a depressor of the lower lip.
During surgery, there are several surgical “danger zones” involving the facial nerve branches. The temporal branch of the facial nerve is at risk for injury, where it crosses the zygomatic arch or “cheek bone.” Injury to the temporal branch leads to brow ptosis (droop), inability to raise the brow and inability to close the eye tightly.
A second danger zone is where the marginal mandibular branch crosses the mandible. Injury to this nerve leads to a crooked smile and an inability to whistle.
A third surgical “danger zone” involves the spinal accessory nerve at Erb’s point. Erb’s point can be located by drawing an imaginary line between the mastoid process and the angle of the mandible. It is is located approximately 6 cm below the midline of that line at the posterior aspect of the sternocleidomastoid muscle. Damage to the spinal accessory nerve leads to a winged scapula, difficulty with shoulder movement and shoulder pain.
The trigeminal nerve, cranial nerve V, is responsible for sensory innervation of the face. The auriculotemporal branch of the trigeminal nerve is the sensory nerve for the anterior aspect of the ear, the lateral temple and the temporal scalp.
The greater auricular nerve is a branch of the cervical plexus and is responsible for sensory innervation of the lateral submandibular region and aspects of the ear.
Injury to the temporal nerve may cause significant cosmetic problems for the patient, but fortunately it does not lead to significant functional problems. If the defect is mild, then botulinum toxin injections into the unaffected side will lead to the brows being at the same level. However, if the defect is severe, a surgical brow lift on the affected side may need to be performed.
Adam Rees, MD, is a graduate of the University of California Los Angeles School of Medicine and a resident in the Department of Dermatology at Baylor College of Medicine in Houston.
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