Ultrasound-guided facial nerve block is useful in the diagnosis and management of a variety of painful conditions, which are subserved by the facial nerve. These conditions include geniculate neuralgia, atypical facial neuralgias, herpes zoster, and postherpetic neuralgia involving the geniculate ganglion (Ramsay Hunt syndrome) and the pain associated with Bell palsy (Fig. 20.1). Ultrasound-guided facial nerve block is also useful in the management of hemifacial spasm and may serve as an adjunctive treatment for essential blepharospasm, Meige syndrome, and other uncommon cranial dystonias (Fig. 20.2).

This technique may also be utilized as a diagnostic maneuver when performing differential neural blockade on an anatomic basis when evaluating difficult-to-diagnose head and neck pain syndromes and when considering a diagnosis of geniculate neuralgia. If sacrifice of the facial nerve is being considered in patients scheduled to undergo surgery on the base of the skull, this technique is useful as a prognostic indicator of the degree of motor and sensory impairment that the patient may experience.

The facial nerve is the seventh cranial nerve, providing sensory, motor, and preganglion parasympathetic fibers to the head. The motor portion of the nerve arises from the facial nerve nucleus of the pons. The sensory portion of the nerve arises from the nervus intermedius at the inferior margin of the pons. It is at the point where the sensory portion of the nerve leaves the pons that it is susceptible to compression by aberrant blood vessels, which can cause a trigeminal neuralgia-like syndrome known as geniculate neuralgia and a facial dystonia known as hemifacial spasm (Fig. 20.3). After leaving the pons, the motor and sensory fibers of the facial nerve join to travel across the subarachnoid space and enter the internal auditory meatus to pass through the petrous temporal bone. It is at this point that swelling and inflammation of the facial nerve can cause Bell palsy (Fig. 20.4). The nerve then exits the base of the skull via the stylomastoid foramen (Fig. 20.5). It passes downward and then turns forward to pass through the parotid gland, where it divides into fibers that provide innervation to the muscles of facial expression. The facial nerve also provides afferent fibers that carry taste from the anterior two-thirds of the tongue (Fig. 20.6).

To perform ultrasound-guided facial nerve block, the patient is placed in supine position with the head turned away from the side to be blocked. The mastoid process and the external acoustic auditory meatus are then identified by palpation (Fig. 20.7). After preliminary identification of these anatomic landmarks, the skin is prepped with antiseptic solution, and 3 mL of local anesthetic is drawn up in a 10-mL sterile syringe, with 40 to 80 mg of depot steroid added if the condition being treated is thought to have an inflammatory component. A linear ultrasound transducer is then placed over the previously identified approximate location in the transverse plane (Fig. 20.8). The anteroinferior border of the mastoid bone at a point just below the external auditory meatus is then identified with ultrasound imaging (Fig. 20.9). The hyperechoic margin of the bone and its acoustic shadow should be easily identifiable. The facial nerve can then be identified as it exits the stylohyoid foramen (Fig. 20.10). Color Doppler can be utilized to identify major blood vessels in proximity to the facial nerve (Fig. 20.11).