Trigeminal (Gasserian) Ganglion Block

Patient Selection

Current practice patterns virtually guarantee that patients undergoing this block will be experiencing facial neuralgia. Patients with severe underlying cardiopulmonary disease who require more than minor facial surgery may be candidates for local anesthetic trigeminal ganglion blocks.

Pharmacologic Choice

Trigeminal ganglion block can be carried out with 1 to 3 mL of local anesthetic; thus, almost any of the local anesthetics is an option.

Anatomy

The trigeminal ganglion is located intracranially and measures approximately 1 × 2 cm. In its intracranial location, it lies lateral to the internal carotid artery and cavernous sinus and slightly posterior and superior to the foramen ovale, through which the mandibular nerve leaves the cranium (Fig. 20-1). From the trigeminal ganglion, the fifth cranial nerve divides into its three principal divisions: the ophthalmic, maxillary, and mandibular nerves. These nerves provide sensation to the region of the eye and forehead, upper jaw (midface), and lower jaw, respectively (see Fig. 20-1). The mandibular division carries motor fibers to the muscles of mastication, but otherwise these nerves are wholly sensory. The trigeminal ganglion is partially contained within a reflection of dura mater, Meckel’s cave. Figures 20-2 and 20-3 show that the foramen ovale is approximately in the horizontal plane of the zygoma, and in the frontal plane is roughly at the level of the mandibular notch. The foramen ovale is slightly less than 1 cm in diameter and is situated immediately dorsolateral to the pterygoid process.

Figure 20-1. Fifth cranial nerve (trigeminal) ganglion anatomy: innervation and peripterygoid relationships.

Figure 20-2. Cross-sectional anatomy: fifth cranial nerve (trigeminal) ganglion and foramen ovale.

Figure 20-3. Coronal anatomy: section through fifth cranial nerve (trigeminal) ganglion.

Position

Patients are placed in a supine position and asked to fix their gaze straight ahead, as if they were looking off into the distance. The anesthesiologist should be positioned at the patient’s side, slightly below the level of the shoulder, so that by looking toward the patient’s face, the perspective shown in Figure 20-4 is observed.

Figure 20-4. Trigeminal ganglion block: anatomy and needle insertion plane.

Needle Puncture

A skin wheal is raised immediately medial to the masseter muscle, which can be located by asking the patient to clench his or her teeth. (It will most often be located approximately 3 cm lateral to the corner of the mouth.) Through this site, as illustrated in Figure 20-5, a 22-gauge, 10-cm needle is inserted as shown at position 1, aided by fluoroscopic guidance. The plane of insertion should be in line with the pupil, as illustrated in Figure 20-4. This will allow the needle tip to contact the infratemporal surface of the greater wing of the sphenoid bone, immediately anterior to the foramen ovale. This occurs at a depth of 4.5 to 6 cm. Once the needle is firmly positioned against this infratemporal region, it is withdrawn and redirected in a stepwise manner until it enters the foramen ovale at a depth of approximately 6 to 7 cm, or 1 to 1.5 cm past the needle length required to contact the bone initially (position 2).

Figure 20-5. Trigeminal ganglion block: anatomy and technique.

As the foramen is entered, a mandibular paresthesia is often elicited. By advancing the needle slightly, one may also elicit paresthesia in the distribution of the ophthalmic or maxillary nerves. These additional paresthesias should be sought in order to verify a periganglionic position of the needle tip. If the only paresthesia obtained is in the mandibular distribution, the needle tip may not have entered the foramen ovale but may be inferior to it while it abuts the mandibular nerve.

Before injection of local anesthetic, careful aspiration of the needle should be performed to check for cerebrospinal fluid (CSF) because the ganglion’s posterior two thirds is enveloped in a reflection of dura, Meckel’s cave. If trigeminal block is being undertaken diagnostically before neurolysis, 1 mL of local anesthetic should now be injected. Nerve block should develop within 5 to 10 minutes; if the block is incomplete, an additional 1 to 2 mL of local anesthetic can be injected or the needle can be repositioned in an effort to obtain a more complete block.